Accurate Dosimetry for Radiobiology.

Purpose: Accurate radiation dose is required to ensure reproducibility in establishing the radiobiological effect in biological systems among institutions. The dose should be the most precise and accurate parameter of the entire process. The goal is a system to provide uniform radiation dose verification among institutions that is traceable to the National Institute of Standards and Technology (NIST) through an Accredited Dosimetry Calibration Laboratory.

Methods And Materials: Radiobiological beams are not NIST traceable but can be approximated based on the radiograph's half value layer. Phantoms have been developed containing detectors to measure the dose from total body irradiation of mice and others. Ionization chambers calibrated to NIST-traceable beams are the best detectors for precise and accurate dose determinations. However, thermoluminescent dosimeters have been mostly used for this application for comparison between institutions.

Results: A comparison of thermoluminescent dosimeters results among surveyed institutions showed a large variation in delivered dose. The range of radiograph doses that were measured deviated from the standard dose by 12% to 42%. The results have an uncertainty of 2.5% at 1 standard deviation. The surveyed radionuclide irradiators demonstrated a dose range variation of 1.6% to 13.5% from target dose. There is less variation among high energy (linacs) because a calibrated ionization chamber is generally used by personnel (eg, medical physicist) and the output is determined for radiation therapy applications as well.

Conclusions: Radiobiological dosimetry is lacking with respect to its precision and accuracy. The accuracy of radiograph calibrations for radiobiology can be estimated to be approximately 5%, because there are no NIST-traceable beams. However, among institutions, the variations can be up to 42%. Intercomparisons between institutions is important to have a clear understanding of the transference of dose between given studies.