Author(s)

Hideharu Miura, Norihisa Masai, Kouichi Yamada, Junichi Sasaki, Ryoong-Jin Oh, Hiroya Shiomi, Muhammad Nauman Usmani, Toshihiko Inoue

Department of Medical Physics & Engineering, Osaka University Graduate School of Medicine, Osaka, Japan.
Miyakojima IGRT Clinic, Osaka, Japan.

The purpose of this study was to compare the Pencil Beam (PB) with Monte Carlo (MC) calculated dosimetric results using phantoms for air cavity region. Measurements in Tough water phantom with air gaps were used to verify the calculated dose. The plane-parallel ionization chamber was moved from 2 mm to 20 mm behind air gap. Calculations were performed for various air gaps (1.0, 2.0, 3.0 and 4.0 cm) and field sizes (4.2 × 4.2, 6.0 × 6.0 and 9.8 × 9.8 cm²). The lateral missing tissue measurement was performed using the radiochromic RT-QA film. Dose difference between PB and chamber measurement near an air gap was greater for smaller field size, larger air gap thickness, and shallower depth behind air gap. As the distance from the phantom edge became shorter, the dose differences of the PB calculation and film measurement became larger. MC calculations were found within 3% agreement to the measured dose distributions. Our results demonstrate an excellent agreement between ionization chamber and radiochromic RT-QA film measurements and MC calculations.

Monte Carlo; Pencil Beam; Air Cavity; Treatment Planning

H. Miura, N. Masai, K. Yamada, J. Sasaki, R. Oh, H. Shiomi, M. Nauman Usmani and T. Inoue, "Evaluation and Commissioning of Commercial Monte Carlo Dose Algorithm for Air Cavity," International Journal of Medical Physics, Clinical Engineering and Radiation Oncology, Vol. 3 No. 1, 2014, pp. 9-13. doi: 10.4236/ijmpcero.2014.31002.