Purpose: To determine the incidence of late rectal complications in patients treated with high dose rate brachytherapy for FIGO Stage IIB, IIIB carcinoma of the uterine cervix, and to evaluate the treatment factors associated with an increased probability of treatment complications.
Methods and materials: Records of 100 patients with FIGO IIB and IIIB cervical carcinoma treated with definitive irradiation using high dose rate intracavitary brachytherapy (HDR-ICR) between 1977 and 1994 were retrospectively reviewed. For each HDR-ICR session, 6-Gy isodose volume was reconstructed retrospectively and the relationship between probability of late rectal complications and several treatment factors, including a specific point dose and parameters representing isodose volume, were examined. Statistical analyses were performed to determine the treatment factors predictive of late rectal complications.
Results: Of patients treated for both stages, 33% and 38% had experienced moderate to severe (Grade 2-4) complications at 3 and 5 years, respectively. Mean value of depth (D) of 6-Gy isodose volume in HDR-ICR in patients with and without complication were 51 mm and 46 mm, respectively (p = 0.0070). A significant difference was noted in complication rate between patients with D > 51 mm and D < or = 51 mm (p = 0.0023). Cumulative Point S (2 cm dorsal from the midpoint of the ovoid sources) dose (p = 0.044), and single or total point S dose by HDR-ICR (p = 0.019, each) were significantly higher in patients who developed complication, whereas these factors did not significantly affect the probability of pelvic control. Multivariate analysis revealed that D was the independent predictor for the endpoint of actuarial complication rate (p = 0.047). No significant difference was noted in the product of L, D, and W value (L x D x W) between patients with less than Grade 2 rectal complication and those with Grade 2-4.
Conclusion: Depth of 6-Gy isodose volume determined three dimensionally (3D) has the predictive value of late rectal complications. This suggests that the shape of the high dose area in HDR-ICR influences the incidence of late rectal complications regardless of its volume.