- Email: [email protected]
532 poster A solid phantom for the verification of postimplant dosimetry with radiographs and CT
Posters
standard loading pattern. The reference isodose for treatment was determined, if possible, according to the maximum diameter of the residual lesion at time of BT. The dose distribution on orthogonal films was reported according to the ICRU recommendations whereas the dose contribution to critical organs on CT was evaluated using the doses in 0.1cc (CTmax), 2cc (CT2cc) and 5 cc (CT5cc) volumes receiving the highest dose on DVH.
Results: We were able to reproduce in all cases the dose distribution that was usually obtained in LDR BT. For rectum, on average CTmax and CT2cc were 0.6 and 0.8 times smaller than the rectal ICRU reference dose. In five cases only, the CTmax was higher than the dose recorded from films (1.3 time the average value) due to the lateral position of the rectum related to the ovoids sources. Rectum mean dose defined from films seemed to be a good estimate for the "true max rectum dose", the ratio between Rmean and CTmax being around 1 in 70% of the cases. For bladder, as expected, the CTmax and the CT2cc were higher than the ICRU dose in 90% of cases (threshold of 1.7). Conclusions: The CT-assisted planning enabled to estimate the dose actually received by the critical organs. The ratio between ICRU dose and CT dose estimation in both rectum and bladder are in accordance with the results already published using the same methodology. These preliminary findings need to be confirmed in a large series. The impact of these CT parameters on complication rates should be assessed prospectively. Grants from Comit~s 21, 58 and 71 Eigue Nationale contre le cancer. 531 poster
Dose rate effect: does it exist clinically in high-dose-rate intraqavitary brachytherapy for cervical cancer using iridium.192 source?
C. Wang, E. Huang, L. Sun, H. Chen Kaohsiung Chang Gung Medical Center, Department of Radiation Oncology, Kaohsiung Hsien, Taiwan Purpose: In-vitro studies in the past have revealed that dose-rate effect was dramatic between 0.01-1 Gy/min. This study is aimed to test if the effect exists clinically in highdose-rate intracavitary brachytherapy (HDR-ICB) for cervical cancer using Iridium-192 with a dose-rate ranging from 0.3-1 Gy/min. Materials and methods: (1) Patients: One hundred and sixty-five patients with cervical cancer were treated with external beam irradiation (EXRT) plus HDR-ICB between May 1993 and December 1996. (2) EXRT: Whole pelvis irradiation 44-45 Gy, and pelvic wall boost to a total of 5459.4 Gy. (3) HDR-ICB scheme: 4.8 Gy for 5 fractions delivered twice a week. (4) HDR facility was microSelectron system (Nucletron Corp.), using a single programmable stepwise Iridium-192 source with active dimensions of 4 mm long by 0.5 mm in diameter. The decaying source was renewed every 3 months, maintaining a therapeutic radioactivity ranging from 367 GBq to 126 GBq. (5) Patients were categorized into two groups, namely Group A vs. Group B, by a cutoff dose-rate of 0.6 Gy/min. Group A consisted of 88 patients w~th dose rate <_ 0.6 Gy/min. Group B consisted of 77 patients with dose rate > 0.6 Gy/min. (6) Endpoints: Pelvic control rate and rectal complication rate. (7) Statistics: Actuarial rate was calculated by Kaplan-Meier product-limit method, and significance tested by Log-rank test. (8) Duration of follow-up: 6.1-9.7 years (median, 7.3 years). Results: (1) Pelvic control rate: Overall, actuarial 5-year pelvic control rate for the entire patients cohort was 90.5%.
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By dose-rate, actuarial 5-year pelvic control rates for Group A ( ~ 0.6 Gy/min, n=88) vs. Group B (> 0.6 Gy/min, n=77) were 92.1% vs. 88.7%, respectively (p=0.505). (2) Complication: Overall, actuarial 5-year proctitis rate for the entire patients cohort was 32.4%. By dose-rate, actuarial 5-year proctitis rate for Group A vs. Group B was 34.4% vs. 30.3%, respectively (p=0.467). (3) For the subset of cases with early stage (IB-IIA, n=67), actuarial 5-year pelvic control rate for Group A (n=31) vs. Group B (n=36) was 92.9% vs. 93.2%, respectively (p=0.836). Actuarial 5-year proctitis rate for Group A (n=31) vs. Group B (n=36) was 23.5% vs. 28.8%, respectively (p=0.701).
Conclusion: Using Iridium-192 for high-dose-rate intracavitary brachytherapy, dose-rate effect in the range of 0.3-1 Gy/min was not demonstrated clinically. 532 poster A solid phantom for the verification of postimplant dosimetry with radiographs and CT
F.-A. Siebert, P. Kohr, G. Kov&cs University Clinic S-H, Campus Kiel, Radiotherapy, Kiel, Germany Introduction: The application of permanent prostate implants using 1251 or l°3pd seed sources is a routine procedure worldwide in many different clinics. Many centers use a set of radiographs for the postimplant dosimetry. This widespread method allows a reconstruction and the determination of the seed positions in the patient with high accuracy. Until now there is no commercial solution available that is able to check the reliability of such reconstruction techniques. Material and methods: To validate the reconstruction of a set of radiographs or CT data in postimptant dosimetry, a new phantom, the Kiel-phantom, was designed. The exactly known positions of the non-radioactive seeds in the phantom can be compared with the results of the reconstruction techniques. The phantom consists of a stack of Perspex ® disks with precisely defined holes for the insertion of dummy seeds. Several disks were designed to simulate many different seed configurations. It is possible to create seed patterns with equally or arbitrarily spaced sources in x- y- or z-direction. In this way it is easy to simulate strong mathematical configurations as well as more realistic ones. Moreover a marker system is attached on the phantom that allows the exact placement with positioning laser devices. With the internal coordinate system the definition of a unique origin and alignment are easy to perform. The phantoms' base is mounted on three nylon screws and its horizontal position can be adjusted with a spirit level. Measurements were carried out with different seed configurations. The reconstructions of the seed coordinates were performed with the treatment planning system (TPS) VariSeed ® 6.7/7.1. For every measurement three radiographs with different gantry angles but fixed focus film distances were used. Results: For non-overlapping seed positions we found very good agreement between the coordinates of the dummy seeds and the reconstructed positions (SD < 0.1 mm) with gantry angles of 0 °, +45 ° and - 4 5 ° . Furthermore measurements with a complex seed distribution in the phantom were carried out. For this study some seeds overlap from more than from one gantry angle. We found out difficulties of the TPS to correctly compute seed positions if two or more sources are placed in a row from more than one
S238
view. The displacements of the seeds reached values up to 3 cm. Conclusion: The Kiel-phantom was designed in lack of existing commercial solutions to investigate seed reconstruction algorithms with high accuracy in the postimplant planning procedure of seeds. We found out a) that the developed phantom is able to check reconstruction techniques with high accuracy and b) that a higher quality assurance of seed reconstruction algorithms is necessary. Especially for overlapping seeds, the tested commercial algorithm has a limited reliability. 533 poster Does 18F-FDG-PET imaging have an impact on cervix cancer management at initial diagnosis and in case of recurrence disease?
C. Brunaud 1, C. Lafond I, A. Bertrand 2, P. O/ivier 2, D. Bourquard 2, P. Henrot 3, V. Beckendorf ~, P. Marie 2, G. Karcher 2, A. Bertrand 1 I Centre Alexis Vautrin, Radiotherapy, Vandoeuvre-I~s-Nancy, France 2University Hospital Brabois, Nuclear Medecine, VandoeuvreI#s-Nancy, France 3Centre Alexis Vaurin, Radiology, Vandoeuvre-I~s-Nancy, France Aim: 18F-FDG-PET imaging (FDG-PET) is a procedure now routinely used in several solid tumours, especially for staging purpose. Only few data are available about the interest of FDG-PET in cervix cancer. The aim of our study was to retrospectively assess the impact of information obtained from FDG-PET in the management of patients with cervix cancer. Material and methods: We retrospectively selected, over a 15 month period, all patients for whom a FDG-PET had been performed as part of the work-up of cervix cancer, either at initial diagnosis or in case of recurrence. Whole body FDGPET acquisitions were performed 60 min after IV injection of 5.5 MBq/kg, using a biograph (SIEMENS) PET-CT imager, with a 3-4 min acquisition time per bed position depending on patient weight. We compared, on a patient by patient basis, the stage defined from conventional imaging (CI) to the one issued from FDG-PET, and we determined for each patient how the FDG-PET data affected the therapeutic strategy. Results: Full data were available for 22 patients, who constituted the study population. Mean age was 50.3 years + 9.6 (37 to 73). FDG-PET was performed at initial diagnosis in 14 cases and in staging of recurrent disease in 8 cases. Conventional imaging included whole body or abdominopelvic Computed Tomography (CT) data in 21 cases and pelvic Magnetic Resonance (MR) data in 7 cases. Compared to CI, 9/22 patients were upstaged by FDG-PET while none was downstaged. Treatment strategy changed because of the FDG-PET results in 10 cases (45%) among whom 4 recurrent disease. Intermodality changes were observed in 5 cases (3 with recurrent disease): 4 times changing from surgery to chemotherapy. Intramodality changes were noted in 5 cases regarding mainly radiotherapy with changes affecting the volume considered (n=2) and changes from curative to palliative intent (n = 3). Conclusion: Although these results should be confirmed by further prospective studies, the high incidence of observed intermodality and intramodality changes, suggests that FDGPET would have to be implemented in the imaging routinely performed in cervix cancer, and especially in situations of recurrent disease.
Posters
534 poster A simple method to evaluate the dose rate in the vicinity of patients undergoing prostate brachytherapy with 1-125 permanent implants
J.C. Rosenwald 1, B. Pentsch ~, S. Solignac ~, M. Timbert ~, I. Clairand 2, J.F. Bottolier-Depois 2, F. Trompiet 2, C. Itie 2, L. Chauveinc ~, J.M. Cosset ~ ~lnstitut Curie, Radiation Therapy Dept, Paris, France 21RSN, Fontenay aux Roses, France The rapid spread of prostate brachytherapy permanent implants raises new radiation safety issues for workers and public. In spite of the high attenuation of low energy emitters (I-125 or Pd-103), the dose around implanted patients cannot be completely ignored and should be evaluated to assess the risk for persons approaching the patient. We have developed a method where the dose rate at close distance from the patients can be easily calculated from the total implanted activity of 1-125 and from the patient body thickness. This method is derived from a series of comprehensive measurements of calibrated seeds under various water depths and at various distances performed with different types of radiation survey meters calibrated in air kerma (assumed later equal to dose) over a range of energies covering the 1-125 spectrum The dose rates, calculated with this method, were then compared to direct measurements performed with a calibrated GM survey meter with contact and at 20 cm distance of a series of 23 patients treated at Institut Curie. It was found experimentally that, for 1-125 photons, the halfvalue thickness was approximately equal to 2 cm of water. Therefore, if the seeds are located at an average depth of d (cm) below the body surface, the dose rate (~JGy.h~) at a distance L (cm) from this surface can be approximated from the following expression: D = AKRT x 2 (-~/2)x (100/(d+L)) 2 where AKRT is the total reference air kerma rate at one meter (U or iJGy.h-~.m 2) of the implant. The calibration process showed that the reading of the GM detector had to be divided by a factor of 3 to give the air kerma rate. The measured dose rates were in the range 20-300 pGy.h -1 on abdomen surface and 4-60 pGy.h -~ at 20 cm distance, with implant depths in the range 8-13 cm and AKRT in the range 25-55 U. The average calculated dose rate was approximately 30% lower than measurements at contact and 30% higher at 20 cm distance. In spite of these discrepancies, considering the huge patient to patient dose rate variation (by a factor of 15 in our series), this method of prediction can be considered as quite acceptable for radiation protection purposes. 535 poster Ultrasound-based versus CT-based HDR brachytherapy planning of the prostate: the influence of anatomic differences on dosimetry
/.K. Ko/kman-Deur/oo, M. de Langen Erasmus MC - University Medical Center Rotterdam, Radiation Oncology, Rotterdam, The Netherlands Introduction: For the implantation of HDR brachytherapy catheters in the prostate, the use of ultra-sound (US) guidance is well established. Until now, it has been common practice in our clinic to make a CT-scan after implantation for use in the dose planning process. Dosimetrically, this procedure is highly accurate, but it is inefficient with respect to patient logistics and speed of planning.
standard loading pattern. The reference isodose for treatment was determined, if possible, according to the maximum diameter of the residual lesion at time of BT. The dose distribution on orthogonal films was reported according to the ICRU recommendations whereas the dose contribution to critical organs on CT was evaluated using the doses in 0.1cc (CTmax), 2cc (CT2cc) and 5 cc (CT5cc) volumes receiving the highest dose on DVH.
Results: We were able to reproduce in all cases the dose distribution that was usually obtained in LDR BT. For rectum, on average CTmax and CT2cc were 0.6 and 0.8 times smaller than the rectal ICRU reference dose. In five cases only, the CTmax was higher than the dose recorded from films (1.3 time the average value) due to the lateral position of the rectum related to the ovoids sources. Rectum mean dose defined from films seemed to be a good estimate for the "true max rectum dose", the ratio between Rmean and CTmax being around 1 in 70% of the cases. For bladder, as expected, the CTmax and the CT2cc were higher than the ICRU dose in 90% of cases (threshold of 1.7). Conclusions: The CT-assisted planning enabled to estimate the dose actually received by the critical organs. The ratio between ICRU dose and CT dose estimation in both rectum and bladder are in accordance with the results already published using the same methodology. These preliminary findings need to be confirmed in a large series. The impact of these CT parameters on complication rates should be assessed prospectively. Grants from Comit~s 21, 58 and 71 Eigue Nationale contre le cancer. 531 poster
Dose rate effect: does it exist clinically in high-dose-rate intraqavitary brachytherapy for cervical cancer using iridium.192 source?
C. Wang, E. Huang, L. Sun, H. Chen Kaohsiung Chang Gung Medical Center, Department of Radiation Oncology, Kaohsiung Hsien, Taiwan Purpose: In-vitro studies in the past have revealed that dose-rate effect was dramatic between 0.01-1 Gy/min. This study is aimed to test if the effect exists clinically in highdose-rate intracavitary brachytherapy (HDR-ICB) for cervical cancer using Iridium-192 with a dose-rate ranging from 0.3-1 Gy/min. Materials and methods: (1) Patients: One hundred and sixty-five patients with cervical cancer were treated with external beam irradiation (EXRT) plus HDR-ICB between May 1993 and December 1996. (2) EXRT: Whole pelvis irradiation 44-45 Gy, and pelvic wall boost to a total of 5459.4 Gy. (3) HDR-ICB scheme: 4.8 Gy for 5 fractions delivered twice a week. (4) HDR facility was microSelectron system (Nucletron Corp.), using a single programmable stepwise Iridium-192 source with active dimensions of 4 mm long by 0.5 mm in diameter. The decaying source was renewed every 3 months, maintaining a therapeutic radioactivity ranging from 367 GBq to 126 GBq. (5) Patients were categorized into two groups, namely Group A vs. Group B, by a cutoff dose-rate of 0.6 Gy/min. Group A consisted of 88 patients w~th dose rate <_ 0.6 Gy/min. Group B consisted of 77 patients with dose rate > 0.6 Gy/min. (6) Endpoints: Pelvic control rate and rectal complication rate. (7) Statistics: Actuarial rate was calculated by Kaplan-Meier product-limit method, and significance tested by Log-rank test. (8) Duration of follow-up: 6.1-9.7 years (median, 7.3 years). Results: (1) Pelvic control rate: Overall, actuarial 5-year pelvic control rate for the entire patients cohort was 90.5%.
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By dose-rate, actuarial 5-year pelvic control rates for Group A ( ~ 0.6 Gy/min, n=88) vs. Group B (> 0.6 Gy/min, n=77) were 92.1% vs. 88.7%, respectively (p=0.505). (2) Complication: Overall, actuarial 5-year proctitis rate for the entire patients cohort was 32.4%. By dose-rate, actuarial 5-year proctitis rate for Group A vs. Group B was 34.4% vs. 30.3%, respectively (p=0.467). (3) For the subset of cases with early stage (IB-IIA, n=67), actuarial 5-year pelvic control rate for Group A (n=31) vs. Group B (n=36) was 92.9% vs. 93.2%, respectively (p=0.836). Actuarial 5-year proctitis rate for Group A (n=31) vs. Group B (n=36) was 23.5% vs. 28.8%, respectively (p=0.701).
Conclusion: Using Iridium-192 for high-dose-rate intracavitary brachytherapy, dose-rate effect in the range of 0.3-1 Gy/min was not demonstrated clinically. 532 poster A solid phantom for the verification of postimplant dosimetry with radiographs and CT
F.-A. Siebert, P. Kohr, G. Kov&cs University Clinic S-H, Campus Kiel, Radiotherapy, Kiel, Germany Introduction: The application of permanent prostate implants using 1251 or l°3pd seed sources is a routine procedure worldwide in many different clinics. Many centers use a set of radiographs for the postimplant dosimetry. This widespread method allows a reconstruction and the determination of the seed positions in the patient with high accuracy. Until now there is no commercial solution available that is able to check the reliability of such reconstruction techniques. Material and methods: To validate the reconstruction of a set of radiographs or CT data in postimptant dosimetry, a new phantom, the Kiel-phantom, was designed. The exactly known positions of the non-radioactive seeds in the phantom can be compared with the results of the reconstruction techniques. The phantom consists of a stack of Perspex ® disks with precisely defined holes for the insertion of dummy seeds. Several disks were designed to simulate many different seed configurations. It is possible to create seed patterns with equally or arbitrarily spaced sources in x- y- or z-direction. In this way it is easy to simulate strong mathematical configurations as well as more realistic ones. Moreover a marker system is attached on the phantom that allows the exact placement with positioning laser devices. With the internal coordinate system the definition of a unique origin and alignment are easy to perform. The phantoms' base is mounted on three nylon screws and its horizontal position can be adjusted with a spirit level. Measurements were carried out with different seed configurations. The reconstructions of the seed coordinates were performed with the treatment planning system (TPS) VariSeed ® 6.7/7.1. For every measurement three radiographs with different gantry angles but fixed focus film distances were used. Results: For non-overlapping seed positions we found very good agreement between the coordinates of the dummy seeds and the reconstructed positions (SD < 0.1 mm) with gantry angles of 0 °, +45 ° and - 4 5 ° . Furthermore measurements with a complex seed distribution in the phantom were carried out. For this study some seeds overlap from more than from one gantry angle. We found out difficulties of the TPS to correctly compute seed positions if two or more sources are placed in a row from more than one
S238
view. The displacements of the seeds reached values up to 3 cm. Conclusion: The Kiel-phantom was designed in lack of existing commercial solutions to investigate seed reconstruction algorithms with high accuracy in the postimplant planning procedure of seeds. We found out a) that the developed phantom is able to check reconstruction techniques with high accuracy and b) that a higher quality assurance of seed reconstruction algorithms is necessary. Especially for overlapping seeds, the tested commercial algorithm has a limited reliability. 533 poster Does 18F-FDG-PET imaging have an impact on cervix cancer management at initial diagnosis and in case of recurrence disease?
C. Brunaud 1, C. Lafond I, A. Bertrand 2, P. O/ivier 2, D. Bourquard 2, P. Henrot 3, V. Beckendorf ~, P. Marie 2, G. Karcher 2, A. Bertrand 1 I Centre Alexis Vautrin, Radiotherapy, Vandoeuvre-I~s-Nancy, France 2University Hospital Brabois, Nuclear Medecine, VandoeuvreI#s-Nancy, France 3Centre Alexis Vaurin, Radiology, Vandoeuvre-I~s-Nancy, France Aim: 18F-FDG-PET imaging (FDG-PET) is a procedure now routinely used in several solid tumours, especially for staging purpose. Only few data are available about the interest of FDG-PET in cervix cancer. The aim of our study was to retrospectively assess the impact of information obtained from FDG-PET in the management of patients with cervix cancer. Material and methods: We retrospectively selected, over a 15 month period, all patients for whom a FDG-PET had been performed as part of the work-up of cervix cancer, either at initial diagnosis or in case of recurrence. Whole body FDGPET acquisitions were performed 60 min after IV injection of 5.5 MBq/kg, using a biograph (SIEMENS) PET-CT imager, with a 3-4 min acquisition time per bed position depending on patient weight. We compared, on a patient by patient basis, the stage defined from conventional imaging (CI) to the one issued from FDG-PET, and we determined for each patient how the FDG-PET data affected the therapeutic strategy. Results: Full data were available for 22 patients, who constituted the study population. Mean age was 50.3 years + 9.6 (37 to 73). FDG-PET was performed at initial diagnosis in 14 cases and in staging of recurrent disease in 8 cases. Conventional imaging included whole body or abdominopelvic Computed Tomography (CT) data in 21 cases and pelvic Magnetic Resonance (MR) data in 7 cases. Compared to CI, 9/22 patients were upstaged by FDG-PET while none was downstaged. Treatment strategy changed because of the FDG-PET results in 10 cases (45%) among whom 4 recurrent disease. Intermodality changes were observed in 5 cases (3 with recurrent disease): 4 times changing from surgery to chemotherapy. Intramodality changes were noted in 5 cases regarding mainly radiotherapy with changes affecting the volume considered (n=2) and changes from curative to palliative intent (n = 3). Conclusion: Although these results should be confirmed by further prospective studies, the high incidence of observed intermodality and intramodality changes, suggests that FDGPET would have to be implemented in the imaging routinely performed in cervix cancer, and especially in situations of recurrent disease.
Posters
534 poster A simple method to evaluate the dose rate in the vicinity of patients undergoing prostate brachytherapy with 1-125 permanent implants
J.C. Rosenwald 1, B. Pentsch ~, S. Solignac ~, M. Timbert ~, I. Clairand 2, J.F. Bottolier-Depois 2, F. Trompiet 2, C. Itie 2, L. Chauveinc ~, J.M. Cosset ~ ~lnstitut Curie, Radiation Therapy Dept, Paris, France 21RSN, Fontenay aux Roses, France The rapid spread of prostate brachytherapy permanent implants raises new radiation safety issues for workers and public. In spite of the high attenuation of low energy emitters (I-125 or Pd-103), the dose around implanted patients cannot be completely ignored and should be evaluated to assess the risk for persons approaching the patient. We have developed a method where the dose rate at close distance from the patients can be easily calculated from the total implanted activity of 1-125 and from the patient body thickness. This method is derived from a series of comprehensive measurements of calibrated seeds under various water depths and at various distances performed with different types of radiation survey meters calibrated in air kerma (assumed later equal to dose) over a range of energies covering the 1-125 spectrum The dose rates, calculated with this method, were then compared to direct measurements performed with a calibrated GM survey meter with contact and at 20 cm distance of a series of 23 patients treated at Institut Curie. It was found experimentally that, for 1-125 photons, the halfvalue thickness was approximately equal to 2 cm of water. Therefore, if the seeds are located at an average depth of d (cm) below the body surface, the dose rate (~JGy.h~) at a distance L (cm) from this surface can be approximated from the following expression: D = AKRT x 2 (-~/2)x (100/(d+L)) 2 where AKRT is the total reference air kerma rate at one meter (U or iJGy.h-~.m 2) of the implant. The calibration process showed that the reading of the GM detector had to be divided by a factor of 3 to give the air kerma rate. The measured dose rates were in the range 20-300 pGy.h -1 on abdomen surface and 4-60 pGy.h -~ at 20 cm distance, with implant depths in the range 8-13 cm and AKRT in the range 25-55 U. The average calculated dose rate was approximately 30% lower than measurements at contact and 30% higher at 20 cm distance. In spite of these discrepancies, considering the huge patient to patient dose rate variation (by a factor of 15 in our series), this method of prediction can be considered as quite acceptable for radiation protection purposes. 535 poster Ultrasound-based versus CT-based HDR brachytherapy planning of the prostate: the influence of anatomic differences on dosimetry
/.K. Ko/kman-Deur/oo, M. de Langen Erasmus MC - University Medical Center Rotterdam, Radiation Oncology, Rotterdam, The Netherlands Introduction: For the implantation of HDR brachytherapy catheters in the prostate, the use of ultra-sound (US) guidance is well established. Until now, it has been common practice in our clinic to make a CT-scan after implantation for use in the dose planning process. Dosimetrically, this procedure is highly accurate, but it is inefficient with respect to patient logistics and speed of planning.