Biomedical subjects

T Pawlicki

Publications and source records attributed to T Pawlicki.

22 records · Page 2Linked to original sources

PubMed1994

Validity of universal wedge equation over the range of 60Cobalt to 25 MV photon beam energies.

PURPOSE: Evaluating the validity of the universal wedge equation over the range of 60Cobalt (60CO) to 25 MV photon beam energies. METHODS AND MATERIALS: The universal wedge equation relates the beam weight of the wedged field to the effective wedge angle produced by combining the wedged field to the nonwedged field and is expressed as tan (theta) = B tan (theta w), where B is the normalized weight imposed on the wedged field, theta w is the maximum wedge angle of the wedge filter, and theta is the effective wedge angle. The isodose distributions from 60Co to 25 MV photon beam energies were used. For each photon energy, the isodose distributions of wedged and nonwedged fields were combined in different proportions. The effective wedge angle was determined from each resultant isodose distribution. RESULTS: The relationship between the weight of wedged field and the effective wedge angle was found to be nonlinear for wedge filters with maximum wedge angle greater than 30 degrees. The universal wedge equation predicts the effective wedge angle to within 2 degrees compared to the measured value.

Cobalt Radioisotopes↗

PubMed1994

Effects of extended SSD on electron-beam depth-dose curves.

The effects of extended source-to-surface distance (SSD) on the electron-beam depth dose curves were examined for five electron beam energies ranging from 6 MeV to 20 MeV. The depth dose curves were measured with the water phantom surface set at 100 cm, 110 cm, and 120 cm from the source. Except for the dose in the build-up region, negligible depth dose curve changes due to extended SSD were observed for electron energies less than or equal to 12 MeV. For electron beams greater than 12 MeV, the percent surface dose decreases and, additionally, the depth of maximum dose shifts deeper into the phantom as the SSD increases. Changes in the rapid falloff region of the depth dose curves were apparent only for the higher energy electron beams, in particular 20 MeV. Extended SSD has no observable effect on the tail portion of the depth dose curves. As such, the energies of the electron beams are not changed significantly by increasing the SSD.

Electrons↗

PubMed1993

Seed strength determination for eye plaque therapy.

Standardized radioactive plaques have been used in the irradiation of intraocular tumors. These plaques have defined slots to accommodate 125I seeds and hence produce predictable isodose distributions. The seed strength has to be adjusted to deliver 100 Gy to the prescription point, which varies with the tumor size. The purpose of this work is to develop lookup tables that relate the seed strength to different prescription distances. Dose rates were determined for a set of standardized eye plaques. Using these dose rates and the source strength decaying expression, the seed strengths were determined as a function of distance along a line through the plaque. Two seed-strength tables were created based on four-day and five-day treatment times delivering a 100 Gy to the prescription distance.

Brachytherapy↗

PubMed1992

Various wedge isodose angles for treatment planning.

Various wedge isodose angles or simply wedge angles smaller than the nominal wedge angle were created by combining the isodose distributions generated from a single physical wedge with the isodose distributions of the open field for the 8-MV photon beam. The particular wedge angle generated depends on the weights imposed on these isodose distributions. The relationship between these weights and the wedge angle were examined and found to be nonlinear. The difference between the wedge angles defined at 10 cm depth and those defined using the 50% isodose curve is less 6 degrees. The present data was fitted using two proposed empirical equations.

Humans↗