Effects of prescription depth, cylinder size, treatment length, tip space, and curved end on doses in high-dose-rate vaginal brachytherapy.
OBJECTIVE
To determine the effects of the prescription depth, cylinder size, treatment length, tip space, and curved end on high-dose-rate vaginal brachytherapy (HDR-VBT) of endometrial cancer.


METHODS
Treatment plans were prescribed and optimized based on points at the cylinder surface or at 0.5-cm depth. Cylinder sizes ranging from 2 to 4 cm in diameter, and treatment lengths ranging from 3 to 8 cm were used. Dose points in various depths were precisely defined along the cylinder dome. The given dose and dose uniformity to a depth of interest were measured by the mean dose (MD) and standard deviation (SD), respectively, among the dose points belonging to the depth. Dose fall-off beyond the 0.5 cm treatment depth was determined by the ratio of MD at 0.75-cm depth to MD at 0.5-cm depth.


RESULTS
Dose distribution varies significantly with different prescriptions. The surface prescription provides more uniform doses at all depths in the target volume, whereas the 0.5-cm depth prescription creates larger dose variations at the cylinder surface. Dosimetric uncertainty increases significantly (>30%) with shorter tip space. Extreme hot (>150%) and cold spots (<60%) occur if no optimization points were placed at the curved end.


CONCLUSIONS
Instead of prescribing to a depth of 0.5 cm, increasing the dose per fraction and prescribing to the surface with the exact surface points around the cylinder dome appears to be the optimal approach.
Li
Shidong
S
Department of Radiation Oncology, Henry Ford Health System, Detroit, Michigan 48202, USA. sli1@hfhs.org
Aref
Ibrahim
I
Walker
Eleanor
E
Movsas
Benjamin
B
D000465:Algorithms; D001918:Brachytherapy / Q000295:instrumentation / Q000379:methods*; D016889:Endometrial Neoplasms / Q000532:radiotherapy*; D004867:Equipment Design; D005260:Female; D006801:Humans; D011879:Radiotherapy Dosage; D014621:Vagina