Optimization of Beam Orientation and Virtual Organ Delineation for Lung IMRT

Abstract

This study demonstrates the feasibility of the proposed intensity-modulated radiotherapy (IMRT) techniques for minimizing the dose to the lungs and organs at risk (OARs) for variations in the number of beams, the orientations of the beams, the virtual organ delineation (VOD) position, the VOD size and the dose constraints in order to optimize the treatment plan for lung cancer. We used 5, 7, 9 and 14 equiangularly-spaced beams and 7 and 9 non-equiangularly-spaced beams. We measured the volume of the lungs receiving at least 20 Gy and 25 Gy (V-20 and V-25) for variations in the orientations of the beams, the VOD position, and the size of the tumor and the contra-lateral lung. For the tumor and the contra-lateral lung, the V-20 and the V-25 values of 14 equiangularly-spaced ports were slightly lower than those of other equiangularly-spaced beam orientations. For non-equiangularly-spaced beam orientations, the lowest V-20 and V-25 values in the tumor and the contral-lateral lung were recorded in ports 7, and 9, respectively. For tumors of the lung, the average values of 7 non-equiangularly-spaced ports were lower than those for 14 equiangularly-spaced ports. The values of V-20 and V-25 for variations in the VOD size and the VOD position showed no significant differences for the lung tumor of patient 1 when the dose constraint of the VOD was 10, 25 and 30 Gy. For the lung tumor, the values of V-20 and V-25 for various VOD sizes and positions ranged from 15 to 37% in patient 2 and from 28 to 45% in patient 3. The values of V-20 and V-25 were within 7% for the contra-lateral lung of patient 1. For patient 2, the values of V-20 and V-25 ranged from 7 to 18%. For the contra-lateral lung of patient 3, the V-20 and V-25 values ranged from 12 to 25%. IMRT techniques with various VOD and beam orientations are important for determine in treatment plans.