High-dose-rate intracavitary brachytherapy: results of analyses of late rectal complications.

PURPOSE: To examine the incidence of radiation-induced late rectal complications by analyzing the data of measured rectal doses in patients with cancer of the uterine cervix treated with high-dose-rate intracavitary brachytherapy. METHODS AND MATERIALS: We measured doses to the rectum in 105 patients with cancer of the cervix during high-dose-rate intracavitary brachytherapy with a semiconductor dosimeter that can measure five points in the rectum simultaneously. On the basis of these measurements, equivalent doses, to which the biologically equivalent doses were converted as if given as fractionated irradiation at 2 Gy/fraction, were calculated as components of the cumulative dose at five rectal points in intracavitary brachytherapy combined with the external whole pelvic dose. RESULTS: The calculated values of equivalent doses for late effects at the rectum ranged from 15 to 100 Gy (median 60 Gy for patients who did not develop complications and 76 Gy for patients who subsequently developed Grade II or III complications). When converted to a graph of absolute rectal complication probability, the data could be fitted to a sigmoid curve. The data showed a very definite dose-response relationship, with a threshold for complications at approximately 50 Gy and the curve starting to rise more steeply at approximately 60 Gy. The steepest part of the curve had a slope equivalent to approximately 4% incidence/1 Gy increase in equivalent doses. CONCLUSION: The radiation tolerance dose, 5% and 50% complication probability, was about 64 and 79 Gy, respectively. Our data almost agree with the prescribed dose for the rectum for the radiation tolerance doses on the basis of the recorded human and animal data. The probability of rectal complications increased drastically after the maximal rectal dose was >60 Gy.

High-dose-rate versus low-dose-rate intracavitary therapy for carcinoma of the uterine cervix: a randomized trial.

BACKGROUND: This was a prospective randomized clinical trial undertaken at our institution to compare low-dose-rate (LDR) intracavitary radiation therapy versus high-dose-rate (HDR) intracavitary radiation therapy for the treatment of cervical carcinoma. METHODS: From January 1984 to December 1997, a total of 132 patients with Stage II or IIIB of invasive carcinoma of the uterine cervix were entered into this randomized study. Treatment arm by HDR or LDR was allocated according to the month of each patient's birth. External irradiation consisted of whole pelvis irradiation and pelvic irradiation. Doses of external irradiation for both groups were identical. The authors used 0.588 as the conversion factor of total intracavitary dose from LDR to HDR. RESULTS: The 5-year disease specific survival rates of Stage II and III patients treated with HDR were 69% and 51% whereas those with LDR were 87% and 60%, respectively. The 5-year pelvic recurrence free survival rates of Stage II and III patients treated with HDR were 89% and 73% whereas those with LDR were 100% and 70%, respectively. There was no significant difference in disease specific survival or pelvic recurrence free survival rates between HDR and LDR. The actuarial complication rate (Radiation Therapy Oncology Group Grade 3, 4, or 5) at 5 years was 10% in the HDR group and 13% in the LDR group, and the difference between the HDR and LDR groups was not statistically significant. CONCLUSIONS: The pelvic control or actuarial complication rates were comparable between HDR and LDR treatment. The difference between the disease specific survival rates for HDR and LDR was not statistically significant for Stage II or III, although in Stage II, patients treated with LDR appeared to have a better survival rate than those treated with HDR.