MATERIALS AND METHODS: CT imaging data from twenty patients with breast or chest wall cancer, either right or left-sided, and with supraclavicular and internal mammary chain lymph nodes were retrieved. The CT data planned with a hybrid VMAT of three different weighting proportions: 30 % using 3DCRT and 70 % using VMAT, 50 % using 3DCRT and 50 % using VMAT, and 70% using 3DCRT and 30 % using VMAT and compared with full 3DCRT and full VMAT plan (classic and five arc design).
RESULTS: The homogeneity and conformity indices were better in the hybrid VMAT plans than in plans using VMAT or 3DCRT alone (P<0.005). Results of all hybrid VMAT plans showed a considerable drop of volumes receiving more than 4Gy, 8Gy or 16Gy in the ipsilateral lung compared to the full VMAT plan (P<0.001). There was a noticeable decrease in the mean dose to the heart and the dose in 5% of the contralateral breast in the plan using 70 % 3DCRT and 30 % VMAT compared to full VMAT (P<0.001). The plan using 70 % 3DCRT and 30% VMAT achieved a balance between the target and surrounding areas, compared to using only 3DCRT or VMAT.
CONCLUSION: A hybrid plan using 70 % 3DCRT contribution achieved a balanced outcome for breast or chest wall irradiation, considering both planning target volume and organs at risk. Utilizing our VMAT arc design, incorporating one shortened arc can significantly reduce doses to organs at risk further. It is important to consider the patient's anatomy when making this decision.