Investigation of dose ratios of hybrid volumetric-modulated arc Therapy plans for nonsmall cell lung cancer.

This study investigated hybrid volumetric-modulated arc therapy (H-VMAT) for the treatment of nonsmall cell lung cancer (NSCLC) by classifying patients based on the tumor location (left or right and upper, middle or low) and planning target volume (PTV) (less than average or greater than average) to determine the optimal VMAT dose ratio by dividing the prescription dose used for H-VMAT planning. The following treatment plans comprising four-field conformal irradiation were created for 51 patients with NSCLC: VMAT with one full arc (f-VMAT); VMAT with two partial arcs (p-VMAT); and hybrid plans. Hybrid plans comprised a combination of f-VMAT and three-dimensional conformal radiation therapy (3D-CRT; fH-VAMT) as well as a combination of p-VMAT and 3D-CRT (pH-VMAT). We evaluated the dose to the organ at risk using lung V5 and V20 Gy, heart V30 and V40 Gy, and the mean heart dose and determined the optimal dose ratio of H-VMAT. H-VMAT resulted in negligible differences in the PTV conformity and homogeneity of fH-VMAT and pH-VMAT regardless of the dose ratio. Compared to fH-VMAT, pH-VMAT significantly reduced low lung doses, particularly those for tumors located in the right and above the heart, and those for larger target volumes. Compared to fH-VMAT, pH-VMAT slightly reduced the heart volume exposed to medium or high doses. The optimal VMAT dose ratios based on the tumor conditions were as follows: 30 % fH-VMAT and 50 % pH-VMAT for left lung tumors; 20 % fH-VMAT and 50 % pH-VMAT for right lung tumors; 20 % fH-VMAT and 50 % pH-VMAT for tumors above the heart; and 50 % fH-VMAT and 50 % pH-VMAT for tumors at the heart level. For smaller tumors, both fH-VMAT and pH-VMAT were set at 50 %. For larger tumors, 20 % fH-VMAT and 50 % pH-VMAT were used. These findings can help optimize treatment planning and guidelines and contribute to improved patient outcomes.