Abstract
ObjectiveTo assess the effects of various treatment planning parameters to identify the optimal gap distance for precise two-segment total body irradiation (TBI) using helical tomotherapy (HT) with fixed jaw mode.Methods and materialsData of a treatment plan for 8 acute leukemia patients (height range: 109–130 cm) were analyzed. All patients underwent total-body computed tomography (CT) with 5-mm slice thickness. A lead wire, placed at 10 cm above the patella, was used to mark the boundary between the two segments. Target volumes and organs at risk were delineated using a Varian Eclipse 10.0 physician’s workstation. Different distances between the lead wire and the boundary of the two targets were used. CT images were transferred to the HT workstation to design the treatment plans, by adjusting parameters, including the field width (FW; 2.5 cm, and 5 cm), pitch (0.287 and 0.430), modulation factor (1.8). The plans were superimposed to analyze the dose distributions in the overlap region when varying target gap distances, FWs, pitches to determine the optimal combinations.ResultsThe pitch did not affect the dose distribution in the overlap region. The dose distribution in the overlap region was mostly homogeneous when the target gap distance was equal to the FW. Increased FW diminished the effect of the target gap distance on the heterogeneous index of the overlap region.ConclusionsIn two-segment TBI treatments by HT with Helix mode, a gap distance equal to the FW may achieve optimal dose distribution in the overlap region.
Highlights
Total body irradiation (TBI) is a radiation therapy technique that forms an important component of the pretreatment of patients for hematopoietic stem cell or bone marrow transplantation [1,2,3,4]
Increased field width (FW) diminished the effect of the target gap distance on the heterogeneous index of the overlap region
This study evaluated the effects of various parameters on the dose distribution in the overlap regions, to establish optimal parameters in Helical tomotherapy (HT)-TBI
Summary
Total body irradiation (TBI) is a radiation therapy technique that forms an important component of the pretreatment of patients for hematopoietic stem cell or bone marrow transplantation [1,2,3,4]. A rotating gantry delivers radiation while the patient table simultaneously moves It can achieve a highly conformal dose distribution for complex clinical targets while protecting organs at risk (OARs) [7]. For a patient less than 135 cm in height, HT can achieve treatment using a single radiation field (i.e., single-segment TBI); for patients with a height exceeding 135 cm, TBI is split into a superior field and an inferior field (i.e., two-segment TBI) [9, 10]. The distance between these two fields is defined as the gap distance. Using an optimal distance can avoid dosimetric hot or cold spots in the overlap region, reducing the chances of radiationrelated complications and treatment failure [11]
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