Scattering foil device for high-energy electron-beam therapy

Impact of Scattering Foil Composition on Electron Energy Distribution in a Clinical Linear Accelerator Modified for FLASH Radiotherapy: A Monte Carlo Study

This study investigates how scattering foil materials and sampling holder placement affect electron energy distribution in electron beams from a modified medical linear accelerator for FLASH radiotherapy. We analyze electron energy spectra at various positions-ionization chamber, mirror, and jaw-to evaluate the impact of Cu, Pb-Cu, Pb, and Ta foils. Our findings show that close proximity to the source intensifies the dependence of electron energy distribution on foil material, enabling precise beam control through material selection. Monte Carlo simulations are effective for designing foils to achieve desired energy distributions. Moving the sampling holder farther from the source reduces foil material influence, promoting more uniform energy spreads, particularly in the 0.5-10 MeV range for 12 MeV electron beams. These insights emphasize the critical role of tailored material selection and sampling holder positioning in optimizing electron energy distribution and fluence intensity for FLASH radiotherapy research, benefiting both experimental design and clinical applications.

The use of scattering foil compensators in electron beam therapy

PURPOSE

This study was undertaken to show that scattering foils could be used as electron beam compensators.

METHODS AND MATERIALS

Two scattering foils were designed to improve the dose homogeneity when a curved surface is irradiated with electrons. One scattering foil, constructed of mylar, was designed for use with a single 6 MeV electron field. The second scattering foil, constructed of lead, was designed to homogenize the dose along the matchline of two abutting electron fields. Measurements with the second compensator were made at energies of 6, 9, and 12 MeV. The compensators were mounted over the topmost opening of the electron cone. A simple method for modeling the effect of the second compensator using a conventional treatment planning system was also evaluated.

RESULTS

When the mylar compensator was placed atop the 25 x 25 cm cone and a Rando phantom irradiated with 6 MeV electrons, the dose at the field edges was increased by about 10%. Use of the lead foil compensator for two abutting fields gave a highly uniform dose along the matchline, without perturbing the isodoses at depth or at the other field edges. Measured hot spots in the Rando phantom for 6 and 9 MeV electrons were 104 and 108%, respectively. The effect of the lead foil compensator was successfully modeled on a conventional treatment planning system by summing beams of different field sizes.

CONCLUSIONS

Both compensators were effective in improving the dose homogeneity within the target volume.