Pencil beam scanning dosimetry for large animal irradiation.
Bottom Line: These events consist primarily of low-energy protons that produce a highly inhomogeneous depth-dose distribution.At a distance of 1200 mm from the isocentre, the Gaussian sigma is 68 mm and 23 mm at 105 MeV and 220 MeV, respectively, when the RS is located on the nozzle.Scan areas of 1400 mm (superior-inferior) by 940 mm (anterior-posterior) and 580 mm by 320 mm are achieved at the extended distances of 4800 mm and 1200 mm, respectively, with dose inhomogeneity <2%.
Affiliation: Department of Radiation Oncology, University of Pennsylvania, 3400 Civic Center Blvd, 2326 TRC, PCAM, Philadelphia, PA 19104, USA firstname.lastname@example.org.Show MeSH
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Mentions: Figure 4 shows the corresponding 2D planned surface doses with the RS located at the nozzle. For 120-MeV protons, the optimally weighted 6 × 4 scanning pattern produces a distribution that is within 2% of the desired dose for the central region, but falls to ∼90% at 600 mm and 500 mm in the SI and AP directions, respectively. To achieve a uniform dose over the maximal area of 1400 mm × 940 mm with a marginal dose at 90% of the central uniform dose, non-uniform spot weights are used along the AP direction. For 140-MeV protons, smaller spots in 10 × 6 scanning patterns have a smaller dose falloff margin with similar 2% dose inhomogeneity in the central regions. For treating multiple animals at an extended distance, the resulting dose inhomogeneity is acceptable. Figure 4 also shows the calculated dose distribution from the 31 × 21 scanning pattern for 220-MeV protons at a distance of 1200 mm. In this case, uniform spot weighting achieves 95% of the central dose over a 580 mm (SI) by 320 mm (AP) area, sufficient to treat a single animal. In comparison with that at the surface, the dose distribution at depths is more homogenous because of the larger spot size, and the field size at depths is larger because of the longer distance from the source. In both whole-body and SPE experiments, a large spot size is acceptable, and therefore animal irradiation was performed with the RS located at the exit of the nozzle.Fig. 4.
Affiliation: Department of Radiation Oncology, University of Pennsylvania, 3400 Civic Center Blvd, 2326 TRC, PCAM, Philadelphia, PA 19104, USA email@example.com.