Program Information
Direct Dose Comparison of Linac-Based Total Body and Total Marrow Irradiation Treatment Plans
G Warrell1*, V Colussi1,2 , D Mansur1,2 , W Swanson2 , G Pereira1,2 , (1) Case Western Reserve University, Cleveland, OH, (2) University Hospitals Cleveland Medical Center, Cleveland, OH
Presentations
SU-F-FS2-1 (Sunday, July 30, 2017) 2:05 PM - 3:00 PM Room: Four Seasons 2
Purpose: Total marrow irradiation (TMI) has been developed as an alternative to total body irradiation (TBI) as conditioning for bone marrow transplantation. The use of intensity-modulated radiation therapy methods permits substantial organ dose sparing and higher prescription dose. This study presents a direct dose comparison of target and organs of risk between TMI and TBI conducted in our institution.
Methods: 5 TMI treatments were planned via multi-isocentric feathered volumetric modulated arc therapy plans (VMAT). The CTV was defined as bones plus spleen, excluding mandible. The PTV was created by a 5mm expansion to the CTV. VMAT was accomplished by inverse planning in Philips Pinnacle (ver9.10) using its collapsed-cone convolution dose calculation algorithm. The treatments were delivered using the 6MV photon beams of Elekta Synergy linacs. The same CT datasets acquired for planning the TMI were used to plan TBIs with 15MV photon extended-field AP/PA plans, using partial lung blocks and a 1cm-thick acrylic beam spoiler, with no compensators. Dose distributions obtained for both plan types were compared.
Results: As anticipated, planned doses to organs at risk were much lower for TMI plans than for TBI plans: reductions to mean dose to the kidneys, lungs, and brain were 55.1%, 41.6%, and 30.6%, respectively (p<0.01). Mean dose reductions to the heart, liver, globes of the eyes, and parotids provided by TMI were 47.5%, 52.0%, 43.5%, and 47.8%, respectively. No significant differences were noted in homogeneity indices for the defined CTV between TMI and TBI plans, although TMI provided superior rib coverage due to the lung blocks required for TBI.
Conclusion: Linac-based TMI plans demonstrate superior dosimetry to extended-field AP/PA TBI fields generated for the same patient datasets. Moreover, treatments in the prone position in TMI are expected to less physically demanding to the patient than TBI treatments in the standing position.
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