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Correlation between Lung Fibrosis and Radiation Therapy Dose after Concurrent Radiation Therapy and Chemotherapy for Limited Small Cell Lung Cancer¹

¹ From the Departments of Radiation Physics (I.I.R., J.A.A., G.S., K.R.H.), Experimental Radiation Oncology (E.L.T.), Biomathematics (S.L.T.), and Radiation Oncology (J.D.C., R.K.), University of Texas M.D. Anderson Cancer Center, 1515 Holcombe Blvd, Box 94, Houston, TX 77030; and the Sarasota Radiation Therapy Regional Center, Sarasota, Fla (T.A.F.). From the 1998 RSNA scientific assembly. Received November 24, 1999; revision requested March 8, 2001; final revision received May 2; accepted May 21. Address correspondence to I.I.R. (e-mail: irosen@mdanderson.org).

PURPOSE: To evaluate the relationship between physician-identified radiographic fibrosis, lung tissue physical density change, and radiation dose after concurrent radiation therapy and chemotherapy for limited small cell lung cancer.

MATERIALS AND METHODS: Fibrosis volumes of different severity levels were delineated on computed tomography (CT) images obtained at 1-year follow-up of 21 patients with complete response to concurrent radiation therapy and chemotherapy for limited small cell lung carcinoma. Delivered treatments were reconstructed with a three-dimensional treatment planning system and geometrically registered to the follow-up CT images. Tissue physical density change and radiation dose were computed for each voxel within each fibrosis volume and within normal lung. Patient responses were grouped per radiation and chemotherapy protocol.

RESULTS: A significant correlation was noted between fibrosis grade and tissue physical density change and fibrosis grade. For doses less than 30 Gy, the probability of observing fibrosis was less than 2% with conventional fractionation and less than 4% with accelerated fractionation. Physical lung density change also showed a threshold of 30–35 Gy. For doses of 30–55 Gy and cisplatin and etoposide (PE) chemotherapy, fibrosis probability was 2.0 times greater for accelerated fractionation compared with conventional fractionation (P < .005) and was correlated to increasing dose for both fractionation schedules.

CONCLUSION: Lung tissue physical density changes correlated well with fibrosis incidence, and both increased with increasing dose greater than a threshold of 30–35 Gy. With concurrent PE chemotherapy, fibrosis probability was twice as great with accelerated fractionation as with once-daily fractionation.

Index terms: Chemotherapy, complications, 60.47 • Lung, fibrosis, 60.47 • Radiations, injurious effects, 60.47