| 1. |
- Ceberg, Sofie, et al.
(författare)
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Evaluation of breathing interplay effects during VMAT by using 3D gel measurements
- 2013
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Ingår i: 7th International Conference on 3D Radiation Dosimetry (IC3DDose). - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 444, s. 012098-012098
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Konferensbidrag (refereegranskat)abstract
- Respiratory motion during dynamic radiotherapy may affect the absorbed dose distribution both by dose-reducing smoothing and by more complicated interplay effects. In this study we present a novel method to determine the relative importance of these two effects. For the two dynamic deliveries studied in this work, the expected target dose reduction due to the smoothing effect was estimated by measurements convolved by the motion function. Remaining absorbed dose differences were attributed to interplay effects between the motion of the gel phantom and the movement of the modulating MLC leaves during modulated arc radiotherapy. The total dosimetric effect due to breathing motion and dynamic MLC motion during VMAT delivery resulted in an average of about 4% target dose reduction. Comparing with only the smoothing effect, the average difference was decreased to around 1%, and the remaining distribution was attributed to interplay effects. Although the interplay effects were small compared to the smoothing effect, the standard deviations of 1.4-2.3% (1SD) were larger than the narrow distribution for repeated stationary measurement with a standard deviation between 0.5-0.9% (1SD).
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| 2. |
- Ceberg, Sofie, et al.
(författare)
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Modelling the dynamic dose response of an nMAG polymer gel dosimeter.
- 2012
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Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 1361-6560 .- 0031-9155. ; 57:15, s. 4845-4853
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Tidskriftsartikel (refereegranskat)abstract
- Gel dosimetry measures the absorbed radiation dose with high spatial resolution in 3D. However, recently published data show that the response of metacrylic-based polymer gels depends on the segmented delivery pattern, which could potentially be a considerable disadvantage for measurements of modern dynamic radiotherapy techniques. The aim of this study is to design a dynamic compartment model for the response of a gel dosimeter, exposed to an arbitrary irradiation pattern (segmented delivery and intensity modulation), in order to evaluate the associated effects on absorbed dose measurements. The model is based on the separation of the protons affecting the magnetic resonance signal (i.e. the R2 value) into six compartments, described by a set of differential equations. The model is used to calculate R2 values for a number of different segmented delivery patterns between 0-4 Gy over 1-33 fractions. Very good agreement is found between calculated and measured R2 values, with an average difference of 0.3 ± 1.1% (1 SD). The model is also used to predict the behaviour of a gel dosimeter exposed to irradiation according to typical IMRT, VMAT and respiratory gating scenarios. The calculated R2 values are approximately independent of the segmented delivery, given that the same total dose is delivered during the same total time. It is concluded that this study helps to improve the theoretical understanding of the dependence of metacrylic-based polymer gel response to segmented radiation delivery.
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| 3. |
- Nordström, Fredrik, et al.
(författare)
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3D geometric gel dosimetry verification of intraprostatic fiducial guided hypofractionated radiotherapy of prostate cancer
- 2010
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Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6596. ; 250, s. 287-291
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Konferensbidrag (refereegranskat)abstract
- This pre-study is aimed to investigate the feasibility of a normoxic polyacrylamide gel (nPAG) dosimeter with implanted gold fiducials to evaluate the geometric precision, including setup correction strategies, in the delivery of hypofractionated treatments. For this purpose a phantom consisting of three parts was constructed: (1) the patient simulating volume, providing realistic scatter conditions and weight, (2) a bottle containing the active dosimetric volume and (3) the gold fiducials and the fiducial support structure. A 6.1 Gy prostate IMRT treatment was delivered to the phantom using the sliding-window technique. The phantom was positioned prior to the treatment using the implanted fiducials and kV on-board imaging. An overlay of the 95% isosurface of the TPS calculated dose distribution and the measured dose distribution using gel showed good agreement. The clinical target volume (CTV) was well centred inside the 95% isodose surface of the measured volume. It was shown for the evaluated case that the use of on-board imaging and integrated setup correction tools could be used to compensate for a deliberately introduced offset in CTV position. The study showed that MRI based nPAG gel dosimetry can be used to verify setup correction procedures using implanted gold fiducials.
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| 4. |
- Ceberg, Sofie
(författare)
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3D Verification of Dynamic and Breathing Adapted Radiotherapy using Polymer Gel Dosimetry
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Polymer gel dosimetry has been used since the 1990s, and several studies have shown that this detector system can be used for verification of static absorbed dose distributions in three dimensions (3D). Its unique properties, such as high resolution, normal tissue equivalence and independency of energy, field size and direction of the incident radiation, should also be advantageous for dosimetric verification of radiotherapy using today’s and tomorrow’s dynamic delivery techniques. However, unfavourable properties have also been reported, such as dose rate-, temperature-, oxygen contamination-, and cooling rate dependencies. It has been shown in this thesis that these shortcomings can be overcome by using a good practice strategy, and that results can be obtained with an uncertainty comparable to other detector systems. Modern dynamic treatment techniques such as for example breathing adapted radiotherapy have created a need for dosimetry during motion, which poses new challenges. The purpose of this thesis was to investigate the performance of polymer gel dosimetry in such situations. For comparison, measurements using 1D, 2D and quasi-3D detector systems, as well as Monte Carlo simulations, were used to validate the results obtained using gel dosimetry. The absorbed dose integrating property during fractionated irradiation delivery was investigated for two different polymer gel systems. A fractionation dependency was observed, especially pronounced for one of the systems. This effect was further investigated using compartment modelling. The results indicated that the dose response was approximately independent of the fractionation scheme, provided that the total absorbed dose was delivered during the same total delivery time. Under respiratory-like motion no influence of the dose rate variation related to motion in and out of the beam was observed. Full 3D absorbed dose verifications were also carried out for advanced delivery techniques involving simultaneous beam intensity modulation and gantry rotation around the patient, so called volumetric modulated arc therapy (VMAT). Using both gel measurements and Monte Carlo simulations it was successfully demonstrated that the VMAT plan was both accurately calculated and delivered as planned. Additionally, the performance of a tumour-tracking system during VMAT delivery was investigated. The dosimetric measurements, obtained using both gel and a bi-planar diode array, verified the improved dose conformity when enabling the target tracking system. In this thesis the unique 3D properties of gel dosimetry were fully utilized, and the known uncertainties were minimized in every step of the procedure. It was shown that polymer gel is a useful tool for relative 3D dosimetry in dynamic and breathing adaptive radiotherapy.
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| 5. |
- Ceberg, Sofie, et al.
(författare)
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Radiotherapy delivery during motion
- 2010
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Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 250
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Tidskriftsartikel (refereegranskat)abstract
- This paper discusses the 3D dosimetric consequences of radiotherapy delivery during two kinds of motion, (i) the respiratory motion by the patient and (ii) the motion by the gantry while rotating around the patient. Respiratory motion primarily compromises treatments in the thorax and abdomen regions. Several strategies to reduce respiratory motion effects have been developed or are under development. The organ motion could for instance be measured and incorporated in the treatment planning, or adapted to by using respiratory gating and tumour-tracking delivery techniques. Gantry motion is involved in various forms of intensity-modulated arc-therapy techniques. The purpose is to increase the modulation by simultaneously varying the MLC positions, the rotation speed of the gantry, and the dose rate during the treatment. The advantage of these techniques is the increased possibility to deliver a high absorbed dose to the target volume while minimizing the dose to normal tissues. However, the dosimetric uncertainties associated with motion, small fields and steep dose gradients, has to be evaluated in detail, and this requires adequate true 3D dose-verification tools.
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| 6. |
- Ceberg, Sofie, et al.
(författare)
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RapidArc treatment verification in 3D using polymer gel dosimetry and Monte Carlo simulation.
- 2010
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Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 1361-6560 .- 0031-9155. ; 55:17, s. 4885-4898
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to verify the advanced inhomogeneous dose distribution produced by a volumetric arc therapy technique (RapidArc) using 3D gel measurements and Monte Carlo (MC) simulations. The TPS (treatment planning system)-calculated dose distribution was compared with gel measurements and MC simulations, thus investigating any discrepancy between the planned dose delivery and the actual delivery. Additionally, the reproducibility of the delivery was investigated using repeated gel measurements. A prostate treatment plan was delivered to a 1.3 liter nPAG gel phantom using one single arc rotation and a target dose of 3.3 Gy. Magnetic resonance imaging of the gel was carried out using a 1.5 T scanner. The MC dose distributions were calculated using the VIMC-Arc code. The relative absorbed dose differences were calculated voxel-by-voxel, within the volume enclosed by the 90% isodose surface (VOI(90)), for the TPS versus gel and TPS versus MC. The differences between the verification methods, MC versus gel, and between two repeated gel measurements were investigated in the same way. For all volume comparisons, the mean value was within 1% and the standard deviation of the differences was within 2.5% (1SD). A 3D gamma analysis between the dose matrices were carried out using gamma criteria 3%/3 mm and 5%/5 mm (% dose difference and mm distance to agreement) within the volume enclosed by the 50% isodose surface (VOI(50)) and the 90% isodose surface (VOI(90)), respectively. All comparisons resulted in very high pass rates. More than 95% of the TPS points were within 3%/3 mm of both the gel measurement and MC simulation, both inside VOI(50) and VOI(90). Additionally, the repeated gel measurements showed excellent consistency, indicating reproducible delivery. Using MC simulations and gel measurements, this verification study successfully demonstrated that the RapidArc plan was both accurately calculated and delivered as planned.
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| 7. |
- Ceberg, Sofie, et al.
(författare)
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Tumor-tracking radiotherapy of moving targets; verification using 3D polymer gel, 2D ion-chamber array and biplanar diode array
- 2010
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Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 250:1, s. 235-239
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to carry out a dosimetric verification of a dynamic multileaf collimator (DMLC)-based tumor-tracking delivery during respiratory-like motion. The advantage of tumor-tracking radiation delivery is the ability to allow a tighter margin around the target by continuously following and adapting the dose delivery to its motion. However, there are geometric and dosimetric uncertainties associated with beam delivery system constraints and output variations, and several investigations have to be accomplished before a clinical integration of this tracking technique. Two types of delivery were investigated in this study I) a single beam perpendicular to a target with a one dimensional motion parallel to the MLC moving direction, and II) an intensity modulated arc delivery (RapidArc®) with a target motion diagonal to the MLC moving direction. The feasibility study (I) was made using an 2D ionisation chamber array and a true 3D polymer gel. The arc delivery (II) was verified using polymer gel and a biplanar diode array. Good agreement in absorbed dose was found between delivery to a static target and to a moving target with DMLC tracking using all three detector systems. However, due to the limited spatial resolution of the 2D array a detailed comparison was not possible. The RapidArc® plan delivery was successfully verified using the biplanar diode array and true 3D polymer gel, and both detector systems could verify that the DMLC-based tumor-tracking delivery system has a very good ability to account for respiratory target motion.
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| 8. |
- Edvardsson, Anneli, et al.
(författare)
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The effect of systematic set-up deviations on the absorbed dose distribution for left-sided breast cancer treated with respiratory gating
- 2013
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Ingår i: 7th International Conference on 3D Radiation Dosimetry (IC3DDose). - : IOP Publishing. - 1742-6596 .- 1742-6588. ; 444, s. 012099-012099
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Konferensbidrag (refereegranskat)abstract
- The aim of this study was 1) to investigate interfraction set-up uncertainties for patients treated with respiratory gating for left-sided breast cancer, 2) to investigate the effect of the inter-fraction set-up on the absorbed dose-distribution for the target and organs at risk (OARs) and 3) optimize the set-up correction strategy. By acquiring multiple set-up images the systematic set-up deviation was evaluated. The effect of the systematic set-up deviation on the absorbed dose distribution was evaluated by 1) simulation in the treatment planning system and 2) measurements with a biplanar diode array. The set-up deviations could be decreased using a no action level correction strategy. Not using the clinically implemented adaptive maximum likelihood factor for the gating patients resulted in better set-up. When the uncorrected set-up deviations were simulated the average mean absorbed dose was increased from 1.38 to 2.21 Gy for the heart, 4.17 to 8.86 Gy to the left anterior descending coronary artery and 5.80 to 7.64 Gy to the left lung. Respiratory gating can induce systematic set-up deviations which would result in increased mean absorbed dose to the OARs if not corrected for and should therefore be corrected for by an appropriate correction strategy.
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| 9. |
- Jönsson, Mattias, et al.
(författare)
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Technical evaluation of different motion-monitoring systems for respiratory gating in radiation therapy
- 2013
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Ingår i: Medical Physics in the Baltic States. - 1822-5721. ; , s. 38-41
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Konferensbidrag (refereegranskat)abstract
- The purpose of this work was to evaluate three motion-monitoring systems: Sentinel (TM), Catalyst (TM) (both C-RAD) and Real-time Position Management (RPM (TM)) system (Varian Medical Systems Inc) for respiratory gating in radiotherapy. To measure the systems. latency, an in-house built circuit with a microcontroller operating a piston was used. The trigger pulse was sent from the gating systems to the accelerator within 300 mu s. However, the response time of the accelerator could be over 300 ms
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| 10. |
- Svensson, Henrik, et al.
(författare)
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An investigation of a potential multipurpose readout modality for two and three-dimensional dosimetry using optical computed tomography scanners
- 2011
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Ingår i: Medical Physics in the Baltic States. - 1822-5721. ; , s. 39-44
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Konferensbidrag (refereegranskat)abstract
- Radiochromic film, polymer gel and radiochromic plastic are three different kinds of dosimeters developed for radiation therapy and suitable for optical readout. In this study, different optical CT scanners are used to scan the dosimeters to find out if they could be used as multi-purpose scanners, i.e. for readout of the different kinds of dosimeters. Promising results are found but further development needs to be done before any of the scanners could be categorized as multi-purpose scanners.
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| 11. |
- Svensson, H., et al.
(författare)
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Feasibility study using MRI and two optical CT scanners for readout of polymer gel and Presage (TM)
- 2013
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Ingår i: 7th International Conference on 3D Radiation Dosimetry (IC3DDose). - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 444, s. 012079-012079
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Konferensbidrag (refereegranskat)abstract
- The aim of this study was to compare the conventional combination of three-dimensional dosimeter (nPAG gel) and readout method (MRI) with other combinations of three-dimensional dosimeters (nPAG gel/Presage (TM)) and readout methods (optical CT scanners). In the first experiment, the dose readout of a gel irradiated with a four field-box technique was performed with both an Octopus IQ scanner and MRI. It was seen that the MRI readout agreed slightly better to the TPS. In another experiment, a gel and a Presage (TM) sample were irradiated with a VMAT field and read out using MRI and a fast laser scanner, respectively. A comparison between the TPS and the volumes revealed that the MRI/gel readout had closer resemblance to the TPS than the optical CT/Presage (TM) readout. There are clearly potential in the evaluated optical CT scanners, but more time has to be invested in the particular scanning scenario than was possible in this study.
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