Abstract
Purpose: To characterize the OneDosePlus™ MOSFET detector, compare its response to both that of a Thomson‐Nielsen MOSFET detector and that of an ionization chamber, and assess its feasibility for use as an in vivo dosimeter. Method and Materials: Using, alternately, a OneDosePlus™ MOSFET detector, a Thomson‐Nielsen MOSFET detector and an ionization chamber—the gold standard, the output of a 6 MV photon beam from a clinical linear accelerator was measured at the depth of dmax = 1.5 cm in a water‐equivalent plastic phantom (i) as a function of field size and SSD for a fixed 0° gantry angle, and (ii) as a function of gantry angle for a fixed field size of 10×10 cm2 and SSD of 100 cm. Field sizes in the range 5×5–40×40 cm2, SSDs in the range 80–120 cm, and gantry angles in the range 0–80° were studied. For each detector, a similar geometrical setup was employed and the same number of monitor units was delivered. MOSFET measurements were normalized to those obtained correspondingly with an ionization chamber, and then compared. Results: The OneDosePlus™ detector exhibited a response to the delivered radiation dose that was consistent with the corresponding Thomson‐Nielsen MOSFET and ionization chamber measurements for all SSDs and field sizes. As expected, the output increased with increasing field size and decreasing SSD. The OneDosePlus™ measurements demonstrated significant angular dependence with respect to gantry angle beyond ∼40°, deviating by as much as 60% from the ion chamber reading at 80°. Conclusion: The OneDosePlus™ detector is suitable for in vivo skin‐dose determination. It provides a direct, reliable dose measurement for a range of field sizes, SSDs and gantry angles. Though significant angular‐dependent corrections are required beyond ∼40° incidence—owing to the detector's asymmetric construction—it is otherwise a highly convenient alternative to the Thomson‐Nielsen MOSFET.
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