ESTRO 37 Abstract book

ESTRO 37

S569

Investigacion en Radiofisica e Instrumentacion Nuclear en Medicina IRIMED, Valencia, Spain

50%, 70%, 94% and 85% for patient 1-5 respectively), whereas the mean CTV HR _TRUS-CT volume was only 15% larger than the MRIref volume (14%, 9%, 28%, 20% and 5% for patient 1-5 respectively) (figure 1).

Purpose or Objective EMBRACE-II recommended reporting vaginal dose points in high-dose-rate brachytherapy (HDRBT) and external beam radiotherapy (EBRT) in cervical cancer treatments. This study aims to evaluate the robustness of these dose points according to interobserver analysis. Material and Methods The vaginal dose points of five cervical cancer patients treated with HDRBT and EBRT were evaluated by 5- blinded medical physicists from the same center. The planning images were MR and CT images for HDRBT and EBRT, respectively. A consensus was previously established by all observers to determine the anatomical references criteria. The vaginal point in Posterior-Inferior Border of Symphysis (PIBS), PIBS+2cm and PIBS–2cm in the caniocaudal direction dose points were obtained for HDRBT and EBRT (Figure 1). Also, the vaginal top dose points were evaluated for HDRBT treatments (Figure 1). The mean, range and standard deviation for these dose points were evaluated for each of the 5 observers. The interobserver variation was assessed by coefficient of variation (COV). The effect of interobserver variation in the total dose (HDRBT+EBRT) recorded was analyzed by estimating the biologically equivalent dose (EQD 2α/β =3), based on two nominal 7 Gy cervical HDRBT plans (two fractions per plan) and 45 Gy cervical EBRT plan. Figure 1. Vaginal dose points: (a) PIBS, PIBS+2cm and PIBS-2cm in MR sagittal image for HDRBT treatment, (b) Vaginal top points in MR axial image for HDR treatment, (c) PIBS, PIBS+2cm and PIBS-2cm in CT sagittal image for EBRT treatment.

Conclusion TRUS combined with CT as imaging modality for contouring the CTV HR in IGABT for LACC is feasible and is reproducible among multiple observers with an acceptable variation. Interobserver variability in comparison to the reference MRI volume is smaller than CT alone. Moreover, combined TRUS-CT substantially reduces the overestimation of the CTV HR volume of CT alone. A dosimetric analysis of the contouring variations is already in progress. PO-1017 Interobserver variability of vaginal dose points reporting in cervical cancer radiotherapy treatment B. Ibanez-Rosello 1 , M. Adria-Mora 1 , J. Vilanova-Ciscar 2 , V. Campo 3 , V. Carmona 1,4 , J. Gimeno-Olmos 1,4 , F. Lliso 1,4 , J. Perez-Calatayud 1,4 1 La Fe University and Polytechnic Hospital, Radiotherapy, Valencia, Spain 2 HGU Gregorio Marañón, Dosimetry and Radiation Protection, Madrid, Spain 3 Araba-Txarritxu Universitary Hospital, Medical Physics and Radiation Protection, Vitoria, Spain 4 IIS La Fe - Universitat de Valencia, Unidad Mixta de