SU-E-T-89: Comparison of a Liquid Ionization Chamber with a Diamond Detector for Relatively Small Photon Field Measurements

Abstract

Purpose: To compare the performance of microLion detector (PTW type 31018, Freiburg, Germany), a new type of micro liquid ionization chamber, with diamonddetector (PTW type 60003, Freiburg, Germany) for small photon fields (< 3×3 cm field size) measurements. Methods: The characteristics of output factor, beam profile and percentage depth dose of the microLion and diamonddetectors were studied. The measurements were performed in a MP3 water phantom under 6 MV photon beam generated from a linear accelerator (Clinac 6EX, Varian Medical Systems, Palo Alto, CA). Output factors of field sizes between 0.5×0.5 cm and 10×10 cm were measured at 10 cm depth in water and normalized to 10×10 cm field size with respect to the detectors. Beam profiles were acquired at 10 cm depth in water with field sizes between 0.5×0.5 cm and 10×10 cm. Percentage depth doses of 1×1 cm and 10×10 cm fields were obtained in the central axis of the beam direction in water and normalized at 10 cm depth in water with respect to the detectors. Results: Both detectors showed nearly the same profiles for 10x10 cm field size, while the beam profile of field size 0.5×0.5 cm with microLion detector was slightly broader. The output factors of microLion detector were slightly higher than the diamonddetector in small field size. The peak of the percentage depth dose of both large and small fields for microLion detector was significantly lower than the diamonddetector. Conclusions: This study demonstrated the spatial resolution of microLion detector is superior to the diamonddetector for small field measurements, especially for measuring beam profiles. The microLion detector showed lower peaks in both large and small fields which may generally represent its under response.