- Email: [email protected]
678 Poster Determination of dose distribution from breast irradiation of an anthropometric phantom by using MRI and ferrous sulphate gel
$206 Wednesday/Thursday, 18-19 September 2002
is often covered by a build-up cap. The thickness of the build up cap is optimised to minimize the correction factor variation. This aims to achieve a more accurate verification of dose delivered. However, diode measurements in electron treatment fields introduce significant disturbance of the dose behind the diode, so the diodes for electron beam measurements are designed with just millimeters of thin build-up, Electron beam radiotherapy is frequently delivered with a range of applicator sizes, field apertures (cut-outs) and at different source-to-surface distances. These introduce large dose variations at the tissue surface due to altered scattering conditions. Consequently, a "naked" diode will be exposed to a considerable large variation in dose with treatment geometry implying a greater need of correction factors. The aim of this study was to assess and analyse the impact of the build-up cap thickness on the values of diode correction factors and further to investigate the costs and benefits in achieving dose verification with high accuracy, The influence of build-up cap thickness and diode characteristics were studled with two commercial diodes designed for measurements in electron beams; EDD2 (Scanditronix) a p-type silicon diode with 2ram build-up cap and E5 (Precitron) an n-type silicon diode with 5mm build-up cap. The diode performance was evaluated using four different linear accelerators, two Varian, one ABB and one Elekta. Electron energies from 4MeV to 22MeV were available. We assessed diode correction factors to account for response variation with energy, applicator, cut-out, SSD and beam incidence. The diode sensitivity variation with accumulated dose and temperature as well as the perturbation of the treatment field caused by each of the two diodes, were also studied, The most appropriate calibration methodology along with advantages and limitations of each type of diode is presented, emphasizing the impact of the differences in build-up cap thickness. The influence of different accelerator types on the correction factors is given and finally, consequences of perturbation effects are discussed. 678
Poster
Determination of dose distribution from breast irradiation o f an anthropometric phantom by using MRI and ferrous suip h a t e gel D. Yalman 1, A. Arican 1, I. Olacak 1, U. A vcibasi2, C. Calli3, A. Haydaroglu 1 1Ege University, Radiation Oncology, Izmir, Turkey 2Ege University, Nuclear Chemistry, Izmir, Turkey 3Ege University, Radiology, Izmir, Turkey Purpose: To obtain the dose distributions in a breast cancer irradiation field of an anthropometric phantom and to compare these with corresponding data calculated with the treatment planning system, Materials and Methods: An anthropometric phantom comparable in size and shape to that of a woman's breast was constituted using a polyester material. Gel was prepared and poured into 8 glass containers of 50 ml each and put in the refrigerator overnight for the gelatin to solidify. One sample was left unirradiated while the other seven were irradiated from 10 to 70 Gy, in 10 Gy intervals. MR images of the containers was taken and the relaxation times were determined. Anthropometric phantom was simulated under the treatment conditions through only lateral and medial tangential fields; lateral and medial tangential fields and 10o angled supraclavicular field; lateral and medial tangential fields and 100 angled supraclavicular field on a tilt board. 50 Gy at a 3-cm-depth was given to supraclavicular region and 50 Gy to the 90% isodose curve for the tangential field for both irradiation techniques. The phantom was filled with the gel and kept in the refrigerator for the overnight and irradiated with 6 MV photonMR images were obtained within 2 hours after the irradiation, Results: Beam projection and irradiation depth of the tangential field was consistent with that of the planning system. Dose value at the reference 90% isodose curve was 46.4 Gy which means that the reference volume received 3.6 Gy less than the calculated. The difference between the planned and the received dose was 7.2%. The dimensions of the 10o angled supraclavicular and the tangential fields and the beam projection were consistent with those of the planned. However dose equivalent value at the reference depth and at the reference 90% isodose curve was 46.4 Gy and the difference between the planned and the received dose was 3.6 Gy for both fields. Dose value at the field junction was approximately 58.2 Gy. A tilt board was used to assess the effect of an inclined surface on junction points. Dose values for the supraclavicular and the tangential fields were 48.2 Gy and 46.4 Gy respectively. At the junction point the dose was beyond the calibration values which could be more than 80 Gy. Conclusion:Ferrous sulpl~ate gel dosimeter seems to be a useful tool for studies of dose distributions and can be used as part of a quality control program after certain improvements are made.
Posters
679 Poster Light contribution
of water
substitute
phantom
in f i l m
dosimetry T. Fuiisaki 1, H. Saitoh2, T. Hiraoka 3, A. Kuwabara 4, S. Abe 1, T. Inada 1 llbaraki Prefectural University of Health Sciences, Radiological Sciences, Ibaraki, Japan 2Tokyo Metropolitan University of Health Sciences, Radiological Sciences, Tokyo, Japan 3Nafionallnstitute of RadiologicalSciences, Chiba, Japan 4Cancer Institute Hospital, Radiation Therapy, Tokyo, Japan Purpose: An unpacked film is generally used in the film dosimetry to avoid the interference induced by the gap between the phantom and the film, and the influence of envelope materials. In this case, the film density may be somewhat overestimated due to the light contribution of Cer-enkov radiation and optical permeability of the phantom. In order to estimate the light contri-bution, the dose distribution was measured using several water substitute phantom. Fur-thermore, novel water substitute phantom, which eliminate light contribution, is described in this report. Methods: Four commercially available water substitute phantoms; WE-211 (Kyoto Kagaku Co., Japan), Mix-DP (Taisei Medical Co., Japan), RMt-451 (GAMMEX Co., US) and PMMA (Goodfel-low Co., UK) and one novel water substitute phantom were used. Cerenkov radiation meas-urements were done in the completely darkened treatment room. Processed phantoms which have one side coated with very thin black carbon film and the other side coated without car-ben film were used for measurement. The unpacked XV-2 film (Eastman Kodak Co., US) was sandwiched between the phantoms. The exposure was performed using 10 MV X-ray and 18 MeV electron beam from a linear accelerator. The off-axis profiles were measured for each beam. Results: The density profiles were varied from the shielded and unshielded sides for each type of ra-diation. This phenomenon may be caused by light emitted in phantom. The estimated ab-sorbed dose of unshielded side is up te 68% higher than shielded side for 10 MV X-ray and 82% for 18 MeV electron beam compared to the actual dose of the shielded side. A novel water substitute phantom which can be used for film dosimetry without light contribution was developed by means of proper adjustment of the ingredient. The density of film also increased with time owing to the optical permeability of the phantom. Conclusion: The dark colored phantoms produce more realistic dose distribution measurements using un-packed films in high-energy film dosimetry by eliminating the effect of Cerenkov radiation. Furthermore, the novel phantom was shown to be unaffected by such local light and by the optical transmission of the phantom. 680
Poster
Three years of experiences on a record and verify system for radiotherapy S. Chauvie 1, M. Stasi 1, B. Baiotto 1, P. Gabriele2, G. Scielzo 1 1Institute for Cancer Research and Treatment - Ordine Mauriziano, Medical Physics, Candiolo (TO), Italy 2Institute for Cancer Research and Treatment - Ordine Mauriziano, Radiotherapy, Candiolo (TO), Italy Purpose: Radiotherapy techniques such as 3-DCRT and IMRT are demanding in terms of both safety and overall treatment control. A computerised Record and Verify system (R&V) is mandatory to handle all this infermation in everyday practice, allowing both controlled delivery of daily treatments and registration of any field parameter for a further check by the staff. Three years of experiences of our Varian R&V is here presented. Materials and methods: The VARiS and Vision R&V is present in our department since the onset. It connects 3 accelerators with accompanying EPID, the simulator, 4 TPS and 20 workstations. A recent upgrade to Generation 6 yields some interesting new features not needing to redesign the way of working into the departments. The training of the personnel was easily made and after some weeks the users digested the new features and the differences from the previous version. In the passage no patient images or data went lost and the two databases merged successfully into a single one which manages images and data. Results: The average number of patients in our centre is established around 110 per month. On average every treatment session is composed of around 2.99 fields, 2.22 of this with MLC. A rough analysis of "what went wrong" comes from the fields added manually after the treatment session that for some reason was made "out of VARiS". It is possible to see that on average 5 fields on t 0000 have been treated out of VARiS, none of this event has been attributable to the R&V's fault. To date any serious application fail-
is often covered by a build-up cap. The thickness of the build up cap is optimised to minimize the correction factor variation. This aims to achieve a more accurate verification of dose delivered. However, diode measurements in electron treatment fields introduce significant disturbance of the dose behind the diode, so the diodes for electron beam measurements are designed with just millimeters of thin build-up, Electron beam radiotherapy is frequently delivered with a range of applicator sizes, field apertures (cut-outs) and at different source-to-surface distances. These introduce large dose variations at the tissue surface due to altered scattering conditions. Consequently, a "naked" diode will be exposed to a considerable large variation in dose with treatment geometry implying a greater need of correction factors. The aim of this study was to assess and analyse the impact of the build-up cap thickness on the values of diode correction factors and further to investigate the costs and benefits in achieving dose verification with high accuracy, The influence of build-up cap thickness and diode characteristics were studled with two commercial diodes designed for measurements in electron beams; EDD2 (Scanditronix) a p-type silicon diode with 2ram build-up cap and E5 (Precitron) an n-type silicon diode with 5mm build-up cap. The diode performance was evaluated using four different linear accelerators, two Varian, one ABB and one Elekta. Electron energies from 4MeV to 22MeV were available. We assessed diode correction factors to account for response variation with energy, applicator, cut-out, SSD and beam incidence. The diode sensitivity variation with accumulated dose and temperature as well as the perturbation of the treatment field caused by each of the two diodes, were also studied, The most appropriate calibration methodology along with advantages and limitations of each type of diode is presented, emphasizing the impact of the differences in build-up cap thickness. The influence of different accelerator types on the correction factors is given and finally, consequences of perturbation effects are discussed. 678
Poster
Determination of dose distribution from breast irradiation o f an anthropometric phantom by using MRI and ferrous suip h a t e gel D. Yalman 1, A. Arican 1, I. Olacak 1, U. A vcibasi2, C. Calli3, A. Haydaroglu 1 1Ege University, Radiation Oncology, Izmir, Turkey 2Ege University, Nuclear Chemistry, Izmir, Turkey 3Ege University, Radiology, Izmir, Turkey Purpose: To obtain the dose distributions in a breast cancer irradiation field of an anthropometric phantom and to compare these with corresponding data calculated with the treatment planning system, Materials and Methods: An anthropometric phantom comparable in size and shape to that of a woman's breast was constituted using a polyester material. Gel was prepared and poured into 8 glass containers of 50 ml each and put in the refrigerator overnight for the gelatin to solidify. One sample was left unirradiated while the other seven were irradiated from 10 to 70 Gy, in 10 Gy intervals. MR images of the containers was taken and the relaxation times were determined. Anthropometric phantom was simulated under the treatment conditions through only lateral and medial tangential fields; lateral and medial tangential fields and 10o angled supraclavicular field; lateral and medial tangential fields and 100 angled supraclavicular field on a tilt board. 50 Gy at a 3-cm-depth was given to supraclavicular region and 50 Gy to the 90% isodose curve for the tangential field for both irradiation techniques. The phantom was filled with the gel and kept in the refrigerator for the overnight and irradiated with 6 MV photonMR images were obtained within 2 hours after the irradiation, Results: Beam projection and irradiation depth of the tangential field was consistent with that of the planning system. Dose value at the reference 90% isodose curve was 46.4 Gy which means that the reference volume received 3.6 Gy less than the calculated. The difference between the planned and the received dose was 7.2%. The dimensions of the 10o angled supraclavicular and the tangential fields and the beam projection were consistent with those of the planned. However dose equivalent value at the reference depth and at the reference 90% isodose curve was 46.4 Gy and the difference between the planned and the received dose was 3.6 Gy for both fields. Dose value at the field junction was approximately 58.2 Gy. A tilt board was used to assess the effect of an inclined surface on junction points. Dose values for the supraclavicular and the tangential fields were 48.2 Gy and 46.4 Gy respectively. At the junction point the dose was beyond the calibration values which could be more than 80 Gy. Conclusion:Ferrous sulpl~ate gel dosimeter seems to be a useful tool for studies of dose distributions and can be used as part of a quality control program after certain improvements are made.
Posters
679 Poster Light contribution
of water
substitute
phantom
in f i l m
dosimetry T. Fuiisaki 1, H. Saitoh2, T. Hiraoka 3, A. Kuwabara 4, S. Abe 1, T. Inada 1 llbaraki Prefectural University of Health Sciences, Radiological Sciences, Ibaraki, Japan 2Tokyo Metropolitan University of Health Sciences, Radiological Sciences, Tokyo, Japan 3Nafionallnstitute of RadiologicalSciences, Chiba, Japan 4Cancer Institute Hospital, Radiation Therapy, Tokyo, Japan Purpose: An unpacked film is generally used in the film dosimetry to avoid the interference induced by the gap between the phantom and the film, and the influence of envelope materials. In this case, the film density may be somewhat overestimated due to the light contribution of Cer-enkov radiation and optical permeability of the phantom. In order to estimate the light contri-bution, the dose distribution was measured using several water substitute phantom. Fur-thermore, novel water substitute phantom, which eliminate light contribution, is described in this report. Methods: Four commercially available water substitute phantoms; WE-211 (Kyoto Kagaku Co., Japan), Mix-DP (Taisei Medical Co., Japan), RMt-451 (GAMMEX Co., US) and PMMA (Goodfel-low Co., UK) and one novel water substitute phantom were used. Cerenkov radiation meas-urements were done in the completely darkened treatment room. Processed phantoms which have one side coated with very thin black carbon film and the other side coated without car-ben film were used for measurement. The unpacked XV-2 film (Eastman Kodak Co., US) was sandwiched between the phantoms. The exposure was performed using 10 MV X-ray and 18 MeV electron beam from a linear accelerator. The off-axis profiles were measured for each beam. Results: The density profiles were varied from the shielded and unshielded sides for each type of ra-diation. This phenomenon may be caused by light emitted in phantom. The estimated ab-sorbed dose of unshielded side is up te 68% higher than shielded side for 10 MV X-ray and 82% for 18 MeV electron beam compared to the actual dose of the shielded side. A novel water substitute phantom which can be used for film dosimetry without light contribution was developed by means of proper adjustment of the ingredient. The density of film also increased with time owing to the optical permeability of the phantom. Conclusion: The dark colored phantoms produce more realistic dose distribution measurements using un-packed films in high-energy film dosimetry by eliminating the effect of Cerenkov radiation. Furthermore, the novel phantom was shown to be unaffected by such local light and by the optical transmission of the phantom. 680
Poster
Three years of experiences on a record and verify system for radiotherapy S. Chauvie 1, M. Stasi 1, B. Baiotto 1, P. Gabriele2, G. Scielzo 1 1Institute for Cancer Research and Treatment - Ordine Mauriziano, Medical Physics, Candiolo (TO), Italy 2Institute for Cancer Research and Treatment - Ordine Mauriziano, Radiotherapy, Candiolo (TO), Italy Purpose: Radiotherapy techniques such as 3-DCRT and IMRT are demanding in terms of both safety and overall treatment control. A computerised Record and Verify system (R&V) is mandatory to handle all this infermation in everyday practice, allowing both controlled delivery of daily treatments and registration of any field parameter for a further check by the staff. Three years of experiences of our Varian R&V is here presented. Materials and methods: The VARiS and Vision R&V is present in our department since the onset. It connects 3 accelerators with accompanying EPID, the simulator, 4 TPS and 20 workstations. A recent upgrade to Generation 6 yields some interesting new features not needing to redesign the way of working into the departments. The training of the personnel was easily made and after some weeks the users digested the new features and the differences from the previous version. In the passage no patient images or data went lost and the two databases merged successfully into a single one which manages images and data. Results: The average number of patients in our centre is established around 110 per month. On average every treatment session is composed of around 2.99 fields, 2.22 of this with MLC. A rough analysis of "what went wrong" comes from the fields added manually after the treatment session that for some reason was made "out of VARiS". It is possible to see that on average 5 fields on t 0000 have been treated out of VARiS, none of this event has been attributable to the R&V's fault. To date any serious application fail-