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Pear-Shaped Based Dose Optimization for HDR Intracavitary Brachytherapy for Cervical Cancer Patients with Small Uterus

S Shen

S Shen*, R Kim, J Duan, X Wu, R Popple, R Cardan, I Brezovich, Univ Alabama Birmingham, Birmingham, AL

SU-E-T-433 Sunday 3:00:00 PM - 6:00:00 PM Room: Exhibit Hall

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-shaped isodose-line near point A level. OARs can be spared without dramatically compromise treatment volume coverage around cervix using Method B.

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