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Evaluation of a small field of view SiPM array detector based on a LGSO:Ce pixellated scintillator
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Abstracts / Physica Medica 32 (2016) 284–339
vide a considerable reduction in treatment time offering a better delivery efficiency. http://dx.doi.org/10.1016/j.ejmp.2016.07.179
RELATIVE DOSIMETRY IN SMALL FIELDS: WHICH DETECTOR TO CHOOSE? S. Dufreneix *, S. Josset, C. Di Bartolo, D. Autret Department of Medical Physics, Integrated Center for Oncology, Nantes – Angers, France ⇑ Corresponding author. Introduction. Small field dosimetry is a challenging area. Since no ideal detector exists, it is recommended that at least three different suitable types be used. However, only one set of measurement is used by the treatment planning system. Purpose. To compare several detectors and select the adequate one. Materials and methods. Profiles, percent-depth-dose and output factors were conducted on a Novalis TrueBeam STx in MLC shaped beams with a field size of 3, 2, 1 and 0.5 cm for three energies (6 MV, 6 MV FFF and 16 MV) as well as in circular cones of 15–4 mm diameter at 6 MV and 6 MV FFF. Depending on the configuration, various detectors were chosen between the Razor diode (IBA), the 60017 diamond (PTW), the CC01 ion chamber (IBA), the SFD diode (IBA) and EBT3 films. For circular cones, a comparison with the Cserie Novalis of another center was conducted. Results. By analyzing the measurements, the following results were high lightened: due to its large sensitive volume (2.2 mm), the diamond was found inadequate for fields smaller than 6 mm diameter. Both diodes were found in agreement but showed some discrepancies with the film due to their high Z material which virtually sharpens the penubra. The deviations observed between the two Novalis were attributed to the different positions of the jaws. Conclusion. In order to keep a unique detector for all small fields measurements, the Razor diode was selected for all energies. Disclosure. No disclosure. http://dx.doi.org/10.1016/j.ejmp.2016.07.180
EVALUATION OF A SMALL FIELD OF VIEW SIPM ARRAY DETECTOR BASED ON A LGSO:CE PIXELLATED SCINTILLATOR S. David, E. Fysikopoulos, N. Kalyvas * Department of Biomedical Engineering, Technological Educational Institute of Athens, Athens, Greece ⇑ Corresponding author. Introduction. Silicon photomultiplier arrays can be used in dedicated small field of view animal imaging detectors and especially in those used to head PET/MR studies in mice due to their small size and flexibility. Ce doped LGSO scintillator crystal is based on a mixture of LSO and GSO orthosilicates (Lu2x-_ Gd 2-2x_ SiO5:Ce – LGSO: Ce) and has attracted researcher’s attention because of high density of 7 g/cm3, high light output (32000 ph/MeV) and fast scintillation decay time (40 ns). Purpose. The purpose of this study is to investigate the behavior of the ArraySL-4 (4 4 element array of 3 3 mm2 silicon photomultipliers) optical detector coupled to a 6 6 LGSO:Ce scintillator
array, with 1.9 1.9 5 mm3 crystal size elements, for possible applications in small field of view PET imaging detectors. Evaluation was carried out with 137Cs radioactive source and results regarding energy resolution and peak to valley ratio are presented. Materials and methods. We have developed a symmetric resistive charge division circuit to read out the signal outputs of 4 4 pixel SiPM array reducing the 16 pixel outputs to 4 position signals. The 4 position signals were acquired using a free running sampling technique. An FPGA (Spartan 6 LX150T) was used for triggering and signal processing of the pulses acquired using free running Analog to Digital Converters. Results and conclusion. Evaluation shows a clear visualization of all discrete scintillator elements. The mean peak to valley ratio of the profiles on the image was measured equal to 13 while the mean energy resolution was measured equal to 18%. http://dx.doi.org/10.1016/j.ejmp.2016.07.181
PRE-TREATMENT QUALITY ASSURANCE OF 220 RAPIDARC PLANS ANALYZED WITH EPIQA SOFTWARE C. Pellegrini, V. Ardu * Radiotherapy Department, IRCCS Policlinico San Donato, Milano, Italy Corresponding author.
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Introduction. Delivery complexity of volumetric modulated arc-therapy (VMAT) requires a pre-treatment verification process. Electronic portal imaging based on a-Si flat panels are utilized for dosimetric purposes mainly for IMRT pre-treatment verification (QA). Purpose. This work is a retrospective analysis of a large dataset of RapidArc routine pre-treatment QA. We report results and analysis of our procedure that combines EPID images and EpiQA commercial software for dose distribution reconstruction. Materials and methods. Dose distribution of 220 patients treated with a VMAT technique on Varian DHX-2100 were analyzed. Tumor sites of selected patients were: 70 esophagus, 100 head-neck and 50 lung. The detector reading, for each arc, is converted to a dose map and compared with the TPS (Eclipse) dose distribution, calculated with a virtual water-phantom (0,125 cm calculation grid). Gamma evaluation index was performed to quantitatively compare measured and calculated results using 3%-3 mm, 4%-3 mm and 4%4 mm agreement criteria. Results. Good result were found for all districts. The average values of G<1 for 3%-3 mm criteria are 98% for lung and esophagus and 97% for head-neck district. Head-neck district present a larger number of arcs with G > 1,5, probably due to the higher modulation. Conclusion. EPID images and EpiQA software use for pre-clinical verification show a very good agreement between calculated and measured dose. This QA procedure is easy also in complex treatments such as VMAT. We plan to investigate this study with a calculation grid of 0,25 cm, obtaining a considerable time sparing. Furthermore we would like to compare results obtained with EpiQA software with other systems for pre-treatment QA. Disclosure. All authors disclose any financial and personal relationships with other people or organizations that could inappropriately bias this presentation. http://dx.doi.org/10.1016/j.ejmp.2016.07.182
Abstracts / Physica Medica 32 (2016) 284–339
vide a considerable reduction in treatment time offering a better delivery efficiency. http://dx.doi.org/10.1016/j.ejmp.2016.07.179
RELATIVE DOSIMETRY IN SMALL FIELDS: WHICH DETECTOR TO CHOOSE? S. Dufreneix *, S. Josset, C. Di Bartolo, D. Autret Department of Medical Physics, Integrated Center for Oncology, Nantes – Angers, France ⇑ Corresponding author. Introduction. Small field dosimetry is a challenging area. Since no ideal detector exists, it is recommended that at least three different suitable types be used. However, only one set of measurement is used by the treatment planning system. Purpose. To compare several detectors and select the adequate one. Materials and methods. Profiles, percent-depth-dose and output factors were conducted on a Novalis TrueBeam STx in MLC shaped beams with a field size of 3, 2, 1 and 0.5 cm for three energies (6 MV, 6 MV FFF and 16 MV) as well as in circular cones of 15–4 mm diameter at 6 MV and 6 MV FFF. Depending on the configuration, various detectors were chosen between the Razor diode (IBA), the 60017 diamond (PTW), the CC01 ion chamber (IBA), the SFD diode (IBA) and EBT3 films. For circular cones, a comparison with the Cserie Novalis of another center was conducted. Results. By analyzing the measurements, the following results were high lightened: due to its large sensitive volume (2.2 mm), the diamond was found inadequate for fields smaller than 6 mm diameter. Both diodes were found in agreement but showed some discrepancies with the film due to their high Z material which virtually sharpens the penubra. The deviations observed between the two Novalis were attributed to the different positions of the jaws. Conclusion. In order to keep a unique detector for all small fields measurements, the Razor diode was selected for all energies. Disclosure. No disclosure. http://dx.doi.org/10.1016/j.ejmp.2016.07.180
EVALUATION OF A SMALL FIELD OF VIEW SIPM ARRAY DETECTOR BASED ON A LGSO:CE PIXELLATED SCINTILLATOR S. David, E. Fysikopoulos, N. Kalyvas * Department of Biomedical Engineering, Technological Educational Institute of Athens, Athens, Greece ⇑ Corresponding author. Introduction. Silicon photomultiplier arrays can be used in dedicated small field of view animal imaging detectors and especially in those used to head PET/MR studies in mice due to their small size and flexibility. Ce doped LGSO scintillator crystal is based on a mixture of LSO and GSO orthosilicates (Lu2x-_ Gd 2-2x_ SiO5:Ce – LGSO: Ce) and has attracted researcher’s attention because of high density of 7 g/cm3, high light output (32000 ph/MeV) and fast scintillation decay time (40 ns). Purpose. The purpose of this study is to investigate the behavior of the ArraySL-4 (4 4 element array of 3 3 mm2 silicon photomultipliers) optical detector coupled to a 6 6 LGSO:Ce scintillator
array, with 1.9 1.9 5 mm3 crystal size elements, for possible applications in small field of view PET imaging detectors. Evaluation was carried out with 137Cs radioactive source and results regarding energy resolution and peak to valley ratio are presented. Materials and methods. We have developed a symmetric resistive charge division circuit to read out the signal outputs of 4 4 pixel SiPM array reducing the 16 pixel outputs to 4 position signals. The 4 position signals were acquired using a free running sampling technique. An FPGA (Spartan 6 LX150T) was used for triggering and signal processing of the pulses acquired using free running Analog to Digital Converters. Results and conclusion. Evaluation shows a clear visualization of all discrete scintillator elements. The mean peak to valley ratio of the profiles on the image was measured equal to 13 while the mean energy resolution was measured equal to 18%. http://dx.doi.org/10.1016/j.ejmp.2016.07.181
PRE-TREATMENT QUALITY ASSURANCE OF 220 RAPIDARC PLANS ANALYZED WITH EPIQA SOFTWARE C. Pellegrini, V. Ardu * Radiotherapy Department, IRCCS Policlinico San Donato, Milano, Italy Corresponding author.
⇑
Introduction. Delivery complexity of volumetric modulated arc-therapy (VMAT) requires a pre-treatment verification process. Electronic portal imaging based on a-Si flat panels are utilized for dosimetric purposes mainly for IMRT pre-treatment verification (QA). Purpose. This work is a retrospective analysis of a large dataset of RapidArc routine pre-treatment QA. We report results and analysis of our procedure that combines EPID images and EpiQA commercial software for dose distribution reconstruction. Materials and methods. Dose distribution of 220 patients treated with a VMAT technique on Varian DHX-2100 were analyzed. Tumor sites of selected patients were: 70 esophagus, 100 head-neck and 50 lung. The detector reading, for each arc, is converted to a dose map and compared with the TPS (Eclipse) dose distribution, calculated with a virtual water-phantom (0,125 cm calculation grid). Gamma evaluation index was performed to quantitatively compare measured and calculated results using 3%-3 mm, 4%-3 mm and 4%4 mm agreement criteria. Results. Good result were found for all districts. The average values of G<1 for 3%-3 mm criteria are 98% for lung and esophagus and 97% for head-neck district. Head-neck district present a larger number of arcs with G > 1,5, probably due to the higher modulation. Conclusion. EPID images and EpiQA software use for pre-clinical verification show a very good agreement between calculated and measured dose. This QA procedure is easy also in complex treatments such as VMAT. We plan to investigate this study with a calculation grid of 0,25 cm, obtaining a considerable time sparing. Furthermore we would like to compare results obtained with EpiQA software with other systems for pre-treatment QA. Disclosure. All authors disclose any financial and personal relationships with other people or organizations that could inappropriately bias this presentation. http://dx.doi.org/10.1016/j.ejmp.2016.07.182