A GPU-based finite-size pencil beam algorithm with 3D-density correction for radiotherapy dose calculation

Targeting at the development of an accurate and efficient dose calculation engine for online adaptive radiotherapy, we have implemented a finite size pencil beam (FSPB) algorithm with a 3D-density correction method on GPU. This new GPU-based dose engine is built on our previously published ultrafast FSPB computational framework [Gu et al. Phys. Med. Biol. 54 6287-97, 2009]. Dosimetric evaluations against Monte Carlo dose calculations are conducted on 10 IMRT treatment plans (5 head-and-neck cases and 5 lung cases). For all cases, there is improvement with the 3D-density correction over the conventional FSPB algorithm and for most cases the improvement is significant. Regarding the efficiency, because of the appropriate arrangement of memory access and the usage of GPU intrinsic functions, the dose calculation for an IMRT plan can be accomplished well within 1 second (except for one case) with this new GPU-based FSPB algorithm. Compared to the previous GPU-based FSPB algorithm without 3D-density correction, this new algorithm, though slightly sacrificing the computational efficiency (~5-15% lower), has significantly improved the dose calculation accuracy, making it more suitable for online IMRT replanning

Algorithm for the reconstruction of dynamic objects in CT-scanning using optical flow

Computed Tomography is a powerful imaging technique that allows non-destructive visualization of the interior of physical objects in different scientific areas. In traditional reconstruction techniques the object of interest is mostly considered to be static, which gives artefacts if the object is moving during the data acquisition. In this paper we present a method that, given only scan results of multiple successive scans, can estimate the motion and correct the CT-images for this motion assuming that the motion field is smooth over the complete domain using optical flow. The proposed method is validated on simulated scan data. The main contribution is that we show we can use the optical flow technique from imaging to correct CT-scan images for motion

Optimizing computed tomography : quality assurance, radiation dose and contrast media

Computed tomography (CT) is an important modality in radiology; it enables imaging of the inside of patients without superimposed anatomy. The radiation dose and quality of a CT image are highly dependent on the CT scanner, the scan settings and, if applicable, the timing and dosage of the intravenous contrast media (CM). The aim of this Thesis was to develop tools and insights that help maximize the value of examinations for patients undergoing CT and to reduce its cost in terms of radiation and CM dose. The Thesis consists of five studies. The first paper was on quality control (QC) of CT, which is the foundation for a radiology clinic: it provides trust that the equipment functions as expected. A new method of performing routine QCs was proposed where the concept of key performance indicators (KPI) was introduced, together with a semi-automatic process allowing for daily QCs. During the time of the study, multiple deviations were discovered that would have been difficult to detect using traditional QCs. Performing QCs more frequently facilitates more extensive trend analysis. The second paper was on automatic tube current modulation (ATCM). A phantom and a method for the characterization of ATCM were developed. These allowed for a characterization of CT scanners from the four main CT vendors in Sweden, summarized in four extensive tables showing how the ATCM responds to changes in scan parameters. More specifically, the tables present how changes in scan settings of the localizer radiograph (LR), scan settings of the acquisition, reconstruction parameters and patient miscentering affect the ATCM. The third paper was on radiation dose estimation uncertainties coupled to the patient table. In most commercial radiation dose estimation software packages for CT, the patient table is not included. That effect was previously unknown but could be shown using Monte Carlo (MC) calculations of CT scans performed with and without the patient table. It was shown that by not including the effect from the patient table in radiation dose estimations, the radiation doses are overestimated by 5% to 23%, depending on the scan mode. The fourth paper evaluated whether the standard LR can be replaced by a low-dose spiral scan, a so-called synthetic LR (SLR). Such an SLR can potentially improve ATCM, CM dosage and CT planning. Radiation doses were estimated using MC, the image quality was compared in a prospective study of ten patients and the impact of miscentering was investigated with a phantom measurement of water equivalent diameters. It was shown that the radiation doses and the image quality of SLR and LRs were similar. Estimated water equivalent diameters were more consistent when calculated from the low-dose spiral scan compared to the LRs. It was concluded that it is feasible to replace the traditional LR with an SLR for CT scan planning. The fifth paper was a continued investigation of the low-dose spiral scan, but with focus on intravenous CM dosage planning. Altogether, 238 patients who had undergone PET/CT and ii for whom body metrics (height and weight) had been acquired were retrospectively analyzed, the CT number enhancement of the liver was measured, and body volumes of muscle and fat were calculated using the attenuation correction CT (low-dose spiral scan). Multiple linear regressions showed that for CM dose planning, the body volumes of muscle and fat are better to use than body weight. However, the adjusted R2 values of all the investigated models were low, indicating that responses to CM dosage are complex and require more research. In this PhD Thesis, tools and insights were developed to improve the imaging stability of the CT scan by developing semi-automatic QC protocols and techniques to better estimate patient size and shape potentially reducing variation in image quality, radiation dose and CM enhancement among patients

A holistic multi-scale approach to using 3D scanning technology in accident reconstruction

Three-dimensional scanning and documentation methods are becoming increasingly employed by law enforcement personnel for crime scene and accident scene recording. Three-dimensional documentation of the victim’s body in such cases is also increasingly used as the field of forensic radiology and imaging is expanding rapidly. These scanning technologies enable a more complete and detailed documentation than standard autopsy. This was used to examine a fatal pedestrian-vehicle collision where the pedestrian was killed by a van whilst crossing the road. Two competing scenarios were considered for the vehicle speed calculation: the pedestrian being projected forward by the impact or the pedestrian being carried on the vehicle’s bonnet. In order to assist with this, the impact area of the accident vehicle was scanned using laser surface scanning, the victim was scanned using postmortem CT and micro-CT and the data sets were combined to virtually match features of the vehicle to injuries on the victim. Micro-CT revealed additional injuries not previously detected, lending support to the pedestrian-carry theory

Three-Dimensional Biplanar Reconstruction of the Scoliotic Spine for Standard Clinical Setup

Tese de Doutoramento. Engenharia Informática. Faculdade de Engenharia. Universidade do Porto. 201

GPU-based ultra fast dose calculation using a finite pencil beam model

Online adaptive radiation therapy (ART) is an attractive concept that promises the ability to deliver an optimal treatment in response to the inter-fraction variability in patient anatomy. However, it has yet to be realized due to technical limitations. Fast dose deposit coefficient calculation is a critical component of the online planning process that is required for plan optimization of intensity modulated radiation therapy (IMRT). Computer graphics processing units (GPUs) are well-suited to provide the requisite fast performance for the data-parallel nature of dose calculation. In this work, we develop a dose calculation engine based on a finite-size pencil beam (FSPB) algorithm and a GPU parallel computing framework. The developed framework can accommodate any FSPB model. We test our implementation on a case of a water phantom and a case of a prostate cancer patient with varying beamlet and voxel sizes. All testing scenarios achieved speedup ranging from 200~400 times when using a NVIDIA Tesla C1060 card in comparison with a 2.27GHz Intel Xeon CPU. The computational time for calculating dose deposition coefficients for a 9-field prostate IMRT plan with this new framework is less than 1 second. This indicates that the GPU-based FSPB algorithm is well-suited for online re-planning for adaptive radiotherapy.Comment: submitted Physics in Medicine and Biolog