An Overview of the Control System for Dose Delivery at the UCSF Dedicated Ocular Proton Beam

Abstract

Since 1978, the University of California San Francisco (UCSF) Ocular Tumor Program has been using particle therapy for treating ocular patients with malignant as well as benign eye disease. Helium ion beams were used initially and were produced by two synchrotron-based systems: first by the 184-inch synchro-cyclotron and later by the Bevalac, at the Lawrence Berkeley National Laboratory (LBNL). Since 1994, protons, produced by a cyclotron-based system at the Crocker Nuclear Laboratory (CNL) Eye Treatment Facility (ETF), have been used for this purpose. The CNL cyclotron produces a 67.5 MeV beam, allowing for a uniquely homogeneous beam for eye treatment, without degradation of the beam or manipulation of the beam line. This paper describes, in detail, the control system for beam delivery, as implemented for measuring and delivering the radiation to ocular tumors at CNL. The control system allows for optimal delivery and rapid termination of the irradiation after the desired dose is achieved. In addition, several safeguard systems are discussed, as these are essential for such a system in the event of failure of software, electronics, or other hardware. The QA analysis shows that the total range of the proton beam is 30.7 ± 1.0 mm in water at iso-center. The beam distal penumbra (80%-20%) is 1.1 mm for a range-modulated beam at a collimator to iso-center distance of 50 mm. Daily QA checks confirm that the range and modulation is within 0.1 mm. The beam flatness and symmetry in a 25 mm diameter beam are ±1%-2%. Variation in the daily dosimetry system, as compared to standard dosimetry, is within ±3.5%, with a mean variation of 0.72(±1.9)% and 0.85(±2.3)% for segmented transmission ionization chambers IC1 (upstream) and IC2 (downstream), respectively. From May 1994 to the end of 2015, UCSF has treated 1838 proton ocular patients at the Davis ETF. During this period, no treatments were missed due to any cyclotron or control system failures.

A Millimeter-Scale Single Charged Particle Dosimeter for Cancer Radiotherapy

“…The prototype ASIC was tested at the proton beam facility in Crocker Nuclear Laboratory (CNL) at University of California, Davis, which has treated more than 1,700 ocular patients with malignant and benign ocular tumors since 1994 [16]- [18]. To assess sensor performance under clinically relevant conditions, the experiment was conducted in the treating room using similar beam settings that are used for patients.…”

A Millimeter-scale Single Charged Particle Dosimeter for Cancer Radiotherapy

“…The prototype ASIC was tested at Crocker Nuclear Laboratory (CNL) at University of California, Davis. The proton beam facility has treated more than 1,700 ocular patients with malignant and benign ocular tumors since 1994 [13]- [15]. Fig.…”