Room: Exhibit Hall
Purpose: To experimentally measure patient scatter factors in a â€œgoodâ€? geometry using a purpose-built test port in maze wall of a Linac room to evaluate measurements and simulated data from previous works.
Methods: A vault at our institution has been constructed with a test port in a maze wall barrier allowing measurement of numerous shielding factors in a good geometry setting, including the patient scatter factor which is dependent on energy, field size, and the incident angle of the beam. Radiation was delivered to a 30 cm diameter cylindrical PMMA phantom at isocenter with a farmer chamber placed within the center. A large volume 30 cc cylindrical chamber was placed 4.5 m from the isocenter on the other side of the test port barrier. Three different accelerating potentials were evaluated: 6 MV, 6 MV FFF, and 10 MV FFF. The field sizes measured were 25, 100, 400, and 1600 cmÂ² for the following angles of incidence: 10Ëš, 20Ëš, 30Ëš, 40Ëš, 60Ëš, 75Ëš, 90Ëš, 105Ëš, 120Ëš, 135Ëš, and 150Ëš. Charge per unit volume was calculated and the ratio between the detectors taken to calculate patient scatter factors.
Results: Results are in reasonable agreement with prior works for patient scatter factors when corrected for the distance of measurement using the inverse-square law. The scatter factor for 25 cmÂ² field size was found to be the largest, in disagreement with the expectation of linearly increasing with field size. One explanation could be due to increased scatter from the jaws and machine head, to be included in future works.
Conclusion: The presented results are in good agreement with previous data when corrected for the inverse-square distance. Previous data were taken at 1m and 2m, and the previously concluded statement holds that the inverse-square law was an appropriate application given the distance from the scatterer.
Not Applicable / None Entered.