Dose comparison between hybrid VMAT, VMAT AND 3DCRT for breast/chest wall irradiation with regional lymph node irradiation

Abstract

Breast radiation treatment is linked to complications like pneumonitis and cardiac toxicity, necessitating dose optimization. 3DCRT has been widely accessible and costeffective but lacks precision in targeting cancer, often resulting in higher doses to surrounding normal tissues. VMAT and IMRT offer improved accuracy but can lead to increased low-dose exposure outside the traditional tangential fields or areas covered by 3DCRT. A new 5-arc volumetric modulated arc therapy (VMAT) design was developed for breast/chest wall treatment in deep inspiration breath-hold (DIBH) and free breathing (FB). This study aims to determine the optimal dose weightage of hybrids compared to VMAT and 3DCRT considering both Planning treatment volume (PTV) and Organs at risk (OARs). Twenty patients with right/left-sided breast/chest wall cancer with lymph node involvement were chosen. All CT data for each patient planned with H-VMAT in three different weighting proportions with 3DCRT base plan: 30-70 (30% 3DCRT and 70% VMAT: H-VMAT30), 50-50 (50% 3DCRT and 50% VMAT: H-VMAT50), 70-30 (70% 3DCRT and 30% VMAT: H-VMAT70) and compared with full 3DCRT and full VMAT plan. Using DIBH, 3DCRT provided better OAR protection than VMAT and H-VMAT plans, while the opposite was better for the FB cases. In both breathing settings, VMAT and H-VMAT performed better in conformity and homogeneity indices than 3DCRT with P<0.005. H-VMAT plans exhibited a significant decrease in V4Gy and V8Gy for the ipsilateral lung compared to VMAT. A significant decrease was observed in the V4Gy of the contralateral lung across all plan types. In DIBH, there was no significant change in D5% to the contralateral breast between VMAT and H-VMAT70, but there was a significant change in the FB setting. There was no significant difference in heart dose reduction for D5% , V12Gy and D mean on the right breast for both breathing settings. However, for the left-sided, there was a significant change in Dmean and V12Gy across all the plans with H-VMAT70 performing better than VMAT. In conclusion, a hybrid plan with a high contribution from 3DCRT 70% achieved a balanced outcome for breast or chest wall irradiation in DIBH considering both PTV and OARs, whereas H-VMAT70 outperformed the 3DCRT in FB cases.