ESTRO 36 Abstract Book

S968 ESTRO 36 2017 _______________________________________________________________________________________________

evaluations were performed. The maximum doses received by the rectum wall, bladder wall, bowels and PTV were analyzed and traced over the five fractions to determine the total dose distribution over the entire prescribed treatment. Results No contour of any of the OAR was exactly similar when CT images were fused to each other. Depending on the depth of the insertion the PTV varied minimally. Each plan was performed independently and cumulated 2 at a time until all 5 fractions were added to the initial fraction. There is a difference between the doses received by the OARs between treatments and between the points of maximum does. The PTV volumes vary from fraction to fraction. The maximum dose varied between 12% and 27% in rectum wall and bladder wall. The minimum dose varied between 2% and 7% in rectum wall and bladder wall. The average dose varied between 9% and 21% in rectum wall and bladder wall. The cumulative treatment does do not indicate a total maximum dose exceeding the tolerances for the rectum and bladder. Conclusion The variation in volumes of OARs and isodoses near the OARs, indicate that the estimated doses to OARs on the planning system may not be the same dose delivered to the patient in all the fractions. There are no major differences between the prescribed dose and the delivered dose over the total number of fractions. Variation in the length of the cylinder part implanted into the vagina and PTV's coverage indicates an inconsistency in the entire vaginal cuff in all five fractions. In some cases, the critical organs will benefit if the consecutive plans will be made after the CT scans are registered with the initial. All the cases studied indicate the need for more detailed study in order to establish a protocol of planning. EP-1788 HDR vs LDR Vaginal brachytherapy: a comparison in terms of outcomes and toxicity R. Autorino 1 , D. Smaniotto 1 , M. Campitelli 1 , L. Tagliaferri 1 , A. Nardangeli 1 , G. Mattiucci 1 , A. Martino 1 , N. Di Napoli 1 , G. Ferrandina 2 , M. Gambacorta 1 , V. Valentini 1 1 Polyclinic University A. Gemelli- Catholic University, Institute of Radiotherapy, Rome, Italy 2 Polyclinic University A. Gemelli- Catholic University, Institute of Oncological Gynecology, Rome, Italy Purpose or Objective To compare the outcomes in terms of survival and toxicity for endometrial carcinoma patients treated with either HDR or LDR vaginal brachytherapy (VBT) after external beam radiotherapy Material and Methods From January 2000 to December 2014, patients with endometrial cancer after radical hysterectomy +/- pelvic and/or lombo-aortic lymphadenectomy were treated with adjuvant radiotherapy (45 Gy, 1.8 Gy/day on the whole pelvis) and subsequential VBT boost (HDR dose was 7 Gy in one fraction prescribed to 0.5 cm from the surface of the applicator; LDR dose was 25 Gy to the vaginal mucosa). The outcomes of patients were evaluated in terms of local control (LC), overall survival (OS) and toxicity (according to CTCAE v 4.0). Results We retrospectively analyzed 200 patients treated with external beam radiation therapy followed by a HDR VBT boost in 78 patients and LDR VBT boost in 122 patients. Patients characteristics are summarized in Table 1.With a median follow-up of 25 months (range 1-163), 5-ys overall suvival (OS) was 98% vs 97% in LDR and HDR group respectively (p=0.37) and 5-ys local control (LC) was 93%, similar in the two groups (p=0.81).At multivariate analyses, any factors (age, stage, grading) seems to have impact on OS (p=0.37) and LC (p=0.81). Patients treated with LDR VBT after external beam radiotherapy had an higher gastrointestinal acute toxicty; probably, this is due

to development of radiation tecnique over the years of this study. No differences was found in terms of acute genitourinary and hematological toxicity. Late toxicity such as vaginal stenosis was registered during regular follow-up visit by clinical evaluation. We didn’t find statistically significant differences between the two modalities (p=0.67). Conclusion With the limits of a restrospective review, there were no differences in survival and late toxicity outcomes for patients receiving LDR or HDR brachytherapy. HDR is safe technique in comparison to LDR modality. A larger database analysis will confirm outcomes and toxicity of HDR VBT in postoperative endometrial cancer. EP-1789 Comparison between MRI based 3D IGABT planning versus standardised BT planning of cervical cancer M. Hedetoft 1 1 Skåne University Hospital, Department of Radiation Physics, Lund, Sweden Purpose or Objective The aim of this study was to investigate if the introduction of MRI based Image Guided Adapted Brachy Therapy (IGABT) treatment planning of cervical cancer in our hospital, has improved the target coverage and reduced the dose to Organs at Risk (OAR) in comparison to standard treatment planning with point A dose prescription. Material and Methods In February 2014 the first brachytherapy treatment of a cervical cancer patient planned with MRI based 3D IGABT technique, was undertaken in Lund. Until the end of August 2016, 38 patients have been treated with this technique resulting in 142 fractions, all of them included in this study. The tumour stages of the patients included were IB1 (n=5), IB2 (n=5), IIA (n=7), IIB (n=16), IIIB (n=5). Each patient received external beam radiation therapy and 2 or 4 brachytherapy fractions depending on the tumour stage. For brachytherapy treatments the interstitial titanium ring and tandem applicator (Varian Medical Systems) were used. To be able to choose if an interstitial treatment would improve the tumour coverage a pre-plan was always done. 21 patients were selected for intracavitary/interstitial implant and 17 for intracavitary implant only. Based on the MRI target volumes, GTV, HR-CTV, IR-CTV and OARs (bladder, rectum, sigmoid and bowel) were contoured according to GEC-ESTRO recommendations. The dwell times were optimised for each fraction, 6.5 Gy/fr and the plans were evaluated according to DVH criteria from the EMBRACE II study. For all fractions the optimised 3D plan was compared to a 2D plan with standardised dwell times, the same pre-plan that was used for patient treatments before starting with the IGABT. The standard plan was based on the same MR images, target volumes and OARs as in the optimised plan. The DVH criteria used for evaluation were EQD2 D 90 for HR- CTV, D 2cm³ for rectum, D 2cm³ for bladder, D 2cm³ for sigmoid and D 2cm³ for bowel. Results All HR-CTVs with volumes <40cm 3 were covered with >90Gy EQD2 for the standard as well as the optimised plans. For 10 patients the standard plan coverage even exceeded 100Gy EQD2. In the optimised plans the dose to OAR could be decreased for 17 patients while still maintaining the target coverage . For larger tumours, HR-CTV >40cm 3 , the dose coverage decreased with standard plans while the optimised plans maintained excellent dose coverage for all plans. With optimisation a good target coverage was obtained at the cost of an increased but acceptable OAR dose. Conclusion In comparison to standardised plans, MRI-based 3D IGABT planning substantially improved target coverage for larger