title: Monte Carlo comparison of superficial dose between flattening filter free and flattened beams.
abstract: This study investigates the superficial dose from FFF beams in comparison with the conventional flattened ones using a Monte Carlo (MC) method. Published phase-space files which incorporated real geometry of a TrueBeam accelerator were used for the dose calculation in phantom and clinical cases. The photon fluence on the central axis is 3 times that of a flattened beam for a 6 MV FFF beam and 5 times for a 10 MV beam. The mean energy across the field in air at the phantom surface is 0.92-0.95 MeV for the 6 MV FFF beam and 1.18-1.30 MeV for the corresponding flattened beam. At 10 MV, the values are 1.52-1.72 and 2.15-2.87 MeV for the FFF and flattened beams, respectively. The phantom dose at the depth of 1 mm in the 6 MV FFF beam is 6% ± 2.5% (of the maximum dose) higher compared to the flattened beam for a 25 × 25 cm(2) field and 14.6% ± 1.9% for the 2 × 2 cm(2) field. For the 10 MV beam, the corresponding differences are 3.4% ± 1.5% and 10.7% ± 0.6%. The skin dose difference at selected points on the patient's surface between the plans using FFF and flattened beams in the head-and-neck case was 6.5% ± 2.3% (1SD), and for the breast case it was 6.4% ± 2.3%. The Monte Carlo simulations showed that due to the lower mean energy in the FFF beam, the clinical superficial dose is higher without the flattening filter compared to the flattened beam.
authors.affiliation: Radiation Oncology Department, Moffitt Cancer Center, Tampa, FL, USA.
authors.forename: Khosrow
authors.initials: K
authors.lastname: Javedan
authors.affiliation: Radiation Oncology Department, Moffitt Cancer Center, Tampa, FL, USA.
authors.forename: Vladimir
authors.initials: V
authors.lastname: Feygelman
authors.affiliation: School of Medicine and Public Health, University of Wisconsin, Madison, WI, USA.
authors.forename: Ray R
authors.initials: RR
authors.lastname: Zhang
authors.affiliation: Radiation Oncology Department, Moffitt Cancer Center, Tampa, FL, USA.
authors.forename: Eduardo G
authors.initials: EG
authors.lastname: Moros
authors.affiliation: Radiation Oncology Department, Moffitt Cancer Center, Tampa, FL, USA.
authors.forename: Candace R
authors.initials: CR
authors.lastname: Correa
authors.affiliation: Radiation Oncology Department, Moffitt Cancer Center, Tampa, FL, USA.
authors.forename: Andy
authors.initials: A
authors.lastname: Trotti
authors.affiliation: Radiation Oncology Department, Moffitt Cancer Center, Tampa, FL, USA.
authors.forename: Weiqi
authors.initials: W
authors.lastname: Li
authors.affiliation: Radiation Oncology Department, Moffitt Cancer Center, Tampa, FL, USA. Electronic address: geoffrey.zhang@moffitt.org.
authors.forename: Geoffrey G
authors.initials: GG
authors.lastname: Zhang
mesh_terms: D001943:Breast Neoplasms / Q000532:radiotherapy; D006258:Head and Neck Neoplasms / Q000532:radiotherapy; D006801:Humans; D009010:Monte Carlo Method; D010315:Particle Accelerators; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D011879:Radiotherapy Dosage; D050397:Radiotherapy, Intensity-Modulated / Q000009:adverse effects / Q000295:instrumentation / Q000379:methods*; D012867:Skin / Q000528:radiation effects
keywords: Flattening filter free; Monte Carlo; Skin dose