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exercised, and with motion of 20 mm or more, considerable disagreement results. The dynamic QA phantom introduced here provides suitable verification for IMRT for targets in motion. Fig 1: Gamma distribution, profiles and Isodose lines for IMRT dynamic delivery verification. Author Disclosure: H.A. Jaradat, None; M. Mehta, None; K. Nelson, Standard Imaging Inc., A. Employment; D. Schmidt, Standard Imaging Inc, A. Employment. 2887 Optimization of IMRT QA With EBT Gafchromic Film F. Schneider 1 , M. Polednik 1 , D. Wolff 1 , A. Delana 2 , F. Lohr 1 , F. Wenz 1 , L. Menegotti 2 1 Department of Radiotherapy and Oncology, Mannheim University Hospital, Mannheim, Germany, 2 Department of Radiotherapy and Oncology, Ospedale Sta. Chiara, Trento, Italy Purpose/Objective(s): Individual patient plan QA for IMRT is usually performed with dosimetry films to provide spatial information. Due to their range of application these films must have several characteristics, among them being constancy within one batch and dose rate independency. Their absorption characteristics should be similar to water. Correlation of optical density (OD) and dose has to be unequivocal. An alternative to the widely used EDR2 films (Kodak) are the self developing Gafchromic EBT films (ISP). In this project Gafchromic EBT films were evaluated with respect to several characteristics essential for IMRT QA. Materials/Methods: To investigate the dependence of OD on dose rate, a linac with 6MV photons was used. Four films were irradiated with the same dose but with different dose rates in the range from 55 to 450 MU/min and were compared with each other. Two calibration films, taken from the same batch, were covering the dose range between 1 and 9 Gy to find out if equal OD is shown under equal irradiation conditions. Depth dose curves (DDC) were measured with films which were positioned in a water phantom. These were compared with the accelerator base data to assess the water equivalence of the films. Finally, several calibration curves were recorded to assign OD to dose. All films were scanned with the Epson Expression 1680 Pro flat bed scanner and were evaluated with VeriSoft from PTW. Results: Dose rate dependence of EBT films is low with maximal OD difference between dose rates of 1% in the range of dose rates studied. Homogeneity among one batch is excellent with a maximum deviation between two films of 0.9%. The comparison of the film DDC with the base data acquired with a water phantom shows a deviation of 1.2% 0.8%. The calibration curves show a logarithmic course. Due to the monotony of the curve, an unequivocal translation of OD to dose is possible. Larger errors (up to 30%) can be caused by the scanning process. When, however, a minimum interval of two minutes is introduced between two scans, if the part of interest of a film is placed in the center of scanner field (20cm x 10cm), the scanned area is small and the automatic colour correction is deactivated, the compound error could be reduced to 3%. Generating correction matrices for individual scanners can help loosen these constraints. It is also important to scan the calibration and the verification film after the same developing time (1h) as the OD changes even in opaque covers (after a month 3.5%). Conclusions: Gafchromic EBT films have excellent characteristics as a dosimetry film with low dose rate dependency, easy handling and self-developing characteristics. It is very important, however, to pay close attention to the choice of scanner and the scanning process itself to reduce variation in the scanning results. Author Disclosure: F. Schneider, None; M. Polednik, None; D. Wolff, None; A. Delana, None; F. Lohr, None; F. Wenz, None; L. Menegotti, None. 2888 Radiation Safety Issues With PET/CT Simulation for Stereotactic Body Radiotherapy W. T. Kearns, W. H. Hinson, C. J. Hampton, J. M. Butler, J. J. Urbanic, D. Starnes, A. F. deGuzman, V. W. Stieber Wake Forest University School of Medicine, Winston-Salem, NC Purpose/Objective(s): To describe the process of PET/CT simulation for stereotactic body radiotherapy (SBRT) and address radiation safety issues. Materials/Methods: Our department performs PET/CT simulations with a dedicated radiation oncology PET/CT scanner (General Electric). Prior to the acquisition and implementation of the dedicated scanner in our department, patients would undergo a diagnostic PET scan. Because the patient was not in the treatment position, the subsequent fusion of the images with a treatment planning CT set was difficult. We have performed the first two PET/CT simulations of SBRT patients in a commercially available stereotactic bodyframe (Elekta). As with all of our PET/CT simulated patients, sophisticated immo- S712 I. J. Radiation Oncology ● Biology ● Physics Volume 66, Number 3, Supplement, 2006
Transcript of 2887
exercised, and with motion of 20 mm or more, considerable disagreement results. The dynamic QA phantom introduced hereprovides suitable verification for IMRT for targets in motion.
Fig 1: Gamma distribution, profiles and Isodose lines for IMRT dynamic delivery verification.
Author Disclosure: H.A. Jaradat, None; M. Mehta, None; K. Nelson, Standard Imaging Inc., A. Employment; D. Schmidt,Standard Imaging Inc, A. Employment.
2887 Optimization of IMRT QA With EBT Gafchromic Film
F. Schneider1, M. Polednik1, D. Wolff1, A. Delana2, F. Lohr1, F. Wenz1, L. Menegotti2
1Department of Radiotherapy and Oncology, Mannheim University Hospital, Mannheim, Germany, 2Department ofRadiotherapy and Oncology, Ospedale Sta. Chiara, Trento, Italy
Purpose/Objective(s): Individual patient plan QA for IMRT is usually performed with dosimetry films to provide spatialinformation. Due to their range of application these films must have several characteristics, among them being constancy withinone batch and dose rate independency. Their absorption characteristics should be similar to water. Correlation of optical density(OD) and dose has to be unequivocal. An alternative to the widely used EDR2 films (Kodak) are the self developing GafchromicEBT films (ISP). In this project Gafchromic EBT films were evaluated with respect to several characteristics essential for IMRTQA.
Materials/Methods: To investigate the dependence of OD on dose rate, a linac with 6MV photons was used. Four films wereirradiated with the same dose but with different dose rates in the range from 55 to 450 MU/min and were compared with eachother. Two calibration films, taken from the same batch, were covering the dose range between 1 and 9 Gy to find out if equalOD is shown under equal irradiation conditions. Depth dose curves (DDC) were measured with films which were positionedin a water phantom. These were compared with the accelerator base data to assess the water equivalence of the films. Finally,several calibration curves were recorded to assign OD to dose. All films were scanned with the Epson Expression 1680 Pro flatbed scanner and were evaluated with VeriSoft from PTW.
Results: Dose rate dependence of EBT films is low with maximal OD difference between dose rates of 1% in the range of doserates studied. Homogeneity among one batch is excellent with a maximum deviation between two films of 0.9%. Thecomparison of the film DDC with the base data acquired with a water phantom shows a deviation of 1.2% � 0.8%. Thecalibration curves show a logarithmic course. Due to the monotony of the curve, an unequivocal translation of OD to dose ispossible.Larger errors (up to 30%) can be caused by the scanning process. When, however, a minimum interval of two minutes isintroduced between two scans, if the part of interest of a film is placed in the center of scanner field (20cm x 10cm), the scannedarea is small and the automatic colour correction is deactivated, the compound error could be reduced to 3%. Generatingcorrection matrices for individual scanners can help loosen these constraints. It is also important to scan the calibration and theverification film after the same developing time (�1h) as the OD changes even in opaque covers (after a month 3.5%).
Conclusions: Gafchromic EBT films have excellent characteristics as a dosimetry film with low dose rate dependency, easyhandling and self-developing characteristics. It is very important, however, to pay close attention to the choice of scanner andthe scanning process itself to reduce variation in the scanning results.
Author Disclosure: F. Schneider, None; M. Polednik, None; D. Wolff, None; A. Delana, None; F. Lohr, None; F. Wenz, None;L. Menegotti, None.
2888 Radiation Safety Issues With PET/CT Simulation for Stereotactic Body Radiotherapy
W. T. Kearns, W. H. Hinson, C. J. Hampton, J. M. Butler, J. J. Urbanic, D. Starnes, A. F. deGuzman, V. W. Stieber
Wake Forest University School of Medicine, Winston-Salem, NC
Purpose/Objective(s): To describe the process of PET/CT simulation for stereotactic body radiotherapy (SBRT) and addressradiation safety issues.
Materials/Methods: Our department performs PET/CT simulations with a dedicated radiation oncology PET/CT scanner(General Electric). Prior to the acquisition and implementation of the dedicated scanner in our department, patients wouldundergo a diagnostic PET scan. Because the patient was not in the treatment position, the subsequent fusion of the images witha treatment planning CT set was difficult. We have performed the first two PET/CT simulations of SBRT patients in acommercially available stereotactic bodyframe (Elekta). As with all of our PET/CT simulated patients, sophisticated immo-
S712 I. J. Radiation Oncology ● Biology ● Physics Volume 66, Number 3, Supplement, 2006
