Effect of different bolus application methods on target dose in radiotherapy after radical mastectomy

To assess the impact of bolus addition methods on the target dose of radiotherapy following radical mastectomy for breast cancer.

Thirty patients who underwent radiotherapy after radical mastectomy between January and August 2023 were included in this study. Each patient underwent two CT scans: CT1 (no bolus) and CT2 (with bolus placed on the chest wall). Using the CT1 images, a virtual bolus was added to create a radiotherapy Plan1 that met clinical and dosimetric requirements. Plan2 was generated from the CT2 images with the added bolus, and Plan3 was derived by copying Plan1 to CT2 to simulate the dose distribution during treatment. Radiotherapy plans were developed using volumetric-modulated arc therapy (VMAT) and intensity-modulated radiotherapy (IMRT) techniques. The dosimetric parameters for the target volume and organs at risk (OAR) were analyzed for each plan.

Statistically significant differences were observed in the homogeneity index (HI) and conformity index (CI) of the target volume when comparing Plan3 to Plan1 and Plan2 in both VMAT and IMRT plans (P < 0.05). Additionally, significant differences in V_107%, CI, and monitor units were found when comparing VMAT to IMRT across all three plans (P < 0.05). No significant differences in OAR doses were found with the VMAT plan. However, the IMRT plan showed significant differences in heart V₃₀ between Plan1 and Plan2 and Plan3 (P < 0.05). Significant differences were also observed between VMAT and IMRT for lung V₅, lung V₃₀, esophagus D_mean, humeral head D_mean, and uninjured breast D_mean across all three plans (P < 0.05).

The addition of a bolus during radiotherapy planning provides a more accurate reflection of the dose distribution in the target area and the dose received by OARs. The VMAT plan achieved better target conformity and significantly reduced monitor units, potentially shortening treatment time and improving machine efficiency.