J Med Assoc Thai 2019; 102 (4):493-502

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Total Marrow Irradiation by Volumetric Modulated Arc Therapy for Treatment of Hematologic Malignancy: A Dosimetric Feasibility Study
Jiarpinitnun C Mail, Worawongsakul R , Sriklay S , Changkaew P , Tangboonduangjit P , Pattaranutaporn P , Swangsilpa T

Objective: The preclinical study was set to investigate the feasibility of volumetric modulated arc therapy (VMAT) technique for the total body irradiation (TBI) and total marrow irradiation (TMI).

Materials and Methods: Computed tomography (CT) simulation data sets for five patients were acquired to create plans for conventional-TBI (C-TBI), VMAT-TBI (V-TBI), and VMAT-TMI (V-TMI). Dose prescription was 12 Gray (Gy) in 2 Gy per fraction, which covered at least 90% of the planning target volume (PTV). Dosimetry of PTV and organs at risk (OARs) were analyzed. ArcCHECK and Radiochromic films were used for verification. Delivery parameters were also recorded.

Results: The average of Dā‚‰ā‚€ of V-TBI and V-TMI were significantly higher than C-TBI (12.15 Gy versus 6.76 Gy, p<0.001). The improvement of homogeneity index (HI) in VMAT over C-TBI (1.15 versus 2.11, p<0.001) was also observed. However, VMAT planning technique could not decrease mean dose of critical organ beyond that by C-TBI technique. The OARs dose ranged from approximately 7.39 to 8.21 Gy for V-TBI and from 5.25 to 10.30 Gy for V-TMI. The average beam on time per fraction of both VMAT plannings were 11 minutes with the mean Gamma Index passing rate of 99.5%.

Conclusion: VMAT technique for TBI could improve dose conformity, homogeneity, and treatment delivery efficacy. The novel TMI could further decrease dose of the other OARs apart from lungs. The pre-treatment quality assurance (QA) confirmed reliability and accuracy. The present study results suggested that VMAT may be a feasible technique for TBI or TMI in the future.

Keywords: Total body irradiation (TBI), Total marrow irradiation (TMI), Volumetric modulated arc therapy (VMAT)

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