TITLE:
Periodic Measurements of Passive Proton Beam Width Using Radiochromic Film in Fixed Gantry System
AUTHORS:
Tomohiro Shimozato, Keisuke Yasui, Hireto Kinou, Fumiaki Komatsu
KEYWORDS:
Proton Beam, Beam Width, Radiochromic Film, Periodic Measurement
JOURNAL NAME:
International Journal of Medical Physics, Clinical Engineering and Radiation Oncology,
Vol.8 No.4,
September
16,
2019
ABSTRACT: Background and Aim: Irradiation methods such as double scattering method
and spot scanning method have been used in proton beam treatment devices.
In the scattering method, a ridge filter or a range modulation wheel is used to
create a spread-out Bragg peak, but the distribution at the patient position
may change due to positional deviation of the incident beam. Therefore, assessment
of the incident position of the beam is very important even in the
scattering method. To investigate the width and distribution of the proton
beam before entering the RMW, a radiochromic film was installed at the outlet
of the transport pipe and the entrance of the profile-monitoring detector. Methods: In this study, the distributions of the beam at the exit of the transport
pipe and the entrance of the monitor detector were measured using
films. The beam width was measured from the full width at half maximum of
the profile obtained from the distribution. Measurements were conducted
every month for 10 months. Results: Beams of widths ranging from 1.82 to
2.30 mm in the horizontal direction and 4.25 to 5.33 mm in the vertical direction
were outputted from the exit of the transport pipe. Beams of widths
ranging from 2.16 to 2.67 mm in the horizontal direction and 4.06 to 5.31
mm in the vertical direction were outputted from the entrance of the monitor
detector. The maximum width fluctuation for 10 months was 0.55 mm in the
horizontal direction and 1.26 mm in the vertical direction at the entrance of
the monitor detector. Conclusions: The distribution was obtained before the
proton beam was scattered by the scatterer, and then we propose a method to
periodically measure and monitor the changes in the beam distributions
every month.