SU‐E‐T‐687: Scatter Factors Comparison of 6MV FFF and Energy Matched 6MV EqFFF
Purpose: To compare the Collimator scatter factor (Sc), Phantom scatter factor (Sp) and Total scatter factors (Sc,p) of 6MV FFF and energy matched 6MV FFF (6MV eqFFF) Methods: The flattening filter and primary collimator are the major sources of producing the scattered radiation. In this study, the field sizes from 5 × 5 cm2 to 40 × 40 cm2 compared for 6MV FFF and 6MV eqFFF. We measured Sc,p with CC 13 chamber at the depth of 10 g/cm2 using IBA blue water phantom and Sc measured with CC 13 chamber at the depth of 10 g /cm2 using columnar phantom (TG 74) for 6MV FFF and 6MV eqFFF x-ray beams from a Siemens — ARTISTE(6MV eqFFF ) and Varian True beam (6MV FFF) linear accelerator. The Sp values derived from the Sc,p and Sc Values. Results: All the values of Sc,p, Sc and Sp are normalized to 10 × 10 cm2 field size. The measured values of Sc,p for 6MV FFF and 6MV eqFFF varies from 0.9404 to 1.0760 and 0.9690 to 1.0283 respectively. The Sc values for 6MV FFF and 6MV eqFFF varies from 0.9880 to 1.133 and 0.9882 to 1.0075 respectively. The Sp values for 6MV FFF and 6MV eqFFF varies from 0.9518 to 1.0619 and 0.9806 to 1.0206 respectively. From the measured values, we found that Sc, Sc,p and Sp factors of 6MV FFF less than 10 × 10cm2 field is similar to the 6MV eqFFF. For greater than 10 × 10 cm2 field size Sc, Sc,p and Sp factors higher for 6MV FFF than 6MV eqFFF. Conclusion: The energy matched 6MV FFF (6MV eqFFF) photon beam producing lesser Scatter radiation compare to the conventional 6MV FFF photon beams for field size more than 10 × 10 cm2.