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The Evaluation of Total Marrow Irradiation Volumetric Modulated Arc Therapy Treatment Planning Using the Millennium and High Definition MLC

D Zuro1*, G Vidal1, C Henson1, C Han2, S Hui3, S Ahmad1, I Ali1, (1) University of Oklahoma Health Sciences Center, Oklahoma City, OK, (2) City of Hope Medical Center, Duarte, CA, (3) Beckman Research Institute, Duarte, CA

Presentations

SU-E-206-8 (Sunday, 7/10/2022) 1:00 PM - 2:00 PM [Eastern Time (GMT-4)]

Room 206

Purpose: The goal of this work is to test the feasibility of treatment planning for total marrow irradiation (TMI) using the high-definition multiple-leaf-collimator (HDMLC) and compare the quality and effectiveness of the HDMLC system to the traditionally used Millennium MLC system.

Methods: Treatment plans were generated using the Eclipse treatment planning system for TMI patients with both the HDMLC and millennium-MLC systems on Varian linear accelerators. Five planning target volumes (PTV) that include bones, ribs, lymph-nodes spleen were covered by 20 Gy dose and two PTVs for the brain and liver were covered by 12 Gy with volumetric-modulated-arc-therapy (VMAT). Eight arcs with four isocenters with asymmetric jaws along the longitudinal patient direction were used for planning. Different dosimetric parameters that include D80, D50, and D10 were used to assess the quality of the plans from the two MLC-systems.

Results: The HDMLC provided a similar conformal dose distribution with a conformality index of 0.85 for both plans. Because of the smaller size of the MLC the HDMLC-plans experienced reduction of 16% in the D50 for the Ribs because of the smaller field size covered by the arcs, while the liver dose increased by 6% because of increased intensity modulation. However, HDMLC-TMI-plans performance was inferior to the millennium MLC considering their smaller effective treatment area. For HDMLC the separation between the arcs should be smaller and more arcs are needed for dose coverage. Furthermore, higher D50 for spleen (38%) and liver (30%) are observed in HDMLC plans because of increased intensity modulation by the smaller leaves.

Conclusion: The treatment plans with the HDMLC provided similar conformal dose to the targets. However, more arcs are needed for adequate dose coverage and higher dose gradients are produced because of increased intensity modulation by the small leaves.

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