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69 Comparative analysis of prostate brachytherapy pre-planning
delineating the location of bulky tumor. We believe our excellent results are largely attributable to our use of erMRI. 68 IMPACT OF TARGET VOLUME COVERAGE WITHRTOG 98-05 GUIDELINES FOR TRANSRECTAL ULTRASOUNDGUIDED PERMANENT 1-125 PROSTATE IMPLANT Eric M. Horwitz, M.D.*, Raj K. Mitra, M.S.*, Indra J. Das, Ph.D.**, Wayne H. Pinover, D.O.*, Alex L. Hanlon, Ph.D.* and Gerald E. Hanks, M.D.* Department of Radiation Oncology, *Fox Chase Cancer Center, and **University of Pennsylvania, Philadelphia, PA, USA Purpose: Despite the wide use of permanent prostate implants for the treatment of early stage prostate cancer, there is no consensus of optimal preimplant planning that results in maximal post-implant target coverage. RTOG 98-05 is a Phase II trial to evaluate the clinical efficacy of prostate implants for organ confined disease and to collect data from multiple institutions to establish quality assurance standards and dosimetric evaluation approaches. The purpose of this study was to compare post-implant target volume coverage and dosimetry between patients treated before and after the RTOG 98-05 guidelines adopted at our institution without changes in our technical procedure. Materials a n d methods: Five consecutive patients treated before the adoption of the RTOG 98-05 guidelines were compared with five consecutive patients treated after implementation of the protocol guidelines. All patients in this study that Tlc/T2a disease with pre-treatment PSA levels < 10 ng/ml and Gleason scores 2-6. Transrectal ultrasound (TRUS) was performed, with the patient in lithotomy position for pre-implant planning. The prescription dose to the target volume was 145 Gy based on the AAPM TG-43 protocol. Pre-implant planning for patients treated before adoption of the protocol guidelines was based on the Clinical Target Volume (CTV) defined by the pre-implant TRUS definition of the prostate, without any volume expansion. The CTV was expanded by 2 to 3 m m in the lateral dimensions and 2 to 3 nun in the anterior dimension for each TRUS axial image, for patients treated according to RTOG 98-05 and defined as the Planning Target Volume (PTV). The expanded most caudad axial definition was projected to a plane 5 m m in the inferior direction. Expansion in the cephalad direction was avoided to prevent intrusion into the bladder. CT scans were obtained three weeks post implant for dosimetry and DVH analysis. The Evaluation Target Volume (ETV) was defined as the post-implant CT definition of the prostate based on American Brachytherapy Society (ABS) recommendations. Implant quality indicator, Di was chosen as the dose that covers i% of the prostate volume. For example, D10o is the dose that covers 100% of the prostate volume. Homogeneity Index (HI) was also studied for each case, which is defined as [ 1-V 15o/Vl00], where V l.s0 and V 10o are the volumes covered within 150% and 100% dose lines, respectively. Results: For the pre-RTOG 98-05 implants, the mean D10o was 75.6% (range: 62-85.6%). After implementation of the protocol guidelines, the mean Dl0o increased to 96.1% (range: 93-99%). These differences were statistically significant (p<0.001). Mean D9o pre-RTOG 98-05 was 83.6% (range: 76.4-92.2%) while mean D90 post RTOG 98-05 was 98.1% (range 96.7-99.4%). These differences were also statistically significant (p<0.007). The mean increase in D10o to the ETV resulting from implementation of the RTOG 98-05 implant guidelines was 20.5% and the corresponding increase in D9o to the ETV was 14.5%. The pre-RTOG HI was 0.563 (range: 0.439-0.676) and post-RTOG HI was 0.352 (range: 0.154-0.47). Again these differences were statistically significant (p<0.015). We have observed generally, a higher HI value that corresponds to a lower Dim or D9o of the ETV. A larger margin between the CTV and the PTV corresponds to a higher HI due to a higher volume of the ETV encompassed by the 150% isodose lines. Conclusions: Implementation of the RTOG 98-05 implant planning guidelines has increased the post-implant D~0o and D9o coverage of the prostate compared with our previous technique. The HI was also improved significantly with the protocol guidelines. Our data confirms the validity of the RTOG 98-05 implant guidelines for pre-implant planning as it relates to enlargement of the CTV to ensure adequate margin between the CTV and the prescription isodose lines. It is expected that with longer follow-up, this consistent high dose coverage of the prostate as a indicated by the Dl00 and D9o should correspond to a better biochemical and clinical outcome. 69 COMPARATIVEANALYSISOF PROSTATE BRACHYTHERAPYPRE-PLANNING James R. Gray, Gregory S. Merrick, David C. Beyer, Daniel H. Clarke, Jay L. Friedland, Donald B. Fuller, Brian J. Moran, John C. Blasko, John Sylvester, Stephen J.M. Banks and Peter D. Grimm for the Prostate Brachytherapy Research Group The Sarah Cannon-Minnie Pearl Cancer Center, 250 N 25 th St, Nashville, TN 37203 Purpose: Prospective multi-institutional studies require standardization in treatment planning and delivery. Differences, where they exist, must be identified and evaluated for significance. A survey has been conducted among the eight participating members of the Prostate Brachytherapy Research Group to compare different planning approaches for transperineal ultrasound-guided permanent Iodine-125 prostate brachytherapy on identical ultrasound images. Materials a n d methods: Ultrasound studies from four patients were reproduced and distributed to each site for planning. Gland size ranged from 22 cc to 56 cc. The clinical information for each case study was included. Each case was considered low risk for extraeapsular spread. Iodine-125 isotope was mandated, with a prescription dose of 145 Gy. The placement and number of seeds and needles as well as activity were left to the discretion of the planning site. Final plans were returned and reproduced on one treatment planning system for comparative analysis of seed and needle use as well as planned dose distribution. Results: Total activity per volume of gland decreased with increasing gland size, ranging from 1.29 +/- 0.12 mCi/cc to 0.84 +/- 0.08 mCi/cc as calculated prior to the institution of NIST-99 calibration. Number of seeds and needles per volume of gland likewise decreased with increasing gland size. Seed number ranged from 3.69 +/- 0.43 seeds/cc to 2.42 +/- 0.31 seeds/cc. Needle number ranged from 0.98 +/- 0.31 to 0.55 +/- 0.04 needles/cc. These parameters varied in a roughly linear fashion over this range of gland sizes. The ratio of the total volume encompassed by the prescription dose to the gland volume also decreased with increasing gland size, ranging from 2.23 to 1.74. Differences in this ratio among sites were considerable. The smallest gland had a planning volume to gland size ratio range of 1.82 to 2.68. Homogeneity, measured as the percentage of the gland receiving 150% and 200% of the prescription dose (V~.s0and V20o), was relatively constant over this size range. The average for all sites ranged from 42.6% and 13.5% respectively in the smallest gland to 47.3% and 15.1% in the largest. However, considerable variation was found between institutions, with the average V~50at different sites ranging from 19.2% to 70.3%. The average V20o ranged from 6.9% to 27.3%
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among different sites. Prescription dose margins around the ultrasound gland edge were measured at base, mid-gland and apex. Base and apex margins varies considerably. Mid-gland posterior margins were fairly uniform, ranging from 1 to 3 mm. Anterior and lateral margins at mid-gland ranged from -1 to 10 m m and 0 to 6 m m respectively. Conclusions: Even among institutions with similar approaches to permanent I-125 prostate brachytherapy, considerable differences were found in the total volume irradiated, the margin of the dose around the gland, and the accepted intensity of dose within the implant. This reflects differing treatment philosophies of the various members of the group, and defines a spectrum of current practice across many active brachytherapy practices. Qualitative analysis of these planning differences will be possible only if outcome data is obtained and linked to the intended planning philosophy. These data are currently being prospectively gathered in a phase 111randomized trial of the Prostate Brachytherapy Research Group. 70 INTRAOPERATIVE CONFORMAL OPTIMIZATION FOR TRANSPERINEAL PROSTATE IMPLANTATIONUSING M R SPECTROSCOPIC IMAGING Michael J. Zelefsky ~, M.D., Gilad Cohen*, M.Sc., Kristen L. Zakian*, Ph.D., Jonathan Dyke*, Ph.D., Jason A. Koutcher*, M.D., Ph.D. Marco Zaider*, Ph.D. Departments of Radiation Oncology, *Medical Physics and Medical Oncology# Memorial Sloan-Kettering Cancer Center, New York, NY, USA Purpose: Recent studies have demonstrated that magnetic resonance spectroscopic imaging (MRSI) of the prostate may effectively distinguish between regions of cancer and normal prostatic epithelium. This diagnostic imaging tool takes advantage of the increased choline versus citrate ratio found in malignant compared normal prostate tissue. A method is described which registers MRSI to intraoperative-obtained ultrasound images and incorporates this information into a treatment planning system to achieve dose escalation to intraprostatic tumor deposits. The purpose of this study is to report our preliminary experience and dosimetric outcome with ten consecutive patients who underwent permanent interstitial implantation using intraoperative computer-based treatment-planning with MRSI optimization. Materials and methods: MRSI was obtained preoperatively for ten patients with clinically localized prostate cancer. The ratios of choline and citrate for the prostate were analyzed, and regions of high risk for malignant cells were identified. The ratios representing peaks on the MR spectrum were calculated on a spatial grid covering the prostate tissue. A procedure for mapping points of interest from the MRSI to the ultrasound images is described. A computer-based treatment planning system was used which relied on a genetic algorithm to determine the optimal seed distribution to achieve maximal target volume reduction and maintain urethra and rectal doses within tolerance ranges. MRSI data was incorporated into the treatment planning system to test the feasibility of dose escalation to positive voxels with relative sparing of surrounding normal tissues. Post-implant CT scans were performed on the same day of the procedure in all cases, and dosimetric guidelines of the American Brachytherapy Society were used to assess implant quality. Results: The intraoperative optimization treatment planning program was able to achieve a minimum dose of 139% - 192% of the 144 Gy prescription to the MRS positive voxels using I- 125 seeds. The percentage of the prostate volume receiving 100% of the prescription dose (V 100) ranged from 92%-97% and the D90 for the target volume ranged from 96%-100%. Despite the dose escalation achieved for the MRSI positive voxels, the urethral and rectal doses were maintained within tolerance ranges. The average and maximal rectal doses ranged from 28-42% and 69115%, respectively. The average and maximal urethral doses ranged from 66-144% and 138-166%, respectively. Conclusions: Using this brachytherapy optimization system, we could demonstrate the feasibility of MRS-optimized dose distributions for I-125 permanent prostate implants. This approach may have an impact on the ability to safely employ dose escalation for patients treated with permanent interstitial implantation and improve outcome for patients with organ confined prostatic cancers. 71 POST IMPLANT DOSIMETRY EVALUATIONFOR PROSTATE INTERSTITIAL BRACHYTHERAPY: A COMPARISON OF TWO COMMONLY USED TECHNIQUES S.K. Saraf, Ph.D., A. Zablow, M.D., R.L. Goodman, M.D., and K.D. Steidley, Ph.D. Department of Radiation Oncology, Saint Barnabas Medical Center, Livingston, NJ 07039 Purpose: Permanent prostate implants using 1-125 and Pd-103 radioactive seeds have been performed for early stage disease. Several techniques for seed implantation have been developed. Two of the most commonly used techniques utilize 1) PREPLAN volume scans, and 2) REAL TIME volume scans. We have compared the two techniques following ABS recommended methodology. Methods and materials: 30 patients were studied, 15 implanted using pre-plan ultrasound scans obtained 2 weeks earlier and the remaining 15 patients using real time scans obtained at the time of seed implantation. A pre-plan scan is usually obtained for all patients, but for patients implanted using real time scans, pre-plan scans were omitted. Three weeks following seed implantation CT Scans along with simulation films were obtained to evaluate the implants. As proposed by ABS, DI00, D90, V100 and V150 indices were calculated for each patient. D100 and D90 are defined as the mPD Dose that covers 100% and 90% of the prostate volume, while V 100 and V 150 are defined as the percentage of the prostate volume that receives 100% and 150% of the prescribed dose. Results: The mPD for Pd-103 and 1-125 implants were 115 Gy and 144 Gy (TG-43) respectively. The pre-plan patients had their implant performed from a plan devised using pre-plan scans. At the time of seed placement, variations in the prostate volume scans were minimized to achieve the dose distribution as close to the pre-planned volume as could be achieved. Such an extra effort is not needed for real time implant technique as the implant is performed on the volume scans obtained at the time of the implant. The following table provides an in-depth comparison of the two techniques used.
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among different sites. Prescription dose margins around the ultrasound gland edge were measured at base, mid-gland and apex. Base and apex margins varies considerably. Mid-gland posterior margins were fairly uniform, ranging from 1 to 3 mm. Anterior and lateral margins at mid-gland ranged from -1 to 10 m m and 0 to 6 m m respectively. Conclusions: Even among institutions with similar approaches to permanent I-125 prostate brachytherapy, considerable differences were found in the total volume irradiated, the margin of the dose around the gland, and the accepted intensity of dose within the implant. This reflects differing treatment philosophies of the various members of the group, and defines a spectrum of current practice across many active brachytherapy practices. Qualitative analysis of these planning differences will be possible only if outcome data is obtained and linked to the intended planning philosophy. These data are currently being prospectively gathered in a phase 111randomized trial of the Prostate Brachytherapy Research Group. 70 INTRAOPERATIVE CONFORMAL OPTIMIZATION FOR TRANSPERINEAL PROSTATE IMPLANTATIONUSING M R SPECTROSCOPIC IMAGING Michael J. Zelefsky ~, M.D., Gilad Cohen*, M.Sc., Kristen L. Zakian*, Ph.D., Jonathan Dyke*, Ph.D., Jason A. Koutcher*, M.D., Ph.D. Marco Zaider*, Ph.D. Departments of Radiation Oncology, *Medical Physics and Medical Oncology# Memorial Sloan-Kettering Cancer Center, New York, NY, USA Purpose: Recent studies have demonstrated that magnetic resonance spectroscopic imaging (MRSI) of the prostate may effectively distinguish between regions of cancer and normal prostatic epithelium. This diagnostic imaging tool takes advantage of the increased choline versus citrate ratio found in malignant compared normal prostate tissue. A method is described which registers MRSI to intraoperative-obtained ultrasound images and incorporates this information into a treatment planning system to achieve dose escalation to intraprostatic tumor deposits. The purpose of this study is to report our preliminary experience and dosimetric outcome with ten consecutive patients who underwent permanent interstitial implantation using intraoperative computer-based treatment-planning with MRSI optimization. Materials and methods: MRSI was obtained preoperatively for ten patients with clinically localized prostate cancer. The ratios of choline and citrate for the prostate were analyzed, and regions of high risk for malignant cells were identified. The ratios representing peaks on the MR spectrum were calculated on a spatial grid covering the prostate tissue. A procedure for mapping points of interest from the MRSI to the ultrasound images is described. A computer-based treatment planning system was used which relied on a genetic algorithm to determine the optimal seed distribution to achieve maximal target volume reduction and maintain urethra and rectal doses within tolerance ranges. MRSI data was incorporated into the treatment planning system to test the feasibility of dose escalation to positive voxels with relative sparing of surrounding normal tissues. Post-implant CT scans were performed on the same day of the procedure in all cases, and dosimetric guidelines of the American Brachytherapy Society were used to assess implant quality. Results: The intraoperative optimization treatment planning program was able to achieve a minimum dose of 139% - 192% of the 144 Gy prescription to the MRS positive voxels using I- 125 seeds. The percentage of the prostate volume receiving 100% of the prescription dose (V 100) ranged from 92%-97% and the D90 for the target volume ranged from 96%-100%. Despite the dose escalation achieved for the MRSI positive voxels, the urethral and rectal doses were maintained within tolerance ranges. The average and maximal rectal doses ranged from 28-42% and 69115%, respectively. The average and maximal urethral doses ranged from 66-144% and 138-166%, respectively. Conclusions: Using this brachytherapy optimization system, we could demonstrate the feasibility of MRS-optimized dose distributions for I-125 permanent prostate implants. This approach may have an impact on the ability to safely employ dose escalation for patients treated with permanent interstitial implantation and improve outcome for patients with organ confined prostatic cancers. 71 POST IMPLANT DOSIMETRY EVALUATIONFOR PROSTATE INTERSTITIAL BRACHYTHERAPY: A COMPARISON OF TWO COMMONLY USED TECHNIQUES S.K. Saraf, Ph.D., A. Zablow, M.D., R.L. Goodman, M.D., and K.D. Steidley, Ph.D. Department of Radiation Oncology, Saint Barnabas Medical Center, Livingston, NJ 07039 Purpose: Permanent prostate implants using 1-125 and Pd-103 radioactive seeds have been performed for early stage disease. Several techniques for seed implantation have been developed. Two of the most commonly used techniques utilize 1) PREPLAN volume scans, and 2) REAL TIME volume scans. We have compared the two techniques following ABS recommended methodology. Methods and materials: 30 patients were studied, 15 implanted using pre-plan ultrasound scans obtained 2 weeks earlier and the remaining 15 patients using real time scans obtained at the time of seed implantation. A pre-plan scan is usually obtained for all patients, but for patients implanted using real time scans, pre-plan scans were omitted. Three weeks following seed implantation CT Scans along with simulation films were obtained to evaluate the implants. As proposed by ABS, DI00, D90, V100 and V150 indices were calculated for each patient. D100 and D90 are defined as the mPD Dose that covers 100% and 90% of the prostate volume, while V 100 and V 150 are defined as the percentage of the prostate volume that receives 100% and 150% of the prescribed dose. Results: The mPD for Pd-103 and 1-125 implants were 115 Gy and 144 Gy (TG-43) respectively. The pre-plan patients had their implant performed from a plan devised using pre-plan scans. At the time of seed placement, variations in the prostate volume scans were minimized to achieve the dose distribution as close to the pre-planned volume as could be achieved. Such an extra effort is not needed for real time implant technique as the implant is performed on the volume scans obtained at the time of the implant. The following table provides an in-depth comparison of the two techniques used.
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