Session Item

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.

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.

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.

HA hydrogel used as a tumour bed marker reduces inter- and intraobserver variability of BT boost target volume delineations. The study has proven, that the delineation variability results in D90 and V100 parameters falling below the recommended threshold. However marking the tumour bed with HA hydrogel minimized the reduction of impact on those parameters comparing to the control group.