TITLE:
In Vivo Dosimetry of an Anthropomorphic Phantom Using the RADPOS for Proton Beam Therapy
AUTHORS:
Ryosuke Kohno, Hidenori Yamaguchi, Kana Motegi, Kenji Hotta, Shie Nishioka, Tetsuo Akimoto
KEYWORDS:
RADPOS, MOSFET, In Vivo Dosimetry, Position Sensor, Proton Beam Therapy
JOURNAL NAME:
International Journal of Medical Physics, Clinical Engineering and Radiation Oncology,
Vol.5 No.3,
August
18,
2016
ABSTRACT: The
radiation positioning system (RADPOS) combines an electromagnetic positioning
sensor with metal oxide semiconductor field-effect transistor (MOSFET)
dosimetry, enabling simultaneous online measurement of dose and spatial
position. Evaluation points can be determined with the RADPOS. The accuracy of in-vivo proton dosimetry was evaluated using
the RADPOS and an anthropomorphic head and neck phantom. MOSFET doses measured
at 3D positions obtained with the RADPOS were compared with treatment plan
values calculated using a simplified Monte Carlo (SMC) method. MOSFET
responses, which depend strongly on the linear energy transfer of the proton
beam, were corrected using the SMC method. The SMC method was used to calculate
only dose deposition determined by the experimental depth-dose distribution and
lateral displacement of protons due to the multiple scattering effect in
materials and incident angle. This method thus enabled rapid calculation of
accurate doses in even heterogeneities. In vivo dosimetry
using the RADPOS, as well as MOSFET doses, agreed with SMC calculations in the
range of ?3.0% to 8.3%. Most measurement errors occurred because
of uncertainties in dose calculations due to the 1-mm position error. The
results indicate that uncertainties in measurement position can be controlled
successfully within 1 mm when using the RADPOS with in-vivo proton dosimetry.