| 1. |
- Ardenfors, Oscar, et al.
(författare)
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Out-of-field doses from secondary radiation produced in proton therapy and the associated risk of radiation-induced cancer from a brain tumor treatment
- 2018
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Ingår i: Physica medica (Testo stampato). - : Elsevier BV. - 1120-1797 .- 1724-191X. ; 53, s. 129-136
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Tidskriftsartikel (refereegranskat)abstract
- PurposeTo determine out-of-field doses produced in proton pencil beam scanning (PBS) therapy using Monte Carlo simulations and to estimate the associated risk of radiation-induced second cancer from a brain tumor treatment.MethodsSimulations of out-of-field absorbed doses were performed with MCNP6 and benchmarked against measurements with tissue-equivalent proportional counters (TEPC) for three irradiation setups: two irradiations of a water phantom using proton energies of 78-147 MeV and 177-223 MeV, and one brain tumor irradiation of a whole-body phantom. Out-of-field absorbed and equivalent doses to organs in a whole-body phantom following a brain tumor treatment were subsequently simulated and used to estimate the risk of radiation-induced cancer. Additionally, the contribution of absorbed dose originating from radiation produced in the nozzle was calculated from simulations.ResultsOut-of-field absorbed doses to the TEPC ranged from 0.4 to 135 mu Gy/Gy. The average deviation between simulations and measurements of the water phantom irradiations was about 17%. The absorbed dose contribution from radiation produced in the nozzle ranged between 0 and 70% of the total dose; the contribution was however small in absolute terms. The absorbed and equivalent doses to the organs ranged between 0.2 and 60 mu Gy/Gy and 0.5-151 mu Sv/Gy. The estimated lifetime risk of radiation-induced second cancer was approximately 0.01%.ConclusionsThe agreement of out-of-field absorbed doses between measurements and simulations was good given the sources of uncertainties. Calculations of out-of-field organ doses following a brain tumor treatment indicated that proton PBS therapy of brain tumors is associated with a low risk of radiation-induced cancer.
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| 2. |
- Lindblom, Emely, et al.
(författare)
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Accounting for Two Forms of Hypoxia for Predicting Tumour Control Probability in Radiotherapy : An In Silico Study
- 2018
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Ingår i: Advances in Experimental Medicine and Biology. - Cham : Springer International Publishing. - 0065-2598 .- 2214-8019. ; 1042, s. 183-187
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Tidskriftsartikel (refereegranskat)abstract
- The progress in functional imaging and dose delivery has opened the possibility of targeting tumour hypoxia with radiotherapy. Advanced approaches apply quantitative information on tumour oxygenation retrieved from imaging in dose prescription. These do not, however, take into account the potential difference in radiosensitivity of chronically and acutely hypoxic cells. It was the aim of this study to evaluate the implications of assuming the same or different sensitivities for the hypoxic cells. An in silico 3D-model of a hypoxic tumour with heterogeneous oxygenation was used to model the probabilities of tumour control with different radiotherapy regimens. The results show that by taking into account the potential lower radioresistance of chronically hypoxic cells deprived of oxygen and nutrients, the total dose required to achieve a certain level of control is substantially reduced for a given fractionation scheme in comparison to the case when chronically and acutely hypoxic cells are assumed to have similar features. The results also suggest that the presence of chronic hypoxia could explain the success of radiotherapy for some hypoxic tumours. Given the implications for clinical dose escalation trials, further exploration of the influence of the different forms of hypoxia on treatment outcome is therefore warranted.
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| 3. |
- Ardenfors, Oscar, et al.
(författare)
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IMPACT OF IRRADIATION SETUP IN PROTON SPOT SCANNING BRAIN THERAPY ON ORGAN DOSES FROM SECONDARY RADIATION
- 2018
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Ingår i: Radiation Protection Dosimetry. - : Oxford University Press (OUP). - 0144-8420 .- 1742-3406. ; 180:1-4, s. 261-266
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Tidskriftsartikel (refereegranskat)abstract
- A Monte Carlo model of a proton spot scanning pencil beam was used to simulate organ doses from secondary radiation produced from brain tumour treatments delivered with either a lateral field or a vertex field to one adult and one paediatric patient. Absorbed doses from secondary neutrons, photons and protons and neutron equivalent doses were higher for the vertex field in both patients, but the differences were low in absolute terms. Absorbed doses ranged between 0.1 and 43 mu Gy. Gy(-1) in both patients with the paediatric patient receiving higher doses. The neutron equivalent doses to the organs ranged between 0.5 and 141 mu Sv. Gy(-1) for the paediatric patient and between 0.2 and 134 mu Sv. Gy(-1) for the adult. The highest neutron equivalent dose from the entire treatment was 7 mSv regardless of field setup and patient size. The results indicate that different field setups do not introduce large absolute variations in out-of-field doses produced in patients undergoing proton pencil beam scanning of centrally located brain tumours.
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| 4. |
- Ardenfors, Oscar, et al.
(författare)
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Organ doses from a proton gantry-mounted cone-beam computed tomography system characterized with MCNP6 and GATE
- 2018
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Ingår i: Physica medica (Testo stampato). - : Elsevier BV. - 1120-1797 .- 1724-191X. ; 53, s. 56-61
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Tidskriftsartikel (refereegranskat)abstract
- PurposeTo determine organ doses from a proton gantry-mounted cone-beam computed tomography (CBCT) system using two Monte Carlo codes and to study the influence on organ doses from different acquisition modes and repeated imaging.MethodsThe CBCT system was characterized with MCNP6 and GATE using measurements of depth doses in water and spatial profiles in air. The beam models were validated against absolute dose measurements and used to simulate organ doses from CBCT imaging with head, thorax and pelvis protocols. Anterior and posterior 190° scans were simulated and the resulting organ doses per mAs were compared to those from 360° scans. The influence on organ doses from repeated imaging with different imaging schedules was also investigated.ResultsThe agreement between MCNP6, GATE and measurements with regard to depth doses and beam profiles was within 4% for all protocols and the corresponding average agreement in absolute dose validation was 4%. Absorbed doses for in-field organs from 360° scans ranged between 6 and 8 mGy, 15–17 mGy and 24–54 mGy for the head, thorax and pelvis protocols, respectively. Cumulative organ doses from repeated CBCT imaging ranged between 0.04 and 0.32 Gy for weekly imaging and 0.2–1.6 Gy for daily imaging. The anterior scans resulted in an average increase in dose per mAs of 24% to the organs of interest relative to the 360° scan, while the posterior scan showed a 37% decrease.ConclusionsA proton gantry-mounted CBCT system was accurately characterized with MCNP6 and GATE. Organ doses varied greatly depending on acquisition mode, favoring posterior scans.
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| 5. |
- Lillhök, J., et al.
(författare)
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RADIATION PROTECTION MEASUREMENTS WITH THE VARIANCE-COVARIANCE METHOD IN THE STRAY RADIATION FIELDS FROM PHOTON AND PROTON THERAPY FACILITIES
- 2018
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Ingår i: Radiation Protection Dosimetry. - : Oxford University Press (OUP). - 0144-8420 .- 1742-3406. ; 180:1-4, s. 338-341
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Tidskriftsartikel (refereegranskat)abstract
- The microdosimetric variance-covariance method was used to study the stray radiation fields from the photon therapy facility at the Technical University of Denmark and the scanned proton therapy beam at the Skandion Clinic in Uppsala, Sweden. Two TEPCs were used to determine the absorbed dose, the dose-average lineal energy, the dose-average quality factor and the dose equivalent. The neutron component measured by the detectors at the proton beam was studied through Monte Carlo simulations using the code MCNP6. In the photon beam the stray absorbed dose ranged between 0.3 and 2.4 mu Gy per monitor unit, and the dose equivalent between 0.4 and 9 mu Sv per monitor unit, depending on beam energy and measurement position. In the proton beam the stray absorbed dose ranged between 3 and 135 mu Gy per prescribed Gy, depending on detector position and primary proton energy.
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| 6. |
- Toma-Dasu, Iuliana, et al.
(författare)
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Evaluating tumor response of non-small cell lung cancer patients with 18F-fludeoxyglucose positron emission tomography: potential for treatment individualization
- 2015
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Ingår i: International Journal of Radiation Oncology, Biology, Physics. - : Elsevier BV. - 0360-3016 .- 1879-355X. ; 91:2, s. 376-384
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Tidskriftsartikel (refereegranskat)abstract
- Objective: To assess early tumor responsiveness and the corresponding effective radiosensitivity for individual patients with non-small cell lung cancer (NSCLC) based on 2 successive 18F-fludeoxyglucose positron emission tomography (FDG-PET) scans.Methods and Materials: Twenty-six NSCLC patients treated in Maastricht were included in the study. Fifteen patients underwent sequential chemoradiation therapy, and 11 patients received concomitant chemoradiation therapy. All patients were imaged with FDG before the start and during the second week of radiation therapy. The sequential images were analyzed in relation to the dose delivered until the second image. An operational quantity, effective radiosensitivity, αeff, was determined at the voxel level. Correlations were sought between the average αeff or the fraction of negative αeff values and the overall survival at 2 years. Separate analyses were performed for the primary gross target volume (GTV), the lymph node GTV, and the clinical target volumes (CTVs).Results: Patients receiving sequential treatment could be divided into responders and nonresponders, using a threshold for the average αeff of 0.003 Gy-1 in the primary GTV, with a sensitivity of 75% and a specificity of 100% (P<.0001). Choosing the fraction of negative αeff as a criterion, the threshold 0.3 also had a sensitivity of 75% and a specificity of 100% (P<.0001). Good prognostic potential was maintained for patients receiving concurrent chemotherapy. For lymph node GTV, the correlation had low statistical significance. A cross-validation analysis confirmed the potential of the method.Conclusions: Evaluation of the early response in NSCLC patients showed that it is feasible to determine a threshold value for effective radiosensitivity corresponding to good response. It also showed that a threshold value for the fraction of negative αeff could also be correlated with poor response. The proposed method, therefore, has potential to identify candidates for more aggressive strategies to increase the rate of local control and also avoid exposing to unnecessary aggressive therapies the majority of patients responding to standard treatment.
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| 7. |
- Ureba, Ana, et al.
(författare)
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Non-linear conversion of HX4 uptake for automatic segmentation of hypoxic volumes and dose prescription
- 2018
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Ingår i: Acta Oncologica. - : Taylor & Francis. - 0284-186X .- 1651-226X. ; 57:4, s. 485-490
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Background: Tumour hypoxia is associated with increased radioresistance and poor response to radiotherapy. Pre-treatment assessment of tumour oxygenation could therefore give the possibility to tailor the treatment by calculating the required boost dose needed to overcome the increased radioresistance in hypoxic tumours. This study concerned the derivation of a non-linear conversion function between the uptake of the hypoxia-PET tracer 18F-HX4 and oxygen partial pressure (pO2).Material and methods: Building on previous experience with FMISO including experimental data on tracer uptake and pO2, tracer-specific model parameters were derived for converting the normalised HX4-uptake at the optimal imaging time point to pO2. The conversion function was implemented in a Python-based computational platform utilising the scripting and the registration modules of the treatment planning system RayStation. Subsequently, the conversion function was applied to determine the pO2 in eight non-small-cell lung cancer (NSCLC) patients imaged with HX4-PET before the start of radiotherapy. Automatic segmentation of hypoxic target volumes (HTVs) was then performed using thresholds around 10 mmHg. The HTVs were compared to sub-volumes segmented based on a tumour-to-blood ratio (TBR) of 1.4 using the aortic arch as the reference oxygenated region. The boost dose required to achieve 95% local control was then calculated based on the calibrated levels of hypoxia, assuming inter-fraction reoxygenation due to changes in acute hypoxia but no overall improvement of the oxygenation status.Results: Using the developed conversion tool, HTVs could be obtained using pO2 a threshold of 10 mmHg which were in agreement with the TBR segmentation. The dose levels required to the HTVs to achieve local control were feasible, being around 70–80 Gy in 24 fractions.Conclusions: Non-linear conversion of tracer uptake to pO2 in NSCLC imaged with HX4-PET allows a quantitative determination of the dose-boost needed to achieve a high probability of local control.
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| 8. |
- Ödén, Jakob, et al.
(författare)
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The influence of breathing motion and a variable relative biological effectiveness in proton therapy of left-sided breast cancer
- 2017
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Ingår i: Acta Oncologica. - : Taylor & Francis. - 0284-186X .- 1651-226X. ; 56:11, s. 1428-1436
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Tidskriftsartikel (refereegranskat)abstract
- Background: Proton breast radiotherapy has been suggested to improve target coverage as well as reduce cardiopulmonary and integral dose compared with photon therapy. This study aims to assess this potential when accounting for breathing motion and a variable relative biological effectiveness (RBE).Methods: Photon and robustly optimized proton plans were generated to deliver 50 Gy (RBE) in 25 fractions (RBE=1.1) to the CTV (whole left breast) for 12 patients. The plan evaluation was performed using the constant RBE and a variable RBE model. Robustness against breathing motion, setup, range and RBE uncertainties was analyzed using CT data obtained at free-breathing, breath-hold-at-inhalation and breath-hold-at-exhalation.Results: All photon and proton plans (RBE=1.1) met the clinical goals. The variable RBE model predicted an average RBE of 1.18 for the CTVs (range 1.14–1.21) and even higher RBEs in organs at risk (OARs). However, the dosimetric impact of this latter aspect was minor due to low OAR doses. The normal tissue complication probability (NTCP) for the lungs was low for all patients (<1%), and similar for photons and protons. The proton plans were generally considered robust for all patients. However, in the most extreme scenarios, the lowest dose received by 98% of the CTV dropped from 96 to 99% of the prescribed dose to around 92–94% for both protons and photons. Including RBE uncertainties in the robustness analysis resulted in substantially higher worst-case OAR doses.Conclusions: Breathing motion seems to have a minor effect on the plan quality for breast cancer. The variable RBE might impact the potential benefit of protons, but could probably be neglected in most cases where the physical OAR doses are low. However, to be able to identify outlier cases at risk for high OAR doses, the biological evaluation of proton plans taking into account the variable RBE is recommended.
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| 9. |
- Ardenfors, Oscar, et al.
(författare)
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Modelling of a proton spot scanning system using MCNP6
- 2017
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Ingår i: International Nuclear Science and Technology Conference. - : Institute of Physics (IOP). ; 860, s. 012025-
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Konferensbidrag (refereegranskat)abstract
- The aim of this work was to model the characteristics of a clinical proton spot scanning beam using Monte Carlo simulations with the code MCNP6. The proton beam was defined using parameters obtained from beam commissioning at the Skandion Clinic, Uppsala, Sweden. Simulations were evaluated against measurements for proton energies between 60 and 226 MeV with regard to range in water, lateral spot sizes in air and absorbed dose depth profiles in water. The model was also used to evaluate the experimental impact of lateral signal losses in an ionization chamber through simulations using different detector radii. Simulated and measured distal ranges agreed within 0.1 mm for R90 and R80 , and within 0.2 mm for R50 . The average absolute difference of all spot sizes was 0.1 mm. The average agreement of absorbed dose integrals and Bragg-peak heights was 0.9%. Lateral signal losses increased with incident proton energy with a maximum signal loss of 7% for 226 MeV protons. The good agreement between simulations and measurements supports the assumptions and parameters employed in the presented Monte Carlo model. The characteristics of the proton spot scanning beam were accurately reproduced and the model will prove useful in future studies on secondary neutrons.
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| 10. |
- Antonovic, Laura, 1982-, et al.
(författare)
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Relative clinical effectiveness of carbon ion radiotherapy: theoretical modelling for H&N tumours
- 2015
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Ingår i: Journal of radiation research. - : Oxford University Press (OUP). - 0449-3060 .- 1349-9157. ; 56:4, s. 639-645
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Tidskriftsartikel (refereegranskat)abstract
- Comparison of the efficiency of photon and carbon ion radiotherapy (RT) administered with the same number of fractions might be of limited clinical interest, since a wide range of fractionation patterns are used clinically today. Due to advanced photon treatment techniques, hypofractionation is becoming increasingly accepted for prostate and lung tumours, whereas patients with head and neck tumours still benefit from hyperfractionated treatments. In general, the number of fractions is considerably lower in carbon ion RT. A clinically relevant comparison would be between fractionation schedules that are optimal within each treatment modality category. In this in silico study, the relative clinical effectiveness (RCE) of carbon ions was investigated for human salivary gland tumours, assuming various radiation sensitivities related to their oxygenation. The results indicate that, for hypoxic tumours in the absence of reoxygenation, the RCE (defined as the ratio of D50 for photons to carbon ions) ranges from 3.5 to 5.7, corresponding to carbon ion treatments given in 36 and 3 fractions, respectively, and 30 fractions for photons. Assuming that interfraction local oxygenation changes take place, results for RCE are lower than that for an oxic tumour if only a few fractions of carbon ions are used. If the carbon ion treatment is given in more than 12 fractions, the RCE is larger for the hypoxic than for the well-oxygenated tumour. In conclusion, this study showed that in silico modelling enables the study of a wide range of factors in the clinical considerations and could be an important step towards individualisation of RT treatments.
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