Conformal microwave array (CMA) applicators for hyperthermia of diffuse chest wall recurrence

Abstract

Purpose: This article summarises the evolution of microwave array applicators for heating large area chest wall disease as an adjuvant to external beam radiation, systemic chemotherapy, and potentially simultaneous brachytherapy.

Methods: Current devices used for thermotherapy of chest wall recurrence are reviewed. The largest conformal array applicator to date is evaluated in four studies: (1) ability to conform to the torso is demonstrated with a CT scan of a torso phantom and MR scan of the conformal water bolus component on a mastectomy patient; (2) specific absorption rate (SAR) and temperature distributions are calculated with electromagnetic and thermal simulation software for a mastectomy patient; (3) SAR patterns are measured with a scanning SAR probe in liquid muscle phantom for a buried coplanar waveguide CMA; and (4) heating patterns and patient tolerance of CMA applicators are characterised in a clinical pilot study with 13 patients.

Results: CT and MR scans demonstrate excellent conformity of CMA applicators to contoured anatomy. Simulations demonstrate effective control of heating over contoured anatomy. Measurements confirm effective coverage of large treatment areas with no gaps. In 42 hyperthermia treatments, CMA applicators provided well-tolerated effective heating of up to 500 cm² regions, achieving target temperatures of T_min = 41.4 ± 0.7°C, T₉₀ = 42.1 ± 0.6°C, T_ave = 42.8 ± 0.6°C, and T_max = 44.3 ± 0.8°C as measured in an average of 90 points per treatment.

Conclusion: The CMA applicator is an effective thermal therapy device for heating large-area superficial disease such as diffuse chest wall recurrence. It is able to cover over three times the treatment area of conventional hyperthermia devices while conforming to typical body contours.

• chest wall recurrence
• conformal applicator
• microwave array
• superficial hyperthermia