A Real-time Image Reconstruction System for Particle Treatment Planning Using Proton Computed Tomography (pCT)

Proton computed tomography (pCT) is a novel medical imaging modality for mapping the distribution of proton relative stopping power (RSP) in medical objects of interest. Compared to conventional X-ray computed tomography, where range uncertainty margins are around 3.5%, pCT has the potential to provide more accurate measurements to within 1%. This improved efficiency will be beneficial to proton-therapy planning and pre-treatment verification. A prototype pCT imaging device has recently been developed capable of rapidly acquiring low-dose proton radiographs of head-sized objects. We have also developed an advanced, fast image reconstruction software based on distributed computing that utilizes parallel processors and graphical processing units. The combination of fast data acquisition and fast image reconstruction will enable the availability of RSP images within minutes for use in clinical settings. The performance of our image reconstruction software has been evaluated using data collected by the prototype pCT scanner from several phantoms.Comment: Paper presented at Conference on the Application of Accelerators in Research and Industry, CAARI 2016, 30 October to 4 November 2016, Ft. Worth, TX, US

Beam Optics for a Scanned Proton Beam at Loma Linda University Medical Center

Abstract Beam scanning in proton therapy is a medical technique to lower the dose to healthy tissue while irradiating a tumor volume. Scanned proton beams for proton radiation therapy require small beam sizes at the tumor location. In beam scanning, a small beam usually less than 1 cm diameter is swept across the tumor volume with two magnets located several meters upstream of the patient. In general, all proton beams in a therapy facility must be transported from the accelerator to the treatment rooms where the scanning systems are located. This paper addresses the problem of transporting the beam without losses to the patient and achieving a small beam at the tumor location in the patient. The strengths of the beam line quadrupoles were allowed to vary to produce the desired beam sizes along the beam lines. Quadrupole strengths were obtained using the beam simulation program TRANSPORT 1 originally from Stanford Linear Accelerator Center in Palo Alto, CA. An enhanced version of the original program by Accel Soft Inc. in San Diego, CA has been used for these studies. Beam size measurements were used for comparison with TRANSPORT to verify the predictions of TRANSPORT calculations

Dynamic Fluence Modulation using Proton CT for Low-dose Imaging in Particle Therapy

International audienceDynamic fluence modulation for computed tomography (CT), i.e. the acquisition of tomographic images with variable, patient-and task-specific fluence fields, offers the potential to substantially reduce local imaging dose. In particular, volume-of-interest (VOI) imaging allows to limit imaging dose to a clinically relevant volume and reduce it elsewhere. In the context of particle therapy, where tomographic data is required for treatment planning the VOI is the treatment beam path. VOI imaging is of particular interest for particle therapy given the very low integral out-of-VOI treatment dose. Proton CT imaging allows for a direct measurement of the proton stopping power with an increased accuracy and a decreased imaging dose compared to x-ray-based CT. In addition, frequent imaging is required to verify patient positioning and to monitor potential anatomical changes, which over the course of a treatment may compromise the planned dose. In this work, we evaluate the performance of a fluence-modulated proton CT algorithm for low-dose in-room imaging. This would allow for recalculation or replanning of the treatment dose according to the anatomy of the day with out-of-VOI dose below 1 mGy. We performed a simulation study and acquired experimental data using a prototype proton CT scanner. By employing a bow-tie-like fluence modulation aiming for constant noise, imaging dose was reduced by 9%. For a VOI imaging task, out-of-VOI dose was reduced by 41% and substantially below 1 mGy. This may pave the way for daily imaging prior to every treatment session aiming to eventually reduce safety margins in particle therapy, thus further reducing normal tissue exposure to therapeutic doses