This study investigates the surface dose and build-up region dosimetry for oblique IMRT beams. The dependence of surface and build-up region doses of 0° (perpendicular incidence) and 75° (oblique incidence) IMRT fields on field size was measured and compared with open field dosimetry. Measurements were performed using a parallel-plate chamber and KODAK EDR2 films in a polystyrene phantom for a 6 cm × 6 cm and a 12 cm × 12 cm, 6 MV photon beam at depths of 0 mm (surface) through dmax. Data were normalized to the dmax value of each field. Four intensity modulated delivery patterns were created and delivered using step-and-shoot IMRT: (1) six static 1 cm × 6 cm strips (IMRTstrip), (2) 12 static 1 cm × 12 cm strips (IMRTstrip), (3) intensity modulated beam patterns created by using the inverse planning optimization software (IMRT opt) for 6 cm × 6 cm, and (4) IMRTstrip for 12 cm × 12 cm field sizes. The percent depth doses (PDDs) of 0°, 6 cm × 6 cm IMRTstrip beam at the surface and 5 mm were lower by 8.8% and 1.6%, respectively, compared to the open field. The PDDs of 75°, 6 cm × 6 cm IMRTstrip beam at the surface and 5 mm were lower by 6.7% and 2.4%, respectively, compared to the open field. This study showed that IMRT itself is not contributing to greater skin doses.
- Build-up region dosimetry
- Intensity modulated radiotherapy (IMRT)
- Oblique incidence
- Surface dose
ASJC Scopus subject areas
- Radiology Nuclear Medicine and imaging