MULTI OBJECTIVE, MULTI-DELIVERY OPTIMIZATION FOR RADIATION THERAPY TREATMENT PLANNING

Abstract Purpose To introduce Multi-Objective, multi-Delivery Optimization (MODO) which generates alternative patient-specific plans emphasizing dosimetric tradeoffs and conformance to quasi-constrained (QC) conditions for multiple delivery techniques. Methods For M delivery techniques and N OARs, MODO generates M(N+1) alternative treatment plans per patient. For 30 locally advanced lung cancer cases, the algorithm was investigated based on dosimetric tradeoffs to four OARs: each lung, heart, and esophagus (N=4) and 4 delivery techniques (4-field coplanar IMRT, 9-field coplanar IMRT, 27-field non-coplanar IMRT, and non-coplanar Arc IMRT) and conformance to QC-conditions including dose to 95% of PTV (PTV-D95), maximum dose to PTV (PTV-Dmax), and spinal cord Dmax. The MODO plan set was evaluated for conformance to QC conditions while simultaneously revealing dosimetric tradeoffs. Statistically significant dosimetric tradeoffs were defined such that the coefficient of determination was >0.8 with dosimetric indices which varied by at least 5 Gy. Results Plans varied mean dose by >5 Gy to ipsilateral lung for 24/30 patients, contralateral lung for 29/30 patients, esophagus for 29/30 patients, and heart for 19/30 patients. In the 600 plans, average PTV-D95 = 67.6±2.1 Gy, PTV-Dmax = 79.8±5.2 Gy, and spinal cord Dmax among allplans was 51.4 Gy. Statistically significant dosimetric tradeoffs reducing OAR mean dose by >5 Gy were evident in 19/30 patients, including multiple OAR tradeoffs of at least 5 Gy in 7/30 cases. The most common statistically significant tradeoff was increasing PTV-Dmax in order to reduce dose to OARs (15/30). The average 4-field plan reduced total lung V20 by 10.4%±8.3% compared to 9-field plans, 7.7%±7.9% compared to 27-field non-coplanar plans, and 11.7% ±10.3% compared to 2-arc non-coplanar plans with corresponding increases in PTV-Dmax of 5.3±5.9 Gy, 4.6±5.6 Gy, and 9.3±7.3 Gy. Conclusions The proposed optimization method produces clinically relevant treatment plans which meet QC conditions and demonstrate variations in OAR doses.