Proceedings of the 51st Annual ASTRO Meeting (SM+), extraprostatic extension (EPE+), or seminal vesicle invasion (SV+). We aim to determine if the type of RP, open (ORP) vs. laparoscopic (LRP), impacted the likelihood of finding these APF, in addition to finding involved lymph nodes (LN). Materials/Methods: From our IRB-approved database, we identified 3384 pts with complete pre-operative and pathologic data who underwent a RP for localized cT1-T2 prostate cancer at Cleveland Clinic from 1997-2007. No pt received neoadjuvant therapy. Sixty-five percent (n = 2212) had ORP and 35% (n = 1172) had LRP. Surgical specimens were examined by dedicated prostate pathologists. Pts were divided into three risk groups per NCCN guidelines based on clinical T stage, biopsy Gleason score, and initial PSA: low-risk (LR), intermediate-risk (IR), and high-risk (HR). Cochran-Armitage trend tests were done to evaluate for a difference in the rates of APFs among the risk groups. Chi-square tests were done to evaluate for a difference in the rates of APFs between ORP and LRP. Results: 57% of pts were LR, 30% IR, and 13% HR. The rates of LR, IR, and HR disease were equivalent between the ORP and LRP series (p = 0.15). Overall, 43% of pts had at least one APF. By risk group, the rate of APF was 31%, 55%, and 67% for LR, IR, and HR pts, respectively (p \ 0.0001). By respective risk group, 21%, 33%, and 36% had SM+ (p \ 0.0001), 16%, 37%, and 56% had EPE+ (p \ 0.0001), and 1%, 7%, and 19% had SV+ disease (p \ 0.0001). The rates of SM+, EPE+, or SV+ were similar between ORP and LRP for each risk group, except for IR pts who had more SV+ with ORP than LRP (9% vs. 5%, p = 0.01). Overall, 44% had LN sampling or dissection, including 14% of LR, 79% of IR, and 95% of HR pts, with similar rates for ORP and LRP. Pts who underwent ORP had a greater number of LNs removed (median 8 vs 5) and were more likely to have documented LN+ (5% vs 1% of those undergoing sampling) than LRP (p \ 0.0001). Among those who had LN sampled, LR pts had LN+ in 0.2% ORP vs. 0% LRP (p = 0.003), IR pts had LN+ in 2% ORP vs. 0.3% LRP (p = 0.05), and HR pts had LN+ in 11% ORP vs. 2% LRP (p = 0.009). Among HR pts, the incidence of LN+ in ORP pts was 17% for $10 LN and 8% for 1-9 LN removed, whereas in LRP pts it was 10% for $10 LN and 1% for 1-9 LN removed. Conclusions: A substantial number of pts undergoing RP have APF for which adjuvant radiotherapy may be indicated (31%, 55%, and 67% of the LR, IR, and HR groups, respectively). The type of surgery did not significantly impact the likelihood of finding these local APF. However, laparoscopic LN dissection underestimates the incidence of LN+ compared to open surgery in HR pts, even when accounting for number of LN sampled. Author Disclosure: R.D. Tendulkar, None; K.L. Stephans, None; C.A. Reddy, None; A. Reuther, None; C. Magi-Galluzzi, None; M. Zhou, None; E.A. Klein, None.
2259
Daily Fiducial Based Tracking of Seminal Vesicle Motion in Image Guided Dose Escalated IMRT: Are We Kidding Ourselves Regarding Seminal Vesicle Coverage?
N. J. Aherne1,2, J. P. Herden1, M. A. Wood1, A. Schaeffer3, J. D. Hill1, A. Last1, C. D. Fuller4, R. Welshman1, T. P. Shakespeare1,2 NCCI, Coffs Harbour NSW, Australia, 2RCS Faculty of Medicine University of New South Wales, Coffs Harbour NSW, Australia, 3Centre for Epidemiology and Research, NSW Health, Sydney, New South Wales, Australia, 4University of Texas Health Sciences at San Antonio, San Antonio, TX 1
Purpose/Objective(s): The seminal vesicles (SVs) are often part of the clinical target volume (CTV) when treating prostate cancer. Uniform margins are typically used when expanding the prostate and SV CTV to the planning target volume (PTV), and these margins are decreasing as we move towards image-guided intensity-modulated radiotherapy (IG-IMRT). However little is known about SV motion independent of the prostate when using prostate fiducial markers (FM) for target verification. We investigated SV interfraction motion and SV CTV coverage when matching to prostate FM, in order to determine the impact of this motion on image guidance strategies. Materials/Methods: Following IRB approval, nine consecutive patients undergoing IG-IMRT with prostate FM had an additional FM inserted into each SV to be used as a surrogate SV CTV. All patients were treated with daily bowel and bladder filling protocols. Target verification during IG-IMRT was by daily online matching to the prostate with electronic portal imaging (EPI) and weekly kilovoltage computed tomography (kvCT). Retrospectively, we matched kvCT prostate FM to the reference prostate FM position on planning CT, then determined SV FM position on kvCT relative to the SV FM position on planning CT. The planning CT SV FMs were expanded 0, 3, 5, 10 and 15mm in three dimensions to determine what expansion would be required for coverage of the SV CTV interfraction motion. We calculated the proportions of overall fractions where bilateral SV CTV coverage occurred for each expansion. Results: There were 89 kVCT images available for review (range 8-11 per patient). There was no expansion required to account for SV motion in 12.35% of fractions analysed. A uniform expansion of 3 mm would cover both SVs in 38.19% of fractions, an expansion of 5 mm was required in 56.17% of fractions, and an expansion of 10 mm was required in 95.5% of all fractions. All SV interfraction motion was accounted for by a 15 mm expansion. Conclusions: Even with daily online imaging, to cover interfraction SV motion 95.5 % of the time an expansion of 10 mm would be required. This implies that some protocols may result in subtherapeutic doses of radiotherapy to the SVs, and that the seminal vesicle PTV expansion needs to be larger than the prostate PTV expansion. Author Disclosure: N.J. Aherne, None; J.P. Herden, None; M.A. Wood, None; A. Schaeffer, None; J.D. Hill, None; A. Last, None; C.D. Fuller, None; R. Welshman, None; T.P. Shakespeare, None.
2260
Pathologic Staging Results in Substantially Higher Risk-stratification Compared with that Predicted by Clinical Risk-stratification in Men with Adenocarcinoma of the Prostate
E. W. Cooke, D. C. Shrieve, J. D. Tward University of Utah Huntsman Cancer Hospital, Salt Lake City, UT Purpose/Objective(s): We compared preoperative clinical staging with pathologic staging following prostatectomy in men with adenocarcinoma of the prostate. We also evaluated the incidence of positive nodes at the time of surgery and compared it to the predicted risk based on the Roach formula.
S297
I. J. Radiation Oncology d Biology d Physics
S298
Volume 75, Number 3, Supplement, 2009
Materials/Methods: Data were obtained from the Surveillance, Epidemiology, and End Results Program (SEER) for the years 2004-2005. Men with adenocarcinoma of the prostate who had complete clinical TNM staging information were included, and descriptive statistics were performed. Results: A total of 59,351 subjects were identified, of whom 14,842 had a prostatectomy with complete pathologic staging. Clinical T-stage was T1c in 65.3%, T2c in 15.8%, T2a in 7.3%, T2b in 2.9%, and was T3 or greater in 3.6%. Pathologic T-stage was T2c in 63%, T2a in 14.6%, T3a in 10.7%, T3b in 6.6%, T2b in 2.7% and T4 in 2.3%. No subjects had a pathologic T-downstaging. Of 14,842 patients with pathologic nodal data, 2.3% had positive nodes, the majority falling into the high risk group. Only 2.9% of clinically or pathologically staged patients had metastatic disease at presentation. There were 12,441 subjects with AJCC stage I-III disease with complete clinical and pathologic TNM staging, Gleason sum, and PSA data. When stratified into low, intermediate and high risk groups based on the D’Amico criteria, 75.7% of clinically staged low risk patients were up-risk-stratified to the high-risk group after prostatectomy. Amongst intermediate risk group patients, 84.6% were up-risk-stratified. Only 0.9% of patients were down-risk-stratified. Utilizing the Roach formula for subjects who had pathologic nodal evaluation, those with a predicted likelihood of positive nodes of 0-5%, 5.1-10%, 10.1%-15%, and .15% were found to have 0.2%, 0.4%, 1.1%, and 6.5% incidence of positive nodes respectively. Conclusions: Complete pathologic staging results in a higher risk-stratification than that predicted by clinical criteria in the majority of patients. This finding can confound the interpretation of outcomes in matched cohort studies comparing surgical to non-surgical treatments for prostate cancer. Nodal positivity is uncommon in men with prostate cancer at diagnosis. Predictive nomograms based on older surgical series significantly overestimate the actual risk of node positive disease in the current era. Author Disclosure: E.W. Cooke, None; D.C. Shrieve, None; J.D. Tward, None.
2261
Is MRI-based Week Three Post-implant Dosimetry Necessary following LDR Prostate Brachytherapy?
R. J. Cohen, N. K. Sharma, K. Ruth, M. K. Buyyounouski, J. Li, K. Crawford, S. J. Feigenberg, D. Y. T. Chen, R. G. Uzzo, E. M. Horwitz Fox Chase Cancer Center, Philadelphia, PA Purpose/Objective(s): (1) To compare the intra-operative trans-rectal ultrasound (TRUS) prostate volume with CT/MRI-based pre-operative, day 0, and week 3 volumes in patients treated with low dose rate (LDR) permanent prostate implants. (2) To determine if MRI-based day 0 dosimetry is sufficiently predictive of week 3 post-implant dosimetry to render week 3 studies unnecessary. Materials/Methods: Patient records of 148 consecutive men treated from 2003-2007 with permanent I-125 prostate implants for favorable risk prostate cancer were retrospectively reviewed. A CT/MRI volume study was performed 1-2 weeks prior to implant to assess prostate anatomy and size. Intra-operatively, a TRUS volume was generated and used for real-time treatment planning with customized needle positions and seed-spacer sequences using the VariseedÒ planning system. In accordance with the American Association of Physics in Medicine Task Group No. 43 (TG-43) recommendations, 145 Gy was prescribed to 100% of the prostate volume. CT and MRI scans were obtained and fused for post-implant dosimetry several hours (day 0) and approximately 21 days (week 3) following the implant. The pre-implant, intra-operative, day 0, and week 3 prostate volumes were compared using a paired t-test. Day 0 and week 3 V100 and D90 were compared using a paired ttest and Pearson correlation. Logistic regression was used to identify significant predictors of week 3 V100.90% and D90.145 Gy. Results: The pre-implant CT/MRI prostate volume was, on average, 5.5cc (15%) smaller than the intra-operative TRUS volume (33.9cc vs. 39.4cc, p \ 0.0001). The mean day 0 prostate volume was larger (52.4cc), but began to re-normalize by week 3 (42.9cc). The mean V100 increased from 82% on day 0 to 88% on week 3 (p \ 0.0001). Likewise, the mean D90 increased from 126 Gy on day 0 to 142 Gy on week 3 (p \ 0.0001). The correlation between the day 0 and week 3 dosimetry was modest (V100 r=0.54; D90 r=0.52). Week 3 V100.90% was positively associated with day 0 V100 (p \ 0.001) and number of seeds implanted (p = 0.04). Week 3 V100.90% was inversely associated with the intra-operative TRUS volume (p = 0.02). Similar results were obtained for week3 D90.145Gy. Conclusions: MRI-based prostate volume is statistically smaller than the TRUS-based volume. Post-implant edema only partially resolves by week 3. The D90 and V100 are significantly different between days 0 and 21. Although the D90 and V100 on day 0 predict for the counterpart values on week 3, the correlation is modest. Positive predictors of V100.90% and D90.145Gy include day 0 V100 and D90, greater number of implanted seeds, and smaller TRUS volume. These results suggest that week 3 post-implant dosimetry should be performed on all patients receiving a permanent LDR prostate implant for quality assurance purposes. Author Disclosure: R.J. Cohen, None; N.K. Sharma, None; K. Ruth, None; M.K. Buyyounouski, None; J. Li, None; K. Crawford, None; S.J. Feigenberg, None; D.Y.T. Chen, None; R.G. Uzzo, None; E.M. Horwitz, None.
2262
Anatomical Differences after Robotic-assisted Radical Prostatectomy (RARP) and Open Prostatectomy (OP): Implications for Radiation Field Design
A. E. Hirsch1,2, M. J. Janicek1, K. Mui3, R. J. Lee3, D. S. Wang1, R. K. Babayan1, A. C. Zumwalt1, A. Ozonoff4, A. L. Zietman2 Boston University Medical Center, Boston, MA, 2Massachusetts General Hospital, Boston, MA, 3Boston University School of Medicine, Boston, MA, 4Boston University School of Public Health, Boston, MA
1
Purpose/Objective(s): RARP is a rapidly emerging alternative to OP for the surgical treatment of localized prostate cancer. The current field design for post-prostatectomy radiation (XRT) is defined by the post-OP pelvis. In this study, we compare the anatomy of the pelvis following RARP to that post-OP to determine if XRT field design should take surgical approach into consideration. Materials/Methods: We conducted an IRB-approved retrospective study of the postoperative pelvic MRI scans for all prostatectomy patients who presented consecutively to the radiation oncology clinic between January 2007 and December 2008. We measured the following anatomical distances in mm in the sagittal plane unless otherwise noted: (a) superior, middle and inferior