Abstract
PurposeTo present the results and discuss potential insights gained through surveys on reference dosimetry practices.MethodsTwo surveys were sent to medical physicists to learn about the current state of reference dosimetry practices at radiation oncology clinics worldwide. A short survey designed to maximize response rate was made publicly available and distributed via the AAPM website and a medical physics list server. Another, much more involved survey, was sent to a smaller group of physicists to gain insight on detailed dosimetry practices. The questions were diverse, covering reference dosimetry practices on topics like measurements required for beam quality specification, the actual measurement of absorbed dose and ancillary equipment required like electrometers and environment monitoring measurements.ResultsThere were 190 respondents to the short survey and seven respondents to the detailed survey. The diversity of responses indicates nonuniformity in reference dosimetry practices and differences in interpretation of reference dosimetry protocols.ConclusionsThe results of these surveys offer insight on clinical reference dosimetry practices and will be useful in identifying current and future needs for reference dosimetry.
Highlights
Determination of absorbed dose in external photon and electron beams is realized by following protocols[1,2] that specify reference conditions and required corrections to the reading of a calibrated reference-class ionization chamber
The addendum to the TG-51 protocol[3] was published in 2011 and includes refinements to the original protocol for high-energy photon beam dosimetry. These instructions only relate to the measurement of absorbed dose, and do not provide guidance on ancillary equipment or measurements of depth-dose curves required for beam quality specification
Of the responses to the SP survey, 96% indicated that a cylindrical ion chamber was used for percentage depth-dose measurements of photon beams for beam quality specification and 70% indicated that a shift was used to convert the detector reading to dose to water and account for the effective point of measurement
Summary
Determination of absorbed dose in external photon and electron beams is realized by following protocols[1,2] that specify reference conditions and required corrections to the reading of a calibrated reference-class ionization chamber. The addendum to the TG-51 protocol[3] was published in 2011 and includes refinements to the original protocol for high-energy photon beam dosimetry. These instructions only relate to the measurement of absorbed dose, and do not provide guidance on ancillary equipment or measurements of depth-dose curves required for beam quality specification. The IEC 607314 report provides specifications required for electrometers but these recommendations are rather generous, allowing a relative combined uncertainty of 1.6%. Tailor et al.[7] and Followill[8] describe guidelines and common sources of error related to the practical clinical implementation of the TG-51 protocol
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