Several groups are developing heating devices for simultaneous thermoradiotherapy to enhance thermal radiosensitization. One of our designs is an applicator for induction of superficial hyperthermia which is also compatible for concomitant operation with a linear accelerator. The dual-frequency system (DFS) design uses parallel-opposed linear arrays and a scanning dual-face reflector. The scanning reflector deflects and distributes, under computer control, the waves coming from the arrays toward the target. The prime design objectives for this design were; 1) compatibility with a linear accelerator; 2) sufficiently non-perturbing and non-attenuating to allow use of medical electron beams; 3) improved lateral conformability of power deposition; and 4) penetration depth control. Technical feasibility, lateral conformability and design optimization studies for a similar one-array system have been previously reported. Here, an acoustic model was developed to investigate die controllability of penetration depth of the DFS design. Results showed that by varying the power outputs from the low and high frequency arrays, the depth of the 50% isopower contour can be controlled over a range of 3 cm. Thermal simulations using the bioheat transfer equation were also performed which demonstrated corresponding changes in the depth of therapeutic isotherms over a 2.5 cm range for different low-to-high frequency power ratios. The results suggest that the DFS may be suitable for heating (sequentially or simultaneously with external beam radiation) extensive superficial tumors, where the distal tumor margin varies over the extent of the tumor, and where underlying bony structures and/or ga.s cavities are present such as in chest-wall lesions.