ESTRO 2022 - Abstract Book

S559

Abstract book

ESTRO 2022

Conclusion Combining the FN and PG measurements effectively halved the required proton intensity. The presented results reflect an ideal detector and reconstruction setup: the next project milestone is to extend the work with reconstructed vertices including resolution effects.

Proffered Papers: Breast, rectum

OC-0629 The use of hyaluronic acid hydrogel as a tumour bed marker in breast cancer brachytherapy.

J. Wierci ń ska 1 , J. Winiecki 1 , A. Wronczewska 2 , A. Lebioda 3 , P. Rhone 4 , K. P ł awski 4 , R. Makarewicz 3

1 Oncology Center in Bydgoszcz, Medical Physics Department, Bydgoszcz, Poland; 2 Oncology Center in Bydgoszcz, Brachyterapy Department, Bydgoszcz, Poland; 3 Oncology Center in Bydgoszcz, Brachytherapy Department, Bydgoszcz, Poland; 4 Oncology Center in Bydgoszcz, Department of Breast Cancer and Reconstructive Surgery, Bydgoszcz, Poland Purpose or Objective To evaluate usefulness of hyaluronic acid (HA) hydrogel as a tumour bed marker in breast conserving therapy (BCT). To analyze inter- (Inter-OV) and intraobserver (Intra-OV) variability of contouring boost target volume (CTV boost) in brachytherapy (BT) and evaluate the impact of target volume delineation variability on dosimetric parameters in breast cancer BT. Materials and Methods 32 patients in the HA group and 30 patients in the control group with an early stage breast cancer were included in the study. During the surgery 1 to 3 ml of HA hydrogel was injected into breast to mark the tumour bed for every patient in the HA group. Moreover, surgical clips were placed underneath the lumpectomy cavity. Patients in the control group were marked only by metal markers. Three radiation oncologists delineated CTV boost twice for every patient. Three parameters were calculated to quantify contouring variability: coefficient of variation for volumes (COV V ), center of mass displacement (CoMd) and conformity index (CI). The dosimetric impact of contouring variability was determined by using an actual, executed treatment plan without any changes in dwell positions and dwell times for other CTV boost delineations and calculating DVH parameters for these structures. D90 and V100 parameters were chosen as a metric. Results The study showed decreased differences of the brachytherapy CTV boost planning. The mean COV V decreased in HA group comparing to control group from 0.26 to 0.17 for Inter-OV analysis and from 0.14 to 0.12 for Intra-OV analysis. The mean CoMd were 6.2 mm and 8.6 mm for Inter-OV calculations and 4.1 mm and 6.6 mm for Intra-OV in the HA and the control group respectively. The mean CI for Inter-OV improved from 0.51 to 0.58 and from 0.62 to 0.69 for Intra-OV in the control and HA group respectively. Applying dwell positions and times from original treatment plan to other CTVs boost resulted in reduction of D90 and V100 values below the plan acceptance requirements in both analyzed groups. However, the decrease in HA group was significantly smaller than in the control group, both for D90 (78,57% vs 67,60%) and V100 (77,37% vs 68,09%) for HA and the control group respectively.