Purpose: Accurate measurement of skin dose in radiation therapy is of considerable clinical importance, especially in treating head‐and‐neck and breast cancers. MOSFET dosimeters have been introduced as a more efficient and easier‐to‐use alternative to TLD and radio‐chromic film for skin dose measurement. However, existing data with standard‐size MOSFET suggest large differences from TLD or film measurements. We investigated the applications of a micro‐MOSFET for skin dose measurements and studied the correlation between the measured surface dose by micro‐MOSFET and the skin dose expected from a Monte Carlo calculation. Method and Materials: 1). Measurements were conducted for normally incident 6MV and 10MV beams onto a flat solid water phantom. MOSFET data were compared with both measurements using a parallel plate ion chamber and a MC dose calculation for the build‐up region. 2). Measurements of surface dose were conducted for 6MV oblique beams incident onto the surface of a semi‐cylindrical solid water phantom. Results were compared to a MC calculated dose in a skin layer extending 2mm down from the surface. Results: For normal beam incidence, depth doses measured by micro‐MOSFET agree within 3% with parallel‐plate ion chamber data and MC calculation; In the build‐up region, comparison of MOSFET data with the MC calculation suggests that the MOSFET has a water‐equivalence thickness of ∼0.5mm. For oblique beams incident on the curved phantom, the micro‐MOSFET measurements correlate well with the MC calculated skin dose for a 6 MV beam, with up to ∼ 6% differences depending on the positions of the MOSFET on the surface. Results from a 10 MV beam will also be presented. Conclusion: Preliminary results indicate that the measured surface dose with a micro‐MOSFET on a curved surface under a 6MV oblique beam irradiations provide a good approximation (within ∼ 6%) of the skin dose.
ASJC Scopus subject areas
- Radiology Nuclear Medicine and imaging