A Pilot Study Of Fdg Pet Lung Uptake After Thoracic Radiation Therapy And New Pulmonary Symptoms

Lung inflammation related to thoracic radiation therapy (RT) in patients (pts) with lung cancer may manifest on post-RT FDG PET scans and may correlate with new pulmonary symptoms. Study subjects were derived from a preexisting departmental database of 120 pts with lung cancer who received definitive or palliative thoracic RT from 2006-15, and who underwent a pre-RT and at least one post-RT PET scan. Patients whose PET scans demonstrated a visually apparent hypermetabolic uptake outside the tumor, corresponding to the irradiated region are subjects of this report. The hypermetabolic regions were contoured using a gradient tool of the commercial segmentation software and the following parameters were derived from contours: SUV (max and mean) and TGA (total glycolytic activity). Patients were excluded if the hypermetabolic region was not distinct from the residual tumor. Contours were drawn by the junior investigator and were verified by the senior radiation oncologist. Medical records of patients were reviewed to identify and grade new pulmonary events (PEV), such as cough, dyspnea, radiation pneumonitis, as per CTCAEv4 scoring system. Other recorded variables included age, gender, RT dose, upper/lower lung tumor location. The relationship between each potential predictor and PEV highest grade was assessed univariably, using two-sided Fisher’s test. Spearman’s rank correlation coefficients were used to estimate the associations between PEV grade and PET parameters. A total of 47 pts were included with the 1st PET scan at the median time of 7 weeks after RT, with 32 having completed a 2nd PET scan at the median time of 5 months. There were 62% females; 68% had lower lung tumors and RT doses were (Gy): 30-50 (17%), 51-60 (28%), and 61-74 Gy (55%). A majority of pts (72%) had at least one PEV (cough: 62%; dyspnea: 55%; pneumonitis: 36%), with 23.4% experiencing Grade > 3 PEV, requiring steroids (28%) or oxygen (19%). PEV grades were: 1-2 (49%); 3-5 (15%). Median PET values were as follows: SUVmax, 4.5 (range: 2-12.2); SUVmean, 2.1 (range: 0.8-4.6); TGA, 153.8 (range: 2.1-2783). There was no apparent correlation between highest PEV grade and SUVmax (p=0.66) or TGA (p=0.16). There was no strong relationship between onset of symptoms with regard to timing of PET scans. The majority of pts with hypermetabolic PET uptake after thoracic RT experienced new pulmonary symptoms, with close to a quarter scored to have Grade > 3 symptoms. This appears higher than the historical control of the 15% Grade >3 acute pulmonary toxicity in the RTOG 0617 trial, suggesting the hypermetabolic lung uptake in the treated region may reflect lung inflammation/pneumonitis, accounting for the symptoms. No relationship was found between the investigated PET parameters and symptom grade. Further investigation will include a matched-pair analysis of pulmonary events of patients without lung uptake.