Author: Kai-Cheng Chuang, Oana I. Craciunescu, Christopher Kelsey, Joseph Kowalski, Nicole Larrier, Xinyi Li, Sheridan G. Meltsner, Anna E. Rodrigues, Yang Sheng, Qiuwen Wu 👨🔬
Affiliation: Duke University, Duke University Medical Center 🌍
Purpose: To clinically implement a Volumetric Modulated Arc Therapy (VMAT) procedure for Total Body Irradiation (TBI) with off-the-shelf tools.
Methods: Patient is treated on linac couch with a hybrid approach of VMAT delivered in Head-First-Supine (HFS) orientation for upper body and intensity-modulated radiation therapy (IMRT) or open fields delivered in Feet-First-Supine (FFS) orientation for lower body.
During CT simulation, patient is immobilized in full-body vacuum bags and scanned in HFS for upper body and FFS orientations for lower body, respectively. These 2 CT scans are merged into single one for planning
During planning in Eclipse V16, the lower body plan (LBP) is created with intensity-modulated radiation therapy (IMRT) or open fields with 2-3 isocenters with a 270° collimator angle. This LBP is used as a base plan for upper body plan (UBP) optimization with junction feathering. The UBP consists of 3-4 isocenters, each has 2 overlapping full arcs with a 90° collimator angle. 1 cm virtual bolus is created as skin flash and removed before final dose calculation. For treatment preparation, the LBP is converted to the FFS orientation by changing the collimator angle to 90°.
Results: Both plans can be completed <2.5h using CT with 3 mm slice thickness. PTV coverage of ~85%, with Dmax < 130% is achievable. The Dmean for lungs-1cm and kidneys can meet the dose constraints and be as low as 30%. PDQA for all fields passed at 100% Gamma passing rate with 3%/2mm criteria. Total MU is about 6000~10000MU assuming 2Gy/fx, and total beam-on time is 10-15 with 600MU/min dose rate. Total treatment time per fraction including imaging and setup is estimated to be ~1.5h.
Conclusion: An efficient clinical workflow was developed for VMAT TBI using existing clinical equipment and techniques, which can be adapted for Total Marrow and Lymphatic Irradiation (TMLI) treatment.