| 1. |
- Stenerlöw, Bo, et al.
(författare)
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Basic radiotherapy research
- 1996
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Ingår i: TSL Progress Report. ; 94-95
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Annan publikation (övrigt vetenskapligt/konstnärligt)
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| 2. |
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| 3. |
- Stenerlöw, Bo, et al.
(författare)
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Biomedical Radiation Research
- 1998
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Ingår i: TSL Progress Report. ; 96-97
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Annan publikation (övrigt vetenskapligt/konstnärligt)
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| 4. |
- Blomquist, Erik, et al.
(författare)
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Positive correlation between occlusion rate and nidus size of proton beam treated brain arteriovenous malformations (AVMs)
- 2016
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Ingår i: Acta Oncologica. - 0284-186X .- 1651-226X. ; 55:1, s. 105-112
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Proton beam radiotherapy of arteriovenous malformations (AVM) in the brain has been performed in Uppsala since 1991. An earlier study based on the first 26 patients concluded that proton beam can be used for treating large and medium sized AVMs that were considered difficult to treat with photons due to the risk of side effects. In the present study we analyzed the result from treating the subsequent 65 patients.MATERIAL AND METHODS: A retrospective review of the patients' medical records, treatment protocols and radiological results was done. Information about gender, age, presenting symptoms, clinical course, the size of AVM nidus and rate of occlusion was collected. Outcome parameters were the occlusion of the AVM, clinical outcome and side effects.RESULTS: The rate of total occlusion was overall 68%. For target volume 0-2cm(3) it was 77%, for 3-10 cm(3) 80%, for 11-15 cm(3) 50% and for 16-51 cm(3) 20%. Those with total regress of the AVM had significantly smaller target volumes (p < 0.009) higher fraction dose (p < 0.001) as well as total dose (p < 0.004) compared to the rest. The target volume was an independent predictor of total occlusion (p = 0.03). There was no difference between those with and without total occlusion regarding mean age, gender distribution or symptoms at diagnosis. Forty-one patients developed a mild radiation-induced brain edema and this was more common in those that had total occlusion of the AVM. Two patients had brain hemorrhages after treatment. One of these had no effect and the other only partial occlusion from proton beams. Two thirds of those presenting with seizures reported an improved seizure situation after treatment.CONCLUSION: Our observations agree with earlier results and show that proton beam irradiation is a treatment alternative for brain AVMs since it has a high occlusion rate even in larger AVMs.
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| 5. |
- Kimstrand, Peter, et al.
(författare)
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A beam source model for scanned proton beams
- 2007
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Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 0031-9155 .- 1361-6560. ; 52:11, s. 3151-3168
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Tidskriftsartikel (refereegranskat)abstract
- A beam source model, i.e. a model for the initial phase space of the beam, for scanned proton beams has been developed. The beam source model is based on parameterized particle sources with characteristics found by fitting towards measured data per individual beam line. A specific aim for this beam source model is to make it applicable to the majority of the various proton beam systems currently available or under development, with the overall purpose to drive dose calculations in proton beam treatment planning. The proton beam phase space is characterized by an energy spectrum, radial and angular distributions and deflections for the non-modulated elementary pencil beam. The beam propagation through the scanning magnets is modelled by applying experimentally determined focal points for each scanning dimension. The radial and angular distribution parameters are deduced from measured two-dimensional fluence distributions of the elementary beam in air. The energy spectrum is extracted from a depth dose distribution for a fixed broad beam scan pattern measured in water. The impact of a multi-slab range shifter for energy modulation is calculated with an own Monte Carlo code taking multiple scattering, energy loss and straggling, non-elastic and elastic nuclear interactions in the slab assembly into account. Measurements for characterization and verification have been performed with the scanning proton beam system at The Svedberg Laboratory in Uppsala. Both in-air fluence patterns and dose points located in a water phantom were used. For verification, dose-in-water was calculated with the Monte Carlo code GEANT 3.21 instead of using a clinical dose engine with approximations of its own. For a set of four individual pencil beams, both with the full energy and range shifted, 96.5% (99.8%) of the tested dose points satisfied the 1%/1 mm (2%/2 mm) gamma criterion.
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| 6. |
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| 7. |
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| 8. |
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| 9. |
- Tilly, Nina, et al.
(författare)
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The influence of RBE variations in a clinical proton treatment plan for a hypopharynx cancer
- 2005
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Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 0031-9155 .- 1361-6560. ; 50:12, s. 2765-2777
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Tidskriftsartikel (refereegranskat)abstract
- Currently, most clinical range-modulated proton beams are assumed to have a fixed overall relative biological effectiveness (RBE) of 1.1. However, it is well known that the RBE increases with depth in the spread-out Bragg peak (SOBP) and becomes about 10% higher than mid-SOBP RBE at 2 mm from the distal edge (Paganetti 2003 Technol. Cancer Res. Treat. 2 413-26) and can reach values of 1.3-1.4 in vitro at the distal edge (Robertson et al 1975 Cancer 35 1664-77, Courdi et al 1994 Br. J. Radiol. 67 800-4). We present a fast method for applying a variable RBE correction with linear energy transfer (LET) dependent tissue-specific parameters based on the alpharef/betaref ratios suitable for implementation in a treatment planning system. The influence of applying this variable RBE correction on a clinical multiple beam proton dose plan is presented here. The treatment plan is evaluated by RBE weighted dose volume histograms (DVHs) and the calculation of tumour control probability (TCP) and normal tissue complication probability (NTCP) values. The variable RBE correction yields DVHs for the clinical target volumes (CTVs), a primary advanced hypopharynx cancer and subclinical disease in the lymph nodes, that are slightly higher than those achieved by multiplying the absorbed dose with RBE=1.1. Although, more importantly, the RBE weighted DVH for an organ at risk, the spinal cord is considerably increased for the variable RBE. As the spinal cord in this particular case is located 8 mm behind the planning target volume (PTV) and hence receives only low total doses, the NTCP values are zero in spite of the significant increase in the RBE weighted DVHs for the variable RBE. However, high NTCP values for the non-target normal tissue were obtained when applying the variable RBE correction. As RBE variations tend to be smaller for in vivo systems, this study-based on in vitro data since human tissue RBE values are scarce and have large uncertainties-can be interpreted as showing the upper limits of the possible effects of utilizing a variable RBE correction. In conclusion, the results obtained here still indicate a significant difference in introducing a variable RBE compared to applying a generic RBE of 1.1, suggesting it is worth considering such a correction in clinical proton therapy planning, especially when risk organs are located immediately behind the target volume.
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| 10. |
- Vidal, Marie, et al.
(författare)
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Beam monitor chamber calibration of a synchro-cyclotron high dose rate per pulse pulsed scanned proton beam
- 2024
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Ingår i: Physics in Medicine and Biology. - : Institute of Physics Publishing (IOPP). - 0031-9155 .- 1361-6560. ; 69:8
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Tidskriftsartikel (refereegranskat)abstract
- Objective: Ionization chambers, mostly used for beam calibration and for reference dosimetry, can show high recombination effects in pulsed high dose rate proton beams. The aims of this paper are: first, to characterize the linearity response of newly designed asymmetrical beam monitor chambers (ABMC) in a 100-226 MeV pulsed high dose rate per pulse scanned proton beam; and secondly, to calibrate the ABMC with a PPC05 (IBA Dosimetry) plane parallel ionization chamber and compare to calibration with a home-made Faraday cup (FC).Approach: The ABMC response linearity was evaluated with both the FC and a PTW 60019 microDiamond detector. Regarding ionometry-based ABMC calibration, recombination factors were evaluated theoretically, then numerically, and finally experimentally measured in water for a plane parallel ionization chamber PPC05 (IBA Dosimetry) through k s saturation curves. Finally, ABMC calibration was also achieved with FC and compared to the ionometry method for 7 energies.Main results: Linearity measurements showed that recombination losses in the new ABMC design were well taken into account for the whole range of the machine dose rates. The two-voltage-method was not suitable for recombination correction, but Jaffe's plots analysis was needed, emphasizing the current IAEA TRS-398 reference protocol limitations. Concerning ABMC calibration, FC based absorbed dose estimation and PPC05-based absorbed dose estimation differ by less than 6.3% for the investigated energies.Significance: So far, no update on reference dosimetry protocols is available to estimate the absorbed dose in ionization chambers for clinical high dose rate per pulse pulsed scanned proton beams. This work proposes a validation of the new ABMC design, a method to take into account the recombination effect for ionometry-based ABMC calibration and a comparison with FC dose estimation in this type of proton beams.
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| 11. |
- Vlachogiannis, Pavlos, et al.
(författare)
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Hypofractionated high-energy proton-beam irradiation is an alternative treatment for WHO grade I meningiomas
- 2017
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Ingår i: Acta Neurochirurgica. - : Springer Science and Business Media LLC. - 0001-6268 .- 0942-0940. ; 159:12, s. 2391-2400
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Tidskriftsartikel (refereegranskat)abstract
- Radiation treatment is commonly employed in the treatment of meningiomas. The aim of this study was to evaluate the effectiveness and safety of hypofractionated high-energy proton therapy as adjuvant or primary treatment for WHO grade I meningiomas. A total of 170 patients who received irradiation with protons for grade I meningiomas between 1994 and 2007 were included in the study. The majority of the tumours were located at the skull base (n = 155). Eighty-four patients were treated post subtotal resection, 42 at tumour relapse and 44 with upfront radiotherapy after diagnosis based on the typical radiological image. Irradiation was given in a hypofractionated fashion (3-8 fractions, usually 5 or 6 Gy) with a mean dose of 21.9 Gy (range, 14-46 Gy). All patients were planned for follow-up with clinical controls and magnetic resonance imaging scans at 6 months and 1, 2, 3, 5, 7 and 10 years after treatment. The median follow-up time was 84 months. Age, gender, tumour location, Simpson resection grade and target volume were assessed as possible prognostic factors for post-irradiation tumour progression and radiation related complications. The actuarial 5- and 10-year progression-free survival rates were 93% and 85% respectively. Overall mortality rate was 13.5%, while disease-specific mortality was 1.7% (3/170 patients). Older patients and patients with tumours located in the middle cranial fossa had a lower risk for tumour progression. Radiation-related complications were seen in 16 patients (9.4%), with pituitary insufficiency being the most common. Tumour location in the anterior cranial fossa was the only factor that significantly increased the risk of complications. Hypofractionated proton-beam radiation therapy may be used particularly in the treatment of larger World Health Organisation grade I meningiomas not amenable to total surgical resection. Treatment is associated with high rates of long-term tumour growth control and acceptable risk for complications.
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| 12. |
- Ahnesjö, Anders, et al.
(författare)
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Detector response modeling
- 2009
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Patent (populärvet., debatt m.m.)abstract
- A detector response correction arrangement and method is proposed for online determination of correction factors for arbitrary positions from arbitrary incident fluence distributions. As modern radiotherapy utilizes more of the available degrees of freedom of radiation machines, dosimetry has to be able to present reliable measurements for all these degrees of freedom. To determine correction factors online during measurement, Monte Carlo technique is used to precalculate fluence pencil kernels from a monodirectional beam to fully describe the particle fluence in an irradiated medium. Assuming that the particle fluence is not significantly altered by the introduction of a small detector volume, the fluence pencil kernels (212) can be integrated (214), and correction factors (216) determined, e.g. by Cavity Theory, in different positions for the detector material.
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| 13. |
- Andersen, C. E., et al.
(författare)
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Medical proton dosimetry using radioluminescence from aluminium oxide crystals attached to optical-fiber cables
- 2007
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576 .- 0167-5087. ; 580:1, s. 466-468
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Tidskriftsartikel (refereegranskat)abstract
- The prime objective of this study is to investigate if radioluminescence (RL) from carbon-doped aluminum oxide (Al2O3:C) crystals potentially can be used for absorbed dose-rate measurements during proton radiotherapy. The RL from two separate (2 mg) Al2O3:C crystals attached to optical-fiber cables were recorded during irradiations in water in a 175 MeV clinical proton beam. The RL response for low-LET protons in the plateau region of the Bragg curve was found to closely resemble that observed for a clinical 6 MV X-ray beam. An identical response was found in the Bragg peak (where the dose-averaged LET is about 4 keV/mu m) for absorbed doses less than 0.3 Gy. For doses in the range of 0.3-3Gy, we observed a significant decrease in luminescence efficiency with LET. At 3 Gy, the luminescence efficiency was about 60% in the Bragg-peak region. The study implies that the RL-signal from Al2O3:C could potentially be suitable for medical proton dosimetry in the 0-0.3 Gy range even without any LET-dependent correction factors.
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| 14. |
- Eklund, Karin, 1978-
(författare)
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Modeling Silicon Diode Dose Response in Radiotherapy Fields using Fluence Pencil Kernels
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In radiotherapy, cancer is treated with ionizing radiation, most commonly bremsstrahlung photons from electrons of several MeV. Secondary electrons produced in photon-interactions results in dose deposition. The treatment response is low for low doses, raises sharply for normal treatment doses and saturates at higher doses. This response pattern applies to both eradication of tumors and to complications in healthy tissues. Well controlled treatments require accurate dosimetry since the uncertainty in delivered dose will be magnified 1 to 5 times in treatment response variations. Techniques that superpose many small radiation fields to concentrate the dose to a localized target are becoming increasingly used. A detector with high spatial resolution suitable for such fields is a silicon diode. To maintain the current accuracy of the dosimetric calibration of 1.5%, diode measurements relative to this calibration should preferably be possible at 0.5% accuracy level. The main limitation of silicon diodes is their over-response to low-energy photons. This problem has been adressed with the insertion of a high atomic number filter in diodes. For modeling diode detector response one must quantify the spectral variations in the irradiated medium resulting from variations of the beam parameters. This requires understanding of the particle transport and can be achieved by Monte Carlo simulations. However, the small dimensions of the detector geometry compared to surrounding medium makes a direct application of Monte Carlo impractical due to the large amount of CPU time necessary to reach statistically satisfactory results. In this work a fast method for spectra calculations is used, based on superposition of mono-energetic fluence pencil kernels. Building on this base a general model for silicon response functions in photon fields is developed. The incident photons are bipartitioned into a low and a high energy component. The high energy part is treated with the Spencer-Attic cavity theory while the low energy part and scattered photons are treated with large cavity theory. The deviations from electron equilibrium are investigated and handled with correction factors. The result is used to correct unshielded diode measurements, with an overall uncertainty less than 0.5%, except for very small fields where the precision is around 1-2%, thus eliminating the need for less predictable shielded diodes for measurements in photon fields.
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| 15. |
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| 16. |
- Grusell, Erik
(författare)
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Comments on 'The influence of dose heterogeneity on tumor control probability in fractionated radiation therapy'
- 2013
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Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 0031-9155 .- 1361-6560. ; 58:18, s. 6585-6589
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- By analyzing the radiobiological model, and the equations derived from the model, it is shown that the main results of the article 'The influence of dose heterogeneity on tumor control probability in fractionated radiation therapy' by Wiklund et al (2011 Phys. Med. Biol. 56 7585-600) are valid only under the condition that the dose to any cell is statistically independent of the dose to any other cell in the same fraction. This condition is in practice not fulfilled for radiotherapy. Hence the main results and most of the discussion are not applicable to fractionated radiation therapy.
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| 17. |
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| 18. |
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| 19. |
- Grusell, Erik
(författare)
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On the definition of absorbed dose
- 2015
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Ingår i: Radiation Physics and Chemistry. - : Elsevier BV. - 0969-806X .- 1879-0895. ; 107, s. 131-135
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: The quantity absorbed dose is used extensively in all areas concerning the interaction of ionizing radiation with biological organisms, as well as with matter in general. The most recent and authoritative definition of absorbed dose is given by the International Commission on Radiation Units and Measurements (ICRU) in ICRU Report 85. However, that definition is incomplete. The purpose of the present work is to give a rigorous definition of absorbed dose. Methods: Absorbed dose is defined in terms of the random variable specific energy imparted. A random variable is a mathematical function, and it cannot be defined without specifying its domain of definition which is a probability space. This is not done in report 85 by the ICRU, mentioned above. Results: In the present work a definition of a suitable probability space is given, so that a rigorous definition of absorbed dose is possible. This necessarily includes the specification of the experiment which the probability space describes. In this case this is an irradiation, which is specified by the initial particles released and by the material objects which can interact with the radiation. Some consequences are discussed. Specific energy imparted is defined for a volume, and the definition of absorbed dose as a point function involves the specific energy imparted for a small mass contained in a volume surrounding the point. A possible more precise definition of this volume is suggested and discussed. Conclusions: The importance of absorbed dose motivates a proper definition, and one is given in the present work. No rigorous definition has been presented before. (C) 2014 Elsevier Ltd. All rights reserved.
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| 20. |
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| 21. |
- Lorin, Stefan, et al.
(författare)
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Development of a compact proton scanning system in Uppsala with a moveable second magnet
- 2000
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Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 0031-9155 .- 1361-6560. ; 45, s. 1151-
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Tidskriftsartikel (refereegranskat)abstract
- A scanned proton beam yields dose distributions that in most cases are superior to passively scattered proton beams and to other external radiation treatment modalities. The present paper gives a description of the scanning system that has been developed at the Svedberg Laboratory (TSL) in Uppsala. The scanning technique and the technical design are described. The solution with a small pole gap of the magnets and a moveable second magnet results in a very compact scanning head, which can therefore be incorporated in a gantry of relatively limited size. A prototype was constructed that has been used to realize various dose distributions with a scanned beam of 180 MeV protons at TSL.
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| 22. |
- Lorin, Stefan, et al.
(författare)
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Reference dosimetry in a scanned pulsed proton beam using ionisation chambers and a Faraday cup
- 2008
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Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 0031-9155 .- 1361-6560. ; 53:13, s. 3519-3529
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Tidskriftsartikel (refereegranskat)abstract
- In order to give the correct dose to a patient, the monitor chamber for a proton scanning system has to be calibrated. As recombination of ion pairs occurs in the monitor chamber, the relation between the number of particles traversing it per time unit and the ionization chamber signal is not linear. A method developed for a scanned pulsed proton beam taking the nonlinear monitor signal into account is described. A vital part of the reference dosimetry procedure is to determine the absorbed dose under reference conditions, which is recommended to be done with an ionization chamber. For a scanned pulsed proton beam, the recombination in the ionization chamber is not negligible and the signal from the ionization chamber has to be corrected. In this work, it is shown that although the pulse length is comparable to the ion transit time the beam can be considered as continuously scanned if the applied high voltage is not too small. Also shown is that the two-voltage formula for a continuous beam is under some conditions applicable for a continuous scanned beam as well.
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| 23. |
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| 24. |
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| 25. |
- Tilly, David, 1974-, et al.
(författare)
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Dose coverage calculation using a statistical shape model : applied to cervical cancer radiotherapy
- 2017
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Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 0031-9155 .- 1361-6560. ; 62:10, s. 4140-4159
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Tidskriftsartikel (refereegranskat)abstract
- A comprehensive methodology for treatment simulation and evaluation of dose coverage probabilities is presented where a population based statistical shape model (SSM) provide samples of fraction specific patient geometry deformations.The learning data consists of vector fields from deformable image registration of repeated imaging giving intra-patient deformations which are mapped to an average patient serving as a common frame of reference. The SSM is created by extracting the most dominating eigenmodes through principal component analysis of the deformations from all patients. The sampling of a deformation is thus reduced to sampling weights for enough of the most dominating eigenmodes that describe the deformations.For the cervical cancer patient datasets in this work, we found seven eigenmodes to be sufficient to capture 90% of the variance in the deformations of the, and only three eigenmodes for stability in the simulated dose coverage probabilities. The normality assumption of the eigenmode weights was tested and found relevant for the 20 most dominating eigenmodes except for the first. Individualization of the SSM is demonstrated to be improved using two deformation samples from a new patient. The probabilistic evaluation provided additional information about the trade-offs compared to the conventional single dataset treatment planning.
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| 26. |
- Tilly, David, 1974-, et al.
(författare)
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Probabilistic optimization of dose coverage in radiotherapy
- 2019
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Ingår i: Physics and Imaging in Radiation Oncology. - : ELSEVIER. - 2405-6316. ; 10, s. 1-6
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Tidskriftsartikel (refereegranskat)abstract
- Background and purpose: Probabilistic optimization is an alternative to margins for handling geometrical uncertainties in treatment planning of radiotherapy where uncertainties are explicitly incorporated in the optimization. We present a novel probabilistic method based on the same statistical measures as those behind conventional margin based planning. Material and methods: Percentile Dosage (PD) was defined as the dose coverage that a treatment plan meet or exceed to a given probability. For optimization, we used the convex measure Expected Percentile Dosage (EPD) defined as the average dose coverage below a given PD. An iterative method gradually adjusted the constraint tolerance associated with the EPD until the desired target PD was met. It was applied to planning of cervical cancer patients focusing on systematic uncertainty caused by organ deformation. The resulting plans were compared to margin based plans using target and organ at risk PDs. Results: The EPD tolerance converged in less than ten iterations to produce a PD within 0.1 Gy of the requested. The PD was on average within 0.5% of the requested PD when validated versus independent scenarios. The rectum volume, extracted from the PDs, receiving 90% of the intended target dose was decreased with 16% for the same target PD in comparison to margin based plans. Conclusions: The proposed probabilistic optimization method enabled prescription of a dose volume histogram metric to a chosen confidence. The probabilistic plans showed improved target dose homogeneity and decreased rectum dose for the same target dose coverage compared to margin based plans.
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| 27. |
- Tilly, David, 1974-, et al.
(författare)
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Probabilistic optimization of the dose coverage – applied to radiotherapy treatment planning of cervical cancer
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Probabilistic (or robust) optimization is an alternative to margins for handling geometrical uncertainties in treatment planning of radiotherapy where the uncertainties are explicitly incorporated in the optimization through sampling of treatment scenarios. We present a probabilistic method based on statistical measures close to those behind conventional margin based planning. The dose planner requests a dose coverage to a specified probability, which the algorithm then attempts to fulfil.We define the Percentile UnderDosage (PUD) as a measure of the target minimum dose coverage probability, i.e. the dose coverage that a treatment plan meet or exceed to a given probability. Margin based planning commonly use the implicit probabilistic treatment criteria that the 90th PUD is at least 95% of the intended dose. For optimization we use the Expected Percentile UnderDosage (EPUD) defined as the average dose coverage below a given PUD. The EPUD is, in contrast to PUD, a convex measure and hence standard optimization techniques can be used to find the optimal treatment plan. We propose an iterative method where a treatment optimization is performed at each iteration and the EPUD tolerance is adjusted gradually until a desired PUD is met.We demonstrate our proposed probabilistic planning method for cervical cancer patients. The uncertainty caused by organ deformation is explicitly included in the probabilistic optimization where a statistical shape model is used to sample scenarios with different deformations. For all patients in this work, the iterative process of finding the EPUD tolerance converged in less than 10 iterations to within 0.1Gy of the requested PUD even though a conservative update scheme was used. The resulting estimated PUD was validated based on 1000 simulated scenarios not part of the optimization yielding an agreement within 1.2% of the requested PUD.
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| 28. |
- Tilly, David, 1974-
(författare)
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Probabilistic treatment planning based on dose coverage : How to quantify and minimize the effects of geometric uncertainties in radiotherapy
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Traditionally, uncertainties are handled by expanding the irradiated volume to ensure target dose coverage to a certain probability. The uncertainties arise from e.g. the uncertainty in positioning of the patient at every fraction, organ motion and in defining the region of interests on the acquired images. The applied margins are inherently population based and do not exploit the geometry of the individual patient. Probabilistic planning on the other hand incorporates the uncertainties directly into the treatment optimization and therefore has more degrees of freedom to tailor the dose distribution to the individual patient. The aim of this thesis is to create a framework for probabilistic evaluation and optimization based on the concept of dose coverage probabilities. Several computational challenges for this purpose are addressed in this thesis.The accuracy of the fraction by fraction accumulated dose depends directly on the accuracy of the deformable image registration (DIR). Using the simulation framework, we could quantify the requirements on the DIR to 2 mm or less for a 3% uncertainty in the target dose coverage.Probabilistic planning is computationally intensive since many hundred treatments must be simulated for sufficient statistical accuracy in the calculated treatment outcome. A fast dose calculation algorithm was developed based on the perturbation of a pre-calculated dose distribution with the local ratio of the simulated treatment’s fluence and the fluence of the pre-calculated dose. A speedup factor of ~1000 compared to full dose calculation was achieved with near identical dose coverage probabilities for a prostate treatment.For some body sites, such as the cervix dataset in this work, organ motion must be included for realistic treatment simulation. A statistical shape model (SSM) based on principal component analysis (PCA) provided the samples of deformation. Seven eigenmodes from the PCA was sufficient to model the dosimetric impact of the interfraction deformation.A probabilistic optimization method was developed using constructs from risk management of stock portfolios that enabled the dose planner to request a target dose coverage probability. Probabilistic optimization was for the first time applied to dataset from cervical cancer patients where the SSM provided samples of deformation. The average dose coverage probability of all patients in the dataset was within 1% of the requested.
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| 29. |
- Tilly, Nina, et al.
(författare)
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Comparison of Monte Carlo calculated electron slowing-down spectra generated by 60Co gamma-rays, electrons, protons and light ions
- 2002
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Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 0031-9155 .- 1361-6560. ; 47:8, s. 1303-19
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Tidskriftsartikel (refereegranskat)abstract
- When analysing the factors affecting the relative biological effectiveness (RBE) of different radiation qualities, it is essential to consider particularly the low-energy slowing-down electrons (around 100 eV to 1 keV) since they have the potential of inflicting severe damage to the DNA. We present a modified and extended version of the Monte Carlo code PENELOPE that enables scoring of slowing-down spectra. mean local energy imparted spectra and average intra-track nearest-neighbour energy deposition distances of the secondary electrons generated by different radiation qualities, such as electrons, photons, protons and light ions in general. The resulting spectra show that the low-linear energy transfer (LET) beams, 60Co gamma-rays and electrons with initial energies of 0.1 MeV and higher, have as expected approximately the same electron slowing-down fluence per unit dose in the biologically important low-energy interval. Consistent with the general behaviour of the RBE of low-energy electrons, protons and light ions, the low-energy electron slowing-down fluence per unit dose is larger than for low-LET beams, and it increases with decreasing initial projectile energy.
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| 30. |
- Tilly, Nina, et al.
(författare)
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Development and verification of the pulsed scanned proton beam at the The Swedberg Laboratory in Uppsala
- 2007
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Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 0031-9155 .- 1361-6560. ; 52:10, s. 2741-2754
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we present the recent developments made for the scanning system for proton beams at TSL in Uppsala, showing that this system is now fully functional being able to produce conformal intensity modulated scan patterns with sufficient accuracy. A new control and supervising system handling the beam delivery including the control of the synchrocyclotron and the scanning system is developed and described in detail. A complete dosimetry system with transmission ionization chambers and a multi-wire ionization chamber for monitoring of the beam during scanning has been constructed. The details of the dose monitors and the position sensitive multi-wire ionization chamber are presented in this work. Furthermore, we have established procedures for verification measurements to ensure the quality of the beam and also methods for calibration of the beam monitors and relative and absolute dosimetry for complex scanned beams.
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| 31. |
- Vatnitsky, S, et al.
(författare)
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Proton dosimetry intercomparison based on the ICRU report 59 protocol
- 1999
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Ingår i: Radiotherapy and Oncology. - 0167-8140 .- 1879-0887. ; 51:3, s. 273-279
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND AND PURPOSE:A new protocol for calibration of proton beams was established by the ICRU in report 59 on proton dosimetry. In this paper we report the results of an international proton dosimetry intercomparison, which was held at Loma Linda University Medical Center. The goals of the intercomparison were, first, to estimate the level of consistency in absorbed dose delivered to patients if proton beams at various clinics were calibrated with the new ICRU protocol, and second, to evaluate the differences in absorbed dose determination due to differences in 60Co-based ionization chamber calibration factors.MATERIALS AND METHODS:Eleven institutions participated in the intercomparison. Measurements were performed in a polystyrene phantom at a depth of 10.27 cm water equivalent thickness in a 6-cm modulated proton beam with an accelerator energy of 155 MeV and an incident energy of approximately 135 MeV. Most participants used ionization chambers calibrated in terms of exposure or air kerma. Four ionization chambers had 60Co-based calibration in terms of absorbed dose-to-water. Two chambers were calibrated in a 60Co beam at the NIST both in terms of air kerma and absorbed dose-to-water to provide a comparison of ionization chambers with different calibrations.RESULTS:The intercomparison showed that use of the ICRU report 59 protocol would result in absorbed doses being delivered to patients at their participating institutions to within +/-0.9% (one standard deviation). The maximum difference between doses determined by the participants was found to be 2.9%. Differences between proton doses derived from the measurements with ionization chambers with N(K)-, or N(W) - calibration type depended on chamber type.CONCLUSIONS:Using ionization chambers with 60Co calibration factors traceable to standard laboratories and the ICRU report 59 protocol, a distribution of stated proton absorbed dose is achieved with a difference less than 3%. The ICRU protocol should be adopted for clinical proton beam calibration. A comparison of proton doses derived from measurements with different chambers indicates that the difference in results cannot be explained only by differences in 60Co calibration factors.
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| 32. |
- Waldeland, Einar, et al.
(författare)
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Radical formation in lithium formate EPR dosimeters after irradiation with protons and nitrogen ions
- 2010
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Ingår i: Radiation Research. - 0033-7587 .- 1938-5404. ; 174:2, s. 251-257
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Tidskriftsartikel (refereegranskat)abstract
- Radical formation in polycrystalline lithium formate monohydrate after irradiation with gamma rays, protons and nitrogen ions at room temperature was studied by continuous-wave electron paramagnetic resonance (EPR) spectroscopy. The linear energy transfer (LET) of the various radiation beams was 0.2, 0.7-3.9 and 110-164 keV/microm for gamma rays, protons and nitrogen ions, respectively. Doses between 5 and 20 Gy were given. The EPR reading (the area under the EPR absorption resonance) increased linearly with dose for all types of radiation. As the LET increased, the relative effectiveness (the EPR reading per dose relative to that for gamma rays) decreased, while the EPR line width increased. Track structure theory and modeling of detector effectiveness predicted the dosimeter response observed after proton and nitrogen-ion irradiation. A semi-empirical line broadening model including dipolar spin-spin interactions was developed that explained the dependence of the line width on LET. The findings indicate that the local radical density in lithium formate is increased after high-LET irradiation.
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| 33. |
- Åström, Lennart, et al.
(författare)
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Two decades of high dose rate brachytherapy with external beam radiotherapy for prostate cancer
- 2018
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Ingår i: Radiotherapy and Oncology. - : Elsevier BV. - 0167-8140 .- 1879-0887. ; 127:1, s. 81-87
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Tidskriftsartikel (refereegranskat)abstract
- Background: High-dose-rate brachytherapy (HDR-BT) has optimal prerequisites in radiotherapy of prostate cancer (PC) with a conformal dose distribution and high doses per fraction giving a biological dose escalation. We report the outcome after HDR-BT and external beam radiotherapy (EBRT) after 20 years of experience.Material and methods: The study includes 623 patients, median age of 66 years, treated from 1995 to 2008 and a median follow up of 11 years (range 2–266 months). Androgen deprivation therapy was given to 429 patients (69%). The HDR-BT was given with two 10 Gy fractions and the EBRT with 2 Gy fractions to 50 Gy.Results: The 10-year PC-specific survival was 100%, 92%, 91%, and 75% for low-, intermediate-, high- and very high-risk patients respectively, and the 10-year probability of PSA relapse was 0%, 21%, 33%, and 65% respectively. The 10-year actuarial prevalence for ≥grade 2 GU- and GI-toxicities were 28% and 12% respectively and for ≥grade 3, 4% and 1% respectively. Urethral stricture was the most frequent GU complication with a 10-year actuarial incidence of 10%. Treatment without dose constraints for the urethra conferred a higher incidence 18%, compared to 5% after 2003 (p < 0.001). Sixteen patients experienced grade 4 GU toxicity, of which 13 were treated before 2003. No grade 4 rectal toxicity was seen.Conclusion: The combination of EBRT and HDR-BT with adequate dose constraints to risk organs provides satisfactory long-term tumour control even in high-risk patients. GI toxicity stabilised but GU toxicity progressed during the 10-year follow up.
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