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A comparison between ultrasound-based real time vs conventional ct-based treatment plan in high-dose-rate brachytherapy for prostate
Abstracts / Brachytherapy 7 (2008) 91e194 Methods and Materials: A total of 43 patients with biopsy proven, early stage prostate cancer were consecutively treated with pulsed-dose-rate (PDR) brachytherapy as sole treatment modality at our institution between 2003 and 2006. The majority of patients had T1c or T2a disease (T1a 13%, T1c 26%, T2a 48%, T2b 10%, T2c 35). All patients had pre-treatment PSA less than 10 ng/mL and Gleason score 6 or less. The PDR-brachytherapy doses ranged from 65 to 70 Gy (20 pts. received 65 Gy, and 23 pts. 70 Gy), given in two sessions (dose per pulse was 0.60 Gy, 0.65 Gy or 0.70 Gy delivered for 24 h per day, night and day, with a time interval of 1 h between two pulses, total time 48e50 hours). Accordingly the Biological Extrapolated Doses (BED) for 65 Gy and 70 Gy were by presumption of a/b 5 3 about 108,3 Gy and 116,7 Gy, and by presumption of a/b 5 10 about 78 Gy and 84 Gy, respectively. Changes in American Urological Association symptom scores and also acute and chronic toxicities according Common Toxicity Criteria scale were assessed. Results: Dosimetric goals were adequately achieved in all patients with a median minimal dose to 90% of the prostate of ~90% of the prescription dose. The dose to the urethra D0.1 cc ranged between 98% to 130% of prescription dose, the dose to the rectum (2 cm2) was between 80 to 95%. No patient required temporary urinary catheter placement for acute obstructive symptoms after brachytherapy. At a median followup of 2 years (1e4 years) there was 3 cases (7%) of grade 1/2 rectal proctitis, no case (0%) grade 3/4 proctitis, 3 cases (7%) of grade 1/2 cystitis, no cases (0%) with dysuria grade 3. At time of analysis by 3 pts. (7%) a PSA-elevation was registered, no local recurrences or distant metastases were verified. Conclusions: Image-guided conformal pulsed-dose-rate brachytherapy is a feasible and safety treatment option for patients with low-risk prostate cancer as dose escalation with minimal associated morbidity. Our doseescalating trial will continue.
PO156 Correlation of a bioeffect model with tumor control in localized prostate cancer treated with low-dose-rate brachytherapy Annette Haworth, Ph.D.1 Martin Ebert, Ph.D.2 David Waterhouse, Ph.D.2 Gillian Duchesne, M.D.3 David Joseph, FRACR.2 1Physical Sciences, Peter MacCallum Cancer Centre, Melbourne, VIC, Australia; 2Radiation Oncology, Sir Charles Gairdner Hospital, Perth, WA, Australia; 3 Radiation Oncology, Peter MacCallum Cancer Centre, Melbourne, VIC, Australia. Purpose: A bioeffect model was developed to predict local control following I-125 implant for localized prostate cancer. The model was tested for its predictive power in identifying patients at risk of local recurrence. Methods and Materials: Seventy-nine patients with biopsy proven adenocarcinoma of the prostate were treated with I-125 radioactive seed implant alone. Prescribed dose was 144 Gy to the periphery of the prostate. Minimum followup time was 36 months. The post-implant dose distribution for each patient was determined using the TG-43 formalism and the D90 (maximum dose received by 90% of the prostate gland) and V100 (percentage volume of the prostate receiving the prescribed dose) calculated. To apply the bioeffect model, the prostate was mathematically divided into 3 cross sections and 4 quadrants. The DVH was determined for each subsection and used to calculate the tumor control probability by applying first a uniform tumor cell density to the entire prostate (UTPC) and secondly by applying a unique tumor cell density to each subsection (ie a non-uniform tumor cell density, NUTCP). Biochemical failure was defined using the Phoenix definition. Results: Preliminary analysis determined a weak correlation for D90 and V100 values below 120 Gy and 80%, respectively, with biochemical failure. Similarly, the UTCP value did appear to weakly correlate with treatment failure. The NUTCP however showed a much stronger correlation when expressed either as a single value representing all TCPs for each of the subsections and when considering only the subsection with the lowest TCP value.
189
PO157 Comparison of pre- and post-implant urethral dosimetry after lowdose-rate brachytherapy for prostate cancer with a simple contrast injection technique Stephanie Lassalle, M.Sc., Yannick Hervieux, M.Sc., Jean-Francois Carrier, Ph.D., Jean-Paul Bahary, M.D., Daniel Taussky, M.D. Radiation Oncology, Centre Hospitalier de l’Universite de Montreal, Montreal, QC, Canada. Purpose: To compare post-implant urethral dosimetry after permanent prostate seed brachytherapy to intraoperative dosimetry by validating a technique using retrograde injection of a contrast agent at Day 30. Methods and Materials: This is an analysis of 83 consecutive prostate cancer patients treated with permanent 125I seed implant. Five patients had cytoreductive hormonal therapy. The implants were done using a 3D transrectal ultrasound-guided intraoperative inverse planning system (FIRST, Nucletron). Intraoperatively, the urethra was visualised with aerated gel in the urinary catheter (18 Fr). Prescribed dose was 144 Gy to the PTV (prostate + 3 mm). The urethra was contoured as a 7-mm diameter circle centered on the catheter. Pre-implant dosevolume constraints for the urethra were (1) isodose encompassing 2% of the urethra (UrD2) <220 Gy, (2) isodose encompassing 5% of the urethra (UrD5) <200 Gy, and (3) volume of the urethra receiving 150% of the prescription dose (UrV150) 5 0. At Day 30 after the implant, a CT-scan was done with the retrograde injection of iodine contrast liquid mixed with aerated lubricated gel into the urethra (Millar et al., Brachytherapy 2006). Urethra was then contoured as anatomically visualised with this retrograde injection. Pre-implant and Day 30 dosimetry of the urethra were compared using a two-tailed Wilcoxon Signed Ranks Test. Results: The retrograde contrast injection technique at Day 30 gave a satisfactory result (visible prostatic urethra on almost all CT-scan images) in only thirty-five patients (42.2%). Comparison of urethral dosimetry on pre-implant and on Day 30 was difficult, because of the important difference in urethral volume. The mean urethral volume was 1.32 cc (range 0.78e1.81) on pre-implant and 0.66 cc (range 0.25e1.71) at Day 30 (p !0.0001). Consequently, all analyzed dosevolume parameters were significantly higher at Day 30 than on intraoperative planning (p!0.0001). Only the volume of the urethra receiving 100% of the prescription dose (UrV100) was significantly higher on pre-implant (mean 1.27 cc) than on Day 30 (mean 0.59 cc) (p !0.0001). Conclusions: Urethral dosimetry on Day 30 obtained by the retrograde injection of a contrast agent yields a satisfactory result in only a minority of patients. Nevertheless, our results show that dosimetric parameters for the urethra obtained by the anatomic contouring of a Day 30 postimplant CT-scan are statistically different from the ones obtained intraoperatively. The impact of this difference on urinary toxicity needs to be determined.
PO158 A comparison between ultrasound-based real time vs conventional ct-based treatment plan in high-dose-rate brachytherapy for prostate Shyam Pokharel, M.S.1 Amir Sadeghi, Ph.D.1,2 Bradley Prestidge, M.D.1,2 1Radiological Science, University of Texas Health Science Center, San Antonio, TX; 2Radiation Oncology, Texas Cancer Clinic, San Antonio, TX. Purpose: The dosimetric coverage, homogeneity and conformity together with the dosimetric objectives to organ at risk (OAR) have always been questionable for CT-based high-dose-rate brachytherapy treatment planning for prostate. This is due to the possible internal pelvic structures movement compounded with possible movement of catheters when a patient is transferred to CT room from operating room and back to the treatment room. Moreover, CT-based prostate volume has always
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Abstracts / Brachytherapy 7 (2008) 91e194
been reported bigger than ultrasound or MRI based volume most probably due to the poor soft tissue contrast in CT images. One of the drawbacks of ultrasound-based real-time treatment plan is that we have less information regarding the dose received by critical structures such as bladder and rectum as these structures are poorly differentiated and can not be visualized well in ultrasound imaging. The purpose of this study is to show that the real time ultrasound based treatment planning together with image fusion will be superior to existing CT-based treatment planning. Methods and Materials: The real-time ultrasound-based treatment planning was performed using Nucletron Oncentra Prostate (SWIFT Version 3) and compared it with CT based treatment planning. The CT based treatment planning was done using Nucletron Plato treatment planning system. Data from 10 patients would be included for initial study for comparison. The image fusion between ultrasound and CT was performed in ‘Oncentra Prostate’ platform so that complementary anatomical information could be obtained from these imaging modalities. Results: In our study, ultrasound based real time HDR brachytherapy treatment planning for prostate has been found easier, more precise and less time consuming for over all treatment planning and dose delivery. All the relevant data from ultrasound-based real-time HDR brachytherapy treatment plan for prostate will be compared and presented to CT-based conventional treatment plan later. Conclusions: Ultrasound-based real-time HDR brachytherapy treatment plan for prostate can be an ideal alternative for any other HDR brachytherapy treatment plans for prostate.
PO159 Outcome of prostate cancer patients treated with combined highdose-rate prostate brachytherapy and external beam radiotherapy at the Windsor Regional Cancer Centre Colvin D. Springer, MB, BS, FRCP, M.Sc., Rick Boyd, M.D., FRCS, Siobhan Ozard, Ph.D., Liz Skeates, R.N., Jennifer Stones, B.Sc. Radiotherapy, Windsor Regional Cancer Centre, Windsor, ON, Canada. Purpose: This is a retrospective review of consecutive patients treated with combined HDR prostate brachytherapy EBRT at the WRCC during the period Oct 2000 to Dec 2006. This is an analysis of the treatment outcome and toxicity of patients treated at a small community canter centre. Methods and Materials: A total of 185 patients were treated during this period. Median followup of 32.8 months with a range of 6.3 to 79.2 months with a range of 6.3 to 79.2 months. Median age at presentation was 60 years (range 49e80). Patients were treated according to their risk category. Patients classified on the basis of T-stage, PSA and Gleason Score in to 9% low risk, 62% intermediate risk and 29% high risk. Low risk patients were treated with HDR monotherapy using a single implant delivering 4 fractions to a total dose of 3,800 cGy. Patients in the intermediate and high risk groups were treated with combined HDR and EBRT. HDR consisted of a single implant delivering 2 or 3 fractions to a total dose of 1,800 to 2,000 cGy. This was followed 2 weeks later by EBRT typically 4,000 to 4,500 Gy in 20 to 25 daily fractions over a 4 to 5 week period. Adjuvant hormonal therapy was used primarily for high risk patients and cytoreductive hormonal therapy was used where indicated. Results: There have been 14 failures; 9- PSA only, 4 bone metastases, 1 lymph nodal metastases. Nine of these were in the high risk and 5 in the intermediate risk group. There were 5 deaths failures, 3 NED and 1 with PSA failure and lung ca. Six other patients developed malignancies during followup; malignant lymphoma e 1, colon ca e 3, esophageal ca1 and lung ca-2. Treatment was well tolerated with less than 5% Grade 3 GI or GU toxicity. Conclusions: With a median followup of 33 month, combined HDR brachytherapy and EBRT is well tolerated with acceptable GI and GU toxicity and results in high local control rate with few recurrences. These results are good not only for patients in the low risk category but also in the intermediate and high risk categories.
PO160 Higher strength seeds for I-125 prostate implants Sarah Elliott, Catherine Beaufort, Jeremy Millar, MBChB, William Buckland. Radiotherapy Centre, Alfred Hospital, Melbourne, Victoria, Australia. Purpose: The optimal air kerma strength for I-125 prostate implants has been widely investigated, with most studies supporting a higher seed strength. At the WBRC, a planning study showed a number of potential advantages for using higher strength seeds for our implants. Following on from this study we report a pilot study of ~0.7U implants. Methods and Materials: We treated 10 men with lower-strength (~0.4U) and 10 men with higher-strength (~0.7U) seeds. Post-implant dosimetry for the target volume, urethra and rectal wall were compared. Information about implant times and acute side-effects at three and six months were collected. Information on morbidity was also collected and analyzed at 1 and 2 years post implant. Results: The mean D90 (%) was 6% lower for the 0.7 U group, and spread over a wider range of values. The mean D90 (%) for the 0.4 U group was 105% 9% and the mean D90 (%) for the 0.7 U group was 99% 16%, suggesting higher strength seeds may be more technically demanding. Rectal wall doses were slightly higher for the 0.7 U group, with a mean D2 (cc) of 123 Gy compared to a mean D2 (cc) of 108 Gy for the lower seed strength group. The mean number of seeds/implant decreased by over 30% for the 0.7 U implants, and the mean needle number decreased by 8, leading to a total implant time savings of 12 minutes. HealthRelated Quality-of-Life surveys to two years showed minimal difference between the two groups. Conclusions: Analysis of postimplant dosimetry revealed mean dosimetry parameters for the higher seed strength implants were comparable to the lower seed strength implants. Although our numbers are small, we are reassured there were no easily discernable clinical differences between high and low strength implants. We are planning to follow our initial group further to allow assessment of longer-term outcomes, and to extend our pilot study.
PO161 Clinical impact of recommended revisions to Cs-131 source data on implant quality indices for prostate permanent seed implants Ravindra Yaparpalvi, M.S., Chandan Guha, M.D., Ph.D. Radiation Oncology, Montefiore Medical Center/AECOM, Bronx, NY. Purpose: To investigate the effect of recent revisions in source data for Cs-131 seeds on prostate implant quality indices. Methods and Materials: CT scans of 11 patients previously implanted with Cs-131 seeds (Isoray Model Cs-1) for combination therapy was utilized for this study. The CT-images were obtained at 7 days post seed implantation in 2.5 mm slice thickness. The prostate, rectum and bladder were contoured in each case. The median CT- based prostate volume was 27 cc (range 20 to 36 cc). The mean implanted activity was 107 mCi (range 81e131 mCi) and median number of seeds implanted were 42 (range 32e52). For each patient, two sets of dose distributions were generated e using ‘‘old’’ and ‘‘revised’’ Cs-131 source data. All plans were evaluated for changes in coverage (V100, V90, V80 and D90), uniformity (V200, V150) and normal tissue doses using ABS recommended guidelines. Dose calculations were performed using Variseed Planning system using AAPM TG-43 formalism. Results: A total of 22 dose distributions were analyzed. In general terms, ‘‘revised’’ dose distributions resulted in decreased - dose coverage, dose uniformity and normal tissue doses compared to ‘‘old’’ dose distributions. Specifically, V200 and V150 increased by mean values of 0.64% (SD 0.17) and 0.58% (SD 0.12) respectively compared to old values. Mean decreases in V100, V90, V80 and D90 values were 0.2% (SD 0.36), 0.3% (SD 0.25), 0.3% (SD 0.13) and 0.6% (SD 0.10) respectively. On average, Rectal and bladder doses decreased by 0.8% (SD 0.11). Conclusions: Differences in dose distributions obtained using ‘‘old’’ and ‘‘revised’’ Cs-131 source data are !1% in magnitude and appear to be clinically insignificant for warranting dose prescription changes.
PO156 Correlation of a bioeffect model with tumor control in localized prostate cancer treated with low-dose-rate brachytherapy Annette Haworth, Ph.D.1 Martin Ebert, Ph.D.2 David Waterhouse, Ph.D.2 Gillian Duchesne, M.D.3 David Joseph, FRACR.2 1Physical Sciences, Peter MacCallum Cancer Centre, Melbourne, VIC, Australia; 2Radiation Oncology, Sir Charles Gairdner Hospital, Perth, WA, Australia; 3 Radiation Oncology, Peter MacCallum Cancer Centre, Melbourne, VIC, Australia. Purpose: A bioeffect model was developed to predict local control following I-125 implant for localized prostate cancer. The model was tested for its predictive power in identifying patients at risk of local recurrence. Methods and Materials: Seventy-nine patients with biopsy proven adenocarcinoma of the prostate were treated with I-125 radioactive seed implant alone. Prescribed dose was 144 Gy to the periphery of the prostate. Minimum followup time was 36 months. The post-implant dose distribution for each patient was determined using the TG-43 formalism and the D90 (maximum dose received by 90% of the prostate gland) and V100 (percentage volume of the prostate receiving the prescribed dose) calculated. To apply the bioeffect model, the prostate was mathematically divided into 3 cross sections and 4 quadrants. The DVH was determined for each subsection and used to calculate the tumor control probability by applying first a uniform tumor cell density to the entire prostate (UTPC) and secondly by applying a unique tumor cell density to each subsection (ie a non-uniform tumor cell density, NUTCP). Biochemical failure was defined using the Phoenix definition. Results: Preliminary analysis determined a weak correlation for D90 and V100 values below 120 Gy and 80%, respectively, with biochemical failure. Similarly, the UTCP value did appear to weakly correlate with treatment failure. The NUTCP however showed a much stronger correlation when expressed either as a single value representing all TCPs for each of the subsections and when considering only the subsection with the lowest TCP value.
189
PO157 Comparison of pre- and post-implant urethral dosimetry after lowdose-rate brachytherapy for prostate cancer with a simple contrast injection technique Stephanie Lassalle, M.Sc., Yannick Hervieux, M.Sc., Jean-Francois Carrier, Ph.D., Jean-Paul Bahary, M.D., Daniel Taussky, M.D. Radiation Oncology, Centre Hospitalier de l’Universite de Montreal, Montreal, QC, Canada. Purpose: To compare post-implant urethral dosimetry after permanent prostate seed brachytherapy to intraoperative dosimetry by validating a technique using retrograde injection of a contrast agent at Day 30. Methods and Materials: This is an analysis of 83 consecutive prostate cancer patients treated with permanent 125I seed implant. Five patients had cytoreductive hormonal therapy. The implants were done using a 3D transrectal ultrasound-guided intraoperative inverse planning system (FIRST, Nucletron). Intraoperatively, the urethra was visualised with aerated gel in the urinary catheter (18 Fr). Prescribed dose was 144 Gy to the PTV (prostate + 3 mm). The urethra was contoured as a 7-mm diameter circle centered on the catheter. Pre-implant dosevolume constraints for the urethra were (1) isodose encompassing 2% of the urethra (UrD2) <220 Gy, (2) isodose encompassing 5% of the urethra (UrD5) <200 Gy, and (3) volume of the urethra receiving 150% of the prescription dose (UrV150) 5 0. At Day 30 after the implant, a CT-scan was done with the retrograde injection of iodine contrast liquid mixed with aerated lubricated gel into the urethra (Millar et al., Brachytherapy 2006). Urethra was then contoured as anatomically visualised with this retrograde injection. Pre-implant and Day 30 dosimetry of the urethra were compared using a two-tailed Wilcoxon Signed Ranks Test. Results: The retrograde contrast injection technique at Day 30 gave a satisfactory result (visible prostatic urethra on almost all CT-scan images) in only thirty-five patients (42.2%). Comparison of urethral dosimetry on pre-implant and on Day 30 was difficult, because of the important difference in urethral volume. The mean urethral volume was 1.32 cc (range 0.78e1.81) on pre-implant and 0.66 cc (range 0.25e1.71) at Day 30 (p !0.0001). Consequently, all analyzed dosevolume parameters were significantly higher at Day 30 than on intraoperative planning (p!0.0001). Only the volume of the urethra receiving 100% of the prescription dose (UrV100) was significantly higher on pre-implant (mean 1.27 cc) than on Day 30 (mean 0.59 cc) (p !0.0001). Conclusions: Urethral dosimetry on Day 30 obtained by the retrograde injection of a contrast agent yields a satisfactory result in only a minority of patients. Nevertheless, our results show that dosimetric parameters for the urethra obtained by the anatomic contouring of a Day 30 postimplant CT-scan are statistically different from the ones obtained intraoperatively. The impact of this difference on urinary toxicity needs to be determined.
PO158 A comparison between ultrasound-based real time vs conventional ct-based treatment plan in high-dose-rate brachytherapy for prostate Shyam Pokharel, M.S.1 Amir Sadeghi, Ph.D.1,2 Bradley Prestidge, M.D.1,2 1Radiological Science, University of Texas Health Science Center, San Antonio, TX; 2Radiation Oncology, Texas Cancer Clinic, San Antonio, TX. Purpose: The dosimetric coverage, homogeneity and conformity together with the dosimetric objectives to organ at risk (OAR) have always been questionable for CT-based high-dose-rate brachytherapy treatment planning for prostate. This is due to the possible internal pelvic structures movement compounded with possible movement of catheters when a patient is transferred to CT room from operating room and back to the treatment room. Moreover, CT-based prostate volume has always
190
Abstracts / Brachytherapy 7 (2008) 91e194
been reported bigger than ultrasound or MRI based volume most probably due to the poor soft tissue contrast in CT images. One of the drawbacks of ultrasound-based real-time treatment plan is that we have less information regarding the dose received by critical structures such as bladder and rectum as these structures are poorly differentiated and can not be visualized well in ultrasound imaging. The purpose of this study is to show that the real time ultrasound based treatment planning together with image fusion will be superior to existing CT-based treatment planning. Methods and Materials: The real-time ultrasound-based treatment planning was performed using Nucletron Oncentra Prostate (SWIFT Version 3) and compared it with CT based treatment planning. The CT based treatment planning was done using Nucletron Plato treatment planning system. Data from 10 patients would be included for initial study for comparison. The image fusion between ultrasound and CT was performed in ‘Oncentra Prostate’ platform so that complementary anatomical information could be obtained from these imaging modalities. Results: In our study, ultrasound based real time HDR brachytherapy treatment planning for prostate has been found easier, more precise and less time consuming for over all treatment planning and dose delivery. All the relevant data from ultrasound-based real-time HDR brachytherapy treatment plan for prostate will be compared and presented to CT-based conventional treatment plan later. Conclusions: Ultrasound-based real-time HDR brachytherapy treatment plan for prostate can be an ideal alternative for any other HDR brachytherapy treatment plans for prostate.
PO159 Outcome of prostate cancer patients treated with combined highdose-rate prostate brachytherapy and external beam radiotherapy at the Windsor Regional Cancer Centre Colvin D. Springer, MB, BS, FRCP, M.Sc., Rick Boyd, M.D., FRCS, Siobhan Ozard, Ph.D., Liz Skeates, R.N., Jennifer Stones, B.Sc. Radiotherapy, Windsor Regional Cancer Centre, Windsor, ON, Canada. Purpose: This is a retrospective review of consecutive patients treated with combined HDR prostate brachytherapy EBRT at the WRCC during the period Oct 2000 to Dec 2006. This is an analysis of the treatment outcome and toxicity of patients treated at a small community canter centre. Methods and Materials: A total of 185 patients were treated during this period. Median followup of 32.8 months with a range of 6.3 to 79.2 months with a range of 6.3 to 79.2 months. Median age at presentation was 60 years (range 49e80). Patients were treated according to their risk category. Patients classified on the basis of T-stage, PSA and Gleason Score in to 9% low risk, 62% intermediate risk and 29% high risk. Low risk patients were treated with HDR monotherapy using a single implant delivering 4 fractions to a total dose of 3,800 cGy. Patients in the intermediate and high risk groups were treated with combined HDR and EBRT. HDR consisted of a single implant delivering 2 or 3 fractions to a total dose of 1,800 to 2,000 cGy. This was followed 2 weeks later by EBRT typically 4,000 to 4,500 Gy in 20 to 25 daily fractions over a 4 to 5 week period. Adjuvant hormonal therapy was used primarily for high risk patients and cytoreductive hormonal therapy was used where indicated. Results: There have been 14 failures; 9- PSA only, 4 bone metastases, 1 lymph nodal metastases. Nine of these were in the high risk and 5 in the intermediate risk group. There were 5 deaths failures, 3 NED and 1 with PSA failure and lung ca. Six other patients developed malignancies during followup; malignant lymphoma e 1, colon ca e 3, esophageal ca1 and lung ca-2. Treatment was well tolerated with less than 5% Grade 3 GI or GU toxicity. Conclusions: With a median followup of 33 month, combined HDR brachytherapy and EBRT is well tolerated with acceptable GI and GU toxicity and results in high local control rate with few recurrences. These results are good not only for patients in the low risk category but also in the intermediate and high risk categories.
PO160 Higher strength seeds for I-125 prostate implants Sarah Elliott, Catherine Beaufort, Jeremy Millar, MBChB, William Buckland. Radiotherapy Centre, Alfred Hospital, Melbourne, Victoria, Australia. Purpose: The optimal air kerma strength for I-125 prostate implants has been widely investigated, with most studies supporting a higher seed strength. At the WBRC, a planning study showed a number of potential advantages for using higher strength seeds for our implants. Following on from this study we report a pilot study of ~0.7U implants. Methods and Materials: We treated 10 men with lower-strength (~0.4U) and 10 men with higher-strength (~0.7U) seeds. Post-implant dosimetry for the target volume, urethra and rectal wall were compared. Information about implant times and acute side-effects at three and six months were collected. Information on morbidity was also collected and analyzed at 1 and 2 years post implant. Results: The mean D90 (%) was 6% lower for the 0.7 U group, and spread over a wider range of values. The mean D90 (%) for the 0.4 U group was 105% 9% and the mean D90 (%) for the 0.7 U group was 99% 16%, suggesting higher strength seeds may be more technically demanding. Rectal wall doses were slightly higher for the 0.7 U group, with a mean D2 (cc) of 123 Gy compared to a mean D2 (cc) of 108 Gy for the lower seed strength group. The mean number of seeds/implant decreased by over 30% for the 0.7 U implants, and the mean needle number decreased by 8, leading to a total implant time savings of 12 minutes. HealthRelated Quality-of-Life surveys to two years showed minimal difference between the two groups. Conclusions: Analysis of postimplant dosimetry revealed mean dosimetry parameters for the higher seed strength implants were comparable to the lower seed strength implants. Although our numbers are small, we are reassured there were no easily discernable clinical differences between high and low strength implants. We are planning to follow our initial group further to allow assessment of longer-term outcomes, and to extend our pilot study.
PO161 Clinical impact of recommended revisions to Cs-131 source data on implant quality indices for prostate permanent seed implants Ravindra Yaparpalvi, M.S., Chandan Guha, M.D., Ph.D. Radiation Oncology, Montefiore Medical Center/AECOM, Bronx, NY. Purpose: To investigate the effect of recent revisions in source data for Cs-131 seeds on prostate implant quality indices. Methods and Materials: CT scans of 11 patients previously implanted with Cs-131 seeds (Isoray Model Cs-1) for combination therapy was utilized for this study. The CT-images were obtained at 7 days post seed implantation in 2.5 mm slice thickness. The prostate, rectum and bladder were contoured in each case. The median CT- based prostate volume was 27 cc (range 20 to 36 cc). The mean implanted activity was 107 mCi (range 81e131 mCi) and median number of seeds implanted were 42 (range 32e52). For each patient, two sets of dose distributions were generated e using ‘‘old’’ and ‘‘revised’’ Cs-131 source data. All plans were evaluated for changes in coverage (V100, V90, V80 and D90), uniformity (V200, V150) and normal tissue doses using ABS recommended guidelines. Dose calculations were performed using Variseed Planning system using AAPM TG-43 formalism. Results: A total of 22 dose distributions were analyzed. In general terms, ‘‘revised’’ dose distributions resulted in decreased - dose coverage, dose uniformity and normal tissue doses compared to ‘‘old’’ dose distributions. Specifically, V200 and V150 increased by mean values of 0.64% (SD 0.17) and 0.58% (SD 0.12) respectively compared to old values. Mean decreases in V100, V90, V80 and D90 values were 0.2% (SD 0.36), 0.3% (SD 0.25), 0.3% (SD 0.13) and 0.6% (SD 0.10) respectively. On average, Rectal and bladder doses decreased by 0.8% (SD 0.11). Conclusions: Differences in dose distributions obtained using ‘‘old’’ and ‘‘revised’’ Cs-131 source data are !1% in magnitude and appear to be clinically insignificant for warranting dose prescription changes.