A multi-institutional survey on technical variations in total body irradiation in Japan

This study aimed to survey technical variations in total body irradiation (TBI) across Japan. A web-based questionnaire investigating technical aspects (irradiation method, in vivo dosimetry, organ shielding, and boluses) of TBI was distributed via the authors' acquaintances in each region of Japan using snowball sampling, and 73 institutions responded. The data were collected from January to April 2024. Three institutions used two distinct irradiation methods, yielding 76 reported techniques. The reported irradiation techniques included long source-to-surface distance (SSD) techniques, which involve using a large field and extended distance; helical intensity-modulated radiation therapy (IMRT) using specialized equipment (e.g., TomoTherapy), moving couch techniques, and volumetric modulated arc therapy (VMAT) using a standard C-arm linac, with responses totaling 60 (79%), 10 (13%), 4 (5%), and 2 (3%), respectively. All institutions performing IMRT-based (helical IMRT and VMAT) TBI used computed tomography simulation with the patient in the supine position and utilized a 6 MV photon beam. Conversely, the long SSD technique exhibited significant variation; while 47 institutions treated patients exclusively in the supine position, others reported using the prone and lateral positions. Furthermore, the photon beam energies varied, with 10 MV (41 responses), 6 MV (20 responses), and 4 MV (1 response) reported. Notably, 17 institutions using long SSD techniques did not perform in vivo dosimetry and 32 did not use boluses. The differences in the methods used to shield the organs were also reported. These variations highlight the need for standardization of in vivo dosimetry, dose homogeneity strategies, and organ-shielding in TBI.