Monte-Carlo-computed dose, kerma and fluence distributions in heterogeneous slab geometries irradiated by small megavoltage photon fields.

Monte-Carlo-computed dose, kerma and fluence distributions in heterogeneous slab geometries irradiated by small megavoltage photon fields. Phys Med Biol. 2020 Jun 02;: Authors: Kumar S, Nahum AE, Chetty IJ Abstract Small-field dosimetry is central to the planning and delivery of radiotherapy to patients with cancer. Small-field dosimetry is beset by complex issues, such as loss of charged-particle equilibrium (CPE), source occlusion and electron scattering effects in low-density tissues. The purpose of the present research was to elucidate the fundamental physics of small fields through the computation of absorbed dose, kerma and fluence distributions in heterogeneous media using the Monte-Carlo method. Absorbed dose and kerma were computed using the DOSRZnrc Monte-Carlo (MC) user-code for beams with square field sizes ranging from 0.25 × 0.25 to 7× 7 cm2 (for 6 MV 'full linac' geometry) and 0.25 × 0.25 to 16 × 16 cm2 (for 15 MV 'full linac' geometry). In the bone inhomogeneity the dose increases (vs. homogeneous water) for field sizes < 1 × 1 cm2 at 6 MV and ≤ 3 × 3 cm2 at 15 MV and decreases (vs. homogeneous water) for field sizes ≥ 3 × 3 cm2 at 6 MV and ≥ 5 × 5 cm2 at 15 MV. In the lung inhomogeneity there is negligible decrease in dose compared to in uniform water for field sizes > 5 × 5 cm2 at 6 MV and ≥ 16 × 16 cm2 at 15 MV, consistent with the Fano theorem. The near-unity value of the absorbed-dose to c...
Source: Physics in Medicine and Biology - Category: Physics Authors: Tags: Phys Med Biol Source Type: research