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A reconstruction method of asymmetric doses profiles in external radiation therapy
Abstracts/Physica Medica 31 (2015) e23–e54
References [1] Létourneau D, Finlay M, O’Sullivan B, Waldron JN, Cummings BJ, Ringash J, et al. Lack of influence of intravenous contrast on head and neck IMRT dose distributions. Acta Oncol (Madr) 2008;47(1):90–4. doi:10.1080/ 02841860701418861. [2] Liu AJ, Vora N, Suh S, Liu A, Schultheiss TE, Wong JYC. Effect of CT contrast on volumetric arc therapy planning (RapidArc and helical tomotherapy) for head and neck cancer. Med Dosim 2015;40(1):32–6. doi:10.1016/j .meddos.2014.07.003. http://dx.doi.org/10.1016/j.ejmp.2015.10.026
25 PRACTICAL IMPLEMENTATION OF A PATIENT SPECIFIC QA ON CYBERKNIFE USING GAFCHROMIC® EBT3 FILM: ONE-YEAR RESULTS ANALYSIS J. Bellec a, F. Jouyaux a, M. Perdrieux a, S. Sorel a, J. Lesnard a, O. Henry a, J.P. Manens a,b, C. Lafond a,b. a Centre Eugène Marquis, Rennes, France; b L.T.S.I., Inserm U1099, Rennes, France Introduction: The Cyberknife® (Accuray) robotic radiosurgery system requires a strict comprehensive quality assurance (QA) program. AAPM-TG135 recommendations mainly focus on machine specific QA. At present, unlike other complex treatment modalities (IMRT, VMAT) the patient specific QA recommendations for Cyberknife are very limited. The purpose of this study is to propose a patient specific protocol based on a systematic pretreatment plan dose verification using radiochromic films and to present the results after one-year of implementation in our institution. Methods: The study was realized on a Cyberknife® M6™ (v10.1) commissioned in February 2014. A pretreatment plan dose verification was done using a Gafchromic® EBT3 film (Ashland) put in a water-equivalent “Baby Blue” phantom (Standard Imaging). The films were scanned with a 10000XL desktop scanner (Epson). The multi-channel methodology of FilmQAPro Software (Ashland) was used for film dose calibration. The comparison of film dose with calculated planar dose was done without dose normalization by gamma index method using Verisoft analysis software (PTW). For each controlled treatment plan, the percentage of accepted dose points and the mean gamma value of a dose criteria of 3% (local) and a distance-to-agreement criteria of 2 mm were reported (threshold: 30% of maximum dose). The targeting accuracy was evaluated by registering the film dose map with the calculated dose map. The statistical process control (SCP) was used for creating control charts and defining acceptability thresholds. Results: 310 treatment plans for cranial and extra-cranial cases were controlled. The mean percentage of accepted points were 97.1% (Standard Deviation (SD): 2.8%) for the 3% (local)/2 mm criteria and the mean gamma value associated was 0.44 (SD: 0.10). The mean geometric deviations between measured and calculated dose distribution was 0.3 mm (SD: 0.7 mm). The acceptability thresholds defined with SCP were 91.0% and 0.67 for the percentage of accepted points and mean gamma value respectively. 11 treatment plans were outside these control limits. The analysis of the assignable causes of these deviations will be discussed. Conclusions: Our pretreatment dose verification methodology using Gafchromic® EBT3 film is adapted to assess the overall dose delivery process on Cyberknife®. This patient specific QA protocol can detect some suboptimal situations not highlighted in an exclusive machine specific QA program. In our institution, it is still applied for each patient with the use of SCP in accordance with our QA protocols already used for other complex treatment modalities. The method is being optimized for the integration of respiratory tracking. http://dx.doi.org/10.1016/j.ejmp.2015.10.027
26 A RECONSTRUCTION METHOD OF ASYMMETRIC DOSES PROFILES IN EXTERNAL RADIATION THERAPY W. Mota a, D. Lemonnier a, M. Diot-Vaschy a,b, R. Gschwind a, F. Tochet a,b. a Université de Franche-Comté – IRMA, Chrono-Environnement, Montbéliard, France; b Service de Radiothérapie, CHRU Jean Minjoz, Besançon, France
e33
Introduction: During the monthly quality control of Varian 2100C accelerator at Besançon’s CHRU an asymmetry of 112% was detected on dose profile axis of photons beam of 18 MV. In order to reevaluate the patients’ dosimetries that could potentially be impacted by this asymmetry, we considered asymmetry incident happened the day after the last previous dosimetric quality control. Bibliography highlighted a lack of methods for this situation. The purpose of this study is to propose a simplified reconstruction method for asymmetric dose profiles to reassess the dosimetry on every affected patients. Methods: A method called «n field method» was applied to compute actual delivered dose for a treatment using an asymmetric beam. Asymmetric beam reconstruction is created by segmenting the field originally used into n fields of various weights. For our dose profiles, a beam is reconstructed by three fields: one field is typical treatment beam delivering minimal dose and two “field-in-field” cause the expected asymmetry. The segmented dose profiles were obtained in the following conditions: SSD = 90 cm, SAD = 100 cm, with our asymmetric beam of 10 cm × 10 cm and 20 cm × 20 cm, was measured with ionization chamber 0.3 cc Semiflex in water phantom PTW MP3 and two matrices of detectors PTW 2DArray seven29 and PTW-Octavius in PMMA. Then, these profiles were studied with Oncentra Master Plan TPS and compared with Monte-Carlo Simulation (Beamnrc code). Dose were recalculated for 21 patients with the profile rebuild using the three fields segmentation. Results: With three field segmentation, the mean and the maximal differences between dose profiles are 0.457% and 1.67%, respectively. This method is enabled to recalculate 21 doses delivered to patients 7 of them received a dose involving a special medical care. It was used with filtered fields. Nowadays, the dynamics wedges are not always verified. The first results using filtered fields showed difficulties to reproduce the asymmetry. Conclusions: The “N fields’-method” allow to rebuild asymmetric profiles. The maximal difference dose is 1.67% the worst case. The study on the filtered fields will be continued. One assumption is to replace the dynamic wedge by a physical wedge and to determine the weighting corrections. http://dx.doi.org/10.1016/j.ejmp.2015.10.028 27 VALIDATION OF THE DOSE CALCULATION ALGORITHM ACUROS XB AND IMPACT OF ITS USAGE IN CLINICAL STEREOTACTIC TREATMENTS T. Younes, L. Vieillevigne. Institut Universitaire du Cancer de Toulouse, Institut Claudius Regaud, France Introduction: The aim of this study was to assess the accuracy of the dose calculation algorithm based on the resolution of Boltzmann equation: “Acuros XB” (AXB) implemented in Eclipse (Varian Medical Systems). To evaluate AXB, we followed the methodology recommended by the IAEA TECDOC 1583 [1]. AXB was also tested for clinical extra cranial stereotactic treatment cases. In all cases, AXB was compared against the Analytical Anisotropic Algorithm (AAA). Methods: The IAEA TECDOC 1583 presents eight different fields configurations in heterogeneous media. All plans were created on a CIRS thorax phantom model 002LFC including different tissue equivalent inserts (water, bone and lung). Measurements were performed with a PinPoint ionization chamber (type 31016, PTW) on Novalis TrueBeam STx for 6 MV and 10 MV photons with and without flattening filter (6FF, 6FFF, 10FF, 10FFF). Measurements of stereotactic treatments were also performed on the CIRS thorax phantom. Results: AXB calculation showed an excellent agreement with measurements for the eight configurations of the IAEA TECDOC 1583. All measurements fulfilled the agreement criterion given in the IAEA TECDOC 1583. The biggest difference between measured and calculated dose in lung was less than 0.6% for all photon energies. Unlike, in the lung region, AAA showed deviations that didn’t met the agreement criterion. Maximum deviations were 4.4%, 3.35%, 2.27% and 1.6% for respectively 6FF, 10FF, 6FFF and 10FFF photon energies. The results in bone region didn’t show a significant difference between both algorithms and this is probably due to the fact that our measurements were performed in a solid water insert placed inside the bone. More studies are ongoing to measure inside the
References [1] Létourneau D, Finlay M, O’Sullivan B, Waldron JN, Cummings BJ, Ringash J, et al. Lack of influence of intravenous contrast on head and neck IMRT dose distributions. Acta Oncol (Madr) 2008;47(1):90–4. doi:10.1080/ 02841860701418861. [2] Liu AJ, Vora N, Suh S, Liu A, Schultheiss TE, Wong JYC. Effect of CT contrast on volumetric arc therapy planning (RapidArc and helical tomotherapy) for head and neck cancer. Med Dosim 2015;40(1):32–6. doi:10.1016/j .meddos.2014.07.003. http://dx.doi.org/10.1016/j.ejmp.2015.10.026
25 PRACTICAL IMPLEMENTATION OF A PATIENT SPECIFIC QA ON CYBERKNIFE USING GAFCHROMIC® EBT3 FILM: ONE-YEAR RESULTS ANALYSIS J. Bellec a, F. Jouyaux a, M. Perdrieux a, S. Sorel a, J. Lesnard a, O. Henry a, J.P. Manens a,b, C. Lafond a,b. a Centre Eugène Marquis, Rennes, France; b L.T.S.I., Inserm U1099, Rennes, France Introduction: The Cyberknife® (Accuray) robotic radiosurgery system requires a strict comprehensive quality assurance (QA) program. AAPM-TG135 recommendations mainly focus on machine specific QA. At present, unlike other complex treatment modalities (IMRT, VMAT) the patient specific QA recommendations for Cyberknife are very limited. The purpose of this study is to propose a patient specific protocol based on a systematic pretreatment plan dose verification using radiochromic films and to present the results after one-year of implementation in our institution. Methods: The study was realized on a Cyberknife® M6™ (v10.1) commissioned in February 2014. A pretreatment plan dose verification was done using a Gafchromic® EBT3 film (Ashland) put in a water-equivalent “Baby Blue” phantom (Standard Imaging). The films were scanned with a 10000XL desktop scanner (Epson). The multi-channel methodology of FilmQAPro Software (Ashland) was used for film dose calibration. The comparison of film dose with calculated planar dose was done without dose normalization by gamma index method using Verisoft analysis software (PTW). For each controlled treatment plan, the percentage of accepted dose points and the mean gamma value of a dose criteria of 3% (local) and a distance-to-agreement criteria of 2 mm were reported (threshold: 30% of maximum dose). The targeting accuracy was evaluated by registering the film dose map with the calculated dose map. The statistical process control (SCP) was used for creating control charts and defining acceptability thresholds. Results: 310 treatment plans for cranial and extra-cranial cases were controlled. The mean percentage of accepted points were 97.1% (Standard Deviation (SD): 2.8%) for the 3% (local)/2 mm criteria and the mean gamma value associated was 0.44 (SD: 0.10). The mean geometric deviations between measured and calculated dose distribution was 0.3 mm (SD: 0.7 mm). The acceptability thresholds defined with SCP were 91.0% and 0.67 for the percentage of accepted points and mean gamma value respectively. 11 treatment plans were outside these control limits. The analysis of the assignable causes of these deviations will be discussed. Conclusions: Our pretreatment dose verification methodology using Gafchromic® EBT3 film is adapted to assess the overall dose delivery process on Cyberknife®. This patient specific QA protocol can detect some suboptimal situations not highlighted in an exclusive machine specific QA program. In our institution, it is still applied for each patient with the use of SCP in accordance with our QA protocols already used for other complex treatment modalities. The method is being optimized for the integration of respiratory tracking. http://dx.doi.org/10.1016/j.ejmp.2015.10.027
26 A RECONSTRUCTION METHOD OF ASYMMETRIC DOSES PROFILES IN EXTERNAL RADIATION THERAPY W. Mota a, D. Lemonnier a, M. Diot-Vaschy a,b, R. Gschwind a, F. Tochet a,b. a Université de Franche-Comté – IRMA, Chrono-Environnement, Montbéliard, France; b Service de Radiothérapie, CHRU Jean Minjoz, Besançon, France
e33
Introduction: During the monthly quality control of Varian 2100C accelerator at Besançon’s CHRU an asymmetry of 112% was detected on dose profile axis of photons beam of 18 MV. In order to reevaluate the patients’ dosimetries that could potentially be impacted by this asymmetry, we considered asymmetry incident happened the day after the last previous dosimetric quality control. Bibliography highlighted a lack of methods for this situation. The purpose of this study is to propose a simplified reconstruction method for asymmetric dose profiles to reassess the dosimetry on every affected patients. Methods: A method called «n field method» was applied to compute actual delivered dose for a treatment using an asymmetric beam. Asymmetric beam reconstruction is created by segmenting the field originally used into n fields of various weights. For our dose profiles, a beam is reconstructed by three fields: one field is typical treatment beam delivering minimal dose and two “field-in-field” cause the expected asymmetry. The segmented dose profiles were obtained in the following conditions: SSD = 90 cm, SAD = 100 cm, with our asymmetric beam of 10 cm × 10 cm and 20 cm × 20 cm, was measured with ionization chamber 0.3 cc Semiflex in water phantom PTW MP3 and two matrices of detectors PTW 2DArray seven29 and PTW-Octavius in PMMA. Then, these profiles were studied with Oncentra Master Plan TPS and compared with Monte-Carlo Simulation (Beamnrc code). Dose were recalculated for 21 patients with the profile rebuild using the three fields segmentation. Results: With three field segmentation, the mean and the maximal differences between dose profiles are 0.457% and 1.67%, respectively. This method is enabled to recalculate 21 doses delivered to patients 7 of them received a dose involving a special medical care. It was used with filtered fields. Nowadays, the dynamics wedges are not always verified. The first results using filtered fields showed difficulties to reproduce the asymmetry. Conclusions: The “N fields’-method” allow to rebuild asymmetric profiles. The maximal difference dose is 1.67% the worst case. The study on the filtered fields will be continued. One assumption is to replace the dynamic wedge by a physical wedge and to determine the weighting corrections. http://dx.doi.org/10.1016/j.ejmp.2015.10.028 27 VALIDATION OF THE DOSE CALCULATION ALGORITHM ACUROS XB AND IMPACT OF ITS USAGE IN CLINICAL STEREOTACTIC TREATMENTS T. Younes, L. Vieillevigne. Institut Universitaire du Cancer de Toulouse, Institut Claudius Regaud, France Introduction: The aim of this study was to assess the accuracy of the dose calculation algorithm based on the resolution of Boltzmann equation: “Acuros XB” (AXB) implemented in Eclipse (Varian Medical Systems). To evaluate AXB, we followed the methodology recommended by the IAEA TECDOC 1583 [1]. AXB was also tested for clinical extra cranial stereotactic treatment cases. In all cases, AXB was compared against the Analytical Anisotropic Algorithm (AAA). Methods: The IAEA TECDOC 1583 presents eight different fields configurations in heterogeneous media. All plans were created on a CIRS thorax phantom model 002LFC including different tissue equivalent inserts (water, bone and lung). Measurements were performed with a PinPoint ionization chamber (type 31016, PTW) on Novalis TrueBeam STx for 6 MV and 10 MV photons with and without flattening filter (6FF, 6FFF, 10FF, 10FFF). Measurements of stereotactic treatments were also performed on the CIRS thorax phantom. Results: AXB calculation showed an excellent agreement with measurements for the eight configurations of the IAEA TECDOC 1583. All measurements fulfilled the agreement criterion given in the IAEA TECDOC 1583. The biggest difference between measured and calculated dose in lung was less than 0.6% for all photon energies. Unlike, in the lung region, AAA showed deviations that didn’t met the agreement criterion. Maximum deviations were 4.4%, 3.35%, 2.27% and 1.6% for respectively 6FF, 10FF, 6FFF and 10FFF photon energies. The results in bone region didn’t show a significant difference between both algorithms and this is probably due to the fact that our measurements were performed in a solid water insert placed inside the bone. More studies are ongoing to measure inside the