Biomedical subjects

Robert Jeraj

Publications and source records attributed to Robert Jeraj.

21 records · Page 2Linked to original sources

PubMed2002

Optimal flattening filter shape of a surface brachytherapy applicator.

As an alternative to standard treatment of superficial lesions with surgery and/or superficial/orthovoltage x-ray irradiation, radioactive moulds can be used. However, close proximity of the source to the treatment region leads to significant dose inhomogeneities in the tissue. Analytical and fast numerical methods have been developed that can calculate a corresponding flattening filter that evens out the dose distribution at the surface. Monte Carlo transport calculations were used to enable accurate treatment of the transport through the geometry. It was found that the use of pre-calculated transport parameters like dependence of the attenuation coefficient and scattering with depth is required for fast calculation of the flattening filter shape. Only 1-2 iterations were needed for a successful convergence to the filter shape that flattens out the dose distribution at the surface to within 1%. The developed methods are very general and could be applied with some minor modifications to other problems, where shaping of the irradiation field is required.

Algorithms↗

PubMed2002

The effect of dose calculation accuracy on inverse treatment planning.

The effect of dose calculation accuracy during inverse treatment planning for intensity modulated radiotherapy (IMRT) was studied in this work. Three dose calculation methods were compared: Monte Carlo, superposition and pencil beam. These algorithms were used to calculate beamlets. which were subsequently used by a simulated annealing algorithm to determine beamlet weights which comprised the optimal solution to the objective function. Three different cases (lung, prostate and head and neck) were investigated and several different objective functions were tested for their effect on inverse treatment planning. It is shown that the use of inaccurate dose calculation introduces two errors in a treatment plan, a systematic error and a convergence error. The systematic error is present because of the inaccuracy of the dose calculation algorithm. The convergence error appears because the optimal intensity distribution for inaccurate beamlets differs from the optimal solution for the accurate beamlets. While the systematic error for superposition was found to be approximately 1% of Dmax in the tumour and slightly larger outside, the error for the pencil beam method is typically approximately 5% of Dmax and is rather insensitive to the given objectives. On the other hand, the convergence error was found to be very sensitive to the objective function, is only slightly correlated to the systematic error and should be determined for each case individually. Our results suggest that because of the large systematic and convergence errors, inverse treatment planning systems based on pencil beam algorithms alone should be upgraded either to superposition or Monte Carlo based dose calculations.

Algorithms↗

PubMedDate not supplied

PET/CT following intensity-modulated radiation therapy for primary lung tumor in a dog.

A primary lung tumor in a dog treated with intensity-modulated radiation therapy was imaged approximately 6 weeks and 1-year posttreatment with combined positron emission tomography (PET) and computed tomography, utilizing the radiotracers 18F-fluorodeoxyglucose and 18F-fluorothymidine. These two tracers allowed discrimination of tumor from inflammation, and demonstrated spread of tumor along airways over time after treatment. Fusion of functional imaging with anatomic imaging is a useful tool, particularly in the field of oncology, with the potential for PET markers that delineate tumor from normal or reactive tissue, and potential or actual response to therapy.

Animals↗