Dosimetric analysis of VMAT-TBI: measurement of organ and junction dose using a whole body anthropomorphic phantom.

Abstract

Total body irradiation (TBI) is an essential component of conditioning regimens for hematopoietic stem cell transplantation. Volumetric Modulated Arc Therapy-TBI (VMAT-TBI) has recently emerged as an innovative alternative to conventional TBI that offers improved dose conformity. However, VMAT-TBI introduces junction regions between adjacent fields, making dosimetric verification crucial for ensuring uniform dose delivery. In addition, measurement of organ dose in organs such as brain, eyes, heart, liver, lung, kidney, and spinal cord is important for minimizing acute and late toxicities. The present study aimed at measuring the organ and junction doses using a whole body anthropomorphic phantom (ATOM 701-D, CIRS, Norfolk, Virginia). This phantom includes capsule-containing thermoluminescence dosimeters (TLDs) at multiple positions within organ and field junction. Computed Tomography (CT) images of the phantom were acquired to delineate different organs and the TLD locations. A treatment plan comprising four sub-plans with three junction fields was generated using the Eclipse treatment planning system (Version 17.0, Varian Medical Systems, Palo Alto, CA) to deliver 95% of the prescription dose to 95% of the planning target volume (PTV). Conformal dose coverage of the PTV was achieved and organ doses were within acceptable tolerances. The percentage deviation between doses measured with the TLDs and those calculated with the treatment planning system (TPS) with respect to prescription dose was evaluated at 38 positions (26 within various organs and 12 within junction regions). Percentage deviations at the 12 positions in the junction regions and 21 positions within organs were within ± 5% with a slightly higher differences ranging from − 6.72% to 7.43% at remaining five positions. The results demonstrate the effectiveness of VMAT-TBI as a promising alternative to conventional TBI, for hematopoietic stem cell transplantation.