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Abstract
BackgroundTo evaluate the combined effect of rotational error and dose gradient on target dose coverage in frameless stereotactic radiotherapy.MethodsThree spherical targets of different diameters (1, 1.5, and 2 cm) were drawn and placed equidistantly on the same axial brain computed tomography (CT) images. To test the different isocenter-target distances, 2.5- and 5-cm configurations were prepared. Volumetric modulated arc therapy plans were created for different dose gradients from the target, in which the dose gradients were modified using the maximum dose inside the target. To simulate the rotational error, CT images and targets were rotated in two ways by 0.5°, 1°, and 2°, in which one rotation was in the axial plane and the other was in three dimensions. The initial optimized plan parameters were copied to the rotated CT sets, and the doses were recalculated. The coverage degradation after rotation was analyzed according to the target dislocation and 12-Gy volume.ResultsA shallower dose gradient reduced the loss of target coverage under target dislocation, and the effect was clearer for small targets. For example, the coverage of the 1-cm target under 1-mm dislocation increased from 93 to 95% by increasing the Paddick gradient index from 5.0 to 7.9. At the same time, the widely accepted necrosis indicator, the 12-Gy volume, increased from 1.2 to 3.5 cm3, which remained in the tolerable range. From the differential dose volume histogram (DVH) analysis, the shallower dose gradient ensured that the dose-deficient under-covered target volume received a higher dose similar to that in the prescription.ConclusionsFor frameless stereotactic brain radiotherapy, the gradient, alongside the margin addition, can be adjusted as an ancillary parameter for small targets to increase target coverage or at least limit coverage reduction in conditions with probable positioning error.
Highlights
Linear accelerators have been widely employed for stereotactic radiosurgery (SRS) and fractionated stereotactic radiation treatment (FSRT)
For the case of r2.5D110 shown in Fig. 2, the 9-Gy volumes were not separated for each target because of the low dose bridges between targets
The combination of the rotational error and gradient variation in our study revealed that decreasing gradient steepness increases the target coverage for the same positional error
Summary
Linear accelerators have been widely employed for stereotactic radiosurgery (SRS) and fractionated stereotactic radiation treatment (FSRT). Yoon et al Radiat Oncol (2021) 16:169 in image-guided radiotherapy (IGRT), the framed era has evolved to noninvasive frameless fixation using a mask [1,2,3,4,5]. Because SRS/FSRT delivers an unusually high dose to the target in a single or few fractions, high targeting accuracy is necessary for complete tumor eradication and normal brain protection. With concerns regarding probable intrafractional error during treatment, several groups have studied target positional accuracy and its dosimetric effect [9,10,11,12]. To evaluate the combined effect of rotational error and dose gradient on target dose coverage in frameless stereotactic radiotherapy
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