Technical Note: Small field dose correction factors for radiochromic film in lung phantoms

Purpose Radiochromic film has been established as a detector that can be used without the need for perturbation correction factors small field dosimetry in water. However, low density media such lung have yet to published. This study calculated required account of radiochromic when equivalent material. Method Monte Carlo simulations were calculate dose Gafchromic EBT3 placed inside phantom. The beam simulated had nominal energy 6 MV and sizes ranged from 10 × mm2 30 mm2. was varied between 0.2 0.3 g/cm3. Each simulation repeated with replaced by material (the same surrounding medium), () dividing film. Results For larger, no required. At 20 size, corrections required, but within approximate accuracy (~2%). significant applied (0.935 0.20 g/cm3 0.963 0.30 g/cm3). values lower than one mean is over-responding. “upstream” lung-water interface close unity; while at downstream marginally smaller those center lung. One centimeter or more away interfaces, factor did not vary function distance (in direction). Away central axis (perpendicular direction), increased slightly (away unity) off-axis distance, before abruptly changing direction penumbra, actually under-responding ~10% outside edges. Conclusion Accurate very fields (15 15 smaller) using requires on high 6.5% size will increase if either decrease further. does depth once charged particle equilibrium established.