Abstract Book

ESTRO 37

S570

Table 1. Mean and range (standard deviation) of the biologically equivalent dose (EQD2) for each dose point of one representative patient treatment.

manner, rays were generated from the centroid of the contour at evenly spaced 5° intervals. The dose points were defined at the intersection between rays emanating from the centroid, and the vaginal contour border. Dose maps were generated for each of the four brachytherapy fractions, followed by a summation of both brachytherapy and external beam radiotherapy using conversion to 2 Gy equivalent doses with an α/β-ratio of 3 Gy for the vagina. A parameter for toxicity prediction was extracted from the dose-surface maps and tested on the reported vaginal toxicity.

Results A method for generating dose-surface maps for the vagina has successfully been developed. It allows for the summation of all brachytherapy fractions and external beam radiotherapy fractions, giving a total image of the dose distribution in the vagina. Figure 2 shows the vaginal dose-map for brachytherapy fraction 1 for one of the patients. From these dose maps extensive quantitative information can be extracted and related to reported toxicity following radiotherapy of cervical cancer. A parameter for correlation to the toxicity was suggested, where the toxicity scores for the patients were correlated to the extent of the high-dose areas in the total dose-surface maps. No clear correlation was found for the included patients. In the future, other quantitative information from the dose-maps should be tested against reported vaginal toxicity from a larger patient cohort.

Conclusion Interobserver variability proved difficulty in reporting the vaginal dose points, especially in the PIB S+2cm, when these are close to active positions. PO-1018 Dose-surface maps as a tool to predict toxicity after radiotherapy for cervical cancer patients I.H. Grimstad 1 , M.R. Arnesen 1 , K. Bruheim 2 , E. Malinen 1,3 , T.P. Hellebust 1,3 1 Oslo University Hospital, Department of Medical Physics, Oslo, Norway 2 Oslo University Hospital, Department of Oncology, Oslo, Norway 3 University of Oslo, Department of Physics, Oslo, Norway Purpose or Objective Over the last decade, advances in image-guided radiotherapy have improved local control and survival of cervical cancer patients. In spite of improved treatment, quality of life studies point to vaginal morbidity and associated sexual dysfunction as important causes of long-term distress for cervical cancer survivors. However, proper methods for assessing the delivered dose to the vagina are lacking. Dose-surface mapping (DSM) is a tool for analyzing the dose distribution in hollow tube-like structures, including volumetric and topographic information. This study aims to develop a tool for producing dose-surface-maps for the vagina of patients treated for cervical cancer, and to test the tool and correlate it to toxicity scores for 10 cervical cancer patients. Material and Methods The method for generating dose-surface maps was developed using Interactive Data Language (IDL), and the concept is illustrated in Figure 1. This tool was tested on ten cervical cancer patients from the EMBRACE study which have all been successfully treated using brachytherapy and external beam radiotherapy. The vaginal contour was delineated. Then, in a slice by slice

Conclusion