ThermoBrachy (TB) applicator

This tech spec was submitted by Androulakis Ioannis as part of the University Technology Exposure Program.

Overview

Problem / Solution

Prostate cancer is the second most common cancer for males worldwide, with about 1 for every 8 men diagnosed during their lifetime. Although High Dose Rate Brachytherapy (HDR-BT) for prostate cancers is a valuable treatment option, single fractions HDR-BT resulted in suboptimal biochemical control of the disease and higher local recurrence rates compared to two or three fraction treatments. Combining HDR-BT with Interstitial Hyperthermia (IHT) on a single catheter enhances tumor cell kill efficiency without increasing the radiation dose. The IHT technique, 27 MHz capacitive coupled (CC) multi-electrode current source (MECS) system, was recognized for its homogenous longitudinal heating pattern, for possessing good temperature steering abilities, and for allowing extensive temperature monitoring. However, its undesired high temperature heterogeneity makes it more of a hot source than a radiofrequency (RF) electromagnetic fields (EMF) device.

 ThermoBrachy applicator features the seamless integration and simultaneous application of the two treatment modalities by serving as an IHT applicator and afterloading catheter for HDR-BT. This complementing and synchronized technique achieves a higher thermal enhancement ratio (TER) and decreases the overall treatment time than the sequential application of radiation and hyperthermia.

Design

The ThermoBrachy applicator is a tube-like structure with three layers: an afterloading catheter at the core, flat copper electrodes, and a thin conformal coating layer at the surface. 

 The electrodes for IHT application are made up of copper layers based on the capacitively coupled principle. A copper wire connects two copper electrodes to the energy source through the circumferential wiring path along the catheter axis. These copper layers are placed on the outer layer of the POM afterloading catheter with a 5mm space between the two. By doing so, the TB applicator obtains highly efficient capacitive coupling of RF-EMF energy with desired heating distributions.

A thin dielectric conformal coating layer of Parylene C covers the outer applicator. The thinner dielectric material greatly improves the delivery of RF-EMF energy in the target volume. This design also ensures biocompatibility and capacitive coupling rather than galvanic contact with the tissue.

The inner cavity of the afterloading catheter is not obstructed and remains fully available to insert the HDR-BT source. Hence, only a slight attenuation of <0.3% on the BT dose distribution is expected because of the additional copper layer. The applicator can simultaneously apply IHT without interfering with the HDR-BT application.

Power is supplied to the electrodes through voltage sources operating in-phase at a frequency of 27 MHz. The two ends of these voltage sources are connected to the electrode and common ground, respectively. A balanced configuration is achieved by setting the phase of half the electrodes to a 180-degree shift. The power and phase of each electrode can be adjusted during treatment to steer the heating pattern both spatially and temporally.

The electrodes feature good temperature homogeneity after 5min of heating in a homogenous phantom under various simulations and experiments.