TITLE:
An Overview of the Control System for Dose Delivery at the UCSF Dedicated Ocular Proton Beam
AUTHORS:
Inder K. Daftari, Kavita K. Mishra, Rajinder P. Singh, Dan J. Shadoan, Theodore L. Phillips
KEYWORDS:
Proton Beam Therapy, Beam Delivery, Control System, Ocular Tumors
JOURNAL NAME:
International Journal of Medical Physics, Clinical Engineering and Radiation Oncology,
Vol.5 No.4,
November
7,
2016
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. The overall
performance, maintenance, and quality assurance of the cyclotron and the ocular
control system have been excellent.