Correction factors for water-proofing sleeves in kilovoltage x-ray beams.

This paper investigates the effect of the waterproofing sleeve on the calibration of kilovoltage photon beams (50-300 kV). The sleeve effect correction factor, ps has been calculated using the Monte Carlo method as the ratios of the air kerma in an air cavity of a cylindrical chamber without the waterproofing sleeve to that with a sleeve. Three sleeve materials have been studied, PMMA, nylon and polystyrene.

Dependence of overall correction factor of a cylindrical ionization chamber on field size and depth in medium-energy x-ray beams.

In this paper we examine the depth and field size dependence of the overall correction factor kch for in-phantom dose determinations in orthovoltage x-ray beams. The overall correction factor is considered to be composed of three contributions, i.e.

Water calorimetry and ionization chamber dosimetry in an 85-MeV clinical proton beam.

In recent years, the increased use of proton beams for clinical purposes has enhanced the demand for accurate absolute dosimetry for protons. As calorimetry is the most direct way to establish the absorbed dose and because water has recently been accepted as standard material for this type of beam, the importance of water calorimetry is obvious. In this work we report water calorimeter operation in an 85-MeV proton beam and a comparison of the absorbed dose to water measured by ionometry with the dose resulting from water calorimetric measurements.

Water calorimetry measurements in a 85 MeV clinical proton beam.

The importance of water calorimetry in clinical proton beam dosimetry has increased for various reasons: there has been an increasing interest in proton therapy from the radiotherapy world; existing dosimetry protocols for clinical proton beams recommend calorimetry as the primary dosimetry method (ie, AAPM and ECHED); water has recently become the reference material for dose specification. For the water calorimetric dose evaluation, the water calorimeter developed in Ghent was used. Ionometry was performed following the ECHED protocol.

Kinetics of [methyl-11C]thymidine in patients with squamous cell carcinoma of the head and neck.

Thymidine labelled with a position emitter and imaging by positron emission tomography has been suggested to measure tumour proliferation in vivo non-invasively. The present study presents a compartmental model which describes the behavior of [methyl-11C]thymidine in tumour tissue and allows quantification of the data using a proliferation parameter (PP). In nine patients with squamous cell carcinoma of the head and neck, 11C-activity over the tumour and the adjacent blood vessels was measured.

Monte Carlo study of electron spectra and dose from backscattered radiation in the vicinity of media interfaces for monoenergetic photons of 50-1250 keV.

In the present paper electron fluence spectra and backscatter dose factors for monoenergetic photons (50, 100, 250 and 1250 keV) are presented. The influence of the atomic number of the backscatter materials glass, bone, steel and titanium is studied. For all radiations increases in dose were found in the immediate vicinity of the interface in a region extending over a distance determined by the photon energy.

Comparison of measured and calculated dose distributions in lung after electron beam treatment of the chest wall.

In this paper a comparison of measured and calculated absorbed dose distributions due to 6 and 8 MeV electron irradiation of a thorax phantom consisting of layers of tissue equivalent materials and infinite cylindrical rib inhomogeneities are presented. Dose measurements, carried out in lung equivalent tissue using thermoluminescent dosimeters for the phantom with and without the rib inhomogeneities, are compared with calculations using a typical two-dimensional (2-D) treatment planning system and EGS4 Monte Carlo calculations. The results show that the used 2-D planning system generally reproduces the dose distribution for the phantom without the cylindrical inhomogeneities.

Scoring of radiation-induced micronuclei in cytokinesis-blocked human lymphocytes by automated image analysis.

The micronucleus assay in human lymphocytes is, at present, frequently used to assess chromosomal damage caused by ionizing radiation or mutagens. Manual scoring of micronuclei (MN) by trained personnel is very time-consuming, tiring work, and the results depend on subjective interpretation of scoring criteria. More objective scoring can be accomplished only if the test can be automated.

Dose conversion factors and linear energy transfer for irradiation of thin blood layers with low-energy X rays.

For irradiation of thin samples of biological material with low-energy X rays, conversion of measured air kerma, free in air to average absorbed dose to the sample is necessary. In the present paper, conversion factors from measured air kerma to average absorbed dose in thin blood samples are given for four low-energy X-ray qualities (14-50 kVp). These factors were obtained by Monte Carlo simulation of a practical sample holder.

Verification of absorbed doses determined with thimble and parallel-plate ionization chambers in clinical electron beams using ferrous sulphate dosimetry.

Absorbed dose values determined with the commonly applied NACP and PTW/Markus parallel-plate chambers and the cylindrical NE2571 Farmer chamber were compared to values obtained with ferrous sulphate dosimetry in a number of electron beams. For the ionometry with the parallel-plate chambers the dose-to-air chamber factor ND (or Ngas) was derived from a 60Co beam calibration free in air with an additional buildup layer of 0.54 g cm-2 graphite as proposed by the protocol for electron dosimetry published by the Netherlands Commission on Radiation Dosimetry.

Conversion factor f for X-ray beam qualities, specified by peak tube potential and HVL value.

Conversion factors of exposure to absorbed dose f in compact bone, muscle, water and adipose tissue are deduced from the measured photon fluence spectra of x-ray beams with potentials from 50 to 250 kV. The results show that accurate determination of f requires beam quality specification not only by the HVL value but also by a second parameter, e.g.