Dose calculation for electron therapy using an improved LBR method

Abstract

In this research, it is shown that the lateral spread parameter σR(z) increases with cutout size. For radii of circular cutout sizes up to the equilibrium range of the electron beam, the increase of σR(z) with the cutout size is linear. The percentage difference of the calculated PDD curve from the measured PDD data for irregularly shaped cutouts was under 1.0% in the region between the surface and therapeutic range of the electron beam. Similar results were obtained for four electron beam energies (6, 9, 12, and 15 MeV).

Planar dose calculation of electron therapy

“…In our previous publications [12,13], we demonstrated that σ R (z) is dependent on the size of the cutout. By considering this size dependence of σ R (z), we illustrated a significant improvement in the accuracy of PDD and output factor calculations.…”

Output calculation of electron therapy at extended SSD using an improved LBR method

“…The depth dose data for this research were collected using a Varian 2100C and an ELEKTA Synergy linear accelerator equipped with a 40×40×40 cm 3 water tank and PTW Dosimetry Diode E. The details of the experimental setup for the depth dose measurements are described in our previous publication. 10 The depth dose curves were measured for electron beam energies of 6,9,12, and 16 MeV on Varian 2100C machine and 6, 9, 12, and 15 MeV on ELEKTA Synergy machine. The data were collected using applicator of sizes of 15×15 cm 2 and 14 × 14 cm 2 for Varian 2100C and ELEKTA Synergy machines, respectively.…”

“…To account for the deviation from Gaussian shape, an empirical function of cutout size and depth dependent σ R (z) has been introduced posthoc. 10 Recently, Gebreamlak et al 10 have shown that at a given z/R p , the σ R (z) value increases linearly with cutout size until the cutout size reaches to the equilibrium range of the electron beam (R eq ). The slope of the curve is the highest near the surface and decreases as z/R p increases.…”

“…Taking the dependence of σ R (z) on cutout size into account Gebreamlak et al 10 calculated the depth dose distribution of an irregularly shaped field at any point P by partitioning the field into n sectors with each sector having an angle of ∆θ = 2π/n. Each sector of the irregularly shaped field has a unique radius and a corresponding σ R (z) value, which was determined from the interpolation of σ R (z) versus R curves.…”

“…In this paper, we will show that the output factor of any irregularly shaped cutout at extended SSD can be calculated by incorporating the SSD eff values of circular cutouts into the improved lateral buildup ratio (LBR) method. 10…”