Abstract
Cone-beam CT (CBCT) images acquired during radiation treatment can be used to recalculate the dose distribution as well as to confirm the treatment location. However, it is difficult to obtain the electron densities (EDs) necessary for dose calculation from CBCT images because of the effects of scatter contamination during CBCT image acquisition. This paper presents a mathematical method for converting the pixel values of CBCT images (CBCT values) into Hounsfield units (HUs) of radiation treatment simulation CT (simCT) images for use in radiation treatment planning. CBCT values are converted into HUs by matching the histograms of the CBCT values with the histograms of the HUs for each slice via linear scaling of the CBCT values. For prostate cancer and head-and-neck cancer patients, the EDs obtained from converted CBCT values (mCBCT values) show good agreement with the EDs obtained from HUs, within approximately 3.0%, and the dose calculated on the basis of CBCT images shows good agreement with the dose calculated on the basis of the simCT images, within approximately 2.0%. Because the CBCT values are converted for each slice, this conversion method can account for variation in the CBCT values associated with differences in body size, body shape, and inner tissue structures, as well as in longitudinally displaced positions from the isocenter, unlike conventional methods that use electron density phantoms. This method improves on conventional CBCT-ED conversion and shows considerable potential for improving the accuracy of radiation treatment planning using CBCT images.
Highlights
A cone-beam computed tomography (CBCT) unit is mounted on most linear accelerators
This paper presents a mathematical method for converting the pixel values of Cone-beam CT (CBCT) images (CBCT values) into Hounsfield units (HUs) of radiation treatment simulation CT images for use in radiation treatment planning
For prostate cancer and head-and-neck cancer patients, the electron densities (EDs) obtained from converted CBCT values show good agreement with the EDs obtained from HUs, within approximately 3.0%, and the dose calculated on the basis of CBCT images shows good agreement with the dose calculated on the basis of the simulation CT (simCT) images, within approximately 2.0%
Summary
The effective use of CBCT images reduces patient setup inaccuracy by rigid image registration between daily CBCT images and radiation treatment simulation CT (simCT) images [1] [2]. CBCT images can be used to recalculate the daily dose to a patient and facilitate the use of adaptive radiation therapy (ART), which accounts for daily anatomical changes in the target and the OARs [4]. The dose calculations in a radiation treatment planning system (RTPS) are performed using an HU-ED or HU-PD conversion table that converts Hounsfield units (HUs) in simCT images into electron densities (EDs) or physical densities (PDs) [5] [6] [7]. It is difficult to convert CBCT values directly into electron densities
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
