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Investigation of Volumetric Modulated Arc Therapy for Total Body Irradiation with Lung Blocks

H Wang

H Wang*, S Tung, C Wang, A Mahajan, B Dabaja, M Martel, UT MD Anderson Cancer Center, Houston, TX

SU-E-T-592 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose:Uncertainties from the use of lung blocks during total body irradiation (TBI) are present due to the process of block cutting and block mounting required for treatment. We investigated the use of volumetric modulated arc therapy (VMAT) to improve clinical TBI practice.

Methods:Two pediatric patients (Pat-1, Pat-2) and one adult patient (Pat-3) had CT scans from head to upper thigh. The treatment targets (12Gy) included bony structures (all patients) and lymph nodes+spleen (LNS) (Pat-1, Pat-3). Three plans were generated in Pinnacle for each patient: TBI plans with AP/PA fields at 380cm SAD with and without lung blocks and a VMAT plan at 100 SAD with 3-4 couch positions. Target coverage V12Gy and dose to lung V6Gy were compared among three plans for each patient. Treatment times as well as doses to other critical structures were also compared for different techniques.

Results:for AP/PA plans, lung blocks reduced lung V6Gy to 28.7%, 6.3% and 24.9% for these three patients from 100% (without block), however, target V12Gy decreased to 72.5%, 68.6%, and 88.7% from 84.9%, 86.3%, 95.5% (without block), respectively. VMAT plan achieved 44.3%, 53.7% and 71.5% for lung V6Gy with excellent target coverage of 91.7%, 96.2% and 95.3%. While lung blocks only be used 3/8 treatments for AP/PA TBI, VMAT plan lung mean doses were 21-35% lower than AP/PA+block technique. Meanwhile, average mean dose to the brain, heart, kidneys and liver was also reduced 40%, 43.7%, 41.1% and 40.6% using VMAT plans. VMAT planning was more challenging when targets include LNS and/or for large patients (shoulder>40cm, Pat-3). Setup and beam-on time for VMAT were comparable to or less than AP/PA technique for Pat-1, Pat-2, but were much longer for Pat-3.

Conclusion:VMAT plans have potential to reduce uncertainties for treating small-medium sized patients who need lung blocks in TBI treatments.

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