SU‐E‐T‐695: Treatment Planning Optimization for Pulsed Low‐Dose‐Rate IMRT of Lung and Head and Neck Cancer

Purpose: Pulsed low dose rate radiotherapy has been used for treatment of recurrent cancer in some institutions. In this work, we use a commercial treatment planning system to generate a 10‐beam IMRT plan for PLDR treatment of lung and head and neck recurrent cancers. Methods: Ten head & neck cases and ten lung cases were investigated. The total dose per fraction was 200cGy, the individual gantry angles were delivered in 3min time intervals, which resulted in an effective dose rate of 6.67cGy/min. The maximum target dose from any particular gantry angle/port must be kept under 40cGy. The Eclipse treatment planning system (Varian Medical Systems, Palo Alto, CA) was used to generate all the IMRT and 3D conformal plans for PLDR treatments. Results: The maximum PTV dose per gantry angle/port for the 10 lung cases ranged from 21.7cGy to 38.7cGy, all of which met the PLDR criterion of Dmax < 40cGy. The maximum PTV dose per gantry angle ranged from 21.3 to 38.5cGy for the 10 head and neck cases, all of which met the requirement of the maximum dose limit of less than 40cGy. For all cases investigated, the IMRT plans were much better than 3D conformal plans in terms of target dose conformity and normal tissue sparing especially for cases with complex relationships between the target and critical structures for PLDR treatment. Conclusion: Manually optimized 10 gantry‐angle IMRT plans generated using existing commercially available treatment planning systems can be applied to PLDR treatments of lung and head and neck cancer. Besides dual‐arc intensity modulated radiotherapy, IMRT can be a viable option for PLDR treatment of complex lung and head and neck recurrent cancers.