Room: Exhibit Hall
Purpose: This Monte Carlo study compared the dose enhancements using water-based (WBC) and silicone-based (SBC) cream on patientâ€™s skin, under flattening-filter (FF) and flattening-filter-free (FFF) photon beams in radiotherapy.
Methods: 6 MV FFF and FF photon beams (field size = 10Ã—10 cmÂ²) based on a Varian linear accelerator were used to determine the dose enhancement factor (DEF), using a phantom containing a skin-care cream layer on top of a skin layer of 1 mm. The isocenter of the linac was set at the skin surface. The photon beams were rotated from 0 to 80á´¼ and the cream thicknesses were varied from 0 to 3 mm. The DEF, defined as the ratio of the skin dose with the cream to the skin dose without the cream, was determined using Monte Carlo simulation (EGSnrc code) with variations of cream thickness and beam angle.
Results: For both the FFF and FF photon beams, the SBC had slightly higher DEF than WBC with variation of skin-care cream thickness (WBC: 1â€“2.1 vs. SBC: 1â€“2.2 for FFF, and WBC: 1â€“2.6 vs. SBC: 1â€“2.8 for FF). The FFF photon beams produced lower skin dose than the FF beams. As the thickness of the cream increased (0â€“3 mm), the skin dose enhancement increased. For the beam obiliquity, as the beam angle was increased, the skin dose increased accordingly. The DEF was higher for all variables at beam angle of 80á´¼ (WBC: 2.1 vs. SBC: 2.2 for FFF, and WBC: 2.5 vs. SBC: 2.7 for FF as cream thickness = 3 mm).
Conclusion: Although the dose enhancement for patients using the skin-care cream product may be considered clinically acceptable, the FFF photon beam may be more favourable than the FF beam, because the FFF beam produces lower skin dose enhancement and requires less treatment time on the patient.