(HRZ10.93, 95% CIZ2.32-51.61; HRZ4.95, 95% CIZ1.03-23.85, respectively). Patients in the high risk group had an increased risk of death compared to patients ...
Poster Viewing E239
Volume 99 Number 2S Supplement 2017 D. Bolton,2 F. Foroudi,2 V.S. Khoo,6 and J. Smith7; 1GenesisCareRadiation Oncology Victoria, Australia, Ringwood, Australia, 2The Austin Hospital, Heidelberg, Australia, 3The Valley Private Hospital, Mulgrave, Australia, 4The Bays Hospital, Mornington, Australia, 5Olivia Newton John Cancer & Wellness Centre, Heidelberg, Australia, 6Royal Marsden Hospital, London, United Kingdom, 7Plain Statistics, Horsham, Australia Purpose/Objective(s): It is well documented that the prostate bed is highly susceptible to inter-fraction motion leading to larger treatment planning margins to account for daily treatment set up uncertainties when matching to bony anatomy. The use of fiducial markers in the prostate bed has significantly improved accuracy of treatment delivery. This pilot study aims to investigate the role and benefits of radio-opaque hydrogel tissue marker in the treatment of post prostatectomy intensity modulated radiation therapy (IMRT). Materials/Methods: Twenty patients treated with IMRT to a dose of 70.2Gy in 39 fractions between Jan 2016 to Jan 2017 were included in this study. All patients underwent transperineal injection of hydrogel tissue marker at the level of vesico-urethral anastomosis and cystoscopically into the posterior bladder wall. Instructions for bladder and bowel preparation to be followed during CT simulation and daily treatments were provided to the patients. Daily on-line cone beam CT matching to the hydrogel tissue marker was performed prior to each treatment and off-sets relative to skin tattoos were recorded in 3 directions: left-right (LR); superior-inferior (SI) and anterio-posterior (AP). Daily image registration using bony matching was then assessed off-line and off-sets relative to skin tattoos were again recorded. The mean and standard deviation of the differences between the hydrogel tissue markers and bony off-sets were calculated for all fractions for each patient; then the overall mean and systematic (S) and random errors (s) for the entire cohort were calculated. The planning target volume (PTV) margin required for bony matching was estimated using van Herk’s formula of 2.5S + 0.7s, which is designed to ensure a minimum dose of 95% of prescribed dose to the clinical target volume (CTV) in 90% of patients. These margins are relative to the hydrogel tissue markers which are assumed to be in the target tissue. Results: A total of 1520 images were analysed. The overall mean shift differences between the hydrogel tissue markers and bones for the entire cohort were LR: 0.13mm (S 0.38mm, s 1.35mm); SI: 0.92mm (S 1.40mm, s 2.50mm) and AP: 0.40mm (S 1.98mm, s 3.18mm). The calculated PTV margins for bony matching relative to hydrogel tissue markers were 1.90mm in LR, 5.25mm in SI and 7.17mm AP directions. Conclusion: Prostate bed motion is independent of pelvic bone anatomy and soft tissue matching has shown to be superior compared with pelvic bone matching. With a required PTV margin of 7.17mm in the AP direction, the use of hydrogel tissue marker can significantly improve treatment set up accuracy even in patients with optimal bowel and bladder preparations who undergo image guidance with pelvic bone matching. This will provide the best CTV coverage whilst minimising the current PTV margin and mitigating bladder and rectal toxicities. Author Disclosure: H. Ho: None. M. Chao: None. S.J. Spencer: None. W. Ding: None. B. Subramanian: None. Y. Chan: None. T. Pham: None. A. Tan: None. D. Lim Joon: None. N. Lawrentschuk: None. S. Sengupta: None. D. Bolton: None. F. Foroudi: None. V.S. Khoo: None. J. Smith: None.
2573 Reducing Errors in Prostate Tracking with an Improved Fiducial Implantation Protocol for Stereotactic Body Radiotherapy (SBRT) O.E. Holmes,1,2 J. Gratton,2 J. Szanto,1,2 E. Vandervoort,1,3 J. Doody,2 E. Henderson,2 S.C. Morgan,2 J. O’Sullivan,3 and S. Malone2; 1The University of Ottawa, Ottawa, ON, Canada, 2The Ottawa Hospital Cancer Centre, Ottawa, ON, Canada, 3The Ottawa Hospital, Ottawa, ON, Canada Purpose/Objective(s): SBRT is an established technique for treating prostate cancer. Robotic SBRT requires implantation of fiducial markers for target tracking. Fiducials must be easily identified on images used for
treatment planning and by the orthogonal KV X-ray imaging system. The spatial distribution of fiducials must allow accurate calculation of a 3D transformation that describes the position of the prostate within the reference frame of the planning CT scan. When we began our robotic prostate SBRT program, we were unable to accurately perform 3D tracking in 23% of patients. As a result we developed a modified fiducial implantation protocol. Materials/Methods: 54 patients with prostate adenocarcinoma were treated with robotic SBRT. For treatment planning purposes, CT planning scans were accurately co-registered to T1 weighted gradient echo and T2 weighted turbo spin echo MR image sequences using transrectally implanted platinum fiducial markers. Due to differences in magnetic susceptibility, platinum markers are better visualized on MRI than gold. For the first 26 patients, fiducials were implanted under ultrasound guidance according to the manufacturer’s fiducial placement guidelines (cohort 1). Unfortunately our initial tracking error rate was high (23%). In Oct 2016 we developed a more rigorous protocol and treated a second cohort of patients accordingly (cohort 2, 28 patients). In the protocol, 4 platinum fiducials were implanted in the postero-lateral peripheral zone in a single coronal plane. Results: In cohort 1, patients had a mean age of 64 years (50 - 74), PSA of 6.6mcg/L (1.1 e 14.7), and prostate volume of 56cc (22 - 125), while in cohort 2 they had a mean age of 65 years (53 - 75), PSA of 6.2 mcg/L (1 12) and prostate volume of 47cc (21 - 106). In all 54 patients’ fiducials were easily visualized and there were no cases of urosepsis related to fiducial implantation. In 6 of 26 patients (23%) from cohort 1 only translational mapping without accurate spatial rotations could be calculated. Accurate 3D tracking (accounting for translations and rotations) was possible in all 28 patients from the protocol group. Conclusion: Adopting a formal fiducial placement protocol improved our ability to identify the position of the prostate during the treatment in the CT planning frame from 77% to 100% reliability. Author Disclosure: O.E. Holmes: None. J. Gratton: None. J. Szanto: None. E. Vandervoort: None. J. Doody: None. E. Henderson: None. S.C. Morgan: Independent Contractor; The Ottawa Hospital Cancer Centre. Honoraria; Amgen, Bayer Healthcare, Janssen, Sanofi. Advisory Board; Bayer Healthcare, Janssen. J. O’Sullivan: None. S. Malone: None.
2574 Racial Comparisons of Prostate Cancer Outcomes in a Unique Military Patient Population Post-Definitive External Beam Radiation Therapy A.R. Horn,1 J.R. Bear,1 D. Brown,2 A.R. Chaurasia,1 A. Gutweiler,3 J.D. Kehrer,3 R.K. Takesuye,3 and H.B. Wilds3; 1Walter Reed National Military Medical Center, Bethesda, MD, 2University of Texas, Austin, TX, 3 Naval Medical Center San Diego, San Diego, CA Purpose/Objective(s): The United States military represents a unique patient population to study prostate cancer outcomes due to a large percentage of minorities, increased level of fitness and universal access to care. We analyzed our military institutional prostate cancer outcomes in a young cohort after definitive external beam radiation therapy, and observed better than expected biochemical free survival (BFS) and overall survival (OS) outcomes for minorities, compared to historical controls. Minority outcomes were also equivalent to outcomes of Caucasians in our cohort. Materials/Methods: Patients who received definitive external beam radiation therapy (EBRT) were eligible (1995-2012). 120 patients with a median age of 63 were included in our cohort. 57% of patients were Caucasian, 43% were minorities including 23% African-American patients. Hazard ratios (HR) and 95% confidence intervals (95% CI) were used to assess the association between OS and BFS among racial groups (Caucasian, African American/Other) stratified by NCCN risk groups (low, intermediate, high). Results: Patients in the high and intermediate risk groups had a higher risk of 10-year PSA failure compared to subjects in the low risk group (HRZ10.93, 95% CIZ2.32-51.61; HRZ4.95, 95% CIZ1.03-23.85, respectively). Patients in the high risk group had an increased risk of death compared to patients in the low risk group (HRZ2.84, 95%
