Second primary malignancies after high-dose-rate 60 Co photon or 252 Cf neutron brachytherapy in conjunction with external-beam radiotherapy for endometrial cancer.

PURPOSE: Second primary malignancies (SPMs) may occur in organs after radiotherapy (RT). This study aimed to determine the rate and distribution of SPMs for photon- or neutron-emitting radiotherapy sources for patients treated for primary endometrial cancer.

METHODS AND MATERIALS: The cohort comprised 426 patients with 5334 patient-years of observation. Patients were treated by different methods of RT from 1990 to 2000. Patients received postoperative 60 Co external-beam radiotherapy (43.4%), external-beam radiotherapy + high-dose-rate (HDR) intracavitary brachytherapy with 60 Co or 252 Cf (42.3%), or HDR intracavitary brachytherapy alone with 60 Co or 252 Cf (14.3%).

RESULTS: Over a 25-year period, 47 SPMs were observed (21 for HDR 60 Co and 26 for HDR 252 Cf). SPMs were observed for 13 patients in the high-intermediate risk group for each radiation source. Patients treated with 60 Co developed SPMs in the urinary tract (1.2%) and in lymphoid/hematopoietic tissues (1.2%). Only three SPM cases (0.7%) were observed in digestive tract. In comparison, the patient group treated with 252 Cf developed SPMs in the digestive tract (1.4%) with the majority in the colon (1.2%), urinary tract (0.9%) primarily the kidneys, and vulva (0.7%). All other SPMs (4.9%) were in the low-risk group. Of these, SPMs in the skin were most prevalent (1.6%) for 60 Co, and breast (1.6%) for 252 Cf, but believed to be caused by factors other than treatment. SPM incidence in the digestive and urinary tracts were similar (2.1%), regardless of radiation source.

CONCLUSIONS: For followup at 25 years, 47 SPMs were observed with no differences in the high-intermediate risk group depending on the RT source.