Use of the Rectal Retractor to Reduce the Rectal Dose in High Dose Rate Intracavitary Brachytherapy for a Carcinoma of the Uterine Cervix

Commercially available rectal retractors can be used in high dose rate intracavitary brachytherapy (HDR ICR) as one of the methods for reducing the rectal dose in radiotherapy for a uterine cervical cancer. However, the extent of the rectal protection achieved using these rectal retractors has not been reported. The aim of the study was to examine the effect of a rectal retractor on reducing the rectal dose in HDR ICR. Thirty patients were treated with HDR ICR using rectal retractors. Tandem and ovoids were applied in 15 patients and ovoids only were used in the other 15 patients. During the simulation, the rectum was filled with barium, and anteroposterior and lateral radiographs were then taken with and without the rectal retractor. Along the anterior rectal wall outlined, 4 to 8 points (median 6) were chosen to calculate the dose for each patient including the rectal point (RP), which is an author-defined rectal point modified from the definition of the rectal reference point in the ICRU report 38. The length of the measured rectum was 3-7 cm (median 5 cm). The bladder point (BP) dose was measured as recommended by the ICRU. The prescription doses to point A varied from 3.5 to 5 Gy (median 4 Gy). Paired comparisons were made on the individual patients by calculating the normalized mean doses of the RP, the maximal point (MP), and the longitudinal average (LA) with and without the rectal retractor. The doses to the bladder points (BP) were also calculated in parallel to the rectal points. The anterior rectal walls were displaced posteriorly after inserting the rectal retractor. In the tandem and ovoids group, the number of patients with a reduced dose in the RP, MP and LA were 14 (93.3%), 12 (80.0%) and 13 (86.7%), respectively. In the ovoids only group, the corresponding figures were 14 (93.3%), 14 (93.3%) and 14 (93.3%). In the tandem and ovoids group, the reduced dose in the RP, MP, and LA dose were 0.52 Gy (13.0%), 0.50 Gy (12.5%), and 0.39 Gy (9.8%), respectively (p 0.05). The mean RP, MP, and LA dose reduction rates of the patient subgroup where the RP dose was 70%. The effect of the rectal dose reduction was significant only in the subgroup of patients who received > 70% of the prescription dose (p < 0.05). The use of the rectal retractor was a simple and an effective method for reducing the rectal dose. It was also considered to be a highly reproducible method, which can replace the time-consuming vaginal gauze packing in HDR-ICR.

Study of Patient's Position to Reduce Late Complications in High Dose Rate Intracavitary Radiation of the Uterine Cervix Cancer / 대한방사선종양학회지

PURPOSE: Radiation proctitis and radiation cystitis are frequent and problematic late complications in patients treated with radiation for the uterine cervix cancer. Authors tried to find out the better patient's position in high dose rate intracavitary radiation to reduce the radiation dose of bladder and rectum. MATERIALS AND METHODS: In 13 patients, Foley catheters were inserted to patients' bladder and rectum and were ballooned with radioopaque dye. After insertion of a tandem and two ovoids, semi-orthogonal anteroposterior and lateral films were taken in both lithotomy and supine position. The rectal point and bladder point were defined according to the criteria recommended in the ICRU Report 38 with modification. Using these films, all patients' bladder and rectal dose were calculated in both positions (the radiation dose of A point was set to 400 cGy). And also, the distance of bladder and rectum from uterine cervical os was calculated in both positions. RESULTS: The average radiation dose of rectum was 240.7 cGy in lithotomy position and 278.3 cGy in supine position, and the average radiation dose of bladder was 303.5 cGy in lithotomy position and 255.8 cGy in supine position. After the paired t-test, the radiation dose of rectum in lithotomy position was marginally significantly lower than that in supine position, while the radiation dose of bladder in lithotomy position was significantly higher than that in supine position. On the other hand, the average distance between rectum and cervical os was 35.2 mm in lithotomy position and 32.3 mm in supine position. and the average distance between bladder and cervical os was 30.4 mm in lithotomy position and 34.0 mm in supine posi-tion. After the paired t-test, the distance between rectum and cervical os in lithotomy position was significantly longer than that in supine position, while the distance between bladder and cervical os in lithotomy position was significantly shorter than that in supine position. CONCLUSION: The radiation dose of bladder can be reduced in supine position and the radiation dose of rectum can be reduced in lithotomy position, so we can choose appropriate position in each patient.