Abstract
The purpose of this study was to develop dosimetry verification procedures for volumetric‐modulated arc therapy (VMAT)‐based total marrow irradiation (TMI). The VMAT based TMI plans were generated for three patients: one child and two adults. The planning target volume (PTV) was defined as bony skeleton, from head to mid‐femur, with a 3 mm margin. The plan strategy similar to published studies was adopted. The PTV was divided into head and neck, chest, and pelvic regions, with separate plans each of which is composed of 2–3 arcs/fields. Multiple isocenters were evenly distributed along the patient's axial direction. The focus of this study is to establish a dosimetry quality assurance procedure involving both two‐dimensional (2D) and three‐dimensional (3D) volumetric verifications, which is desirable for a large PTV treated with multiple isocenters. The 2D dose verification was performed with film for gamma evaluation and absolute point dose was measured with ion chamber, with attention to the junction between neighboring plans regarding hot/cold spots. The 3D volumetric dose verification used commercial dose reconstruction software to reconstruct dose from electronic portal imaging devices (EPID) images. The gamma evaluation criteria in both 2D and 3D verification were 5% absolute point dose difference and 3 mm of distance to agreement. With film dosimetry, the overall average gamma passing rate was 98.2% and absolute dose difference was 3.9% in junction areas among the test patients; with volumetric portal dosimetry, the corresponding numbers were 90.7% and 2.4%. A dosimetry verification procedure involving both 2D and 3D was developed for VMAT‐based TMI. The initial results are encouraging and warrant further investigation in clinical trials.PACS number: 87.55.Qr
Highlights
Total body irradiation (TBI) is commonly used in conjunction with chemotherapy as a conditioning regimen prior to bone marrow transplantation in patients with hematological malignancies
This may be advantageous in pediatric cases due to concern regarding developmental abnormalities and late radiation effects associated with conventional TBI.[4]
The objective of this study is to develop dosimetry quality assurance procedure involving both 2D and 3D volumetric verifications, which is desirable for a large planning target volume (PTV) in the case of total marrow irradiation (TMI)
Summary
Total body irradiation (TBI) is commonly used in conjunction with chemotherapy as a conditioning regimen prior to bone marrow transplantation in patients with hematological malignancies. Compared to conditioning regimens based on chemotherapy alone, TBI is advantageous because it is independent of factors such as blood supply, drug activation, metabolism, or hepatic or renal function. Lung blocks are often used in conventional TBI. TBI is constrained by toxicities to OARs, which limits opportunity for dose escalation. Conformal TBI techniques could reduce dose to OARs and permit dose escalation. This may be advantageous in pediatric cases due to concern regarding developmental abnormalities and late radiation effects associated with conventional TBI.[4]
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