Measurement of Head Scatter Factor for Linear Accelerators using Indigenously Designed Columnar Mini Phantom

A columnar mini phantom is designed as recommended by ESTRO to measure the Head Scatter Factor (S_c) for 6 MV beam of two linear accelerators. The measurement of S_c at different orientations of the chamber, parallel and perpendicular at 1.5 cm depth predicts the deviation of 2.05% and 1.9% for Elekta and Siemens linear accelerators respectively. The measurement of S_c at 1.5 cm is higher compared to 10 cm depth for both the linear accelerators suggesting the electron contamination at 1.5 cm depth. The effect of wedges on S_c yields a significant contribution of 3.5% and 5% for Siemens and Elekta linear accelerators respectively. The collimator exchange effect reveals the opening of upper jaw increases the S_c irrespective of the linear accelerator. The result emphasizes the need of S_c measurement at 10 cm. The presence of wedge influences the S_c value and the SSD has no influence on S_c. The measured S_c values are in good agreement with the published data.