Characterization of a synthetic single crystal diamond detector for dosimetry in spatially fractionated synchrotron x-ray fields

• Published in: Medical physics (Lancaster) 2016-07, Vol.43 (7), p.4283-4293
• Main Authors: Livingstone, Jayde, Stevenson, Andrew W., Butler, Duncan J., Häusermann, Daniel, Adam, Jean-François
• Format: Article
• Language: English
• Subjects: 60 APPLIED LIFE SCIENCES; BEAMS; biomedical equipment; BIOMEDICAL RADIOGRAPHY; Calibrating of instruments or apparatus; Calibration; DEPTH DOSE DISTRIBUTIONS; diamond; DOSE RATES; DOSIMETRY; Dosimetry/exposure assessment; ENERGY DEPENDENCE; Equipment Design; Field size; Gas‐filled counters: ionization chambers, proportional, and avalanche counters; Instrumentation and Detectors; Ion beams; ionisation chambers; IONIZATION CHAMBERS; KEV RANGE 10-100; KEV RANGE 100-1000; Linear Models; Measurement of nuclear or x‐radiation; Medical Physics; MONOCRYSTALS; Particle beam detectors; Photons; Physics; RADIATION PROTECTION AND DOSIMETRY; radiation therapy; Radiometry - instrumentation; Radiometry - methods; RADIOTHERAPY; Radiotherapy - instrumentation; Radiotherapy - methods; Ring currents; Scintigraphy; Standards and calibration; Storage rings; synchrotron radiation; SYNCHROTRONS; Testing or calibrating of apparatus or arrangements provided for in groups G01D1/00 to G01D15/00; Therapeutic applications, including brachytherapy; Tubes for determining the presence, intensity, density or energy of radiation or particles; Water; with scintillation detectors; X-Rays
• ISSN: 0094-2405; 2473-4209
• DOI: 10.1118/1.4953833

Purpose: Modern radiotherapy modalities often use small or nonstandard fields to ensure highly localized and precise dose delivery, challenging conventional clinical dosimetry protocols. The emergence of preclinical spatially fractionated synchrotron radiotherapies with high dose-rate, sub-millimetric parallel kilovoltage x-ray beams, has pushed clinical dosimetry to its limit. A commercially available synthetic single crystal diamond detector designed for small field dosimetry has been characterized to assess its potential as a dosimeter for synchrotron microbeam and minibeam radiotherapy. Methods: Experiments were carried out using a synthetic diamond detector on the imaging and medical beamline (IMBL) at the Australian Synchrotron. The energy dependence of the detector was characterized by cross-referencing with a calibrated ionization chamber in monoenergetic beams in the energy range 30–120 keV. The dose-rate dependence was measured in the range 1–700 Gy/s. Dosimetric quantities were measured in filtered white beams, with a weighted mean energy of 95 keV, in broadbeam and spatially fractionated geometries, and compared to reference dosimeters. Results: The detector exhibits an energy dependence; however, beam quality correction factors (kQ ) have been measured for energies in the range 30–120 keV. The kQ factor for the weighted mean energy of the IMBL radiotherapy spectrum, 95 keV, is 1.05 ± 0.09. The detector response is independent of dose-rate in the range 1–700 Gy/s. The percentage depth dose curves measured by the diamond detector were compared to ionization chambers and agreed to within 2%. Profile measurements of microbeam and minibeam arrays were performed. The beams are well resolved and the full width at halfmaximum agrees with the nominal width of the beams. The peak to valley dose ratio (PVDR) calculated from the profiles at various depths in water agrees within experimental error with PVDR calculations from Gafchromic film data. Conclusions: The synthetic diamond detector is now well characterized and will be used to develop an experimental dosimetry protocol for spatially fractionated synchrotron radiotherapy.