were considered. FIGO stage distribution was the following: 4 had stage IB, 33 had IIB (7 out of 33 with distal parametrial invasion), 7 had IIIB tumors (all because parametrial invasion up to pelvic wall) and 1 had IVA tumor. Treatment consisted in 3DCRT (45 Gy in 25 fr.) with concomitant chemotherapy (weekly cisplatin 40 mg m2) followed by MR/CT based IGABT (4 fractions of 7 Gy within 2 insertion with 1 week interval with Elekta Utrecht applicator). A stringent bladder filling and bowel

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... ation protocol is routinely used at our institution. At 1 st application, T2 MRI and i.v. contrasted CT (day 1 CT) with applicator in place were performed with an interval of 30 min (MR slice thickness 3,5 mm without gaps; CT thickness 2mm). Direct applicator reconstruction on MR images was performed and dose optimized to target volumes and OAR delineated on MR according GEC ESTRO recommendations. After patient treatment, original MR and CT datasets were fused based on the applicator coordinates and HRCTV contours from MR dataset transferred to CT. Further OARs were re-delineated on day 1 CT, applicator reconstructed and the original MR optimized plan recalculated on CT images. DVH parameters for OAR delineated on day1 CT were recorded (Intrafraction variability). On the following day, a second CT was performed (2mm slice thickness). Furthermore day 2 CT was fused with the day 1 CT on the applicator coordinates and the original MR based HRCTV contours (present on CT day 1) transferred from day 1 CT to day 2 CT. OAR were then delineated on day 2 CT and the original MR optimized plan recalculated on CT day 2 images. DVH parameters for OAR delineated on day 2 CT were recorded (interfraction variability). We assume in our study design that intra-fraction variability is predominantly due to systematic contouring uncertainties introduced by OAR delineation on different imaging modalities and less importantly by eventual OAR movements. We expect that interfraction variability to be of higher magnitude and predominantly due to OAR movements. Results: Results are summarized in Tab 1. The magnitude of intra-and inter-fraction variability is very low probably with no clinical relevance in the vast majority of patients. Intraand inter-fraction HRCTV and OAR variability is similar. Conclusions: Presented data together with previously published reports from Lang S. et al. (R&O 2013) seems to suggest that, in a protocol of four fractions within 2 different applications no re-planning is needed to safely deliver the second BT fraction of each application if an OAR filling protocol is applied. Nevertheless before applying this concept in the clinical routine more data are warranted. Purpose/Objective: To review doses achieved in the treatment of locally advanced cervical cancer at the Northern Ireland Cancer Centre compared to standards set by GEC-ESTRO since the introduction of image guided high dose rate brachytherapy. To compare outcomes both in terms of recurrence and survival and long term toxicity with published outcomes. Materials and Methods: Retrospective review of clinical notes and radiotherapy prescriptions of all patients with locally advanced cervical ca treated at the Northern Ireland Cancer Centre from 2008-2013. Results: 188 patients with locally advanced cervical cancer were treated with radical intent with a median age 47.4 years (23.3 -79.80.4). Median follow up is 25.5 months. 180/188 had concurrent cisplatin. CT scanning was carried out after each intra-cavity insertion and used to contour OAR and to identify Point A. Equivalent doses in 2Gy fractions (EQD2) were calculated combining external beam radiotherapy and brachytherapy doses. αβ 10 was used for tumour and αβ3 used for organs at risk. Median dose to point A EQD2 was 76.4Gy (66.5-79.3) with 68 patients receiving less than <75Gy. Median dose to rectum was 65.5Gy (57.2-82.6)with 3 patients receiving more than 75Gy.Median dose to bowel was70.7Gy (55.5-79.2) with 26 patients receiving over 75Gy.Median dose to bladder was 80.5Gy (551-97.8) with 3 receiving greater than 95Gy. Pelvic recurrence at 3 years was 12.2% with distant metastasis 8.5% . Overall Survival (OS) at 3years was 74%. There was a documented pelvic or distant recurrence at 3years in 30.8% of node positive patients and 9.45% of node negative patients(p=0.005). Grade 3/4 late bowel and bladder toxicity of 7.9 and 6.3% respectively were documented. There were no significant differences in dose delivered in those patients who developed bladder or bowel toxity compared to those who did not. Mean dose to bowel in those who had Grade 3/4 toxicity was 71.2Gy and 70.0Gy without (p=0.20). Mean dose to bladder in those with GD3/4 bladder toxicity was78.9Gy and 79.6Gy without (p=0.81). Repeat MRI in the final week of radiotherapy was introduced in 2010 and performed in 97 patients. In those who had a complete response at final week MRI (30) there was 1 pelvic recurrence compared to 22 pelvic recurrences in those who had partial response or stable disease(77) (p=.0035).