Biomedical subjects

J Uusi-Simola

Publications and source records attributed to J Uusi-Simola.

4 recordsLinked to original sources

PubMed2005

An international dosimetry exchange for boron neutron capture therapy. Part I: Absorbed dose measurements.

An international collaboration was organized to undertake a dosimetry exchange to enable the future combination of clinical data from different centers conducting neutron capture therapy trials. As a first step (Part I) the dosimetry group from the Americas, represented by MIT, visited the clinical centers at Studsvik (Sweden), VTT Espoo (Finland), and the Nuclear Research Institute (NRI) at Rez (Czech Republic). A combined VTT/NRI group reciprocated with a visit to MIT. Each participant performed a series of dosimetry measurements under equivalent irradiation conditions using methods appropriate to their clinical protocols. This entailed in-air measurements and dose versus depth measurements in a large water phantom. Thermal neutron flux as well as fast neutron and photon absorbed dose rates were measured. Satisfactory agreement in determining absorbed dose within the experimental uncertainties was obtained between the different groups although the measurement uncertainties are large, ranging between 3% and 30% depending upon the dose component and the depth of measurement. To improve the precision in the specification of absorbed dose amongst the participants, the individually measured dose components were normalized to the results from a single method. Assuming a boron concentration of 15 microg g(-1) that is typical of concentrations realized clinically with the boron delivery compound boronophenylalanine-fructose, systematic discrepancies in the specification of the total biologically weighted dose of up to 10% were apparent between the different groups. The results from these measurements will be used in future to normalize treatment plan calculations between the different clinical dosimetry protocols as Part II of this study.

Biophysical Phenomena↗

PubMed2004

Quality assurance procedures for the neutron beam monitors at the FiR 1 BNCT facility.

In order to assure the stability of the beam, the reliability of the beam monitoring system and the quality of the patient dose delivered, several procedures are followed at the FiR 1 epithermal beam in Finland. Routine procedures include in-phantom activation measurements before each patient treatment and a long-term follow-up of the results. The sensitivity of the beam monitors to external objects in the beam and to variations in the control rod positions in the reactor has been checked and found insignificant. The linearity of the beam monitor channels has been checked with activation measurements. It was found that due to saturation effects a correction of 11% has to be applied when extrapolating results from experiments at low power to full power using the reference monitor channel. The correction is even larger for other channels with higher count rates.

Boron Neutron Capture Therapy↗

PubMed2004

Dosimetric comparison at FiR 1 using microdosimetry, ionisation chambers and computer simulation.

Tissue equivalent proportional counter microdosimetry has been applied in the dosimetry of epithermal neutron beams as they can provide an independent and accurate method to determine gamma ray and neutron absorbed doses. Dosimetric comparison has been performed using a tissue equivalent proportional counter, dual ionisation chambers and DORT computer code at FiR 1 boron neutron capture therapy facility in Espoo, Finland. The three methods were applied to determine neutron and gamma ray absorbed doses at 25, 40, 60 and 120 mm depths along the beam centerline in a water-filled PMMA phantom. The determined absorbed doses were found to agree within the limits of the estimated uncertainties.

Boron Neutron Capture Therapy↗

PubMed2003

Study of the relative dose-response of BANG-3 polymer gel dosimeters in epithermal neutron irradiation.

Polymer gels have been reported as a new, potential tool for dosimetry in mixed neutron-gamma radiation fields. In this work, BANG-3 (MGS Research Inc.) gel vials from three production batches were irradiated with 6 MV photons of a Varian Clinac 2100 C linear accelerator and with the epithermal neutron beam of the Finnish boron neutron capture therapy (BNCT) facility at the FiR 1 nuclear reactor. The gel is tissue equivalent in main elemental composition and density and its T2 relaxation time is dependent on the absorbed dose. The T2 relaxation time map of the irradiated gel vials was measured with a 1.5 T magnetic resonance (MR) scanner using spin echo sequence. The absorbed doses of neutron irradiation were calculated using DORT computer code, and the accuracy of the calculational model was verified by measuring gamma ray dose rate with thermoluminescent dosimeters and 55Mn(n,gamma) activation reaction rate with activation detectors. The response of the BANG-3 gel dosimeter for total absorbed dose in the neutron irradiation was linear, and the magnitude of the response relative to the response in the photon irradiation was observed to vary between different gel batches. The results support the potential of polymer gels in BNCT dosimetry, especially for the verification of two- or three-dimensional dose distributions.

Boron Neutron Capture Therapy↗