Comparison of high and low dose rate remote afterloading for cervix cancer and the importance of fractionation.

Analysis of the data obtained from a survey of 56 institutions treating a total of over 17,000 cervix cancer patients with high dose rate (HDR) remote afterloading, shows that the average fractionation regimen is about 5 fractions of 7.5 Gy each to Point A, regardless of stage of disease. Comparison with historical controls treated by the same clinicians at low dose rate (LDR), showed that 5-year survival was statistically significantly better for HDR versus LDR for Stage III patients (47.2% compared to 42.6%, P = 0.005) and for all patients pooled together (60.8% vs. 59.0% P = 0.045). Morbidity rates were considerably lower for HDR versus LDR for both severe (2.23% vs. 5.34%, P less than 0.001) and moderate plus severe complications (9.05% vs. 20.66%, P less than 0.001). There is an apparent geometrical advantage of HDR intracavitary therapy in that there is a reduction in the "hot-spot" rectal and bladder doses relative to Point A of, on average, (13 +/- 4)% for the HDR compared to the LDR treatments. Fractionation of the HDR treatments significantly influenced toxicity: morbidity rates were highly significantly lower for Point A doses/fraction less than or equal to 7 Gy compared with greater than 7 Gy for both severe injuries (1.28% vs. 3.44%, P less than 0.001) and moderate plus severe (7.58% vs. 10.51%, P less than 0.001). The effect of dose/fraction on cure rates was equivocal. Finally, the data showed that for conversion from LDR to HDR the total dose to Point A was reduced on average by a factor 0.54 +/- 0.06.