Effect of High-Dose-Rate ¹⁹²Ir Source Activity on Late Rectal Bleeding After Intracavitary Radiation Therapy for Uterine Cervix Cancer

Purpose

This retrospective study analyzed the effect of the activity of high-dose-rate (HDR) ¹⁹²Ir source on late rectal bleeding after HDR intracavitary radiotherapy (ICRT) in patients with uterine cervix cancer.

Methods and Materials

One hundred thirty-two patients who underwent HDR-ICRT and external beam radiotherapy (EBRT) were analyzed. The rectal point dose in ICRT was calculated by inserting a lead wire into the rectal lumen and summed with the whole-pelvic EBRT dose. The rectal biologic effective dose (BED) was calculated. The relationship between averaged source activity or the BED and late rectal bleeding were analyzed.

Results

Three-year actuarial rectal bleeding probabilities were 46% (≥100 Gy₃) and 18% (≤ 100 Gy₃), respectively (p < 0.005). When patients were divided into four groups according to rectal BED (≥ or ≤100 Gy₃) and source activity (≥ or ≤2.4 cGy.m².h⁻¹), the group with both a high BED and high activity showed significantly greater probability (58% at 3 years; p < 0.005). It was noted that the probability of the group with BED of 100 Gy₃ or greater was high, but that was not the case with 2.4 cGy.m².h⁻¹ or less.

Conclusion

This is the first clinical report concerning the source activity effect of HDR ¹⁹²Ir on late rectal bleeding in patients undergoing HDR-ICRT. This suggests that when source activity is higher than 2.4 cGy.m².h⁻¹, ICRT should be performed with more caution not to exceed 100 Gy₃ in total.

High-dose-rate, Cervical cancer, Intracavitary radiation therapy, Late morbidity, Brachytherapy