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EP-1364 EVALUATION OF DOSE CONTROL SYSTEM IMPLEMENTATION IN A TOMOTHERAPY HI-ART UNIT
S518
Conclusions: The beam characteristics, linearity and dose delivery at low monitor unit have been studied comparing two different LINAC working modes. Differences in the dose delivery and problems in the reproducibility of the flatness have been found. Anyway, these results do not have clinical implications. EP-1364 EVALUATION OF DOSE CONTROL SYSTEM IMPLEMENTATION IN A TOMOTHERAPY HI-ART UNIT J.A. Ramos Pacho1, S. Garcia Repiso1, J. Hernandez Rodriguez1, C. Martin Rincon1, J.M. Verde Velasco1, E. De Sena Espinel1, M.E. Perez Alvarez1, J.M. Delgado Aparicio1 1 Hospital Universitario, Medical Physics and Radiation Protection, Salamanca, Spain Purpose/Objective: Tomotherapy Hi-Art radiation unit consists of a linear accelerator that can rotate around the treatment couch while it is moving at constant speed, i.e., it works like a CT unit but with a treatment aim. This unit has a binary MLC of 64 leaves moving continuously during irradiation time. These and other characteristics allow a helical IMRT treatment. This kind of units had not a feedback loop between the dose monitor chambers and the magnetron, so it can’t be assured that the dose rate output is constant during treatment. We observed a drift in the dose rate of about 2% down for large treatment times. To solve this problem, Tomotherapy Inc. is installing a dose servo namely DCS (Dose Control System), which controls the magnetron current to adjust the dose rate output automatically. Our hospital is the second institution in Europe in which the DCS has been installed. In this paper measurements performed before and after the implementation of dose servo are compared. Materials and Methods: To evaluate the dose rate drift, a rotational plan of 510 seconds long has been developed. This time is a usual treatment time and long enough to ensure a complete observation of this effect. The plan has a period of 17 seconds, in which the MLC leaves are fully open and the treatment couch is stationary. Charge measurements have been performed with Exradín A1SL Slimline Miniature Shonka IC (Standard Imaging) of 0.056 cm3, placed into the closest to the center hole of the Cheese Phantom and connected to the TomoElectrometer. Using the TomoElectrometer software (TEMS) we obtain a plot of charge collected every second vs time. These data have been processed, plotting the cycle-integrated charge vs time to avoid dose rate oscillations due to rotation of the gantry. Results:
The graph shows that the dose rate is more stable after the dose servo implementation. Conclusions: The dose servo installation allows a more accurate dose delivering during the irradiation and a improvement of treatment quality. EP-1365 VERIFICATION OF THE 3D DOSE DISTRIBUTION IN SPINAL RADIOSURGERY BY USING AGEL DOSIMETER D. Lee1, H. Chung2 1 Inje University IlsanPaik Hospital, Neurosurgery, Goyang, Korea Republic of 2 Seoul National University, Neurosurgery, Seoul, Korea Republic of
ESTRO 31
Purpose/Objective: The aim of this study was to compare the 3D relative dose distribution between the commercially available BANG3gel dosimeter(MGS Research Inc., CT,USA) and clinical plan dosimetry applied to spinal tumor patients, as well as to compare gel dosimetry and film dosimetry of the axial plane of the isocenter. To validate polymer gel dosimetry for IMRS dose distribution verification are compared the dose maps with the dose maps obtained from calculated dosimetry with the treatment planning system Materials and Methods: BANG3gel dosimeter and Gafchromic EBT film (ISP, NJ, USA) were used to compare the dose distribution between gel and planned dosimetry of the axial plane at the isocenter. The BANG3gel was designed for use in our study in the dose range of 0 – 20 Gy by using a response modifier. To obtain a polymer gel dosimeter calibration curve, 8 test vials containing the gel were irradiated at dose levels of 1, 2, 3, 5, 7, 10, 15, and 20 Gy. We performed radiosurgery treatment on the gel and film by delivering the radiation to the target as a marginal dose and saving the spinal cord as an OAR. Results: We measured both the gel and the film dosimeter in the axial plane. Quantitative evaluation of these results is expressed as DTA. The results show good agreement between the 2 methods at the selected plane. The DTA values of the 80% and 50% isodose lines were within 1.0 mm and 3.0 mm, respectively. The DTA value of the OAR profile was within 1.0 mm in both gel and film dosimetry. In the coronal direction between the gel and the treatment planning calculations with 1 plane passing through the isocenter. The DTA values of the 80% and 50% isodose lines were within 1.0 mm and 3.0 mm, respectively. In the sagittal direction from the gel and the treatment planning calculations with 1 plane passing through the isocenter plane. The DTA values of the 80% and 50% isodose lines were within 1.1 mm and 2.0 mm, respectively. Conclusions: The data shown in this study support the conclusion that gel dosimetry can produce 3D dose mapping of sufficient quality for dosimetry verification. We observed good agreement between the measured and the calculated dose distribution, within 1 mm in the high-dose gradient region. In addition to sufficiently verifying the 3D dose distributions, we found that the gel dosimeter was a useful tool for preclinical dosimetry before performing radiosurgery treatment. Therefore, use of gel dosimetry is sufficient for verifying complex dose distributions in the field of radiosurgery. EP-1366 TO EVALUATE THE DELIVERY EFFICIENCY OF SLIDING-WINDOW VERSUS STEP AND SHOOT TECHNIQUES USING PORTAL DOSIMETRY V. Fusco1, R. Caivano2, M. Cozzolino2, G. Califano2, A. Fiorentino1, C. Chiumento1, S. Clemente2 1 IRCCS CROB, Radiotherapy, Rionero in Vulture, Italy 2 IRCCS CROB, Medical Physics, Rionero in Vulture, Italy Purpose/Objective: To evaluate the delivery efficiency of dynamic (DMLC) and segmental (SMLC, also known as ''step-and-shoot'') Intensity Modulated Radiation Therapy (IMRT) techniques, using Portal Dosimetry (PD) in Treatment Planning System Eclipse (8.6 version). Materials and Methods: 7 Head and Neck (HN) patients treated in our Institute with IMRT DMLC technique were retrospectively selected for the study. Plans were also re-calculated with SMLC at 5, 10 and 20 levels of intensity. A total of 107 fields/sub fields were analyzed. The dosimetric verification was performed with Portal Dosimetry system into Eclipse, the agreement between calculated and measured fluence was evaluated using the gamma index (maximum γmax, average γavg, percentage of points with γ%≤1). The images were acquired at a source-detector distance (SDD) of 100 cm, in integrated mode with 30 frames per second (fps), projecting each field on the EPID at gantry 0°. Measures, keeping the real clinical gantry angles, were also carried out to assess the effect of gantry rotation on the dosimetric results. Results: For all techniques measurements are well within the acceptable criteria γavg< 0.5, γ% ≤ 1 greater than 95% (99.8%, 99.7%, 99.4%, 99.0% for DMLC and SMLC 20,10,5 respectively). γmax improves (+19.5%) increasing the numbers of intensity levels from 5 to 20 and using DMLC (+34%). Delivery efficiency for all tecniques was affected by gantry angles and leaves traveling direction, improvements for SMLC compared to DMLC were observed increasing the number of intensity levels. Conclusions: A good agreement between calculated and measured fluence was obtained for both DMLC and SMLC techniques and levels. The effect of gantry rotation as well as leaves traveling direction opposite to the gravitational force influence results for all techniques in particular for SMLC at low intensity levels.
Conclusions: The beam characteristics, linearity and dose delivery at low monitor unit have been studied comparing two different LINAC working modes. Differences in the dose delivery and problems in the reproducibility of the flatness have been found. Anyway, these results do not have clinical implications. EP-1364 EVALUATION OF DOSE CONTROL SYSTEM IMPLEMENTATION IN A TOMOTHERAPY HI-ART UNIT J.A. Ramos Pacho1, S. Garcia Repiso1, J. Hernandez Rodriguez1, C. Martin Rincon1, J.M. Verde Velasco1, E. De Sena Espinel1, M.E. Perez Alvarez1, J.M. Delgado Aparicio1 1 Hospital Universitario, Medical Physics and Radiation Protection, Salamanca, Spain Purpose/Objective: Tomotherapy Hi-Art radiation unit consists of a linear accelerator that can rotate around the treatment couch while it is moving at constant speed, i.e., it works like a CT unit but with a treatment aim. This unit has a binary MLC of 64 leaves moving continuously during irradiation time. These and other characteristics allow a helical IMRT treatment. This kind of units had not a feedback loop between the dose monitor chambers and the magnetron, so it can’t be assured that the dose rate output is constant during treatment. We observed a drift in the dose rate of about 2% down for large treatment times. To solve this problem, Tomotherapy Inc. is installing a dose servo namely DCS (Dose Control System), which controls the magnetron current to adjust the dose rate output automatically. Our hospital is the second institution in Europe in which the DCS has been installed. In this paper measurements performed before and after the implementation of dose servo are compared. Materials and Methods: To evaluate the dose rate drift, a rotational plan of 510 seconds long has been developed. This time is a usual treatment time and long enough to ensure a complete observation of this effect. The plan has a period of 17 seconds, in which the MLC leaves are fully open and the treatment couch is stationary. Charge measurements have been performed with Exradín A1SL Slimline Miniature Shonka IC (Standard Imaging) of 0.056 cm3, placed into the closest to the center hole of the Cheese Phantom and connected to the TomoElectrometer. Using the TomoElectrometer software (TEMS) we obtain a plot of charge collected every second vs time. These data have been processed, plotting the cycle-integrated charge vs time to avoid dose rate oscillations due to rotation of the gantry. Results:
The graph shows that the dose rate is more stable after the dose servo implementation. Conclusions: The dose servo installation allows a more accurate dose delivering during the irradiation and a improvement of treatment quality. EP-1365 VERIFICATION OF THE 3D DOSE DISTRIBUTION IN SPINAL RADIOSURGERY BY USING AGEL DOSIMETER D. Lee1, H. Chung2 1 Inje University IlsanPaik Hospital, Neurosurgery, Goyang, Korea Republic of 2 Seoul National University, Neurosurgery, Seoul, Korea Republic of
ESTRO 31
Purpose/Objective: The aim of this study was to compare the 3D relative dose distribution between the commercially available BANG3gel dosimeter(MGS Research Inc., CT,USA) and clinical plan dosimetry applied to spinal tumor patients, as well as to compare gel dosimetry and film dosimetry of the axial plane of the isocenter. To validate polymer gel dosimetry for IMRS dose distribution verification are compared the dose maps with the dose maps obtained from calculated dosimetry with the treatment planning system Materials and Methods: BANG3gel dosimeter and Gafchromic EBT film (ISP, NJ, USA) were used to compare the dose distribution between gel and planned dosimetry of the axial plane at the isocenter. The BANG3gel was designed for use in our study in the dose range of 0 – 20 Gy by using a response modifier. To obtain a polymer gel dosimeter calibration curve, 8 test vials containing the gel were irradiated at dose levels of 1, 2, 3, 5, 7, 10, 15, and 20 Gy. We performed radiosurgery treatment on the gel and film by delivering the radiation to the target as a marginal dose and saving the spinal cord as an OAR. Results: We measured both the gel and the film dosimeter in the axial plane. Quantitative evaluation of these results is expressed as DTA. The results show good agreement between the 2 methods at the selected plane. The DTA values of the 80% and 50% isodose lines were within 1.0 mm and 3.0 mm, respectively. The DTA value of the OAR profile was within 1.0 mm in both gel and film dosimetry. In the coronal direction between the gel and the treatment planning calculations with 1 plane passing through the isocenter. The DTA values of the 80% and 50% isodose lines were within 1.0 mm and 3.0 mm, respectively. In the sagittal direction from the gel and the treatment planning calculations with 1 plane passing through the isocenter plane. The DTA values of the 80% and 50% isodose lines were within 1.1 mm and 2.0 mm, respectively. Conclusions: The data shown in this study support the conclusion that gel dosimetry can produce 3D dose mapping of sufficient quality for dosimetry verification. We observed good agreement between the measured and the calculated dose distribution, within 1 mm in the high-dose gradient region. In addition to sufficiently verifying the 3D dose distributions, we found that the gel dosimeter was a useful tool for preclinical dosimetry before performing radiosurgery treatment. Therefore, use of gel dosimetry is sufficient for verifying complex dose distributions in the field of radiosurgery. EP-1366 TO EVALUATE THE DELIVERY EFFICIENCY OF SLIDING-WINDOW VERSUS STEP AND SHOOT TECHNIQUES USING PORTAL DOSIMETRY V. Fusco1, R. Caivano2, M. Cozzolino2, G. Califano2, A. Fiorentino1, C. Chiumento1, S. Clemente2 1 IRCCS CROB, Radiotherapy, Rionero in Vulture, Italy 2 IRCCS CROB, Medical Physics, Rionero in Vulture, Italy Purpose/Objective: To evaluate the delivery efficiency of dynamic (DMLC) and segmental (SMLC, also known as ''step-and-shoot'') Intensity Modulated Radiation Therapy (IMRT) techniques, using Portal Dosimetry (PD) in Treatment Planning System Eclipse (8.6 version). Materials and Methods: 7 Head and Neck (HN) patients treated in our Institute with IMRT DMLC technique were retrospectively selected for the study. Plans were also re-calculated with SMLC at 5, 10 and 20 levels of intensity. A total of 107 fields/sub fields were analyzed. The dosimetric verification was performed with Portal Dosimetry system into Eclipse, the agreement between calculated and measured fluence was evaluated using the gamma index (maximum γmax, average γavg, percentage of points with γ%≤1). The images were acquired at a source-detector distance (SDD) of 100 cm, in integrated mode with 30 frames per second (fps), projecting each field on the EPID at gantry 0°. Measures, keeping the real clinical gantry angles, were also carried out to assess the effect of gantry rotation on the dosimetric results. Results: For all techniques measurements are well within the acceptable criteria γavg< 0.5, γ% ≤ 1 greater than 95% (99.8%, 99.7%, 99.4%, 99.0% for DMLC and SMLC 20,10,5 respectively). γmax improves (+19.5%) increasing the numbers of intensity levels from 5 to 20 and using DMLC (+34%). Delivery efficiency for all tecniques was affected by gantry angles and leaves traveling direction, improvements for SMLC compared to DMLC were observed increasing the number of intensity levels. Conclusions: A good agreement between calculated and measured fluence was obtained for both DMLC and SMLC techniques and levels. The effect of gantry rotation as well as leaves traveling direction opposite to the gravitational force influence results for all techniques in particular for SMLC at low intensity levels.