Abstract
BackgroundTo investigate the feasibility of using dual-energy CT (DECT) for tissue segmentation and kilovolt (kV) dose calculations in pre-clinical studies and assess potential dose calculation accuracy gain.MethodsTwo phantoms and an ex-vivo mouse were scanned in a small animal irradiator with two distinct energies. Tissue segmentation was performed with the single-energy CT (SECT) and DECT methods. A number of different material maps was used. Dose calculations were performed to verify the impact of segmentations on the dose accuracy.ResultsDECT showed better overall results in comparison to SECT. Higher number of DECT segmentation media resulted in smaller dose differences in comparison to the reference. Increasing the number of materials in the SECT method yielded more instability. Both modalities showed a limit to which adding more materials with similar characteristics ceased providing better segmentation results, and resulted in more noise in the material maps and the dose distributions. The effect was aggravated with a decrease in beam energy. For the ex-vivo specimen, the choice of only one high dense bone for the SECT method resulted in large volumes of tissue receiving high doses. For the DECT method, the choice of more than one kind of bone resulted in lower dose values for the different tissues occupying the same volume. For the organs at risk surrounded by bone, the doses were lower when using the SECT method in comparison to DECT, due to the high absorption of the bone. SECT material segmentation may lead to an underestimation of the dose to OAR in the proximity of bone.ConclusionsThe DECT method enabled the selection of a higher number of materials thereby increasing the accuracy in dose calculations. In phantom studies, SECT performed best with three materials and DECT with seven for the phantom case. For irradiations in preclinical studies with kV photon energies, the use of DECT segmentation combined with the choice of a low-density bone is recommended.
Highlights
To investigate the feasibility of using dual-energy Computed Tomography (CT) (DECT) for tissue segmentation and kilovolt dose calculations in pre-clinical studies and assess potential dose calculation accuracy gain
This study has demonstrated the high impact of incorrect material segmentation on the dose calculation accuracy for kV photon beams employed in small animal irradiators, using the different imaging modalities: single energy CT (SECT) and dual-energy CT (DECT)
The DECT method enabled the employment of a higher number of materials increasing accuracy in dose calculations
Summary
To investigate the feasibility of using dual-energy CT (DECT) for tissue segmentation and kilovolt (kV) dose calculations in pre-clinical studies and assess potential dose calculation accuracy gain. Pre-clinical radiation studies with small animal models play a significant role in the understanding of cancer radiobiology. Such studies aim towards mimicking human treatment capabilities so that specific validated radiation therapies in animal models can be successfully translated into patient radiotherapy (RT) trials [1]. Accurate preclinical radiation targeting requires accurate image guiding. In the kV energy range, the photo-electric effect is increasingly important and its interaction probability is Vaniqui et al Radiation Oncology (2017) 12:181 strongly dependent on the effective atomic number of the tissues (Ze3ff4) [3]. In Monte Carlo (MC) dose calculations, every voxel of the CT scan has a mass density assigned based on the HU value through an empirical calibration
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