SU-E-J-255: Clinical Benefit of Accounting for Intrafraction Lung Tumor System Deformation: First Treatment Planning Study

Abstract

Purpose: Lung tumor and affected lymph nodes may change their relative positions during treatment, manifesting in the deformation of the multi‐target tumor system. Comparing to the current standard care, this study aims to quantify the clinical benefit if the deformation is ideally tracked. Methods: Six lung cancer patients at stage IIIA were included in this study. For the current standard care treatment, an IMRT plan was created on the reference phase and dose of the same plan was calculated on each phase. The planning target volume (PTV) was 5 mm expansion of the internal target volume (ITV) defined as the summation of the clinical target volumes (CTV) of all phases. For the ideally‐tracked treatment, an individual IMRT plan was created for each phase with 5 and 2 mm CTV‐to‐PTV margins. Dose of each phase was deformed and summed to the reference phase. All plans were normalized so that the equivalent uniform dose (EUD) of the CTV was the same at 74 Gy. EUD and the normal tissue complication probabilities (NTCP) of the spinal cord, esophagus, heart and lung were compared for the three treatment scenarios. Results: The EUD of the spinal cord, esophagus, heart and lung was 31.3±9.9, 55.5±11.7, 32.6±16.1, and 16.8±3.2 Gy for the standard‐care plan, 30.9±10.1, 54.2±12.1, 31.2±15.7, and 15.6±2.6 Gy for the ideally‐tracked plan with 5 mm PTV margin, and 29.0±10.6, 50.7±13.6, 29.4±15.1 and 14.3±2.6 Gy for the ideally‐tracked plan with 2 mm PTV margin, respectively. The greatest NTCP reduction was 3.5% (9.5%) for esophagitis, 4.4% (20.5%) for pericarditis and 11.8% (16.2%) for pneumonitis in ideally‐tracked treatment with 5 (2) mm PTV margin. Conclusion: The toxicity to the critical organs can be greatly reduced if the tumor system deformation can be compensated with high accuracy and precision which allows PTV margin to be reduced to 2 mm. The authors acknowledge funding support from the Australian NHMRC Australia Fellowship, Sydney Medical School Summer Research Scholarships, NHMRC Project Grant APP1042375 and US NIH/NCI R01CA93626.