- Email: [email protected]
686 poster DOSIMETRY COMPARISON BETWEEN TG-43 AND MONTE CARLO CALCULATIONS USING THE FREIBURG FLAP FOR SKIN HDR BRACHYTHERAPY
S 274
B RACHYTHERAPY: P HYSICS
tor was fixed in a custom made jig, designed to hold the IUT approx. centred in the tank and at least 10cm away from any scattering surfaces.Dose fall-off data was collected to allow inter-comparison of each chamber to the MC data.The PTW chambers used were: PinPoint (PP) Chambers 31014 and 31016 (3D); Dosimetry Diodes P 60008 (shielded) and E 60012 (unshielded). Both chamber types were chosen because they provide very high spatial resolution. Additionally the PPs are ideal for small fields and the diodes have high sensitivity.The effective points of measurement for the PP chambers were established.Profiles were collected at multiple depths and distances from the IUT to generate isodose plots in various planes. Data was collected using PTW MEPHYSTO v7.42 and analysed using PTW MEPHYSTO mc2 v.1.3. PTW VeriSoft v.4.0 was used to compare the isodoses to the TPS using gamma analysis.
were implanted 1 cm center to center uniformly. Postimplant dosimetric verification was accomplished by obtaining a CT scan of the implant volume just after the whole implant procedure. Results: The mean PTV volume was 101 cc for the ten patients. 80 seeds were implanted on the average, with the single seed activity of 0.5-0.8 mCi. The mean activity implanted per cc PTV was 0.69 mCi. The mean D90 was 91.5 Gy, and V100 (the percentage of the PTV volume receiving 100% of the prescription dose) was 85.5%. The mean V150 and V200 were 68.9% and 52.1%. The mean mPD (minimum peripheral dose) was 38.5 Gy. Conclusions: Satisfactory dosimetric distribution can be achieved with CTguided 125 I seeds implant for recurrent rectal cancer. Uniform implants result in inhomogeneous dose distribution, and low dose in the peripheral region of targets due to the constraints of bony structures and organs at risk for some patients. 686 poster DOSIMETRY COMPARISON BETWEEN TG-43 AND MONTE CARLO CALCULATIONS USING THE FREIBURG FLAP FOR SKIN HDR BRACHYTHERAPY J. Vijande1 , F. Ballester1 , G. Domingo2 , Z. Ouhib3 , M. D. C. Pujades4 , J. Pérez-Calatayud4 U NIVERSITY OF VALENCIA, Department of Atomic, Molecular and Nuclear Physics , Burjassot, Spain 2 E RESA VALENCIA, Department of Radiation Oncology, Valencia, Spain 3 LYNN C ANCER I NSTITUTE OF B OCA R ATON C OMMUNITY H OSPI, Radiation Oncology, Delray Beach , USA 4 H OSPITAL U NIVERSITARIO L A F E, Department of Radiation Oncology, Valencia, Spain 1
Results: The accuracy of positional readouts of the tank was established to be ±0.2mm. The daily positioning of the source was within ±0.5mm of expected. The centre of the source was established daily and for each detector using profiles in both directions.Comparison of dose fall-off curves with the MC and TPS data showed very good agreement for all detectors, with PP 31014 being the best: when normalised to 15mm the distance to agreement is ≤0.5mm (when distance to source ≤50mm) and magnitude of absolute difference is ≤1.3 percentage points. However, all the curves were found to fall off more slowly than the MC and TPS data. The two diodes over-responded at distance: at 60mm there was an absolute percentage difference of ~1.5% compared with the MC data.Detailed analysis of the isodose data is being performed. Conclusions: The PTW MP3 water tank is suitable for dosimetric measurements of the HDR brachytherapy source and it is possible to collect data as is required for this study.All chambers seem acceptable for collection of HDR 192 Ir dosimetric data, with the PinPoint 31014 being the most suitable.Comparison of dose fall-off curves shows excellent agreement with the modelling of the source by the TPS; further comparison with full isodose data will complete the study. 685 poster DOSIMETRIC VERIFICATION OF CT-GUIDED 125I SEED IMPLANTAT IN RECURRENT RECTAL CANCER R. Yang1 , J. Wang2
Purpose: Freiburg Flap (FF) is a flexible mesh surface mold with channels of flexible implants tubes 1 cm apart. This device is used in HDR Brachytherapy for skin treatment. It consists of a large sheet of connected plastic pellets of 1 cm in diameter that can be cut to sizes to accommodate the target area with additional margins.The main purpose of the present work is to compare the delivered dose to the skin surface and to the prescription depth (5 mm) using TG-43 data (full scatter conditions in water) and Monte Carlo (MC) predicted dose (taken into account air surrounding the FF and its density and composition).It is of special interest to evaluate the possible existence of a scatter defect on the skin. Materials: A 5 mesh formed by silicon spheres of 1 cm diameter has been considered. The phantom was a 3000 cm3 water cube surrounded by dry air. The FF applicator is located on one of the sides in direct contact with water. Primary and secondary dose, including contributions due to x-rays and bremsstrahlung photons, have been stored using voxels z = 0.25 mm in depth into the water phantom and x = y = 1 mm parallel to the FF.The mHDRv2 source (Nucletron BV, Veenendaal, The Netherlands) has been simulated as described in Daskalov et al. [Med. Phys. 25(1998)2200-2208]. As a benchmark and as dose kernels, two different source positions were chosen: at the center of the central sphere, and between two adjacent central spheres. Experimental measurements have been done using radiochromic films (RF).The superposition principle (SP) was applied to compare the dose distribution as calculated by TPS using TG-43 data with that obtained applying SP but using kernels from individual source positions as described above. A clinically optimized plan treatment was obtained locating the source at 35 different positions. The dwell times from this plan were used to derive the realistic dose rate distribution using the kernels previously obtained. Results: MC and RF measured dose distributions agree within 3% in the source vicinity, therefore validating the MC data. In these kernels the scatter defect is up to 15% when the source at located in the center of the sphere and up to 25% when the source is between two spheres.The comparison of the TPS plan with that calculated using kernels are illustrated in the figure that shows the ratio between the TPS dose distribution and that obtained from MC. Maximum deviations between these two distributions are of the order of 4 - 6%, well within tolerance limits, in both surface and 5 mm depth (1 cm from source positions) which is the typical prescription depth. Conclusions: Deviations in the dose distributions for a standard treatment using TG-43 data with respect to that calculated taking into account the composition and shape of the FF and the surrounding air is lower than 5%. Therefore, this simulation support the validity of the TPS used in clinical practice with the FF.
1
P EKING U NIVERSITY 3 RD H OSPITAL, Department of Radiation Oncology, Beijing, China 2 U NIVERSITY OF B EIJING, Department of Radiation Oncology, Beijing, China Purpose: To verify the postimplant dose distribution achieved in recurrent rectal cancer patients treated with CT-guided 125 I seed implant. Materials: Ten recurrent rectal cancer patients treated with CT-guided 125 I seed implant were selected for this study. Pre-implant plans were designed one week before the implant, with the prescription dose of D90 (the dose received by 90% of the target) of 100 Gy for planning target volume (PTV). Implant needles were inserted according to the pre-implant plans, with the interval of 1 cm and in parallel to each other under CT guidance. The seeds
687 poster EFFECT OF USING DIFFERENT U/S PROBE STANDOFF MATERIALS IN IMAGE GEOMETRY FOR BRACHYTHERAPY S. Diamantopoulos1 , S. Butt1 , N. Milickovic1 , Z. Katsilieri1 , V. Kefala1 , P. Zogal2 , G. Sakas3 , D. Baltas1 1 K LINIKUM O FFENBACH G MB H, Department of Medical Physics and Engineering, Offenbach am Main, Germany 2 M EDCOM, Darmstadt, Germany 3 F RAUNHOFER IGD, Cognitive Computing and Medical Imaging, Darmstadt, Germany
B RACHYTHERAPY: P HYSICS
tor was fixed in a custom made jig, designed to hold the IUT approx. centred in the tank and at least 10cm away from any scattering surfaces.Dose fall-off data was collected to allow inter-comparison of each chamber to the MC data.The PTW chambers used were: PinPoint (PP) Chambers 31014 and 31016 (3D); Dosimetry Diodes P 60008 (shielded) and E 60012 (unshielded). Both chamber types were chosen because they provide very high spatial resolution. Additionally the PPs are ideal for small fields and the diodes have high sensitivity.The effective points of measurement for the PP chambers were established.Profiles were collected at multiple depths and distances from the IUT to generate isodose plots in various planes. Data was collected using PTW MEPHYSTO v7.42 and analysed using PTW MEPHYSTO mc2 v.1.3. PTW VeriSoft v.4.0 was used to compare the isodoses to the TPS using gamma analysis.
were implanted 1 cm center to center uniformly. Postimplant dosimetric verification was accomplished by obtaining a CT scan of the implant volume just after the whole implant procedure. Results: The mean PTV volume was 101 cc for the ten patients. 80 seeds were implanted on the average, with the single seed activity of 0.5-0.8 mCi. The mean activity implanted per cc PTV was 0.69 mCi. The mean D90 was 91.5 Gy, and V100 (the percentage of the PTV volume receiving 100% of the prescription dose) was 85.5%. The mean V150 and V200 were 68.9% and 52.1%. The mean mPD (minimum peripheral dose) was 38.5 Gy. Conclusions: Satisfactory dosimetric distribution can be achieved with CTguided 125 I seeds implant for recurrent rectal cancer. Uniform implants result in inhomogeneous dose distribution, and low dose in the peripheral region of targets due to the constraints of bony structures and organs at risk for some patients. 686 poster DOSIMETRY COMPARISON BETWEEN TG-43 AND MONTE CARLO CALCULATIONS USING THE FREIBURG FLAP FOR SKIN HDR BRACHYTHERAPY J. Vijande1 , F. Ballester1 , G. Domingo2 , Z. Ouhib3 , M. D. C. Pujades4 , J. Pérez-Calatayud4 U NIVERSITY OF VALENCIA, Department of Atomic, Molecular and Nuclear Physics , Burjassot, Spain 2 E RESA VALENCIA, Department of Radiation Oncology, Valencia, Spain 3 LYNN C ANCER I NSTITUTE OF B OCA R ATON C OMMUNITY H OSPI, Radiation Oncology, Delray Beach , USA 4 H OSPITAL U NIVERSITARIO L A F E, Department of Radiation Oncology, Valencia, Spain 1
Results: The accuracy of positional readouts of the tank was established to be ±0.2mm. The daily positioning of the source was within ±0.5mm of expected. The centre of the source was established daily and for each detector using profiles in both directions.Comparison of dose fall-off curves with the MC and TPS data showed very good agreement for all detectors, with PP 31014 being the best: when normalised to 15mm the distance to agreement is ≤0.5mm (when distance to source ≤50mm) and magnitude of absolute difference is ≤1.3 percentage points. However, all the curves were found to fall off more slowly than the MC and TPS data. The two diodes over-responded at distance: at 60mm there was an absolute percentage difference of ~1.5% compared with the MC data.Detailed analysis of the isodose data is being performed. Conclusions: The PTW MP3 water tank is suitable for dosimetric measurements of the HDR brachytherapy source and it is possible to collect data as is required for this study.All chambers seem acceptable for collection of HDR 192 Ir dosimetric data, with the PinPoint 31014 being the most suitable.Comparison of dose fall-off curves shows excellent agreement with the modelling of the source by the TPS; further comparison with full isodose data will complete the study. 685 poster DOSIMETRIC VERIFICATION OF CT-GUIDED 125I SEED IMPLANTAT IN RECURRENT RECTAL CANCER R. Yang1 , J. Wang2
Purpose: Freiburg Flap (FF) is a flexible mesh surface mold with channels of flexible implants tubes 1 cm apart. This device is used in HDR Brachytherapy for skin treatment. It consists of a large sheet of connected plastic pellets of 1 cm in diameter that can be cut to sizes to accommodate the target area with additional margins.The main purpose of the present work is to compare the delivered dose to the skin surface and to the prescription depth (5 mm) using TG-43 data (full scatter conditions in water) and Monte Carlo (MC) predicted dose (taken into account air surrounding the FF and its density and composition).It is of special interest to evaluate the possible existence of a scatter defect on the skin. Materials: A 5 mesh formed by silicon spheres of 1 cm diameter has been considered. The phantom was a 3000 cm3 water cube surrounded by dry air. The FF applicator is located on one of the sides in direct contact with water. Primary and secondary dose, including contributions due to x-rays and bremsstrahlung photons, have been stored using voxels z = 0.25 mm in depth into the water phantom and x = y = 1 mm parallel to the FF.The mHDRv2 source (Nucletron BV, Veenendaal, The Netherlands) has been simulated as described in Daskalov et al. [Med. Phys. 25(1998)2200-2208]. As a benchmark and as dose kernels, two different source positions were chosen: at the center of the central sphere, and between two adjacent central spheres. Experimental measurements have been done using radiochromic films (RF).The superposition principle (SP) was applied to compare the dose distribution as calculated by TPS using TG-43 data with that obtained applying SP but using kernels from individual source positions as described above. A clinically optimized plan treatment was obtained locating the source at 35 different positions. The dwell times from this plan were used to derive the realistic dose rate distribution using the kernels previously obtained. Results: MC and RF measured dose distributions agree within 3% in the source vicinity, therefore validating the MC data. In these kernels the scatter defect is up to 15% when the source at located in the center of the sphere and up to 25% when the source is between two spheres.The comparison of the TPS plan with that calculated using kernels are illustrated in the figure that shows the ratio between the TPS dose distribution and that obtained from MC. Maximum deviations between these two distributions are of the order of 4 - 6%, well within tolerance limits, in both surface and 5 mm depth (1 cm from source positions) which is the typical prescription depth. Conclusions: Deviations in the dose distributions for a standard treatment using TG-43 data with respect to that calculated taking into account the composition and shape of the FF and the surrounding air is lower than 5%. Therefore, this simulation support the validity of the TPS used in clinical practice with the FF.
1
P EKING U NIVERSITY 3 RD H OSPITAL, Department of Radiation Oncology, Beijing, China 2 U NIVERSITY OF B EIJING, Department of Radiation Oncology, Beijing, China Purpose: To verify the postimplant dose distribution achieved in recurrent rectal cancer patients treated with CT-guided 125 I seed implant. Materials: Ten recurrent rectal cancer patients treated with CT-guided 125 I seed implant were selected for this study. Pre-implant plans were designed one week before the implant, with the prescription dose of D90 (the dose received by 90% of the target) of 100 Gy for planning target volume (PTV). Implant needles were inserted according to the pre-implant plans, with the interval of 1 cm and in parallel to each other under CT guidance. The seeds
687 poster EFFECT OF USING DIFFERENT U/S PROBE STANDOFF MATERIALS IN IMAGE GEOMETRY FOR BRACHYTHERAPY S. Diamantopoulos1 , S. Butt1 , N. Milickovic1 , Z. Katsilieri1 , V. Kefala1 , P. Zogal2 , G. Sakas3 , D. Baltas1 1 K LINIKUM O FFENBACH G MB H, Department of Medical Physics and Engineering, Offenbach am Main, Germany 2 M EDCOM, Darmstadt, Germany 3 F RAUNHOFER IGD, Cognitive Computing and Medical Imaging, Darmstadt, Germany