Abstract Book

ESTRO 37

S571

Based on the created total dose-surface maps it is feasible to extract quantitative dose parameters which can be used to assess if there is a correlation between vaginal toxicity and these parameters. For the patients of this study no clear correlation was found between the width of the high-dose areas of the dose-maps and the reported toxicity .

months had an impact on the local control rate (p < 0.01). Conclusion The results of HDR Interstitial brachytherapy have shown an acceptable local control and overall survival rates along with tolerable toxicities and morbidity in recurrent H&N cancers. Based on these encouraging results, prospective clinical trials are warranted using HDR Interstitial Brachytherapy in recurrent H&N cancers to decrease late toxicity.

Poster: Brachytherapy: Head and neck

Poster: Brachytherapy: Physics

PO-1019 HDR Interstitial brachytherapy in Recurrent head and neck cancer: An effective Salvage option V. Pareek 1 , R. Bhalavat 1 , M. Chandra 1 , P. Nandakumar 2 , P. Bauskar 2 , L. Nellore 1 1 Jupiter Hospital, Radiation Oncology, Mumbai, India 2 Jupiter Hospital, Radiation Physics, Mumbai, India Purpose or Objective High Dose Rate (HDR) Interstitial Brachytherapy has an established role in head and neck malignancies and offers good survival rates, however, there are scant data on improved local control (LC) and treatment-related complications in patients with recurrent head and neck (H&N) cancers. We present our results in patients with recurrent H&N cancers treated with interstitial HDRBT in terms of survival and toxicity outcomes and also assess the prognostic factors associated with reirradiation with HDR Brachytherapy. Material and Methods A total of 30 patients with recurrent H&N cancers were treated with HDR interstitial brachytherapy between January 2010 and December 2016. Primarily, 6 had received EBRT alone, 6 had underwent surgery alone and 13 had both the treatment modalities received. Of these, 75% received radical brachytherapy and 25% received external beam radiation therapy (EBRT) followed by brachytherapy boost. The treatment sites were oral cavity (18/30) and oropharynx (12/25). The median dose was 4.5 Gy twice per day with median total dose with brachytherapy of 40.5Gy in radical and 27Gy for EBRT cases. The EBRT median total was 46Gy. HDR Interstitial Brachytherapy was initiated from next day of implant and after removal of the catheters, the patients were followed up as per the institutional protocol and were assessed for survival outcomes and toxicities. Results With a median follow-up of 25 months, 4 local recurrences were observed within first year of follow up after the procedure. The 2-year local control and overall survival outcomes for the entire group were 58.3% and 83.3%, respectively. The 4-year disease free survival was 50% and distant metastases was seen in 33.3% at 5 years. The dosimetric assessment revealed D90 – 4.07Gy, V100 – 90.3%, V150 – 23.7% and V200 – 12.5%. Homogeneity index and Dose Non Uniformity Ratio were 0.71 and 0.37 respectively. Mean interval between the EBRT and Brachytherapy was 16 days. Median implant volume was 85 cc. On toxicity assessment, xerostomia, altered taste and dysphagia was seen as major complications albeit in grade I and II. Grade III toxicity was only 2% and no Grade IV Toxicity was seen. BED and EQD2 of 44Gy and 38Gy respectively were significant in preventing late toxicities and improve the survival outcomes. Pre-treatment volume >85 cc had a negative impact on the overall survival (26 months vs 12 months; p = 0.02) and time interval between primary and recurrence more than 15

PO-1020 Better plans and easy plan selection via bi- objective optimization for HDR prostate brachytherapy S.C. Maree 1 , E.S. Kooreman 1 , N.H. Luong 2 , N. Van Wieringen 1 , A. Bel 1 , E.C.M. Rodenburg 1 , K.A. Hinnen 1 , G.H. Westerveld 1 , B.R. Pieters 1 , P.A.N. Bosman 2 , T. Alderliesten 1 1 Academic Medical Center, Radiation oncology, Amsterdam, The Netherlands 2 Centrum Wiskunde & Informatica, Amsterdam, The Netherlands Purpose or Objective In treatment planning for HDR prostate brachytherapy (BT), the trade-off between dose to the target volumes and dose to the organs at risk (OARs) is optimized. To achieve this with a traditional planning method (e.g., IPSA, HIPO), its parameters must be tuned iteratively. In our clinic, the plan is manually fine-tuned further using graphical optimization. These approaches are patient- dependent, require experience, and may lead to sub- optimal plans under clinical time pressure. Resulting plans are evaluated by the dose-volume indices (DVIs) of the clinical protocol, but also by visual inspection of the dose distribution. In this work, we analysed clinical planning sessions to formulate a bi-objective optimization model from which multiple plans follow that exemplify the trade-offs in treatment planning, and validated its usage by an observer study. Material and Methods HDR BT plan optimization sessions of 5 prostate cancer patients were filmed and changes in DVIs over time were recorded. After studying these recordings, a bi-objective optimization model was formulated that directly considers the DVIs of the clinical protocol. A coverage objective (i.e., least coverage index ) was formed from the criteria on the target volumes, and a sparing objective (i.e., least sparing index ) from the criteria on the OARs (Table 1). The clinical protocol is satisfied when both have a value >0. A recent multi-objective evolutionary algorithm (MOEA) was tailored to generate a large set of plans, a Pareto front , representing different high-quality trade-offs between coverage and sparing. The planning process is thereby intuitively facilitated without the need of parameter tuning. Finally, the clinical plan and 5 plans selected from the Pareto front (Fig.1b) were blindly presented to 1 BT technician and 3 brachytherapists in a retrospective observer study. Each observer was asked to select the best and worst plan.