Miniature microwave applicator for murine bladder hyperthermia studies

Abstract

Purpose Novel combinations of heat with chemotherapeutic agents are often studied in murine tumor models. Currently, no device exists to selectively heat small tumors at depth in mice. In this project, we modelled, built and tested a miniature microwave heat applicator, the physical dimensions of which can be scaled to adjust the volume and depth of heating to focus on the tumor volume. Of particular interest is a device that can selectively heat murine bladder. Materials and Methods Using Avizo® segmentation software, we created a numerical mouse model based on micro-MRI scan data. The model was imported into HFSS™ simulation software and parametric studies were performed to optimize the dimensions of a water-loaded circular waveguide for selective power deposition inside a 0.15ml bladder. A working prototype was constructed operating at 2.45GHz. Heating performance was characterized by mapping fiber-optic temperature sensors along catheters inserted at depths of 0-1mm (subcutaneous), 2-3mm (vaginal), and 4-5mm (rectal) below the abdominal wall, with the mid-depth catheter adjacent to the bladder. Core temperature was monitored orally. Results Thermal measurements confirm the simulations which demonstrate that this applicator can provide local heating at depth in small animals. Measured temperatures in murine pelvis show well-localized bladder heating to 42-43°C while maintaining normothermic skin and core temperatures. Conclusions Simulation techniques facilitate the design optimization of microwave antennas for use in pre-clinical applications such as localized tumor heating in small animals. Laboratory measurements demonstrate the effectiveness of a new miniature water-coupled microwave applicator for localized heating of murine bladder.

Theoretical analysis, design and development of a 27-MHz folded loop antenna as a potential applicator in hyperthermia treatment

“…The results above are comparable and similar to those reported by other research groups that have used circular or loop-based antenna set-ups for hyperthermia treatment and at a variety of operation frequencies [1][2][3]17]. With our study we are sharing our experience concerning the introduction of a new deep heating system which has some new advantages with the already reported systems in the literature:…”

A pilot clinical trial of intravesical mitomycin-C and external deep pelvic hyperthermia for non-muscle-invasive bladder cancer

“…Unfortunately, intravesical chemotherapy does not eliminate the risk of recurrence and at least a third of subjects treated with intravesical chemotherapy will still recur. One strategy that has been shown to increase the efficacy of intravesical chemotherapy is bladder hyperthermia, a treatment where the bladder is heated to enhance the effectiveness of the chemotherapeutic agent filling the bladder [5–7]. Hyperthermia has numerous effects on the tumour micro-environment [8], but the most important known effect in bladder cancer is that it makes existing bladder chemotherapies more effective.…”

Overview of bladder heating technology: matching capabilities with clinical requirements

“…Salahi et al describe the heating performance of a 1 cm diameter water filled circular waveguide microwave antenna designed specifically for heating small rodent bladders. (63) Another microwave antenna designed for small volume heat treatments has been reported previously (64, 65) with heating patterns that demonstrate feasibility of treating small animal bladders. Snow et al report the feasibility of heating in vivo pig bladder with no acute toxicity using a small array of 915 MHz square slot dual concentric conductor antennas.…”

“…Rodent studies are most common though larger animals are also used to model the human treatment situation more closely. Since human bladder capacity is approximately 500 ml,(62) the small size of bladder in mice (~ 0.15 ml) and rats (~ 1 – 1.5 ml) requires different heating systems(58, 63). Farm pigs are also used for preclinical studies, with bladder volumes ranging from 250 ml to larger than human bladders.…”