SU-E-T-433: Pear-Shaped Based Dose Optimization for HDR Intracavitary Brachytherapy for Cervical Cancer Patients with...

Currently, CT has been widely used for HDR planning as MRI is not widely available for tumor imaging. Conventional pear-shaped isodose distribution may not be discarded completely because of possible microscopic diseases into parametrium/uterus. For patients with small uterus, organs at risk (OARs) can fall inside 100% conventional pear-shaped isodose-line. This study compares two pear-shaped based dose optimization methods for OARs sparing.

Seven cervical cancer patients with small uterus were evaluated using 2 methods. For Method A, with conventional dwell-time loading, point A lateral distance was reduced until all OARs' D2cc were within the dose limits. For Method B, a reference target volume was generated using conventional pear-shaped 100% isodose- surface. While isodose-line near the point A was adjusted for OARs sparing, isodose-line surrounding ovoids were optimized to match the reference target volume. For equivalent OAR sparing, 100% isodose-line width (lateral dimension) at 1 cm inferior to point A (-1 cm) and at across centers of ovoids (ovoid) were compared between the 2 methods.

OARs fall inside conventional 100% isodose-line in all cases. Median position of hot spots was 0.2 cm (range -;1.2 to 2.9 cm) superior to point A. Using Method A, point A lateral distance was adjusted to 1.4-1.7 cm for OARs sparing. Median width of 100% isodose-line was 5.82 cm at ovoid level, and 4.50 cm at -1 cm level. At ovoid level, median width of 100% isodose-line was reduced by 9(8-13)% for Method A, and was unchanged for Method B. At -1 cm level, median width of 100% isodose-line was reduced by 19(2- 33)% for Method A, and 11(0-15)% for Method B.

for patients with small uterus, OARs are often fall inside 100% pear-s haped isodose-line near point A level. OARs can be spared without dramatically compromise treatment volume coverage around cervix using Method B.