A physical dosimetry intercomparison for BNCT

• Published in: Medical physics (Lancaster) Vol. 29; no. 5; pp. 898 - 904
• Main Authors: Riley, Kent J., Binns, Peter J., Greenberg, Dennis D., Harling, Otto K.
• Format: Journal Article
• Language: English
• Published: United States American Association of Physicists in Medicine 01-05-2002
• Subjects: Biophysical Phenomena; Biophysics; BNCT; boron; Boron Neutron Capture Therapy; dosimetry; dosimetry intercomparison; Dosimetry/exposure assessment; Error analysis; Fast Neutrons - therapeutic use; Gas‐filled counters: ionization chambers, proportional, and avalanche counters; Gold; Graphite; Humans; ionisation chambers; Ionization chambers; neutron absorption; neutron detection; neutron flux; Neutron radiation effects; Neutrons; Phantoms, Imaging; Photons; Photons - therapeutic use; Polymethyl Methacrylate; radiation therapy; Radiometry - instrumentation; Radiometry - methods; Radiometry - statistics & numerical data; Radiotherapy Dosage; Research reactors; thermal neutrons; Thermoluminescent dosimeters; Water; dosimetry intercomparison; BNCT; thermal neutrons
• ISSN: 0094-2405; 2473-4209
• DOI: 10.1118/1.1473133

An intercomparison of physical dosimetry methods used at the Massachusetts Institute of Technology (MIT) and Brookhaven National Laboratory was completed to enable retrospective analysis of BNCT trials. Measurements were performed under reference conditions pertinent to clinical irradiations at the epithermal neutron beam facility of the Brookhaven Medical Research Reactor (BMRR) using procedures developed at MIT during similar trials. Thermal neutron flux was determined from gold foil activation experiments and good agreement was found between the depth profiles measured in-phantom by the two groups. At a depth of 3.5 cm where the measured flux is greatest, the ratio of the MIT/BMRR measurements is
1.01±0.10
if the same reporting procedures are applied. Photon and fast neutron absorbed dose rates were assessed using ionization chambers with separate graphite and A-150 plastic walls. Measurement of the in-phantom photon depth dose component agreed favorably with that previously reported by the BMRR group using thermoluminescent dosimeters. At a depth of 3.5 cm the ratio of the MIT measurements to those made by the BMRR group was
0.89±0.12.
In-air measurements of the fast neutron and photon absorbed dose rates agreed within the limits of experimental uncertainty. Additional studies were performed in the ellipsoidal water phantom regularly used for beam characterizations at MIT. No significant differences in the thermal neutron flux measured in either a solid PMMA cube or an ellipsoidal shaped water phantom were observed on the central axis of the beam. This study confirms the reproducibility and uniformity of dosimetry measurements performed by the two independent groups undertaking BNCT trials in the USA and provides the physical data necessary to compare BMRR treatment protocols with those applied at Harvard-MIT.