Cone beam CT dose reduction in prostate radiotherapy using Likert scale methods

Abstract

Objective: To use a Likert scale method to optimize image quality (IQ) for cone beam CT (CBCT) soft-tissue matching for image-guided radiotherapy of the prostate. Methods: 23 males with local/locally advanced prostate cancer had the CBCT IQ assessed using a 4-point Likert scale (4 5 excellent, no artefacts; 3 5 good, few artefacts; 2 5 poor, just able to match; 1 5 unsatisfactory, not able to match) at three levels of exposure. The lateral separations of the subjects were also measured. The Friedman test and Wilcoxon signed-rank tests were used to determine if the IQ was associated with the exposure level. We used the point-biserial correlation and a x 2 test to investigate the relationship between the separation and IQ.Results: The Friedman test showed that the IQ was related to exposure (p 5 2 3 10 27) and the Wilcoxon signed-rank test demonstrated that the IQ decreased as exposure decreased (all p-values ,0.005). We did not find a correlation between the IQ and the separation (correlation coefficient 0.045), but for separations ,35 cm, it was possible to use the lowest exposure parameters studied. Conclusion:We can reduce exposure factors to 80% of those supplied with the system without hindering the matching process for all patients. For patients with lateral separations ,35 cm, the exposure factors can be reduced further to 64% of the original values. Advances in knowledge: Likert scales are a useful tool for measuring IQ in the optimization of CBCT IQ for soft-tissue matching in radiotherapy image guidance applications.

Why small towns can not share the benefits of urbanization in China?

“…Content analysis involves combing and mining the documents and files, which is widely used in social science research (Weber, 1990;Yu et al, 2015). Likert scale scoring method is a proven effective approach to scale responses in conducting survey research (Rasmussen, 1989;Rogers et al, 2001;Langmack et al, 2015;Peng et al, 2015). Following the above research procedures, discussions are conducted on the implications of those significant barriers.…”

Registration accuracy with the low dose kilovoltage cone-beam CT: A phantom study

“…However, they did not consider the effect of dose reduction on the registration results, only visually evaluating the image quality at the image registration. 12 By evaluating the results of the image registration, we identified the minimum imaging dose that still allowed image registration accuracy for IGRT to be maintained. Sykes et al evaluated the impact of reducing the projection numbers on image quality and image registration, but image registration was performed only on the head, which did not require soft tissue matching.…”

“… 8–11 The methods available for reducing the imaging dose include reduction of the mAs value, the projection number used for reconstruction, and the scan length, the use of a filter, and changing of the imaging angle. 12–17 The mAs value has a linear correlation with imaging dose, 1 and it can be adjusted at the time of imaging, with the imaging dose being estimated simultaneously. However, a reduction in the imaging dose increases noise, which leads to deterioration in image quality.…”

Optimisation of Varian TrueBeam head, thorax and pelvis CBCT based on patient size

“…Indeed currently, no technological method for optimising patient dose during a linac-based CBCT is available. Strategies for optimising CT and CBCT patient dose and image quality based on patient size have been reported in the literature [18][19][20][21][22][23][24][25][26][27] and presented at national conferences. 28,29 Optimisation of CBCT has focussed primarily on patient size optimisation of mAs settings for pelvis protocols.…”