Radiation Dosimetry of a Conformal Heat-brachytherapy Applicator

Abstract

The purpose of this paper is to report the radiation dosimetric characteristics of a new combination applicator for delivering heat and radiation simultaneously to large area superficial disease <1.5 cm deep. The applicator combines an array of brachytherapy catheters (for radiation delivery) with a conformal printed circuit board microwave antenna array (for heat generation), and a body-conforming 5-10 mm thick temperature-controlled water bolus. The rationale for applying both modalities simultaneously includes the potential for significantly higher response rate due to enhanced synergism of modalities, and lower peak toxicity due planning. This novel applicator should prove useful for the treatment of diffuse chestwall disease located over contoured anatomy that may be difficult to treat with single field external beam therapy. By delivering heat and radiation simultaneously, increased synergism is expected with a TER in the range of 2-5. Lowering radiation dose by an equivalent factor may produce lower radiation toxicity with similar efficacy, while preserving the option of subsequent retreatment(s) with thermoradiotherapy in order to further extend patient survival.

Multilayer conformal applicator for microwave heating and brachytherapy treatment of superficial tissue disease

“…The dielectric spacer is used to increase the brachytherapy source to skin distance in order to homogenize the radiation dose delivered to the target as described in Taschereau et al [25]. The additional separation also minimizes interaction between the brachytherapy sources and fiber-optic thermometry sensors, as recommended in previous investigations [40].…”

“…A nearly uniform thickness waterbolus is important for optimal heating of superficial tissue as flexible PCB microwave antenna arrays have been designed for most uniform heating when coupled through a thin layer of water <9 mm thick [23,24]. Although minor variations in bolus thickness can be accommodated by varying the microwave power [24] and radiation dwell time characteristics [25], maintaining a stable bolus thickness profile from initial set-up until the end of treatment delivery is critical to delivering the pre-planned doses.…”

“…The brachytherapy catheters are attached parallel to each other with 1 cm spacing to facilitate uniform irradiation of the superficial tissue target as reported previously [25].…”

Size reduction and radiation pattern shaping of multi-fed DCC slot antennas used in conformal microwave array hyperthermia applicators

“…The potential benefits of a hybrid applicator/system capable of delivering at the same time heat and radiation led few research groups to develop new combination applicators [29–32], such as the one developed by this group for concurrent microwave heating and brachytherapy treatment of large area surface [32–33]. Differently from the commercially available waveguides, the applicator is light, conformable, comfortable and able to cover any large area.…”

Progress on thermobrachytherapy surface applicator for superficial tissue disease

“…It has been shown in laboratory settings that the thermal enhancement ratio in tumor is much higher with concurrent delivery of heat and radiation than with sequential treatments. The potential benefits of increasing the thermal enhancement ratio from about 1.5 for sequential treatments to 2.5 or higher for simultaneous treatments have led to development of new combination applicators capable of simultaneous therapy [29–32]. One such applicator developed by this group for concurrent microwave heating and brachytherapy treatment of large area surface disease such as chest wall recurrence of breast cancer was reported in [32–33].…”