Output factor determination based on Monte Carlo simulation for small cone field in 10-MV photon beam

• Published in: Radiological physics and technology Vol. 11; no. 2; pp. 192 - 201
• Main Authors: Fukata, Kyohei, Sugimoto, Satoru, Kurokawa, Chie, Saito, Akito, Inoue, Tatsuya, Sasai, Keisuke
• Format: Journal Article
• Language: English
• Published: Singapore Springer Singapore 01.06.2018; Springer Nature B.V
• Subjects: Collimation; Computer simulation; Diode detectors; Imaging; Ionization chambers; Medical and Radiation Physics; Medicine; Medicine & Public Health; Monte Carlo simulation; Nuclear Medicine; Photon beams; Radiology; Radiotherapy; Sensors; Small field; Dosimetry; Monte Carlo; SRS
• ISSN: 1865-0333; 1865-0341
• DOI: 10.1007/s12194-018-0455-4

The difficulty of measuring output factor (OPF) in a small field has been frequently discussed in recent publications. This study is aimed to determine the OPF in a small field using 10-MV photon beam and stereotactic conical collimator (cone). The OPF was measured by two diode detectors (SFD, EDGE detector) and one micro-ion chamber (PinPoint 3D chamber) in a water phantom. A Monte Carlo simulation using simplified detector model was performed to obtain the correction factor for the detector measurements. About 12% OPF difference was observed in the measurement at the smallest field (7.5 mm diameter) for EDGE detector and PinPoint 3D chamber. By applying the Monte Carlo-based correction factor to the measurement, the maximum discrepancy among the three detectors was reduced to within 3%. The results indicate that determination of OPF in a small field should be carefully performed. Especially, detector choice and appropriate correction factor application are very important in this regard.