RADIORESPONSE OF THYMOMAS VERIFIED WITH HISTOLOGIC RESPONSE

Patterns of radiologic response of 10 thymomas treated by preoperative radiotherapy (RT) (18-20 Gy/2 weeks) were determined in conjunction w ith histologic response. Changes in tumor volume were evaluated with C T scans obtained 5 to 36 days before and 14 to 24 days after the initi ation of RT and before surgery. The extent of tumor volume reduction ( TR) varied widely (40-78%), while the mean daily volume decrement expr essed as a percentage of the pre-RT tumor volume correlated significan tly with the pre-RT tumor volume. Histologically, the tumors, all of w hich were resected 17 to 33 days after RT initiation, generally consis ted of predominant fibrous tissues, rare necrotic foci, and few epithe lial cells. The TR did not correlate with pre-RT tumor volume, observa tion period, histologic subtype, or quantity of remaining epithelial c ells. The TR of thymomas does not predict RT impact on tumor cells but does reflect the quantity of inherent tumor stroma.