Dose rate effect in ICRU rectal dose of intracavitary radiotherapy for uterine cervix cancer. Six-fractions HDR and three-fractions LDR in three weeks

The ICRU rectal doses by intracavitary radiotherapy (ICRT) using Tandem and Ovoid in 144 patients with uterine cervix cancer were calculated. Eighty four of 144 patients were treated by external radiotherapy (ERT) and low dose rate ICRT (45-55 Gy/3 fractions/3 weeks to point A), and 60 were treated by ERT and high dose rate ICRT (30 Gy/6 fractions/3 weeks). A sigmoid curves of the ICRU rectal dose by ICRT versus rectal injury rate of NIRS grade 2 or higher for each whole pelvis dose by ERT were established. The 10% rectal injury doses were determined for each of the whole pelvis ERT doses, 0 Gy, 10 Gy, 20 Gy and 21 Gy, from the sigmoid curve. The 10% complication doses were LDR: 41 Gy, HDR: 51 Gy, in whole pelvis ERT dose of 0 Gy group. The dose rate effect LDR/HDR was 1.24. It was 1.17 in ERT 10 Gy group, 1.23 in ERT 20 Gy group, 1.26 in ERT 21 Gy group. It was 1.24 in ERT 0-20 Gy group. (author)