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Dosimetry audits in radiotherapy in Poland
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Abstracts / Physica Medica 30 (2014) e1ee15
at the national level with IAEA assistance. The national counterparts conduct the TPS audit at local radiotherapy centres through on-site visits. TPS calculated doses are compared with ion chamber measurements performed in an anthropomorphic phantom for eight test cases per algorithm/beam. The set of pre-defined agreement criteria is used to analyze the performance of TPSs. Results: TPS audit was carried out in sixty radiotherapy centers in eight European countries e Estonia, Hungary, Latvia, Lithuania, Serbia, Slovakia, Poland and Portugal. In total, 190 data sets (combination of algorithm and beam quality) have been collected and reviewed. Dosimetry problems requiring interventions were discovered in about 10 % of datasets. In addition, suboptimal beam modelling in TPSs was discovered in a number of cases. Conclusions: The TPS audit project using the IAEA methodology has verified the treatment planning system calculations for 3D conformal radiotherapy in a group of radiotherapy centres in Europe. It contributed to achieving better understanding of the performance of TPSs and helped to resolve issues related to imaging, dosimetry and treatment planning. DOSIMETRY AUDITS IN RADIOTHERAPY IN THE CZECH REPUBLIC Irena Koniarova, Daniela Ekendahl, Ivana Horakova, Michaela Kapucianova, Vladimir Dufek. National Radiation Protection Institute, Prague, Czech Republic Background: The independent audits in radiotherapy are carried out by the National Radiation Protection Institute as a part of the regulatory authority activity since 1996. The system includes TLD postal audits (external radiotherapy) and on-site audits (external radiotherapy and brachytherapy). TLD audit can be performed in several versions differing in the scope and focus of dose measurements. Basic TLD audit consists in beam calibration check. Each clinically used beam must undergo it at least once per two years. During 1997 e 2013, a total of 1435 beams have been thus controlled. Advanced versions of TLD audit focused on more complex conditions of irradiation (non-reference geometries, MLC fields, small IMRT fields, inhomogeneities) have been performed in the case of a request or research studies. On-site audit is performed after the commissioning of each unit. The absorbed dose to water (or RAKR for brachytherapy), beam quality, output and wedge factors, PDD, MLC positioning, MLC transmission, and dosimetric leaf gap (where applicable) are controlled. Mechanical parameters (isocenter stability, radiation field size, table parameters, etc.) are evaluated as well. A number of 535 megavoltage photon and electron external beams, 103 kilovoltage external beams, and 32 brachytherapy sources have been controlled since 1996. 2 proton beams were checked in 2013. Checks of non-dosimetric parameters and imaging functions of TPS with QUASAR phantoms can be performed on request. In addition, 19 departments (23 treatment plans) have been checked using a special pelvic phantom in end-to-end audit for IMRT and IMAT prostate treatment in 2013. Delivered doses to PTV and rectum were measured with ionisation chambers in 3 planes. Planar dose distribution has been verified with EBT2 film. Retrospectively, it was possible to make DVHs analysis and compare all IMRT plans for the pelvic phantom showing common planning practice in the Czech Republic for photon IMRT and proton radiotherapy. Conclusion: The audits revealed several significant errors that might potentially lead to an accident. All results can be analysed retrospectively, showing trends related to chosen indicators. DOSIMETRY AUDITS IN RADIOTHERAPY IN GREECE C.J. Hourdakis, A. Boziari, V. Kamenopoulou. Greek Atomic Energy Commission Background: Greek Atomic Energy Commission (EEAE) has been running dosimetry audits by means of on-site visits in all Greek radiotherapy (RT) and brachytherapy (BT) centers, since 2002. Two rounds (2002-2006 and 2006-2011) have been completed, the 3rd being in progress. Materials and Methods: Dosimetry measurements and QC tests were performed at RT and BT systems (linacs, 60Co and 192Ir HDR) using EEAE’s phantoms and equipment. (a) The systems’ performance was evaluated through mechanical and radiation tests. (b) Relative (TPR20,10, R50 , PDD) and absolute dosimetry (absorbed dose to water) was performed at photon
and electron beams according to IAEA-TRS-398 protocol. For BT beams, the reference air kerma rate was determined. The difference, dr, of the values measured by EEAE, DM, to the stated by RT center, DS , was calculated (dr¼DM/DS-1). (c) MU calculations (by TPS or manually) were assessed at various irradiation conditions (depth, fields, wedges, etc), by comparing DM (at same irradiation conditions and MU) to Ds for the same MU. (d) The overall RT procedure (CT, simulation, planning, verification, irradiation) was assessed qualitatively and quantitatively, using a solid water phantom, with inhomogeneities and tissue deficits, irradiated at multiple photon beams. The measured dose was compared to the TPS stated dose. Results: More than 90% of the linacs and less than 80% of 60Co showed satisfactory mechanical performance. Relative dosimetry for photons and electrons was accurate in most cases (>95%). Photons beam absolute dosimetry showed that in 95% of beams dr<3%. For electrons, 80% of the beams exhibited dr<3%. All BT beams showed dr<3%. In comparing TPS output data, 86% of the beams showed dr<3%, and 3% of the beams dr>5%. Dosimetry assessment of the overall RT procedure, showed that in 90% cases dr<5%, and in 5% cases dr>7%. Improvement of dosimetry accuracy between the rounds was observed. Discussion: Dosimetry audits contributed significantly to the dosimetry accuracy and homogeneity improvement, in the country. On site visits gave the opportunity to resolve all discrepancies and enhance knowledge dissemination. DOSIMETRY AUDITS IN RADIOTHERAPY IN POLAND ski, J. Rostkowska. Department of Medical Physics, W. Bulski, K. Chełmin Maria Sklodowska-Curie Memorial Cancer Centre and Institute of Oncology, Warsaw Purpose: The Secondary Standard Dosimetry Laboratory (SSDL) of the Medical Physics Department of the Centre of Oncology in Warsaw has become a member of the IAEA/WHO international network of such laboratories in 1988. The SSDL has been carrying-out the external postal TLD audits since 1991. In the presentation the scope of dosimetry audits in Poland is overviewed. Materials and methods: TLD runs for on axis measurements in nonreference conditions were performed in Co-60, X-ray and electron beams. In recent years the audits were extended to off-axis measurements (symmetric and asymmetric fields) and to MLC shaped irregular fields. A heterogeneous cubic-shaped phantom developed in the frame of IAEA Coordinated Research Project was used for the audits. The phantom consists of frame made of polystyrene and the bone or lung inhomogeneity slabs. Another phantom, an anthropomorphic CIRS 002LFC thorax phantom, was used for dosimetry checks according to the IAEA-TECDOC-1583 report. Results: The results of the TLD postal audit in non-reference conditions for on axis measurements are in the majority o cases within the ±3.5% tolerance limit which is usually used for reference conditions. Nine Polish radiotherapy centers (of total 30) were audited with the use of the IAEA cubic phantom. Generally most of the results from TLD and ionizing chamber were within ±5% tolerance. Seven radiotherapy centers in Poland have been audited with the CIRS phantom so far. Eight cases with different beam geometry and accessories representing different complexity of the plan were performed on six different TPS. All algorithm/beam datasets showed passing-rate higher than 50% of predefined agreement criteria. Conclusions: Over the last 20 years the postal TLD audits fulfilled their role and remain the primary and well established dosimetric audit method. The measurements allow to the detect limitations of TPS calculation algorithms. The audits performed with the use of the IAEA heterogeneous phantom and with the CIRS phantom seem to be an effective tool for detecting errors in radiotherapy procedures. EUROPEAN DIAGNOSTIC REFERENCE LEVELS IN PAEDIATRIC IMAGING Stephen Evans. Head of Medical Physics, Northampton General Hospital, UK Children are at a much higher risk compared to adults from developing cancer from exposure to the same quantity of ionising radiations. For many radiodiagnostic examinations, significant variations in the levels of
Abstracts / Physica Medica 30 (2014) e1ee15
at the national level with IAEA assistance. The national counterparts conduct the TPS audit at local radiotherapy centres through on-site visits. TPS calculated doses are compared with ion chamber measurements performed in an anthropomorphic phantom for eight test cases per algorithm/beam. The set of pre-defined agreement criteria is used to analyze the performance of TPSs. Results: TPS audit was carried out in sixty radiotherapy centers in eight European countries e Estonia, Hungary, Latvia, Lithuania, Serbia, Slovakia, Poland and Portugal. In total, 190 data sets (combination of algorithm and beam quality) have been collected and reviewed. Dosimetry problems requiring interventions were discovered in about 10 % of datasets. In addition, suboptimal beam modelling in TPSs was discovered in a number of cases. Conclusions: The TPS audit project using the IAEA methodology has verified the treatment planning system calculations for 3D conformal radiotherapy in a group of radiotherapy centres in Europe. It contributed to achieving better understanding of the performance of TPSs and helped to resolve issues related to imaging, dosimetry and treatment planning. DOSIMETRY AUDITS IN RADIOTHERAPY IN THE CZECH REPUBLIC Irena Koniarova, Daniela Ekendahl, Ivana Horakova, Michaela Kapucianova, Vladimir Dufek. National Radiation Protection Institute, Prague, Czech Republic Background: The independent audits in radiotherapy are carried out by the National Radiation Protection Institute as a part of the regulatory authority activity since 1996. The system includes TLD postal audits (external radiotherapy) and on-site audits (external radiotherapy and brachytherapy). TLD audit can be performed in several versions differing in the scope and focus of dose measurements. Basic TLD audit consists in beam calibration check. Each clinically used beam must undergo it at least once per two years. During 1997 e 2013, a total of 1435 beams have been thus controlled. Advanced versions of TLD audit focused on more complex conditions of irradiation (non-reference geometries, MLC fields, small IMRT fields, inhomogeneities) have been performed in the case of a request or research studies. On-site audit is performed after the commissioning of each unit. The absorbed dose to water (or RAKR for brachytherapy), beam quality, output and wedge factors, PDD, MLC positioning, MLC transmission, and dosimetric leaf gap (where applicable) are controlled. Mechanical parameters (isocenter stability, radiation field size, table parameters, etc.) are evaluated as well. A number of 535 megavoltage photon and electron external beams, 103 kilovoltage external beams, and 32 brachytherapy sources have been controlled since 1996. 2 proton beams were checked in 2013. Checks of non-dosimetric parameters and imaging functions of TPS with QUASAR phantoms can be performed on request. In addition, 19 departments (23 treatment plans) have been checked using a special pelvic phantom in end-to-end audit for IMRT and IMAT prostate treatment in 2013. Delivered doses to PTV and rectum were measured with ionisation chambers in 3 planes. Planar dose distribution has been verified with EBT2 film. Retrospectively, it was possible to make DVHs analysis and compare all IMRT plans for the pelvic phantom showing common planning practice in the Czech Republic for photon IMRT and proton radiotherapy. Conclusion: The audits revealed several significant errors that might potentially lead to an accident. All results can be analysed retrospectively, showing trends related to chosen indicators. DOSIMETRY AUDITS IN RADIOTHERAPY IN GREECE C.J. Hourdakis, A. Boziari, V. Kamenopoulou. Greek Atomic Energy Commission Background: Greek Atomic Energy Commission (EEAE) has been running dosimetry audits by means of on-site visits in all Greek radiotherapy (RT) and brachytherapy (BT) centers, since 2002. Two rounds (2002-2006 and 2006-2011) have been completed, the 3rd being in progress. Materials and Methods: Dosimetry measurements and QC tests were performed at RT and BT systems (linacs, 60Co and 192Ir HDR) using EEAE’s phantoms and equipment. (a) The systems’ performance was evaluated through mechanical and radiation tests. (b) Relative (TPR20,10, R50 , PDD) and absolute dosimetry (absorbed dose to water) was performed at photon
and electron beams according to IAEA-TRS-398 protocol. For BT beams, the reference air kerma rate was determined. The difference, dr, of the values measured by EEAE, DM, to the stated by RT center, DS , was calculated (dr¼DM/DS-1). (c) MU calculations (by TPS or manually) were assessed at various irradiation conditions (depth, fields, wedges, etc), by comparing DM (at same irradiation conditions and MU) to Ds for the same MU. (d) The overall RT procedure (CT, simulation, planning, verification, irradiation) was assessed qualitatively and quantitatively, using a solid water phantom, with inhomogeneities and tissue deficits, irradiated at multiple photon beams. The measured dose was compared to the TPS stated dose. Results: More than 90% of the linacs and less than 80% of 60Co showed satisfactory mechanical performance. Relative dosimetry for photons and electrons was accurate in most cases (>95%). Photons beam absolute dosimetry showed that in 95% of beams dr<3%. For electrons, 80% of the beams exhibited dr<3%. All BT beams showed dr<3%. In comparing TPS output data, 86% of the beams showed dr<3%, and 3% of the beams dr>5%. Dosimetry assessment of the overall RT procedure, showed that in 90% cases dr<5%, and in 5% cases dr>7%. Improvement of dosimetry accuracy between the rounds was observed. Discussion: Dosimetry audits contributed significantly to the dosimetry accuracy and homogeneity improvement, in the country. On site visits gave the opportunity to resolve all discrepancies and enhance knowledge dissemination. DOSIMETRY AUDITS IN RADIOTHERAPY IN POLAND ski, J. Rostkowska. Department of Medical Physics, W. Bulski, K. Chełmin Maria Sklodowska-Curie Memorial Cancer Centre and Institute of Oncology, Warsaw Purpose: The Secondary Standard Dosimetry Laboratory (SSDL) of the Medical Physics Department of the Centre of Oncology in Warsaw has become a member of the IAEA/WHO international network of such laboratories in 1988. The SSDL has been carrying-out the external postal TLD audits since 1991. In the presentation the scope of dosimetry audits in Poland is overviewed. Materials and methods: TLD runs for on axis measurements in nonreference conditions were performed in Co-60, X-ray and electron beams. In recent years the audits were extended to off-axis measurements (symmetric and asymmetric fields) and to MLC shaped irregular fields. A heterogeneous cubic-shaped phantom developed in the frame of IAEA Coordinated Research Project was used for the audits. The phantom consists of frame made of polystyrene and the bone or lung inhomogeneity slabs. Another phantom, an anthropomorphic CIRS 002LFC thorax phantom, was used for dosimetry checks according to the IAEA-TECDOC-1583 report. Results: The results of the TLD postal audit in non-reference conditions for on axis measurements are in the majority o cases within the ±3.5% tolerance limit which is usually used for reference conditions. Nine Polish radiotherapy centers (of total 30) were audited with the use of the IAEA cubic phantom. Generally most of the results from TLD and ionizing chamber were within ±5% tolerance. Seven radiotherapy centers in Poland have been audited with the CIRS phantom so far. Eight cases with different beam geometry and accessories representing different complexity of the plan were performed on six different TPS. All algorithm/beam datasets showed passing-rate higher than 50% of predefined agreement criteria. Conclusions: Over the last 20 years the postal TLD audits fulfilled their role and remain the primary and well established dosimetric audit method. The measurements allow to the detect limitations of TPS calculation algorithms. The audits performed with the use of the IAEA heterogeneous phantom and with the CIRS phantom seem to be an effective tool for detecting errors in radiotherapy procedures. EUROPEAN DIAGNOSTIC REFERENCE LEVELS IN PAEDIATRIC IMAGING Stephen Evans. Head of Medical Physics, Northampton General Hospital, UK Children are at a much higher risk compared to adults from developing cancer from exposure to the same quantity of ionising radiations. For many radiodiagnostic examinations, significant variations in the levels of