Abstract
A robust method for voxel by voxel enhancement of Cone-beam CT (CBCT) images using a priori knowledge from the planning Computed Tomography (pCT) scan has been developed and used to evaluate the dosimetric accuracy of pCT based CBCT correction method for SBRT dose verification in lung metastasis. This is a retrospective study under which SBRT is carried out in 10 patients presented with lung metastasis. pCT images of patients were acquired and treatment planning was carried out on Varian Eclipse (V11) for 30 Gy in 5 fractions. Daily imaging using CBCT has been done for each patient with an On-Board Imaging system. CBCT is corrected using Matlab function considering CT as fixed and CBCT as moving, the images are registered. Planning target volume (PTV), lung, heart and spine were recontoured on uncorrected CBCT and corrected CBCT separately and the calculated plan on CT is recalculated on both the CBCTs. The dose distribution between the pCT and both the CBCT images were compared. A paired sample test was performed to test the variations. The distribution of pixel intensity of corrected CBCT is closer to the pCT than the uncorrected CBCT. The maximum percentage difference between the corrected CBCT and pCT is 1% in PTV evaluation, which is 3.5% between uncorrected CBCT and pCT. The method increases the accuracy of CBCT density values and enabling the use of CBCT images for dose calculation in radiotherapy.
Highlights
In the age of progressive external beam radiation therapy, image guidance has become important to reduce the random as well as systematic errors in the patient setups
Numbers of studies have investigated the utilization of Cone-beam Computed Tomography (CT) (CBCT) for dose calculation [2, 3] as CBCT images are easy to acquire before treatment whereas repeat CT during the course of radiotherapy is difficult for patients
A robust method for voxel by voxel enhancement of Cone beam CT (CBCT) images using a priori knowledge from the planning Computed Tomography scan has been developed and used to evaluate the dosimetric accuracy of pCT based CBCT correction method for stereotactic body radiation therapy (SBRT) dose verification in lung metastasis
Summary
In the age of progressive external beam radiation therapy, image guidance has become important to reduce the random as well as systematic errors in the patient setups. CBCT images for each treatment fraction can provide sufficient anatomical information for correcting setup errors and can be used for adaptive radiotherapy where the treatment plan is modified based on regular imaging throughout the treatment course. Numbers of studies have investigated the utilization of CBCT for dose calculation [2, 3] as CBCT images are easy to acquire before treatment whereas repeat CT during the course of radiotherapy is difficult for patients. The importance of CBCT is limited to image guidance it can be utilized for treatment planning and dose verification for patients during their course of radiotherapy.
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