ESTRO 37 Abstract book

ESTRO 37

S570

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 manner, rays were generated from the centroid of the contour at evenly spaced 5° intervals. The dose points

Results Interobserver COV for PIBS, PIBS+2cm and PIBS-2cm were 2.2%, 40.2% and 6.5%, respectively. Dose variability in PIBS+2cm could be due to the proximity to the active positions of the source in some HDRBT treatments cases. COV was very similar between the vaginal top dose points, which was around 15% in all of them. The highest interobserver dose point variation yielded a vaginal dose difference up to 24.3 Gy EQD2, without taking into account the PIBS+2cm where a very extreme difference resulted due to its proximity to the active length tandem. The mean of estimated intraobserver variation for the reported dose points was around 5%. The mean, minimum, maximum and dose difference received by the vaginal dose points for each parameter are shown in the Table 1. Table 1. Mean and range (standard deviation) of the biologically equivalent dose (EQD2) for each dose point of one representative patient treatment.