SU-FF-T-243: Feasibility of Using Stereotactic Body Radiation as An Alternative to HDR for the Treatment of GYN Sites

Abstract

Purpose: Brachytherapy is frequently used to boost volumes at risk in the treatment of gynecological tumors. Not all the centers have an HDR, or LDR capabilities, however, all have a linear accelerator. We evaluated the possibility of using external beam radiation therapy using Stereotactic Body Radiation Therapy (SBRT) or Intensity Modulated SBRT (IM‐SBRT) approach. Method and Materials: Volumes covered by the HDR prescription were used to define a CTV, with a prescription of 3250 cGy to the CTV over 5 fractions. Planning started with 36 equi‐spaced non‐coplanar beams and beam weight optimization was used to choose the most effective beam orientations. Then, unmodulated beams produced the SBRT plans and by allowing beam modulation IM‐SBRT plans were generated. Both absolute and film dosimetry were performed to ensure accurate deliverability. Results: At least 96% of the CTV was covered by the prescription dose for SBRT and IM‐SBRT plans. Relative to the original HDR plan, bladder dose reduced by 12.8% and 38.5% by SBRT and IM‐SBRT respectively. Rectal dose increased by 49.3% using SBRT and decreased by 5.1% using IM‐SBRT. As expected, The integral dose outside CTV was higher in SBRT and IM‐SBRT approaches. Conclusion: SBRT and IM‐SBRT methods provided similar tumor coverage to HDR. IM‐SBRT reduced dose to bladder and rectal point. In the near future we will be evaluating a novel new device to localize the anatomy on a daily basis so that a precise delivery is possible.