A Prospective Study to Evaluate Clinical Radiation Induced Pneumonitis in Lung Cancer Patients and its Dose Response Relationship with Radiotherapy

Purpose: This study was initiated to evaluate incidence, grade and dosimetric correlation of Clinical Radiation Induced Pneumonitis (RIP) (≥ grade 2) in lung cancer patients undergoing radical radiotherapy. Methods and Materials: From August, 2012 to November, 2013, 85 lung cancer patients received curative 3D CRT. On follow up 14 patients developed symptomatic pneumonitis (≥ Grade 2 as per RTOG Toxicity criteria). They underwent CT thorax/PET-CT at 3 monthly follow-up which were co-registered with planning CT images. Changes in lung density were graded as patchy, discrete and solid consolidation and contoured. Isodose surface enveloping these contours and mean doses received were noted. Result: At a median follow up of 12.5 months, incidence of clinical ≥Grade 2 RIP was 16.5%. Inclusion of mediastinum in the target volume and higher stage of disease were found to be indicators of increased risk of ≥Grade 2 RIP. Lung volumes showing patchy/discrete consolidation decreased from 3rd to 6th month and then plateaued while solid consolidation appeared at 6 months, increased at 9 months but then decreased at 12 months. Percentage isodoses encompassing grade 2 radiological RIP were between 80-85% and mean doses were between 45-48Gy. However for grade 3/4 RIP corresponding values were 90-95% and 50-54Gy. Conclusion: Incidence of ≥Grade 2 RIP with conformal RT was 16.5%. V20 alone may not be a sufficient predictor for RIP and one should consider conformal RT planning to restrict even higher isodoses beyond the PTV.