Author(s)

Jon Feldman^1,2, Itzhak Orion¹

¹Nuclear Engineering, Ben Gurion University of the Negev, Beer Sheva, Israel.
²Sharett Institute of Oncology, Hadassah University Hospital, Jerusalem, Israel.

Purpose: Cylindrical ionization chambers as the PinPoint and the CC01 have high-spatial resolution and cylindrical symmetry in relevance to small fields. Dosimetry of newly advanced technologies that include non-coplanar beams, such as in Gamma-Knife, VMAT and IMRT treatment plans, the angular dependence of the ion chamber is essential. Therefore in this study we simulated two common used ion chambers using a Monte Carlo method. Methods: The angular dependence for the CC01 and the PinPoint were calculated for a vast angular range in a cylindrical water phantom for two LINAC photon beams, 6 MV and 15 MV. The calculations were performed for fully structural description of each ion chamber using Monte Carlo code, in order to reveal unsymmetrical response dose higher than 2% in medical applications. The calculated dose response, for the CC01 ion chamber, was validated with measurements. Results: The CC01 ion chamber showed a very small angular dependence compared to the PinPoint ion chamber. The relative angular dependence amplitude of the PinPoint was about 12% in the range of 0° - 110°. Conclusions: The differences in the ion chambers structure led to the variations in the relative angular dependence amplitude. Therefore, when choosing a detector, not only the volume of the ionization chamber but also its structure must be taken into consideration.

Dosimetry, CC01, PinPoint, Linac, Monte Carlo

Feldman, J. and Orion, I. (2016) Small Volume Ionization Chambers Angular Dependence and Its Influence on Point-Dose Measurements. International Journal of Medical Physics, Clinical Engineering and Radiation Oncology, 5, 26-32. doi: 10.4236/ijmpcero.2016.51003.