A hybrid radiation detector for simultaneous spatial and temporal dosimetry

In this feasibility study an organic plastic scintillator is calibrated against ionisation chamber measurements and then embedded in a polymer gel dosimeter to obtain a quasi-4D experimental measurement of a radiation field. This hybrid dosimeter was irradiated with a linear accelerator, with temporal measurements of the dose rate being acquired by the scintillator and spatial measurements acquired with the gel dosimeter. The detectors employed in this work are radiologically equivalent; and we show that neither detector perturbs the intensity of the radiation field of the other. By employing these detectors in concert, spatial and temporal variations in the radiation intensity can now be detected and gel dosimeters can be calibrated for absolute dose from a single irradiation

Design and evaluation of electron beam energy degraders for breast boost irradiation

BACKGROUND: For breast cancer patients who require electron boost energies between 6 and 9 MeV, an energy degraders (ED) in the 9 MeV beamline was specially designed and manufactured to increase the skin dose of 6 MeV and to reduce the penetration depth of 9 MeV beams. METHODS: We used Monte Carlo (MC) techniques as a guide in the design of ED for use with linear accelerators. In order to satisfy percent depth dose (PDD) characteristics and dose profile uniformity in water, the shape and thickness of Lucite® ED in the 9 MeV beamline was iteratively optimized and then manufactured. The ED geometry consists of a truncated cone attached on top of a plane plate, with total central thickness of 1.0 cm. The ED was placed on the lower most scraper of the electron applicator. The PDDs, profiles, and output factors were measured in water to validate the MC-based design. RESULTS: Skin doses with the EDs increased by 8–9 %, compared to those of the 9 MeV beam. The outputs with the EDs were 0.882 and 0.972 for 10 × 10 and 15 × 15 cm(2) cones, respectively, as compared to that of a conventional 9 MeV beam for a 10 × 10 cm(2) cone. The X-ray contamination remained less than 1.5 %. In-vivo measurements were also performed for three breast boost patients and showed close agreement with expected values. CONCLUSIONS: The optimally designed ED in the 9 MeV beamline provides breast conserving patients with a new energy option of 7 MeV for boost of the shallow tumor bed. It would be an alternative to bolus and thus eliminate inconvenience and concern about the daily variation of bolus setup