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To create practical lookup tables containing percent depth dose (PDD) and profile parameters of electron beams and to demonstrate clinical application of the lookup tables to skin cancer treatment to ensure target coverage in a clinical setup.
Materials and methods
For 6 and 9 MeV electron energies, PDDs and profiles at clinically relevant depths [i.e., R95 (distal depth of 95% maximum dose), R90, R85 and R80] were measured in water at 100 cm source-to-surface distance for an 10×10 cm2 open field and circular cutouts with diameters of 4, 5, 6, 7 and 8 cm. Then PDD parameters along with profile parameters such as width of isodose lines and penumbra at the clinically relevant depths were determined. Output factors for the cutouts were measured at dmax in water and solid water.
With PDD and profile parameters, dosimetry lookup tables were generated. Based upon the lookup tables, target coverage at prescribed depths was retrospectively reviewed for three skin cancer cases. The lookup tables suggested larger cutouts for adequate target coverage.
Dosimetry lookup tables for electron beam therapy should include profile parameters at clinically relevant depths and be provided to clinicians to ensure target coverage in a clinical setup.
We evaluated water-equivalent slabs as an alternative to a bolus to reduce radiation dose to the underlying lungs during electron scar boost irradiation in breast cancer patients with a thin chest wall undergoing post-mastectomy radiation therapy.
Materials and methods
Percent depth doses (PDDs) and attenuation factors were obtained for 6 MeV (the lowest electron energy in most clinics) with solid water slabs (1–10 mm by 1 mm increments) placed on top of electron cones. Scatter dose to contralateral breast caused by the solid water slabs was measured on a human-like phantom using two selective scar boost patient setups.
The PDD plots showed that the solid water slabs had similar dosimetric effects to the bolus with lower skin dose to ipsilateral breast for the same thickness. Slab attenuation and scatter dose to the contralateral breast were increased by ~220% and by a factor of 3 with a 5 mm slab, respectively.
Our results demonstrate the feasibility of using water-equivalent slabs to reduce lung dose for electron scar boost treatment in mastectomy patients with a thin chest wall. However, the increases in treatment time and scatter dose to the contralateral breast are the disadvantages of this approach.
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