Volumetric Modulated Arc Therapy (VMAT) in the Treatment of Localized Prostate Cancer: Initial Experience in 200 Patients

S380

International Journal of Radiation Oncology  Biology  Physics

(nPSA) and time to nPSA (TnPSA) following salvage radiation therapy (SRT) for biochemical failure post-radical prostatectomy. We evaluated the impact of nPSA and TnPSA on biochemical failure (BF), distant metastasis (DM), prostate cancer-specific mortality (PCSM), and overall mortality (OM) following SRT. Materials/Methods: Four hundred sixty patients who received SRT without androgen deprivation therapy at our institution were included in this retrospective study. Univariate and multivariate analysis was performed using Kaplan-Meier methods and Cox proportional-hazards regression, respectively. A prognostic model using the identified prognostic variables was developed and validated in randomly allocated training and validation patient cohorts. Results: Median follow-up post-SRT was 62 months. Median nPSA postSRT was undetectable (interquartile range [IQR] <0.1-0.3 ng/mL) and median TnPSA was 6.7 months (IQR 4.4-11.1). On univariate analysis, a detectable nPSA (p < 0.01) and TnPSA <6 months (p6 months were assigned a score of 1. Those with a detectable nPSA and a TnPSA <6 months were assigned a score of 2. In the training cohort, the Nadir Score model strongly predicted BF (hazard ratio [HR]: 3.9, p < 0.0001) and DM (HR: 2.8, p < 0.0001), and was the only statistically significant predictor of PCSM (HR: 2.7, p Z 0.0003) and OM (HR: 1.7, p Z 0.002) on multivariate analysis. The model produced similar 5-year rates of BF (p < 0.0001), DM (p Z 0.0001), PCSM (p Z 0.02), and OM (p Z 0.02) in the validation cohort. For patients with a Nadir Score of 2 in the validation cohort, 5-year rates of BF, DM, PCSM, and OM were 96%, 42%, 24%, and 30%, respectively. Conclusions: The combination of a detectable nPSA and a TnPSA <6 months after SRT strongly predicts patients at the highest risk for DM, PCSM, and OM. Patients with a detectable nPSA who reached nadir within 6 months following SRT are unlikely to have clinically localized disease and should be considered for prompt initiation of systemic therapies. Author Disclosure: W.C. Jackson: None. S.B. Johnson: None. Y. Song: None. B. Foster: None. H.M. Sandler: None. G.S. Palapattu: None. F.Y. Feng: None. D.A. Hamstra: None.

and no one experienced Grade 3 GU toxicity. Five patients (2.5%) developed late Grade 2 rectal bleeding. Two patients (1%) experienced Grade 3 rectal toxicity requiring either one or more transfusions or a laser cauterization procedure. No Grade 4 rectal complications have been observed. The 3-year actuarial likelihood of late  Grade 2 rectal bleeding was 3%. Sixteen patients (8%) experienced late Grade 2 GU toxicity, and no one developed Grade 3 GU toxicity. The 3-year actuarial likelihood of late  Grade 2 GU toxicity was 8.7%. The 3-year actuarial PSA relapse-free survival rates for low, intermediate, and high risk group patients stratified according to NCCN criteria were 100%, 100%, and 93%, respectively. Conclusions: Our initial data demonstrate the feasibility of VMAT in patients with localized prostate cancer. Acute and late rectal toxicities seem to be dramatically reduced compared with what has been observed with conventional radiation therapy techniques. Short-term PSA control rates were excellent. Based on our promising initial experiences, VMAT has established the novel mode of conformal radiation delivery system for localized prostate cancer at our institution. Further studies in a larger population are required to determine longterm results in VMAT. Author Disclosure: K. Shiraishi: None. K. Yamamoto: None. A. Haga: None. A. Sakumi: None. M. Futaguchi: None. A. Nomoto: None. T. Onoe: None. K. Nakagawa: None.

2460 Volumetric Modulated Arc Therapy (VMAT) in the Treatment of Localized Prostate Cancer: Initial Experience in 200 Patients K. Shiraishi, K. Yamamoto, A. Haga, A. Sakumi, M. Futaguchi, A. Nomoto, T. Onoe, and K. Nakagawa; University of Tokyo, Tokyo, Japan Purpose/Objective(s): To report initial experience of biochemical outcomes and the acute and late toxicity in 200 patients with clinically localized prostate cancer treated with volumetric modulated arc therapy (VMAT). Materials/Methods: Between November 2007 and September 2011, 200 patients with clinically localized prostate cancer were treated with VMAT. Treatment planning systems used were Ergo++ in 77 patients and Pinnacle in 123 patients. All plans were based on an inverse-planning approach. A total of 181 patients (90%) were treated to 76 Gy, and 17 patients (9%) were treated to 72 Gy. Brachytherapy boost technique (seed implantation) before VMAT was used in 2 patients. Acute and late toxicities were scored according to CTCAE grading scales. PSA relapse was defined according to Phoenix (nadir+2) definition. The mean follow-up time was 36 months (range, 6-68 months). Results: Two patients (1%) developed acute  Grade 2 GI toxicity. Thirty-nine patients (19%) developed acute  Grade 2 GU symptoms,

Poster Viewing Abstract 2461; Table

IO urethra PO urethra P value IO prostate PO prostate P value

2461 Comparison of Intraoperative and Postoperative Dosimetric Parameters for the Urethra and Prostate in Patients Undergoing Low-Dose-Rate Prostate Brachytherapy O. Algan, Z. Nicholas, I. Ali, P. Sindhwani, and S. Ahmad; University of Oklahoma Health Science Center, Oklahoma City, OK Purpose/Objective(s): To compare the doses delivered to the prostate and urethra using low-dose rate brachytherapy, as measured intra-operatively (IO) during the procedure and immediately post-operatively (PO). Materials/Methods: This was a retrospective study done in a single institution and included thirteen patients who were discharged home with a Foley catheter after undergoing prostate brachytherapy for localized prostate cancer (9 patients were monotherapy, 4 were boost therapy). All patients underwent brachytherapy utilizing non-stranded I-125 seeds and dynamic intra-operative dosimetric planning. Patients were seen one day after the brachytherapy procedure for a limited CT scan of the pelvis for brachytherapy dosimetric evaluation. The Foley catheter localized the urethra for contouring purposes. All dosimetric plans were generated on a brachytherapy treatment planning system. The V150, 100, 90 and 50, along with the D100, 90, 50 and 5 were recorded for both the IO and PO evaluation. Statistical analysis between the two groups was performed using a 2-tailed paired t-test. Results: The dosimetric parameters for the IO and PO studies are shown in Table. In general, the dosimetric parameters measured on the PO study were smaller than the IO study. Comparing the IO and PO values for the urethra, the mean urethral volume was 0.88 cc vs 1.21 cc. The mean (and range) V150 values for the IO and PO studies were 13.7% (range, 0% 50.68%) vs 0.35% (range, 0% - 3.7%), p Z 0.018. The mean values for V100 and D50 for the urethra were 81.68% vs 52.34%, p Z 0.002 and 176.5 Gy vs 139.5 Gy, p < 0.001. For the prostate gland, the mean prostate volume was larger on the PO study (41.2 cc vs 36.1 cc, p < 0.001) in comparison to the IO study. Similar to the urethral findings, the V150,

Intraoperative (IO) and postoperative (PO) prostate brachytherapy dosimetric parameters

Vol

V150

V100

V90

V50

D100

D90

D50

D5

0.88 cc 1.21 cc < .001 36.1 cc 41.2 cc < .001

13.7% 0.35% .018 72.6% 58.11% < .001

81.68% 52.34% .002 95.8% 93.02% .032

85.92% 71.69% .002 97.50% 96.35% .205

98.43% 96.57% .407 100% 100% .632

76.89 Gy 71.18 Gy .573 85.4 Gy 80.6 Gy .288

102.13 Gy 94.03 Gy .451 161.4 Gy 147.6 Gy < .001

176.5 Gy 139.5 Gy < .001 244.7 Gy 167.8 Gy < .001

203.1 Gy 167.2 Gy < .001