Dosimetric accuracy of the cone‐beam CT‐based treatment planning of the Vero system: a phantom study

Abstract

We report an investigation on the accuracy of dose calculation based on the cone‐beam computed tomography (CBCT) images of the nonbowtie filter kV imaging system of the Vero linear accelerator. Different sets of materials and tube voltages were employed to generate the Hounsfield unit lookup tables (HLUTs) for both CBCT and fan‐beam CT (FBCT) systems. The HLUTs were then implemented for the dose calculation in a treatment planning system (TPS). Dosimetric evaluation was carried out on an in‐house‐developed cube phantom that consists of water‐equivalent slabs and inhomogeneity inserts. Two independent dosimeters positioned in the cube phantom were used in this study for point‐dose and two‐dimensional (2D) dose distribution measurements. The differences of HLUTs from various materials and tube voltages in both CT systems resulted in differences in dose calculation accuracy. We found that the higher the tube voltage used to obtain CT images, the better the point‐dose calculation and the gamma passing rate of the 2D dose distribution agree to the values determined in the TPS. Moreover, the insert materials that are not tissue‐equivalent led to higher dose‐calculation inaccuracy. There were negligible differences in dosimetric evaluation between the CBCT‐ and FBCT‐based treatment planning if the HLUTs were generated using the tissue‐equivalent materials. In this study, the CBCT images of the Vero system from a complex inhomogeneity phantom can be applied for the TPS dose calculation if the system is calibrated using tissue‐equivalent materials scanned at high tube voltage (i.e., 120 kV).PACS number(s): 87.55.de, 87.56.Fc, 87.57.qp

A review of dose calculation approaches with cone beam CT in photon and proton therapy

“…Commercial phantoms are now available that provide additional material perpendicular to the CT slices (depth), although a number of authors [33,43,54,55] have reported mimicked this by adding additional material either side of the standard electron density phantoms described above. Differences from the reference dose of less than 0.8% were reported using the Gammex RMI467 phantom [34,46,56] and generally less than 2.0% using CIRS062M phantom when used with extra slabs of water equivalent material to increase the scatter [43,54]. Hatton et al [33] reported mean dose differences up to 22.0% from ionisation chamber measurements when applying a calibration curve from a large diameter phantom to a smaller object, and up to 12.0% when a calibration curve from a small phantom was used for a larger object.…”

“…Both deformable image registration [27][28][29] and artificial intelligence-based methods [16,[30][31][32] were adopted for generating vCT in dose calculation studies. Only two studies reported on the use of farmer chambers and Gafchromic films to measure the actual ground truth dose [33,34] and the measured dose was compared both with the pCT and the CBCT calculated dose.…”

Comparisons of Hounsfield Unit Linearity between Images Reconstructed using an Adaptive Iterative Dose Reduction (AIDR) and a Filter Back-Projection (FBP) Techniques

“…The evaluation is important because, CT analysis currently begins to use quantitative analysis techniques, where accuracy of HU values and its linearity are considered as main indicators [35]. In addition, the CT scanner with IR methods is sometime used in treatment planning where HU accuracy also determines the accuracy of dose planning on radiotherapy to produce better therapeutic outcomes [36]. Although there were several studies evaluating image quality and dose reduction in the IR method [19][20][21][22][23][24][25], the linearity evaluation of HU values has never been carried out.…”

“…The HU linearity evaluation is an important parameter to quantitatively investigate the image quality for maintaining the accuracy of the diagnosis process [35]. Moreover, in the treatment planning systems of radiotherapy, the HU linearity is also as an essential parameter to determine the accuracy of dose planning [36]. Therefore, this research aims to evaluate HU linearity generated by IR techniques and compared to the those acquired by FBP techniques.…”

Adaptive radiotherapy and the dosimetric impact of inter- and intrafractional motion on the planning target volume for prostate cancer patients

“…The system was used to acquire a kV/kV-OIP and a volumetric CBCT data set using a clockwise rotation (315-45°) of one kV-imager with the following parameters:~100 kV, 100 mA, 5 s; 3 mm slice thickness and 512 × 512 matrix size. The field of view (FOV) is restricted to 200 mm in diameter and 150 mm in length [27,28]. All patients were first arranged to skin markers.…”