Abstract Book

ESTRO 37

S577

sparing devices. Results with and without hydrogel spacer implantation were as follows: D 1cc was 7.96±0.22 Gy and 8.43±0.40 Gy, respectively; and the maximum dose to the rectum was 13.50±0.30 Gy and 11.90±0.55 Gy, respectively. Reduction in maximum dose (p < 0.001) and D 1cc (p = 0.046)) to the rectum is observed in cases implementing the hydrogel rectal spacer. Considering a typical HDR prostate brachytherapy dose prescription of 27.0 Gy (two 13.5 Gy fractions) and an α/β = 3.0 for rectum, the average maximum EQD2 point dose for patients receiving hydrogel implants was 59.74±2.79 Gy compared to 71.92±2.36 Gy (p < 0.001) for those treated without the device. Conclusion DVH analysis for the patient sampling with hydrogel implantation demonstrated statistically significant reduction in D max and D 1cc metrics. When compared to plans without hydrogel implants, the average EQD2 of the max point dose to rectum for patients receiving hydrogel implants was lower and fell within the TD5/5 of 60 Gy, as recommended by Emami et al. Future clinical evaluation of these patients may allow for a statistical relationship between the observed dose reduction and clinical toxicity. PO-1028 Acute urinary retention and hematuria in prostate cancer patients treated with HDR-BT L.C. Mendez 1 , A. Ravi 2 , C.L. Tseng 1 , H. Chung 1 , M. Paudel 2 , M. Wronski 2 , M. Davidson 2 , A. Loblaw 1 , G. Morton 1 1 Odette Cancer Centre - University of Toronto, Radiation Oncology, Toronto, Canada 2 Odette Cancer Centre - University of Toronto, Medical Physics, Toronto, Canada Purpose or Objective To study first month post-procedural urinary retention and hematuria in prostate cancer patients treated with 15Gy high dose rate brachytherapy (HDR-BT). Material and Methods Patients treated with 15Gy HDR-BT followed by external beam radiation therapy (EBRT) were evaluated in this unmatched case-control study. All patients had intermediate or high-risk prostate cancer and received HDR-BT and EBRT at Sunnybrook-Odette Cancer Centre (Toronto, Canada) with over one month of post- procedure follow up time. Urinary retention and hematuria requiring catheterization were retrospectively collected together with time to event (from procedure date) and length of Foley catheter use. Clinical characteristics (age, baseline PSA, clinical stage, Gleason score, International Prostate Symptom Score (IPSS), use of androgen deprivation therapy (ADT), alpha-blocker, 5α-reductase inhibitor) and treatment specifications (number of afterloading catheters, prostate V100, V150, V200, D90, urethra DMax and D10) were also obtained. Variables were described with appropriate measures of central tendency and dispersion. Univariate and multivariate binary logistic regression analysis were used to determine predictors of post-BT complications. Statistics was performed in STATA 13.0 and a p-value < 0.05 was considered statistically significant. Results 400 patients treated with 15Gy HDR-BT were collected, but only 224 were included in this analysis as 176 received EBRT outside of the institution. Patients clinical and treatment characteristics are shown in Table 1. In total, 22 patients (9.8%) required catheter placement due to acute urinary retention in a median time to catheter

insertion of 2 days (ITQ: 0-2). Ten other patients (4.4%) developed hematuria requiring urinary catheter insertion ± continuous bladder irrigation. Except for one, all patients with hematuria were catheterized on the day of the procedure. Total median time with urinary catheter was 3 days (ITQ: 2-55). Prior use of ADT, alpha-blockers or 5α-reductase inhibitors was statistically associated with urinary retention in the univariate logistic regression analysis. Odds ratio and p-value are shown in Table 2. In multivariate analysis, only use of alpha-blocker remained significant (OR: 3.86, p=0.01) for urinary retention, with ADT showing a tendency for significance (OR: 2.89, p=0.053).

Conclusion The rate of acute urinary retention and hematuria post HDR-BT was approximately 10% and 4%, respectively. Previous use of alpha-blocker was found to associate with urinary retention and likely reflects the higher degree of obstructive urinary function in this population. IPSS was not found to be a predictor, however only 130 patients (58%) had IPSS reported and the score value registered may be confounded by concomitant use of alpha- blockers. Neo-adjuvant ADT may independently associate with urinary retention post-BT.

Poster: Brachytherapy: Anorectal

PO-1029 Contact x-ray brachytherapy for rectal cancer following chemoradiotherapy is cost-effective C. Rao 1,2 , F.M. Smith 3 , A.P. Martin 4 , A.S. Dhadda 5 , A. Stewart 6 , S. Gollins 7 , B. Collins 8 , T. Athanasiou 1 , A. Sun Myint 9 1 Imperial College London, Department of Surgery and Cancer, London, United Kingdom