equivalents (EQD2) for bladder and rectum were calculated using a prescription of 4Gy x 6 fractions with a/b of 3. Results: Five plans were evaluated from 5 patients with vaginal cancer (2) and endometrial cancer (3) with gross vaginal cuff recurrences. Each patient was planned with separate plans representing each individual insertion. The average GTV and PTV taken from the 14 plans was 5.00 cm 3 and 6.30 cm 3 , respectively with a PTV average depth of 1.1 cm. The median number of loaded catheters used in each optimized plan was 3 (range, 2-4 catheters). The average D99, D95 to PTV for all plans was 3.89 Gy and 3.92 Gy, respectively. Average D2cm 3 to bladder was 3.02 Gy (range 1.01- 4.36 Gy), and average D2cm 3 to rectum was 3.22 Gy (range 2.23-5.08 Gy). The average maximum dose to ipsilateral vaginal mucosa was 12.79 Gy (range 2.04- 33.0 Gy,) while the average maximum dose to the contralateral vaginal mucosa was 9.8 Gy (range 0.99 Gy- 7.46 Gy.) Average EQD2 total for 45 Gy external beam and 6 fractions of 4 Gy for bladder and rectum was 67.5 Gy and 69.5 Gy, respectively. Conclusions: Although ABS Consensus Guidelines for vaginal cancer suggest that lesions with a thickness exceeding 5 mm cannot be adequately treated with a vaginal cylinder, we demonstrate that with the Multichannel Balloon Capri TM applicator, PTV depths averaging 1cm from vaginal surface were able to be prescribed using a multicatheter approach with clinically acceptable bladder, rectal and vaginal doses. Preliminary data suggests that the use of the Multicatheter Capri TM applicator may be an alternative approach to using an interstitial implant for selected patients with small vaginal recurrences located at the rectovaginal septum, however, a larger cohort of patients with long-term follow-up is required to assess long-term clinical outcomes using this technical approach. Figure 1. PTV in red shown with fiducial markers located on right lateral vaginal wall for patient treated with Capri TM multichannel vaginal appli- cator demonstrating 100% isodose line of 4 Gy in yellow, and the rectum and bladder contoured in green and orange, respectively. PO19 Acute Catheter Complications from Perineal Interstitial Brachytherapy (ISBT) in Gynecological Cancer Patients: A Prospective Analysis of Organ Injury, Infections and Radiological Needle Intrusions Eric Leung, MD 1 , Lucas Mendez, MD 1 , Pencilla Lang, MD 1 , Laura D’Alimonte, MRT(T) 1 , Adam Gladwish, MD 1 , David D’Souza, MD 2 , Chirag Patel, MD 1 , Lisa Barbera, MD 1 . 1 Sunnybrook Health Sciences Centre, Odette Cancer Centre, Toronto, ON, Canada; 2 London Health Sciences Centre, London, ON, Canada. Purpose: Interstitial Brachytherapy (ISBT) is an effective component in the treatment of gynecological cancers due to its ability to achieve highly conformal doses of radiation to the target. However, there are concerns of potential acute complications from this technique due to the apparent invasiveness of interstitial catheter needles. As a result, ISBT has yet to be widely adopted in radiation oncology centres. The goal of this study is to evaluate the safety of ISBT applicator implantations by studying the acute complications and radiological organ needle intrusions in patients treated with the perineal template technique. Materials and Methods: 49 patients at a single institution treated with high-dose rate perineal ISBT from September 2014 to April 2016 were included in a prospective registry trial. Median age of patients was 65 with a total of 16 cervical cancer patients, 13 vaginal, 13 recurrent endometrial, 2 vulva and 3 others. ISBT insertions were performed using a perineal template with a clinically-guided technique (no real-time imaging). Post-procedure, patients underwent CT or MRI with no attempt to adjust needle depth or positioning after review of images. Post- operative adverse events were graded with CTCAE V3.0 during inpatient stay and at the 6-week follow-up visit. CT planning images were independently reviewed by two radiation oncology trainees to record the number of needles intruded into organs. Discrepancies were resolved by a board-certified radiologist. Results: Median follow-up time was 3 months. 42 patients were initially treated with external beam radiation therapy to the pelvis with a dose of 45 Gy (median). A total of 76 applicator insertions were performed; 22 patients received 1 implant while 27 had two. The median number of needles used for each insertion was 17 and 19 respectively; 28 patients had radiological evidence of needle intrusion(s) to at least one pelvic organ. From the 76 insertions, the most commonly intruded organs were bladder (18 needles) followed by bowel (15) and rectum (12). A total of 9 acute toxicities could be attributable to interstitial needles; 4 patients developed hematuria during inpatient stay (2 G1, 2 G2) while no gastrointestinal complications were found. 4 patients developed perineal infections post-procedure (3 G2, 1 G1); 1 patient had vaginal bleeding requiring transfusion. Conclusions: Perineal ISBT is an effective treatment for locally-advanced gynecological cancers. Despite occasional observed radiological catheter intrusions, there are low rates of organ complications from this procedure. No acute bowel injury from needles were found in any patients. Concern of needle complications from ISBT should not be a barrier to adopting this technique for effective treatment of locally advanced tumors. PO20 Feasibility Study of Toxicity Outcomes Using GEC- ESTRO Contouring Guidelines on CT Based Instead of MRI-Based Planning in Locally Advanced Cervical Cancer Patients Johann I. Tang, MBBS, FRANZCR 1 , Vicky Koh, MBBS, FRANZCR 1 , Teng Hwee Tan, MBBS, FRANZCR 1 , Bok Ai Choo, MBBS, FRCR 1 , Jeffery Low, MBBS, FRCS 2 . 1 Radiation Oncology, National Cancer Institute Singapore, Singapore, Singapore; 2 Gynaeoncology, National Cancer Institute Singapore, Singapore, Singapore. Purpose: To report late rectal and bladder toxicity outcomes of a CT-based image-guided brachytherapy (IGBT) technique for treatment of cervical cancer. Materials and Methods: Between 2008 and 2014, 95 women with International Federation of Gynecology and Obstetrics stage IB to IVA cervical carcinoma treated with definitive concurrent cisplatin-based chemotherapy and external beam radiation therapy 50.4 Gy in 28 fractions followed by planned prescription dose of 7 Gy  4 fractions of high-dose-rate IGBT was retrospectively reviewed. At each implantation, all patients had a urinary catheter in situ and received bowel enema before undergoing planning CT simulation. A high-risk clinical target volume (HRCTV) as per GEC-ESTRO guidelines and the entire cervix, rectum, and bladder was contoured on the simulation CT according to Radiation Therapy Oncology Group Gynaecology Contouring Atlas. Reported doses to HRCTV and organs at risk were recorded. Toxicities S74 Abstracts / Brachytherapy 16 (2017) S14eS118