Delineating the relationship between Point A prescription dose and pelvic lymph node doses in intracavitary high-dose-rate brachytherapy treatment of cervical cancer for use in low- and middle-income countries.

PURPOSE

To define the relationship between the Point A prescription dose and the dose delivered to various pelvic lymph node groups during high-dose-rate (HDR) brachytherapy treatment of cervical cancer. In less developed countries, brachytherapy is often done without three-dimensional image guidance, instead relying on plain radiography and prescription to Point A. A defined relationship between Point A dose and lymph node doses would help physicians in these health care settings to more accurately estimate nodal doses.

METHODS AND MATERIALS

Treatment data from 50 fractions of HDR brachytherapy of cervical cancer were reviewed, the pelvic lymph nodes were contoured, and dose-volume histogram parameters were obtained. Dose-volume histogram parameters for each contour were normalized as a percentage of the corresponding Point A dose. All nodal groups were divided into left and right sides, except the presacral nodal group.

RESULTS AND CONCLUSIONS

Mean Point A doses were bilateral (Bil) 5.92 Gy ± 0.58, left (L) 5.93 ± 0.59, and right (R) 5.92 ± 0.59. Mean normalized D90 values for the various lymph node groups were as follows-obturator: Bil 20.3% ± 4.5, L 20.5% ± 4.4, and R 20.2% ± 5.2; external iliac: Bil 9.5% ± 2.9, L 10.0% ± 3.1, and R 9.5% ± 3.0; internal iliac: Bil 12.2% ± 3.5, L 12.1% ± 3.4, and R 12.9% ± 4.7; common iliac: Bil 4.3% ± 1.6, L 4.3% ± 1.6, and R 4.3% ± 1.7; and presacral: 8.7% ± 3.4. These relationships can serve as a useful tool for evaluating lymph node doses during HDR brachytherapy of cervical cancer in facilities performing two-dimensional treatment planning and those with limited resources.