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EP-1433: Photoneutron Flux Measurement via NAA in a Radiotherapy Bunker with an 18 MV Linear Accelerator
S764 ESTRO 36 _______________________________________________________________________________________________
with cervical cancer (CC) were treated with radical radiochemotherapy. 17 pts with CC were treated palliative with radiotherapy, 10 pts with hepatic lesions (1 HCC and 9 meta ad hepar) treated with chemotherapy, 7 pts with pancreatic ca treated with chemotherapy, 2 breast ca treated with chemotherapy ( 1 with RT and 1 with CT), 11pts with lung ca treated with chemotherapy , 7 pts with rectal ca. treated with radiotherapy, 4 pts with ca. of sigmoid colon treated with chemotherapy, 2 pts with gastric ca. treated with chemotherapy and 1 with radiotherapy. The Celsius TCS hyperthermia system, an electro-hyperthermia, with a maximum output of up to 500 Watts was used. Two different electrode sizes were applied externally by physical means to the region with tumour in a targeted and controlled manner. The aim was to increase the temperature to 41 oC - 42oC, one session lasted 60min. It was combined with either chemotherapy or radiotherapy twice per week. Toxicity of the skin was evaluated at every session with RTOG/EORTC classification system. The tolerance of treatment was ranged as Group 1: very good if there were 1-2 pauses because of discomfort with no other symptoms, Group 2: good- 3-4 pauses because of discomfort and skin toxicity Grade 1, Group 3: poor- > 4 pauses or shortening of hyperthermia course because of itching and skin toxicity>=Gr 2. Results Local deep hyperthermia was easily tolerated. 78 pts didn’t report any problems and were assigned to Group 1. 16 pts were assigned to Group 2 and only 2 pts to the group “poor”. Toxicity was generally mild and never of grade 3. 1/10 pts felt pain in the last few minutes of the session. Acute radiation toxicity was the same with or without hyperthermia. There was a reduced tolerance of hyperthermia in obese persons, with folds of skin on the abdomen. This is primarily due to the fact that between folds of skin sweat is collected what increases negative impression from temperature. All patients with tumours located in pelvis, reported pressure on the coccyx. We haven’t observed any increased vaginal bleeding during radical and palliative treatment of CC. Conclusion Tolerance associated with hyperthermia was very good and most patients felt comfortable during this treatment. Acute toxicity of the skin during the treatment was low. EP-1432 Advantage of butterfly-vmat versus vmat in mediastinal tumors J. Luna1, A. Ilundain1, S. Gómez-Tejedor1, D. Esteban1, M. Rincón1, J. Olivera1, W. Vásquez1, I. Prieto1, L. Guzmán1, J. Vara1 1 Fundación Jiménez Díaz, Radiation Oncology, Madrid, Spain Purpose or Objective There is a growing concern about the risks of late adverse effects in young people who receive mediastinal radiotherapy. The amazing technical advance has achieved better planned treatments. At present, the new focus of interest is to minimize the low doses in organs at risks (OARs) Material and Methods We present our first results of a new protocol in our Department for mediastinal radiotherapy. This protocol includes the comparison of two treatment plannings for every patient: volumetric modulated arc therapy (VMAT), and Butterfly VMAT (a technique developed by the University of Turin, Radiation Oncology Unit). VMAT was performed with a double arc of 360º. B-VMAT consisted of 2 coplanar arcs of 60º (gantry starting angles 150º and 330º) and 1 no-coplanar arc of 60º (gantry starting angles 330º, couch angle 90º).
Until now, five patients have been included: Three mediastinal lymphomas in young women (total dose 36 Gy in two cases and 30 Gy in the other one), one patient diagnosed of hemangiopericytoma located at internal mammary chain (total dose 50 Gy) and the fifth patient diagnosed of thymoma (54 Gy) In the dose- volume histogram, regarding the PTV, the parameters analyzed were V95, V98, V107, Medium dose, Homogeneity index (HI) and conformity index (CI). For OARS- (heart, lung and breast) and body, several dosimetric parameters were registered. Results Our results show similar data in PTV coverage, IH and CI. Regarding the OARs, dosimetric parameters were equivalent in lung, heart and body. However, breast doses were clearly lower with B-VMAT, mainly the lowest doses (V4 and V10). For V4 , the medium value was 45.6% (7.8% – 63.1%) for VMAT and 21.5 % (0.7%- 60.1%) for B-VMAT. For V10, the VMAT medium value was 23.2% (0%37.2%) and the B-VMAT medium value was 8.9% (0%24.4%). Conclusion B-VMAT for mediastinal tumors is clearly superior to usual VMAT for breast doses, mainly the low doses, and equivalent in the rest of dosimetric parameters. Although the inclusion of more patients is needed, our preliminary results show B-VMAT like a great technical advance in mediastinal radiotherapy. Electronic Poster: Physics track: Basic dosimetry and phantom and detector development EP-1433 Photoneutron Flux Measurement via NAA in a Radiotherapy Bunker with an 18 MV Linear Accelerator T. Gulumser1, Y. Ceçen1, A.H. Yeşil1 1 Akdeniz University- School of Medicine, Department of Radiation Oncology, Antalya, Turkey Purpose or Objective In cancer treatment, high energy X-rays are used which are produced by linear accelerators (LINACs). If the energy of these beams is over 8 MeV, photonuclear reactions occur between the bremsstrahlung photons and the metallic parts of the LINAC. As a result of these interactions, neutrons are also produced as secondary radiation products (γ,n) which are called photoneutrons. The study aims to map the photoneutron flux distribution within the LINAC bunker via neutron activation analysis (NAA) using indium-cadmium foils. Material and Methods The radiotherapy bunker hosts a Philips SLI-25 LINAC which is used for experimental studies. The measurements are taken at the highest energy of the LINAC which corresponds to 18 MeV bremsstrahlung photons. Indium and cadmium foils were used at 91 different points within the bunker. Neutron activation was performed by irradiating the room with 10000 monitor units (MU) at different gantry angles. The field was 40x40 cm2 open. The activated indium foils are then counted in a High Purity Germanium (HPGe) detector system. Since indium has a high absorption cross section for thermal and epithermal neutrons, bare indium foil irradiation results in flux information of that region. However cadmium has high absorption cross section in the epithermal and fast region. If one filters the indium foils by cadmium coatings, the difference in the count yields thermal fluxes which are of interest for the doses to the patients in radiotherapy. Results Result of the analysis shows that the maximum neutron flux in the room occurs at just above of the LINAC head towards to gun direciton. This is expected since most of
S765 ESTRO 36 _______________________________________________________________________________________________
the neutrons are produced when the electron beam hits the tungsten target and then the primary collimation occurs. Both the target and the primary collimator are located at the top of the gantry head. The maximum thermal neutron flux obtained is 3x105 neutrons/cm2.second which is higher than a standard americium-beryllium (Am-Be) neutron source. At the isocenter plane (SSD=100 cm), the fluxes were 5.4x104 at the center, 1.5x104 at 2.5 m away and 9.9x103 n/cm2.s at the room wall which is 3.8 m away from isocenter. The flux at the maze entrance was measured nearly six in a ten thousand less (81 n/cm2.s).
comparison. The standard deviation of all the measurements was 5.6 % with the maximum variation between two results being 42 %. Conclusion This exercise gave an indication of the consistency of the small-field dosimetry being performed in Australia at the present time. There is no currently accepted protocol for these measurements and a wide range of detectors are being used with correction factors being applied from a variety of sources. The dissemination of the small-field methods and techniques currently being used will aid the consistency of these measurements.
Conclusion The neutron flux distribution within the bunker was measured with detail using 91 points. Neutron flux distribution within the bunker found and the graph was plotted. Thus neutron flux can found any desired point in the room by iterations. The flux decreases as we move away the isocenter which is compatible with the literature. The magnitude of the neutron fluxes shows that there is a significant amount of neutron dose within the room. The corresponding neutron dose to the patient however is only 0.1-0.3 % of the total dose. However, neutrons have a high RBE and this unwanted dose is not calculated with the TPS. The future work would be to compare the results with the Monte Carlo simulations.
EP-1435 Evaluation of single material and multimaterial patient-specific, 3D-printed radiotherapy phantoms D. Craft1, E. Burgett2, R. Howell1 1 The University of Texas MD Anderson Cancer Center, Radiation Physics, Houston, USA 2 Idaho State Univeresity, Department of Nuclear Engineering, Pocatello Idaho, USA
EP-1434 Comparison of small-field output factor measurements C. Oliver1, V. Takau1, D. Butler1, I. Williams1 1 ARPANSA, Radiotherapy, Yallambie, Australia Purpose or Objective The Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) held a comparison in April 2016 whereby participants came to ARPANSA and measured the output factor of a 5 mm cone . The goal of the comparison was to compare the consistency of the small-field output factor measured by independent medical physicists with their own apparatus. Material and Methods The participants measured the output factor of the 5 mm cone using a 6 MV photon beam at a source to surface distance of 95 cm and depth in water of 5 cm. ARPANSA provided a 3D scanning water tank for detector positioning but all detectors were brought by participants. The participant was asked to measure the output factor as accurately as possible. All post measurement analysis, correction factor determination and uncertainty calculations were supplied by the participant. Results
Fifteen groups travelled to ARPANSA and a total of thirty independent measurements of the output factor were made. The most popular method of measurement was with film but measurements were also made with ionisation chambers, semiconductor detectors, diamond detectors and a scintillation detector. A large volume ionisation chamber measuring dose area product was also used in the
Purpose or Objective Anthropomorphic phantoms are used in a variety of ways in radiation therapy for both research and quality assurance purposes. Most anthropomorphic phantoms are of generalized patients, but 3D printing technology can be used to fabricate patient-realistic phantoms for special QA and verification procedures. Most 3D printers, however, can only print in one or two materials at a time, so true patient heterogeneity is limited. In this study, we examined two different patient specific, 3D printed phantoms created based on the same patient to determine the accuracy of single and multi-material phantoms. Material and Methods The phantoms used in this study were designed from the clinical CT data for a post-mastectomy patient treated at our institution. The CT data was trimmed to remove the patient’s head and arms to preserve anonymity and simplify printing. Phantom 1 was designed by converting the trimmed CT data into a 3D model with a CT threshold of >-500 Hounsfield units (HU). This model was sliced into 2.5-cm-thick sagittal slices and printed one slice at a time. All slices were printed with polylactic acid (PLA) representing all body tissues, but with air cavities and lower density regions like the lungs left open. Sagittal slices were chosen for their superior fit with each other, and minimal material warping relative to axial slices. Phantom 2 was designed by converting the CT data into three separate 3D models with a CT threshold of <-147 HU for air cavities, -147 to 320 HU for soft tissue, and >320 HU for bone. The models were sliced into 1-cm-thick axial slices, and printed. The slices were printed from the soft tissue model using a custom formulated high impact polystyrene (HIPS) with the air and bone models left open. After printing, the open bone model sections were filled with a liquid resin polymer with an equivalent density to bone. The phantoms were evaluated for their materials and overall accuracy to the original patient CT. Blocks of PLA, HIPS, and the bone resin material were all imaged to determine their average HU. The phantoms were also each imaged and registered with each other and the original patient CT to determine the consistency and accuracy of each phantom. Results The materials used and their properties are summarized in Table 1. Phantom 1 was fabricated from PLA, which isn’t particularly tissue equivalent, but did print relatively consistently. The bone resin and HIPS of phantom 2 more accurately reflect tissue heterogeneity, but have more variations in their printed consistency.
with cervical cancer (CC) were treated with radical radiochemotherapy. 17 pts with CC were treated palliative with radiotherapy, 10 pts with hepatic lesions (1 HCC and 9 meta ad hepar) treated with chemotherapy, 7 pts with pancreatic ca treated with chemotherapy, 2 breast ca treated with chemotherapy ( 1 with RT and 1 with CT), 11pts with lung ca treated with chemotherapy , 7 pts with rectal ca. treated with radiotherapy, 4 pts with ca. of sigmoid colon treated with chemotherapy, 2 pts with gastric ca. treated with chemotherapy and 1 with radiotherapy. The Celsius TCS hyperthermia system, an electro-hyperthermia, with a maximum output of up to 500 Watts was used. Two different electrode sizes were applied externally by physical means to the region with tumour in a targeted and controlled manner. The aim was to increase the temperature to 41 oC - 42oC, one session lasted 60min. It was combined with either chemotherapy or radiotherapy twice per week. Toxicity of the skin was evaluated at every session with RTOG/EORTC classification system. The tolerance of treatment was ranged as Group 1: very good if there were 1-2 pauses because of discomfort with no other symptoms, Group 2: good- 3-4 pauses because of discomfort and skin toxicity Grade 1, Group 3: poor- > 4 pauses or shortening of hyperthermia course because of itching and skin toxicity>=Gr 2. Results Local deep hyperthermia was easily tolerated. 78 pts didn’t report any problems and were assigned to Group 1. 16 pts were assigned to Group 2 and only 2 pts to the group “poor”. Toxicity was generally mild and never of grade 3. 1/10 pts felt pain in the last few minutes of the session. Acute radiation toxicity was the same with or without hyperthermia. There was a reduced tolerance of hyperthermia in obese persons, with folds of skin on the abdomen. This is primarily due to the fact that between folds of skin sweat is collected what increases negative impression from temperature. All patients with tumours located in pelvis, reported pressure on the coccyx. We haven’t observed any increased vaginal bleeding during radical and palliative treatment of CC. Conclusion Tolerance associated with hyperthermia was very good and most patients felt comfortable during this treatment. Acute toxicity of the skin during the treatment was low. EP-1432 Advantage of butterfly-vmat versus vmat in mediastinal tumors J. Luna1, A. Ilundain1, S. Gómez-Tejedor1, D. Esteban1, M. Rincón1, J. Olivera1, W. Vásquez1, I. Prieto1, L. Guzmán1, J. Vara1 1 Fundación Jiménez Díaz, Radiation Oncology, Madrid, Spain Purpose or Objective There is a growing concern about the risks of late adverse effects in young people who receive mediastinal radiotherapy. The amazing technical advance has achieved better planned treatments. At present, the new focus of interest is to minimize the low doses in organs at risks (OARs) Material and Methods We present our first results of a new protocol in our Department for mediastinal radiotherapy. This protocol includes the comparison of two treatment plannings for every patient: volumetric modulated arc therapy (VMAT), and Butterfly VMAT (a technique developed by the University of Turin, Radiation Oncology Unit). VMAT was performed with a double arc of 360º. B-VMAT consisted of 2 coplanar arcs of 60º (gantry starting angles 150º and 330º) and 1 no-coplanar arc of 60º (gantry starting angles 330º, couch angle 90º).
Until now, five patients have been included: Three mediastinal lymphomas in young women (total dose 36 Gy in two cases and 30 Gy in the other one), one patient diagnosed of hemangiopericytoma located at internal mammary chain (total dose 50 Gy) and the fifth patient diagnosed of thymoma (54 Gy) In the dose- volume histogram, regarding the PTV, the parameters analyzed were V95, V98, V107, Medium dose, Homogeneity index (HI) and conformity index (CI). For OARS- (heart, lung and breast) and body, several dosimetric parameters were registered. Results Our results show similar data in PTV coverage, IH and CI. Regarding the OARs, dosimetric parameters were equivalent in lung, heart and body. However, breast doses were clearly lower with B-VMAT, mainly the lowest doses (V4 and V10). For V4 , the medium value was 45.6% (7.8% – 63.1%) for VMAT and 21.5 % (0.7%- 60.1%) for B-VMAT. For V10, the VMAT medium value was 23.2% (0%37.2%) and the B-VMAT medium value was 8.9% (0%24.4%). Conclusion B-VMAT for mediastinal tumors is clearly superior to usual VMAT for breast doses, mainly the low doses, and equivalent in the rest of dosimetric parameters. Although the inclusion of more patients is needed, our preliminary results show B-VMAT like a great technical advance in mediastinal radiotherapy. Electronic Poster: Physics track: Basic dosimetry and phantom and detector development EP-1433 Photoneutron Flux Measurement via NAA in a Radiotherapy Bunker with an 18 MV Linear Accelerator T. Gulumser1, Y. Ceçen1, A.H. Yeşil1 1 Akdeniz University- School of Medicine, Department of Radiation Oncology, Antalya, Turkey Purpose or Objective In cancer treatment, high energy X-rays are used which are produced by linear accelerators (LINACs). If the energy of these beams is over 8 MeV, photonuclear reactions occur between the bremsstrahlung photons and the metallic parts of the LINAC. As a result of these interactions, neutrons are also produced as secondary radiation products (γ,n) which are called photoneutrons. The study aims to map the photoneutron flux distribution within the LINAC bunker via neutron activation analysis (NAA) using indium-cadmium foils. Material and Methods The radiotherapy bunker hosts a Philips SLI-25 LINAC which is used for experimental studies. The measurements are taken at the highest energy of the LINAC which corresponds to 18 MeV bremsstrahlung photons. Indium and cadmium foils were used at 91 different points within the bunker. Neutron activation was performed by irradiating the room with 10000 monitor units (MU) at different gantry angles. The field was 40x40 cm2 open. The activated indium foils are then counted in a High Purity Germanium (HPGe) detector system. Since indium has a high absorption cross section for thermal and epithermal neutrons, bare indium foil irradiation results in flux information of that region. However cadmium has high absorption cross section in the epithermal and fast region. If one filters the indium foils by cadmium coatings, the difference in the count yields thermal fluxes which are of interest for the doses to the patients in radiotherapy. Results Result of the analysis shows that the maximum neutron flux in the room occurs at just above of the LINAC head towards to gun direciton. This is expected since most of
S765 ESTRO 36 _______________________________________________________________________________________________
the neutrons are produced when the electron beam hits the tungsten target and then the primary collimation occurs. Both the target and the primary collimator are located at the top of the gantry head. The maximum thermal neutron flux obtained is 3x105 neutrons/cm2.second which is higher than a standard americium-beryllium (Am-Be) neutron source. At the isocenter plane (SSD=100 cm), the fluxes were 5.4x104 at the center, 1.5x104 at 2.5 m away and 9.9x103 n/cm2.s at the room wall which is 3.8 m away from isocenter. The flux at the maze entrance was measured nearly six in a ten thousand less (81 n/cm2.s).
comparison. The standard deviation of all the measurements was 5.6 % with the maximum variation between two results being 42 %. Conclusion This exercise gave an indication of the consistency of the small-field dosimetry being performed in Australia at the present time. There is no currently accepted protocol for these measurements and a wide range of detectors are being used with correction factors being applied from a variety of sources. The dissemination of the small-field methods and techniques currently being used will aid the consistency of these measurements.
Conclusion The neutron flux distribution within the bunker was measured with detail using 91 points. Neutron flux distribution within the bunker found and the graph was plotted. Thus neutron flux can found any desired point in the room by iterations. The flux decreases as we move away the isocenter which is compatible with the literature. The magnitude of the neutron fluxes shows that there is a significant amount of neutron dose within the room. The corresponding neutron dose to the patient however is only 0.1-0.3 % of the total dose. However, neutrons have a high RBE and this unwanted dose is not calculated with the TPS. The future work would be to compare the results with the Monte Carlo simulations.
EP-1435 Evaluation of single material and multimaterial patient-specific, 3D-printed radiotherapy phantoms D. Craft1, E. Burgett2, R. Howell1 1 The University of Texas MD Anderson Cancer Center, Radiation Physics, Houston, USA 2 Idaho State Univeresity, Department of Nuclear Engineering, Pocatello Idaho, USA
EP-1434 Comparison of small-field output factor measurements C. Oliver1, V. Takau1, D. Butler1, I. Williams1 1 ARPANSA, Radiotherapy, Yallambie, Australia Purpose or Objective The Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) held a comparison in April 2016 whereby participants came to ARPANSA and measured the output factor of a 5 mm cone . The goal of the comparison was to compare the consistency of the small-field output factor measured by independent medical physicists with their own apparatus. Material and Methods The participants measured the output factor of the 5 mm cone using a 6 MV photon beam at a source to surface distance of 95 cm and depth in water of 5 cm. ARPANSA provided a 3D scanning water tank for detector positioning but all detectors were brought by participants. The participant was asked to measure the output factor as accurately as possible. All post measurement analysis, correction factor determination and uncertainty calculations were supplied by the participant. Results
Fifteen groups travelled to ARPANSA and a total of thirty independent measurements of the output factor were made. The most popular method of measurement was with film but measurements were also made with ionisation chambers, semiconductor detectors, diamond detectors and a scintillation detector. A large volume ionisation chamber measuring dose area product was also used in the
Purpose or Objective Anthropomorphic phantoms are used in a variety of ways in radiation therapy for both research and quality assurance purposes. Most anthropomorphic phantoms are of generalized patients, but 3D printing technology can be used to fabricate patient-realistic phantoms for special QA and verification procedures. Most 3D printers, however, can only print in one or two materials at a time, so true patient heterogeneity is limited. In this study, we examined two different patient specific, 3D printed phantoms created based on the same patient to determine the accuracy of single and multi-material phantoms. Material and Methods The phantoms used in this study were designed from the clinical CT data for a post-mastectomy patient treated at our institution. The CT data was trimmed to remove the patient’s head and arms to preserve anonymity and simplify printing. Phantom 1 was designed by converting the trimmed CT data into a 3D model with a CT threshold of >-500 Hounsfield units (HU). This model was sliced into 2.5-cm-thick sagittal slices and printed one slice at a time. All slices were printed with polylactic acid (PLA) representing all body tissues, but with air cavities and lower density regions like the lungs left open. Sagittal slices were chosen for their superior fit with each other, and minimal material warping relative to axial slices. Phantom 2 was designed by converting the CT data into three separate 3D models with a CT threshold of <-147 HU for air cavities, -147 to 320 HU for soft tissue, and >320 HU for bone. The models were sliced into 1-cm-thick axial slices, and printed. The slices were printed from the soft tissue model using a custom formulated high impact polystyrene (HIPS) with the air and bone models left open. After printing, the open bone model sections were filled with a liquid resin polymer with an equivalent density to bone. The phantoms were evaluated for their materials and overall accuracy to the original patient CT. Blocks of PLA, HIPS, and the bone resin material were all imaged to determine their average HU. The phantoms were also each imaged and registered with each other and the original patient CT to determine the consistency and accuracy of each phantom. Results The materials used and their properties are summarized in Table 1. Phantom 1 was fabricated from PLA, which isn’t particularly tissue equivalent, but did print relatively consistently. The bone resin and HIPS of phantom 2 more accurately reflect tissue heterogeneity, but have more variations in their printed consistency.