Dose measurement in heterogeneous phantoms with an extrapolation chamber

A Phantom-Embedded Extrapolation Chamber (PEEC) is used for determining absolute dose in solid water and bone phantom materials irradiated with photon (cobalt-60) and electron (9 and 15 MeV) beams. The dose is determined using the modified Spencer-Attix cavity theory equation. The restricted stopping power ratios L¯_air^med solid water and bone material are calculated with Monte Carlo simulations of our actual beams. The determination of dose with PEEC is relatively simple and does not involve any troublesome correction factors that are common in determination of dose with standard cylindrical ionization chamber protocols. The dose measured in solid water with the PEEC agrees to within 0.5% with the dose measured in solid water with a standard Farmer chamber and the TG-21 protocol. The dose measured in solid water and bone material agrees to within 0.5% with results of Monte Carlo calculations. These results suggest that the PEEC may be used reliably in measuring the absolute dose not only in Solid Water but also in other clinically relevant materials, such as bone and lung