Optimization of beam orientation and virtual organ delineation for lung IMRT

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 (V₂₀ and V₂₅) 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 V₂₀ and the V₂₅ values of 14 equiangularlyspaced ports were slightly lower than those of other equiangularly-spaced beam orientations. For non-equiangularly-spaced beam orientations, the lowest V₂₀ and V₂₅ 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 V₂₀ and V₂₅ 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 V20 and V25 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 V₂₀ and V₂₅ were within 7% for the contra-lateral lung of patient 1. For patient 2, the values of V₂₀ and V₂₅ ranged from 7 to 18%. For the contra-lateral lung of patient 3, the V₂₀ and V₂₅ values ranged from 12 to 25%. IMRT techniques with various VOD and beam orientations are important for determine in treatment plans.