Possible Misinterpretation of Demarcated Solid Patterns of Radiation Fibrosis on CT Scans as Tumor Recurrence in Patients Receiving Hypofractionated Stereotactic Radiotherapy for Lung Cancer

Purpose To retrospectively analyze opacity changes near primary lung cancer tumors irradiated by using hypofractionated stereotactic radiotherapy (HSRT) to determine the presence or absence of tumor recurrence. Methods and Materials After review-board approval for a retrospective study, we examined data from 50 patients treated with curative intent for proven or highly suspected localized peripheral-lung cancer and followed up for at least 12 months. All patients had received 50 Gy in five fractions (80% isodose) and were followed up monthly with chest X-ray until clinical and X-ray findings stabilized. Follow-up computed tomography scans were performed 1 and 3 months after HSRT and thereafter at 3-month intervals during the first 2 years. Results Median follow-up was 30.4 months (range, 12.0–73.8 months). Abnormal opacities that were suspicious for recurrent tumor appeared in 20 patients at a median of 20.7 months (range, 5.9–61.4 months). Only 3 patients were finally found to have recurrence; 14 were recurrence free but were suspected to have fibrosis, and findings for the other 3 patients were considered equivocal because of a short follow-up period (≤6 months). Conclusion Radiation fibrosis, which may occur 1 year or longer after completion of HSRT, is difficult to distinguish from tumor recurrence. Even when opacities increase on follow-up radiologic scans, recurrence cannot be diagnosed conclusively based on image findings; biopsy occasionally is warranted.