Modelling of a 188W/188Re beta line source for coronary brachytherapy by means of EGS4 Monte Carlo simulations

The radial depth-dose distribution of a 188W/188Re beta line source measured with novel, ultra-thin TLDs in a PMMA phantom: comparison with Monte Carlo simulations

The radial depth-dose distribution of a prototype 188W/188Re beta particle line source of known activity has been measured in a PMMA phantom, using a novel, ultra-thin type of LiF:Mg,Cu,P thermoluminescent detector (TLD). The measured radial dose function of this intravascular brachytherapy source agrees well with MCNP4C Monte Carlo simulations, which indicate that 188Re accounts for > or = 99% of the dose between 1 mm and 5 mm radial distance from the source axis. The TLDs were calibrated using a 90Sr/90Y beta secondary standard. Several correction factors are calculated using analytical and Monte Carlo methods. An analysis of the measurement uncertainty is made. Since it is partly determined by components of uncertainty arising from random effects, repeated measurements yield a lower uncertainty. The expanded uncertainty in the absolute dose at 2 mm radial distance equals 11%, 10%, 9% and 8% for 1, 2, 3 and 5 measurements, respectively. After a correction for source non-uniformity, the measured dose rate per unit source activity at 2 mm radial distance equals (1.53 +/- 0.16) Gy min(-1) GBq(-1) (2sigma), in agreement with the value of (1.45 +/- 0.01) Gy min(-1) GBq(-1) (2sigma) predicted by the MCNP4C simulations.

Intravascular brachytherapy of the coronary arteries

This is a review of the relatively recently developed field of intravascular brachytherapy of coronary arteries. It presents a brief overview of the discipline of coronary angioplasty describing the problem of restenosis and discusses the potential for ionizing radiation to overcome this problem. It examines the various methods that have been used to irradiate the coronary arteries comparing their advantages and disadvantages. Special consideration is given to seeds and wires in the artery, radioactive liquids in the angioplasty balloon and radioactive stents. Passing reference is made to a number of other methods that have also been proposed, but which are not commonly used to irradiate the coronary arteries at present. The dosimetry of each of the major techniques is discussed and the data from different laboratories compared. Specific consideration is given to the need for centring of the radioactive source and the factors affecting the selection of a dose prescription. A brief review of recent clinical trials is followed by an examination of possible future directions in this field including the use of intravascular ultrasound to improve dosimetry, the use of gas-filled balloons to enhance the penetration of beta-emitting sources and the use of gamma-emitting stents to overcome the problems associated with edge restenosis.

On the applicability of the AAPM TG-60/TG-43 dose calculation formalism to intravascular line sources: proposal for an adapted formalism

Despite the widely recognized usefulness of the AAPM TG-43 brachytherapy dose calculation formalism, a straightforward application of this approach to describe the dose distribution about intravascular line sources as proposed by TG-60 may be difficult or even impossible, especially when these line sources emit low-energy photons or beta particles. The causes of these limitations are investigated and illustrated by means of some numerical examples. In order to solve the observed limitations an adapted formalism is proposed, intended specifically for the description of the dose rate distribution about line sources but conceptually similar to the TG-43/TG-60 formalism. Several examples are presented to illustrate the usefulness of the proposed line source dose calculation formalism.