Quality assurance of patient dosimetry in boron neutron capture therapy

The verification of the correctness of planned and executed treatments is imperative for safety in radiotherapy. The purpose of the present work is to describe and evaluate the quality assurance (QA) procedures for patient dosimetry implemented at the boron neutron capture therapy (BNCT) facility at Studsvik, Sweden. The dosimetric complexity of the mixed neutron/photon field during BNCT suggests a careful verification of routine procedures, specifically the treatment planning calculations. In the present study, two methods for QA of patient dosimetry are presented. The first is executed prior to radiotherapy and involves an independent check of the planned absorbed dose to be delivered to a point in the patient for each treatment field. The second QA procedure involves in vivo dosimetry measurements using post-treatment activation analysis. Absorbed dose conversion factors taking the difference in material composition and geometry of the patient and the PMMA phantom used for reference dosimetry were determined using the Monte Carlo method. The agreement of the QA procedure prior to radiotherapy reveals an acceptably small deviation for 60 treatment fields of +/-4.2% (1 SD), while the in vivo dosimetry method presented may benefit from improvements, as the deviations observed were quite substantial (+/-12%, 1 SD), and were unlikely to be due to actual errors in the clinical dosimetry

Reference dosimetry at the boron neutron capture therapy facility at Studsvik

The purpose of this publication was to present and evaluate the methods for reference dosimetry in the epithermal neutron beam at the neutron capture therapy facility at Studsvik. Measurements were performed in a PMMA phantom and in air using ionization chambers and activation probes in order to calibrate the epithermal neutron beam. Appropriate beam-dependant calibration factors were determined using Monte Carlo methods for the detectors used in the present publication. Using the presented methodology, the photon, neutron and total absorbed dose to PMMA was determined with an estimated uncertainty of +/- 5.0%, +/- 25%, and +/- 5.5% (2 SD), respectively. The uncertainty of the determination of the photon absorbed dose was comparable to the case in conventional radiotherapy, while the uncertainty of the neutron absorbed dose is much higher using the present methods. The thermal neutron group fluence, i.e., the neutron fluence in the energy interval 0-0.414 eV, was determined with an estimated uncertainty of +/- 2.8% (2 SD), which is acceptable for dosimetry in epithermal neutron beams

Simulation of the effect of inhomogeneties in TEM transmission cells using the FDTD-method.

The finite difference time domain (FDTD)-method is applied to model transverse electromagnetic (TEM) transmission cells in three dimensions. The perturbation of the TEM-mode and the standard field distribution in the TEM-cell, due to inhomogeneous materials placed inside the cell cavity, is evaluated. Particularly, the dependence of the disturbance of the TEM-mode on the dimensions of the material and its position in the TEM-cell is studied. Also the absorption of the electromagnetic fields in the lossy materials, placed in the cell, is calculated

Electromagnetic field calculations used for exposure experiments on small animals in TEM cells

Three-dimensional electromagnetic calculations for loaded transverse electromagnetic (TEM) transmission cells are presented. Based on those calculations a prediction of the perturbation of the standard uniform field in the TEM-cell, due to the scattering by inhomogeneous structures placed inside the cell cavity, is given. The influence of the dimensions of a lossy structure and its position in the TEM-cell on its absorption of the electromagnetic fields is presented. Knowing the perturbation of the uniform field is important for good interpretation of the biological experimental results