RESUMO
PURPOSE: Accurate measurement of out-of-field dose in radiotherapy directly impacts beam data modeling in treatment planning systems, verification of implanted electronic devices/lens/fetus dose, secondary cancer risk estimation, and organ-at-risk dose reporting. When performing out-of-field dosimetry, it is therefore imperative that the response of the detector has been well characterized. Due to the softening of the radiation beam out-of-field, many detectors will exhibit energy dependence. This study investigated the energy dependence of a range of clinical available detectors over typical energies experienced out-of-field. METHODS: The response of detectors to photon beams from 70 kV to 6 MV was measured. The relative change in response from 6 MV down to 70 kV highlighted the expected deviation in the response of detectors that would typically be calibrated in-field for use out-of-field. RESULTS: The Pinpoint detector displayed the most energy-independent response over the energy range investigated. The Micro-Lion detector was the only detector to show an under-response to all low-energy beams relative to 6 MV. The diode-type detectors showed the largest energy dependence. CONCLUSIONS: When considering detectors for use in out-of-field dose measurements, it is important that the energy dependence is investigated over a low-energy range as out-of-field the energy spectra comprise a larger component of photons in the 50-100-keV range. This study highlights the variation in response of a range of clinically available detectors to low-energy radiation beams relative to 6 MV for out-of-field dosimetry. The Pinpoint detector was the most energy-independent detector with a response close to unity over the entire energy range investigated.
