William Chu

Instrumentation for treatment of cancer using proton and light‐ion beams

Clinical trials using accelerated heavy charged‐particle beams for treating cancer and other diseases have been performed for nearly four decades. Recently there have been worldwide efforts to construct hospital‐based medically dedicated proton or light‐ion accelerator facilities. To make such accelerated heavy charged‐particle beams clinically useful, specialized instruments must be developed to modify the physical characteristics of the particle beams in order to optimize their biological and clinical effects. This article reviews the beam modifying devices and associated dosimetric equipment developed specifically for controlling and monitoring the clinical beams.

Wobbler facility for biomedical experiments

A system for spreading relativistic heavy ion beams into large uniform radiation fields has been developed. The charged particles passing through the system are deflected into azimuthally symmetric distributions which can then be superimposed to produce dose distributions as large as 30 cm in diameter with less than +/- 3.5% variation in uniformity.

Patient positioning for protontherapy using a proton range telescope

Abstract A method is described for imaging integrated density along the beam path in phantoms that makes use of high energy proton beams. An application of the technique is in the positioning of patients in a proton therapy radiation facility. It makes use of a proton range telescope for density variation and X - Y detectors for planar positioning. The principle of the method was tested at a proton energy of 66 MeV. Good visual quality is seen in the tests. The measurements are compared with detailed Monte Carlo simulations, and good agreement is found. We apply the simulations to high energy proton beams (245 MeV) and show that the method should provide good visual quality and sensitivity for positioning at the higher energies necessary for whole body therapy.

Accelerated helium-ion beams for radiotherapy and stereotactic radiosurgery

A new beam line for radiotherapy and radiosurgery with accelerated helium-ion beams has been set up at the Bevalac. The new treatment room has been equipped with a very precise patient positioner in order to utilize the superior dose localization properties of light-ion beams. The beam spreading and shaping system is described, the trade-offs involved in positioning the beam modifying devices are discussed, and the physical properties of the generated radiation fields are reported. The Bragg peak modulation by axial beam stacking employing a variable range shifter is explained and the control system including beam monitoring and dosimetry is presented.

Multisegmented ionization chamber dosimetry system for light ion beams

Abstract A system for measuring doses delivered by light ions has been developed for use in the treatment of cancer patients at the Biomedical Facility at the Bevalac. Dose distributions for treatment areas as large as 30 cm by 30 cm with 2.5 cm by 2.5 cm spatial resolution can be measured in real-time for use with dynamic beam delivery systems where precision and fast response time are required. Ionization chambers with transverse spatial resolution of 2 mm have also been made for measurements requiring fine spatial resolution.

Wobbler Dosimetry for the Biomedical Program at the LBL Bevalac

A system for measuring delivered dose and dose distributions has been developed for use with the wobbler beam delivery system. The system allows rapid termination of an irradiation when hardware of software monitors indicate the required dose has been delivered. In addition several safeguard systems are required by such an active system in event of a failure of the wobbler, associated electronic hardware or the computer. Computer graphic displays allow operator monitoring of the irradiation on a pulse by pulse basis.

Radiological changes on CT after stereotactic body radiation therapy to non-spine bone metastases: a descriptive series

BACKGROUND In recent years, stereotactic body radiation therapy (SBRT) has become increasingly used for the management of non-spine bone metastases. Few studies have examined the radiological changes in bone metastases after treatment with SBRT and there is no consensus about what constitutes radiologic response to therapy. This article describes various changes on CT after SBRT to non-spine bone metastases in eight selected cases. METHODS A retrospective review was conducted for patients treated with SBRT to non-spine bone metastases between November 2011 and April 2014 at Sunnybrook Health Sciences Centre. A musculoskeletal radiologist identified eight illustrative cases of interest and provided a description of the findings. RESULTS Different radiological changes following SBRT were described, including: remineralization of lytic bone metastases, demineralization of sclerotic bone metastases, pathologic fracture, size progression and response in different lesions, as well as lung fibrosis after SBRT to a rib metastasis. CONCLUSIONS We reviewed the radiological images of eight selected cases after SBRT to nonspine bone metastases and a number of characteristic findings were highlighted. We recommend future studies to correlate radiologic changes with clinical outcomes including pain relief, toxicity and long-term local control.

High Energy Beam Transport System for a Heavy Ion Medical Accelerator

A beam transport system for a Heavy Ion Medical Accelerator is presented. The design allows for ease of tuning, similarity of tuning between different beam lines, and future expansion of the number of beamlines. An option for generating secondary beams with acceptable transmission losses to all treatment areas is also included in the design, as is a vertical beamline option for use with patients in a horizontal position.

Poster — Thur Eve — 16: 4DCT simulation with synchronized contrast injection of liver SBRT patients

Stereotactic body radiation therapy (SBRT) has recently emerged as a valid option for treating liver metastases. SBRT delivers highly conformai dose over a small number of fractions. As such it is particularly sensitive to the accuracy of target volume delineation by the radiation oncologist. However, contouring liver metastases remains challenging for the following reasons. First, the liver usually undergoes significant motion due to respiration. Second, liver metastases are often nearly indistinguishable from the surrounding tissue when using computed tomography (CT) for imaging making it difficult to identify and delineate them. Both problems can be overcome by using four dimensional CT (4DCT) synchronized with intravenous contrast injection. We describe a novel CT simulation process which involves two 4DCT scans. The first scan captures the tumor and immediately surrounding tissue which in turn reduces the 4DCT scan time so that it can be optimally timed with intravenous contrast injection. The second 4DCT scan covers a larger volume and is used as the primary CT dataset for dose calculation, as well as patient setup verification on the treatment unit. The combination of two 4DCT scans, short and long, allows visualization of the liver metastases over all phases of breathing cycle while simultaneously acquiring long enough 4DCT dataset suitable for planning and patient setup verification.

Heavy Ion Beam Studies and Imaging with a Multiplane Multiwire Proportional Chamber

A 16-plane multiwire proportional chamber is used to accurately measure intensity profiles of heavy ion beams at the Bevalac. An imaging capability has now been developed for the system, allowing for reconstruction of 3-dimensional representation of radiological objects using heavy ion beams.