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A Novel IMRT Planning Technique to Spare Sacral Bone Marrow in Pelvic Cancer Patients

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S McGuire

S McGuire*, S Bhatia , W Sun , Y Menda , L Ponto , B Gross , J Buatti , University Of Iowa, Iowa City, IA


SU-E-J-125 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: Develop an IMRT planning technique that can preferentially spare sacral bone marrow for pelvic cancer patients.

Methods: Six pelvic cancer patients (two each with anal, cervical, and rectal cancer) were enrolled in an IRB approved protocol to obtain FLT PET images at simulation, during, and post chemoradiation therapy. Initially, conventional IMRT plans were created to maintain target coverage and reduce dose to OARs such as bladder, bowel, rectum, and femoral heads. Simulation FLT PET images were used to create IMRT plans to spare bone marrow identified as regions with SUV of 2 or greater (IMRT-BMS) within the pelvic bones from top of L3 to 5mm below the greater trochanter without compromising PTV coverage or OAR sparing when compared to the initial IMRT plan. IMRT-BMS plans used 8-10 beam angles that surrounded the subject. These plans were used for treatment. Retrospectively, the same simulation FLT PET images were used to create IMRT plans that spared bone marrow located in the sacral pelvic bone region (IMRT-FAN) also without compromising PTV coverage or OAR sparing. IMRT-FAN plans used 16 beam angles every 12° anteriorly from 90° – 270°. Optimization objectives for the sacral bone marrow avoidance region were weighted to reduce ≤V10.

Results: IMRT-FAN reduced dose to the sacral bone marrow for all six subjects. The average V5, V10, V20, and V30 differences from the IMRT-BMS plan were -2.2 ± 1.7%, -11.4 ± 3.6%, -17.6 ± 5.1%, and -19.1 ± 8.1% respectively. Average PTV coverage change was 0.5% ± 0.8% from the conventional IMRT plan.

Conclusion: An IMRT planning technique that uses beams from the anterior and lateral directions reduced the volume of sacral bone marrow that receives ≤10Gy while maintaining PTV coverage and OAR sparing. Additionally, the volume of sacral bone marrow that received 20 or 30 Gy was also reduced.

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