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EP-1378 INVESTIGATING THE EFFECT OF DOSE RATE ON THE DURATION OF IMRT QA PROCEDURE
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phantom. An angular dose dependency of the MatriXX detector was required and previously characterized. The final evolution to a 3D evaluation of a VMAT plan is achieved by combining the MatriXX device with the COMPASS software (IBA Dosimetry). The measuring set allows us to reconstruct a 3D dose distribution on to the CT images of the patient based on measured fluence placing the detector on a gantry holder as in the first arrangement. The system also permits to recalculate the dose on the CT scan of the patient as another TPS. Results: 75 VMAT plans have been measured. Chamber-based point dose measurements have a mean percentage difference of -0.51% ± 0.32% from planned dose. 44 plans have been tested using the first solution (detector + gantry holder), obtaining a mean gamma passing rate of 99.50% ± 0.41% (see figure). 31 plans have been measured using the second solution (detector + cubic phantom), obtaining a mean gamma passing rate of 99.05% ± 0.67% for the coronal plane and 98.19% ± 1.10% for the sagittal plane (see figure). 3D VMAT evaluation using COMPASS software have been used in several patients in conjunction with the other solutions.
S523
measurement, the results were again highly consistent (≤0.3%). The comparison results were reported in Table 1 in detail.
Conclusions: Our study shows that accuracy of QA procedure is not reduced by the recalculation using different dose rate. Since the higher dose rate reduces QA processing time, the IMRT QA can be carried out for the dose rate of 600 MU/min even if the treatment of patients is delivered at 300 MU/min. EP-1379 A COMPARISON OF VERIFICATIONS IN DIFFERENT METHODS FOR IMRT PLANS Y. Yin1, J. Chen1, D. Li2 1 Shandong Cancer Hospital, Radiation Physics, Jinan, China 2 Shandong Normal University, College of Physics and Electronics, Jinan, China
Conclusions: 2D detector arrays can be successfully used for VMAT patient-specific QA using external devices, as the gantry holder or specific phantoms. 3D plan verification based on patient anatomy can be successfully done using the COMPASS software. EP-1378 INVESTIGATING THE EFFECT OF DOSE RATE ON THE DURATION OF IMRT QA PROCEDURE A. Canbolat1, H. Kivanc1, Y. Yedekci1, A. Dogan1, T. Yolcu1, M. Yeginer1, D. Yildiz1 1 Hacettepe Medical School, Department of Radiation Oncology, Ankara, Turkey Purpose/Objective: Work-load of medical physicists has recently increased due to the using of IMRT technique in most of radiation oncology centers. IMRT technique requires lots of QA procedure, which takes a long time, for many patients in one day. Therefore, the radiotherapy centers which have a tight schedule in IMRT QA tend to perform this procedure quickly. The purpose of this study is to investigate the accuracy of IMRT QA performed with different dose rates for the same plan. Materials and Methods: In this study, IMRT plans were created for 5 patients using Eclipse TPS v8.9 (Varian Medical Systems). The reference dose rate for these plans was 300 MU/min. Then each plan was recalculated with different dose rates (100, 200, 400, 500, 600 MU/min) after optimization process. IMRT QA procedures were prepared on the 2D-Array and Universal phantom for all plans to measure 2D dose distribution and point dose, respectively. Dose distribution acquired with 2D-Array measurement for each plan was compared with reference dose rate measurement using gamma analyze (3mm, %3). Absolute point dose values acquired with PTW 30010 detector using the alternative dose rates were compared with reference dose rate measurement for each patient QA. Results: Even though recreating the same IMRT plans with higher dose rate caused higher MU, fraction delivery time of high dose rate is less than low dose rate. 2-D dose distributions for the different dose rates of each plan were compared using gamma analyze. The consistency of the plans was ≥96%. When the dose distribution of the different dose rates were compared with the reference dose rate for the same plan, the gamma analysis was found 100%. Point dose measurements for different dose rates were less than 3% when compared the point dose data acquired from treatment planning system. When these measurements were compared with the reference dose rate
Purpose/Objective: The aim was to investigate the practicability and accuracy of ionization chamber array in different measuring ways for the identical IMRT plans. Materials and Methods: 20 cases with head&neck tumor (2011, May to 2011, Nov) were enrolled. Using Varian Eclipse version 8.6 treatment planning system, 9-field IMRT plans were generated for each case. All plans were delivered to Varian Trilogy accelerator for pre-treatment verification. The verification tool is ionization chamber array (MatriXX, OmniPro-I'mRT v1.7, IBA) with muti-cube and angle sensor. Each plan was measured in two ways: a). all fields were arranged at 0º; b). fields to deliver at their planned angles. All fields measured in two ways were generated into separate verification-plan. The plan fluences and measured dose reconstruction were compared with a criteria of 3%/3mm. The γ value of each same-name field were analysed using two-tailed t test. Results: For the fields at 0º, 40º, 160º, 200º, 240º and 320º in the TPS plans, there' s no significant difference with P values > 0.05. For the fields at 80º, 120º and 280º, the λ values differed significantly with P < 0.05. 0
40
80
120
160
200
240
280
320
a(%) 98.5±0.5 98.3±0.7 98.7±0.7 98.1±0.8 98.3±0.6 98.7±0.9 98.5±0.5 98.1±0.7 98.4±0.5 b(%) 98.3±0.7 98.2±0.9 95.1±1.9 95.9±1.4 98.3±1.0 98.4±0.8 98.0±1.2 95.4±1.7 98.1±0.9
Conclusions: The comparison results showed that measurements keep consistent at most angles. Even equiped with angle sensor, there is still effects to measurement results at angles close to horizon. Therefore, the verification arranging all fields at 0º is better but not ideal than the real delivery. EP-1380 MEASUREMENTS OF PERIPHERAL PHOTON DOSE IN CONFORMAL RADIOTHERAPY B. Palma Fernández1, M.R. Expósito1, F. Sansaloni2, J.I. Lagares2, J.L. Muñiz2, R. Linares3, F. Morán-Fitch1, J.A. Terrón4, B. Sánchez-Nieto5, F. Sánchez-Doblado1 1 Universidad de Sevilla, Depto. de Fisiología Médica y Biofísica, Seville, Spain 2 Centro de Investigaciones Energéticas Medioambientales y Tecnológicas (CIEMAT), Depto. de Tecnología, Madrid, Spain 3 Hospital Infanta Luisa, Servicio Radiofísica, Seville, Spain 4 Hospital Univ. Virgen Macarena, Servicio Radiofísica, Seville, Spain 5 Pontificia Univ. Católica de Chile, Depto. Física, Santiago, Chile Purpose/Objective: In radiotherapy (RT) treatments, dose deposition happens not only in the region used for planning, but also in the rest
phantom. An angular dose dependency of the MatriXX detector was required and previously characterized. The final evolution to a 3D evaluation of a VMAT plan is achieved by combining the MatriXX device with the COMPASS software (IBA Dosimetry). The measuring set allows us to reconstruct a 3D dose distribution on to the CT images of the patient based on measured fluence placing the detector on a gantry holder as in the first arrangement. The system also permits to recalculate the dose on the CT scan of the patient as another TPS. Results: 75 VMAT plans have been measured. Chamber-based point dose measurements have a mean percentage difference of -0.51% ± 0.32% from planned dose. 44 plans have been tested using the first solution (detector + gantry holder), obtaining a mean gamma passing rate of 99.50% ± 0.41% (see figure). 31 plans have been measured using the second solution (detector + cubic phantom), obtaining a mean gamma passing rate of 99.05% ± 0.67% for the coronal plane and 98.19% ± 1.10% for the sagittal plane (see figure). 3D VMAT evaluation using COMPASS software have been used in several patients in conjunction with the other solutions.
S523
measurement, the results were again highly consistent (≤0.3%). The comparison results were reported in Table 1 in detail.
Conclusions: Our study shows that accuracy of QA procedure is not reduced by the recalculation using different dose rate. Since the higher dose rate reduces QA processing time, the IMRT QA can be carried out for the dose rate of 600 MU/min even if the treatment of patients is delivered at 300 MU/min. EP-1379 A COMPARISON OF VERIFICATIONS IN DIFFERENT METHODS FOR IMRT PLANS Y. Yin1, J. Chen1, D. Li2 1 Shandong Cancer Hospital, Radiation Physics, Jinan, China 2 Shandong Normal University, College of Physics and Electronics, Jinan, China
Conclusions: 2D detector arrays can be successfully used for VMAT patient-specific QA using external devices, as the gantry holder or specific phantoms. 3D plan verification based on patient anatomy can be successfully done using the COMPASS software. EP-1378 INVESTIGATING THE EFFECT OF DOSE RATE ON THE DURATION OF IMRT QA PROCEDURE A. Canbolat1, H. Kivanc1, Y. Yedekci1, A. Dogan1, T. Yolcu1, M. Yeginer1, D. Yildiz1 1 Hacettepe Medical School, Department of Radiation Oncology, Ankara, Turkey Purpose/Objective: Work-load of medical physicists has recently increased due to the using of IMRT technique in most of radiation oncology centers. IMRT technique requires lots of QA procedure, which takes a long time, for many patients in one day. Therefore, the radiotherapy centers which have a tight schedule in IMRT QA tend to perform this procedure quickly. The purpose of this study is to investigate the accuracy of IMRT QA performed with different dose rates for the same plan. Materials and Methods: In this study, IMRT plans were created for 5 patients using Eclipse TPS v8.9 (Varian Medical Systems). The reference dose rate for these plans was 300 MU/min. Then each plan was recalculated with different dose rates (100, 200, 400, 500, 600 MU/min) after optimization process. IMRT QA procedures were prepared on the 2D-Array and Universal phantom for all plans to measure 2D dose distribution and point dose, respectively. Dose distribution acquired with 2D-Array measurement for each plan was compared with reference dose rate measurement using gamma analyze (3mm, %3). Absolute point dose values acquired with PTW 30010 detector using the alternative dose rates were compared with reference dose rate measurement for each patient QA. Results: Even though recreating the same IMRT plans with higher dose rate caused higher MU, fraction delivery time of high dose rate is less than low dose rate. 2-D dose distributions for the different dose rates of each plan were compared using gamma analyze. The consistency of the plans was ≥96%. When the dose distribution of the different dose rates were compared with the reference dose rate for the same plan, the gamma analysis was found 100%. Point dose measurements for different dose rates were less than 3% when compared the point dose data acquired from treatment planning system. When these measurements were compared with the reference dose rate
Purpose/Objective: The aim was to investigate the practicability and accuracy of ionization chamber array in different measuring ways for the identical IMRT plans. Materials and Methods: 20 cases with head&neck tumor (2011, May to 2011, Nov) were enrolled. Using Varian Eclipse version 8.6 treatment planning system, 9-field IMRT plans were generated for each case. All plans were delivered to Varian Trilogy accelerator for pre-treatment verification. The verification tool is ionization chamber array (MatriXX, OmniPro-I'mRT v1.7, IBA) with muti-cube and angle sensor. Each plan was measured in two ways: a). all fields were arranged at 0º; b). fields to deliver at their planned angles. All fields measured in two ways were generated into separate verification-plan. The plan fluences and measured dose reconstruction were compared with a criteria of 3%/3mm. The γ value of each same-name field were analysed using two-tailed t test. Results: For the fields at 0º, 40º, 160º, 200º, 240º and 320º in the TPS plans, there' s no significant difference with P values > 0.05. For the fields at 80º, 120º and 280º, the λ values differed significantly with P < 0.05. 0
40
80
120
160
200
240
280
320
a(%) 98.5±0.5 98.3±0.7 98.7±0.7 98.1±0.8 98.3±0.6 98.7±0.9 98.5±0.5 98.1±0.7 98.4±0.5 b(%) 98.3±0.7 98.2±0.9 95.1±1.9 95.9±1.4 98.3±1.0 98.4±0.8 98.0±1.2 95.4±1.7 98.1±0.9
Conclusions: The comparison results showed that measurements keep consistent at most angles. Even equiped with angle sensor, there is still effects to measurement results at angles close to horizon. Therefore, the verification arranging all fields at 0º is better but not ideal than the real delivery. EP-1380 MEASUREMENTS OF PERIPHERAL PHOTON DOSE IN CONFORMAL RADIOTHERAPY B. Palma Fernández1, M.R. Expósito1, F. Sansaloni2, J.I. Lagares2, J.L. Muñiz2, R. Linares3, F. Morán-Fitch1, J.A. Terrón4, B. Sánchez-Nieto5, F. Sánchez-Doblado1 1 Universidad de Sevilla, Depto. de Fisiología Médica y Biofísica, Seville, Spain 2 Centro de Investigaciones Energéticas Medioambientales y Tecnológicas (CIEMAT), Depto. de Tecnología, Madrid, Spain 3 Hospital Infanta Luisa, Servicio Radiofísica, Seville, Spain 4 Hospital Univ. Virgen Macarena, Servicio Radiofísica, Seville, Spain 5 Pontificia Univ. Católica de Chile, Depto. Física, Santiago, Chile Purpose/Objective: In radiotherapy (RT) treatments, dose deposition happens not only in the region used for planning, but also in the rest