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20 poster IN VIVO DOSIMETRY WITH MOSFETS DURING INTRA-OPERATIVE RADIOTHERAPY FOR PARTIAL BREAST IRRADIATION
S ATURDAY, M AY 7, 2011
P OSTER DISCUSSION
S 11
Conclusions: The availability of data from several centres active in IORT treatments may allow to perform data analysis useful to disseminate knowledge about clinical and technical aspects of this radiation modality and to dispose a basis for further clinical multicenter trials.
Poster Rapporteur Session: Physics, Techniques, Dosimetrics I 20 poster IN VIVO DOSIMETRY WITH MOSFETS DURING INTRA-OPERATIVE RADIOTHERAPY FOR PARTIAL BREAST IRRADIATION A. Petoukhova1 , K. van Wingerden1 , P. Koper1 , H. Ceha1 , A. Verbeek-de Kanter1 , A. Marinelli2 , J. van der Sijp2 , H. Struikmans1 1 R ADIOTHERAPY C ENTRE W EST, The Hague, Netherlands 2 M EDICAL C ENTER H AAGLANDEN, Department of Surgery, The Hague, Netherlands Purpose: In vivo dosimetry is an important tool to check whether the delivered dose and the planned dose are the same. For intra-operative radiotherapy (IORT) in partial breast irradiation (PBI), this is especially relevant because the dose is delivered in a single fraction. The purpose of this study was to compare the given dose to the planned dose in breast conserving therapy. Materials: During the period May 2010 - October 2010, nineteen elderly (60+) patients, diagnosed with breast cancer (tumour diameter < 3 cm) were treated with IORT while in vivo dosimetry with MOSFETs (metal-oxide semiconductor field-effect transistors, Thomson Nielsen TN-502RD) was performed. For each patient, PBI with a total dose of 21 Gy at 90% was given during the operation according to the ELIOT study (1). All patients were irradiated with electron beams generated with an IORT dedicated mobile accelerator (Mobetron, INTRAOP, USA). The in vivo dose measurements were done by attaching the first detector under the bolus at the end of the applicator and the second detector attached behind the protection plate (6 mm aluminium plus 3 mm copper), which was used to shield the thorax. Calibration of the MOSFET detectors was determined by measuring the absolute dose with a Roos ionization chamber on the same day. The calibration measurements were performed with the electron beams of the Mobetron in a homemade PMMA phantom at dose maximum for each energy. The usability of MOSFETs for IORT was studied before (2). Results: The results of in vivo dosimetry are shown in the table. For patient 10, the measured entry dose deviates by -9.1%, probably because of multiple relocations of the applicator. The used applicator diameter range between 4 cm and 6.5 cm. The tip angle of the applicator was 0, 15 and 30 for 58%, 5% and 37% of patients, respectively.
Conclusions: In vivo MOSFET dosimetry during IORT was successful for PBI. The measured entry dose for the breast tissue agrees within 1.6% with the expected dose. The results of MOSFET measurements behind the protection plate are lower than calculated based on the transmission measurements in the primary beam through the plate. For our patients, the dose to the thoracic wall and lungs was lower than 2 Gy even if 12 MeV was applied. 1. Intra M, Luini A, Gatti G, et al, Surgery (2006) 140:467-71. 2. J. Penninkhof, K. van Wingerden, J. van Egmond, et al, Radiother Oncol (2008), 88 (Supplement 2),S387.
21SRVWHU CHARACTERIZATION OF REINFORCED MICRO MOSFETS: GROUPING OF CALIBRATION COEFFICIENTS AND DOSE RESPONSE J. Lopez-Tarjuelo1 , J. D. Quirós Higueras1 , N. de Marco-Blancas1 , A. Santos Serra1 , A. Bouché-Babiloni2 , C. Ferrer Albiach2 , V. Morillo-Macías2 C ONSORCIO H OSPITALARIO P ROVINCIAL DE C ASTELLÓN, Servicio de Radiofísica y Protección Radiológica, Castelló de la Plana, Spain 2 C ONSORCIO H OSPITALARIO P ROVINCIAL DE C ASTELLÓN, Servicio de Oncología Radioterápica, Castelló de la Plana, Spain 1
Purpose: Intraoperative Electron Radiotherapy (IOERT) treatment consists of single fraction irradiation. Therefore, in vivo absorbed dose monitoring is desirable for verification, recording and correction. MOSFET detectors have been investigated for these purposes. Reinforced MOSFETs are made by manufacturer to enhance the mechanical endurance of MOSFETs. As we are concerned that MOSFETs are expendable and linac occupation is usually very high, we have characterized our dosimetric system with the intention of optimizing their use as the first stage of reporting in vivo absorbed doses in our treatments. Materials: Three reinforced MOSFET model mobile MOSFET TN-502RDMH (Best Medical Canada Ltd., Ontario, Canada) have been calibrated with an Elekta Precise linac. They were put in their calibration jig and irradiated with a 10x10 cm2 applicator at the depth corresponding to the maximum dose with energies of 4, 6, 9, 12, 15 and 18 MeV. Calibration coefficients (CC) were analyzed to group them in order to determine if the same coefficient could be applied to various energies in future calibrations. Dose response deviation from linearity and dose rate response have been assessed too. Results: ANOVA analysis of the calibration coefficients concluded that the CCs for 6, 9 and 12 MeV were compatible (p ≥ 0.239), which means that it is possible to calibrate one MOSFET with one of these energies and apply its CC to the other two energies without taking more measurements. The same happened with 15 and 18 MeV (p ≥ 0.459). Calibrations for 4 MeV should be performed separately.Lack of reproducibility was better than 0.8% when considering 90% of all CCs.Deviation from linearity was measured to be within 2% from 20 to 400 monitor units (MU).Dose rate response variation was better than 0.5% from 50 MU/min to 400 MU/min. Conclusions: Dosimetric characterization of reinforced micro MOSFETs has been presented as the first stage of dose delivery verification in IOERT. It is possible to calibrate each MOSFET for only 6 MeV and measure 9 and 12 MeV with the same CC and do the same with 15 and 18 MeV. These features allow us to save linac time and to increase the MOSFETs lifetime.Longer irradiations properly optimized should be considered to test linearity above 400 UM because damage to the detectors accumulates.Lack of reproducibility and lack of constancy with variable dose rate under calibration conditions are lower than the allowed deviation during absorbed dose verification in other radiotherapy techniques.Supported by grants PSE-300000-2009-5 and IPT300000-2010-3. Ministerio de Ciencia e Innovacipanish Government.
P OSTER DISCUSSION
S 11
Conclusions: The availability of data from several centres active in IORT treatments may allow to perform data analysis useful to disseminate knowledge about clinical and technical aspects of this radiation modality and to dispose a basis for further clinical multicenter trials.
Poster Rapporteur Session: Physics, Techniques, Dosimetrics I 20 poster IN VIVO DOSIMETRY WITH MOSFETS DURING INTRA-OPERATIVE RADIOTHERAPY FOR PARTIAL BREAST IRRADIATION A. Petoukhova1 , K. van Wingerden1 , P. Koper1 , H. Ceha1 , A. Verbeek-de Kanter1 , A. Marinelli2 , J. van der Sijp2 , H. Struikmans1 1 R ADIOTHERAPY C ENTRE W EST, The Hague, Netherlands 2 M EDICAL C ENTER H AAGLANDEN, Department of Surgery, The Hague, Netherlands Purpose: In vivo dosimetry is an important tool to check whether the delivered dose and the planned dose are the same. For intra-operative radiotherapy (IORT) in partial breast irradiation (PBI), this is especially relevant because the dose is delivered in a single fraction. The purpose of this study was to compare the given dose to the planned dose in breast conserving therapy. Materials: During the period May 2010 - October 2010, nineteen elderly (60+) patients, diagnosed with breast cancer (tumour diameter < 3 cm) were treated with IORT while in vivo dosimetry with MOSFETs (metal-oxide semiconductor field-effect transistors, Thomson Nielsen TN-502RD) was performed. For each patient, PBI with a total dose of 21 Gy at 90% was given during the operation according to the ELIOT study (1). All patients were irradiated with electron beams generated with an IORT dedicated mobile accelerator (Mobetron, INTRAOP, USA). The in vivo dose measurements were done by attaching the first detector under the bolus at the end of the applicator and the second detector attached behind the protection plate (6 mm aluminium plus 3 mm copper), which was used to shield the thorax. Calibration of the MOSFET detectors was determined by measuring the absolute dose with a Roos ionization chamber on the same day. The calibration measurements were performed with the electron beams of the Mobetron in a homemade PMMA phantom at dose maximum for each energy. The usability of MOSFETs for IORT was studied before (2). Results: The results of in vivo dosimetry are shown in the table. For patient 10, the measured entry dose deviates by -9.1%, probably because of multiple relocations of the applicator. The used applicator diameter range between 4 cm and 6.5 cm. The tip angle of the applicator was 0, 15 and 30 for 58%, 5% and 37% of patients, respectively.
Conclusions: In vivo MOSFET dosimetry during IORT was successful for PBI. The measured entry dose for the breast tissue agrees within 1.6% with the expected dose. The results of MOSFET measurements behind the protection plate are lower than calculated based on the transmission measurements in the primary beam through the plate. For our patients, the dose to the thoracic wall and lungs was lower than 2 Gy even if 12 MeV was applied. 1. Intra M, Luini A, Gatti G, et al, Surgery (2006) 140:467-71. 2. J. Penninkhof, K. van Wingerden, J. van Egmond, et al, Radiother Oncol (2008), 88 (Supplement 2),S387.
21SRVWHU CHARACTERIZATION OF REINFORCED MICRO MOSFETS: GROUPING OF CALIBRATION COEFFICIENTS AND DOSE RESPONSE J. Lopez-Tarjuelo1 , J. D. Quirós Higueras1 , N. de Marco-Blancas1 , A. Santos Serra1 , A. Bouché-Babiloni2 , C. Ferrer Albiach2 , V. Morillo-Macías2 C ONSORCIO H OSPITALARIO P ROVINCIAL DE C ASTELLÓN, Servicio de Radiofísica y Protección Radiológica, Castelló de la Plana, Spain 2 C ONSORCIO H OSPITALARIO P ROVINCIAL DE C ASTELLÓN, Servicio de Oncología Radioterápica, Castelló de la Plana, Spain 1
Purpose: Intraoperative Electron Radiotherapy (IOERT) treatment consists of single fraction irradiation. Therefore, in vivo absorbed dose monitoring is desirable for verification, recording and correction. MOSFET detectors have been investigated for these purposes. Reinforced MOSFETs are made by manufacturer to enhance the mechanical endurance of MOSFETs. As we are concerned that MOSFETs are expendable and linac occupation is usually very high, we have characterized our dosimetric system with the intention of optimizing their use as the first stage of reporting in vivo absorbed doses in our treatments. Materials: Three reinforced MOSFET model mobile MOSFET TN-502RDMH (Best Medical Canada Ltd., Ontario, Canada) have been calibrated with an Elekta Precise linac. They were put in their calibration jig and irradiated with a 10x10 cm2 applicator at the depth corresponding to the maximum dose with energies of 4, 6, 9, 12, 15 and 18 MeV. Calibration coefficients (CC) were analyzed to group them in order to determine if the same coefficient could be applied to various energies in future calibrations. Dose response deviation from linearity and dose rate response have been assessed too. Results: ANOVA analysis of the calibration coefficients concluded that the CCs for 6, 9 and 12 MeV were compatible (p ≥ 0.239), which means that it is possible to calibrate one MOSFET with one of these energies and apply its CC to the other two energies without taking more measurements. The same happened with 15 and 18 MeV (p ≥ 0.459). Calibrations for 4 MeV should be performed separately.Lack of reproducibility was better than 0.8% when considering 90% of all CCs.Deviation from linearity was measured to be within 2% from 20 to 400 monitor units (MU).Dose rate response variation was better than 0.5% from 50 MU/min to 400 MU/min. Conclusions: Dosimetric characterization of reinforced micro MOSFETs has been presented as the first stage of dose delivery verification in IOERT. It is possible to calibrate each MOSFET for only 6 MeV and measure 9 and 12 MeV with the same CC and do the same with 15 and 18 MeV. These features allow us to save linac time and to increase the MOSFETs lifetime.Longer irradiations properly optimized should be considered to test linearity above 400 UM because damage to the detectors accumulates.Lack of reproducibility and lack of constancy with variable dose rate under calibration conditions are lower than the allowed deviation during absorbed dose verification in other radiotherapy techniques.Supported by grants PSE-300000-2009-5 and IPT300000-2010-3. Ministerio de Ciencia e Innovacipanish Government.