Volumetric Modulated Arc Therapy Enabled Total Body Irradiation (VMAT-TBI) Vs. Conventional TBI (ctbi): A Comparison of Treatment Outcomes and Toxicities

Purpose/Objective(s) Volumetric modulated arc therapy enabled TBI (VMAT-TBI) is a novel form of TBI that allows for accurate and comfortable treatment of a patient in the supine position in a standard-size vault. While the technique and initial institutional experiences are now well reported, minimal data exist comparing clinical outcomes and toxicities to conventional TBI (cTBI). We sought to compare patients at our institution who received VMAT-TBI vs. cTBI, with the hypothesis that treatment outcomes and toxicities would be similar between the two groups. Materials/Methods An IRB-approved, retrospective review was performed of all patients treated with TBI (N=95) at our institution from 2010-2020. In the cTBI group (N=51), 26 patients (51%) received low-dose TBI (2-4 Gy in 1 fraction) while 25 (49%) received standard-dose TBI (12-13.2 Gy in 6-8 fractions BID). In the VMAT-TBI group (N=44), 12 (27%) received low-dose TBI while 32 (73%) received standard-dose TBI. Primary endpoints include Kaplan-Meier estimates of overall survival (OS) and relapse free survival (RFS), as well as rates of toxicities (CTCAE v5) and graft versus host disease (GVHD) (Glucksberg). Statistical software was used to compare groups with student's T-test for survival outcomes and Chi-square analysis for toxicities. Results With a median follow up of 28 months, the survival outcomes between the two groups were similar. The 1- and 2-year OS for VMAT-TBI vs. cTBI were 90% vs. 76% (p=0.055) and 79% vs. 67% (p=0.142), respectively, and 1- and 2-year RFS were 88% vs. 59% (p=0.152) and 71% vs. 45% (p=0.152), respectively. The median time to relapse after transplant were 11.3 months vs. 12.2 months (p=0.421). Toxicities were compared only among those receiving standard-dose TBI. Common toxicities among patients in both the VMAT-TBI and cTBI cohorts included diarrhea (91% vs. 76%, p=0.133) and fatigue (78% vs 68%, p=0.389). VMAT-TBI patients experienced lower rates of nausea than cTBI patients (48% vs. 84%, p=0.006) but higher overall rates of mucositis (94% vs. 72%, p=0.025) and grade 3+ mucositis (84% vs. 28%, p<0.001). Rates of pneumonitis (13% vs. 8%, p=0.583) and nephrotoxicity (13% vs 12%, p=0.954) were similar in both groups. Rates of GVHD were similar between both cohorts for skin (45% vs 55%, p=0.306), gut (18% vs 18%, p=0.987), liver (12% vs 16%, p=0.405), and lung (8% vs. 9%, p=0.853). Conclusion Patients treated with VMAT-TBI appear to have similar outcomes and toxicities as those treated with cTBI, with the exceptions of lower nausea and higher oral mucositis, which is likely multifactorial but may be related to higher dose to the oral cavity. The current advantages of VMAT-TBI include improved treatment accuracy, patient comfort, and access as able to treat without an extended vault. However, the main advantage of VMAT-TBI is its dose modulation ability, allowing for new treatment strategies such as simultaneous integrated boost and further normal tissue sparing, which may ultimately result in better treatment outcomes with lower toxicities.