LOCAL HYPERTHERMIA OF N2 N3 CERVICAL LYMPH-NODE METASTASES - CORRELATION OF TECHNICAL/THERMAL PARAMETERS AND RESPONSE/

Purpose: Patients with advanced head and neck carcinomas, primarily no nresectable as well as recurrent cases, were treated in multimodality regimens with radiotherapy, chemotherapy, and local hyperthermia. Comm ercially available microwave and radiowave applicators were used in 50 patients with N2/N3 cervical lymph node metastases during more than 2 50 heat treatments. To assess technical suitability, the achieved powe r densities and thermal parameters were tested for correlation with an atomical and geometrical factors. To assess effectiveness, the respons e was compared with derived parameters of the achieved temperature dis tributions. Methods and Materials: The temperature measurement points (in thermometry catheters) documented by computerized tomography are l abeled according to tissue depth, shielding by osseous structures, and location in relation to the external applicators. Relative and absolu te specific absorption rates (SAR) and cooling coefficients are extrac ted from the temperature-time curves. Time-averaged temperature-positi on curves are evaluated to obtain index temperatures (T-90, T-50, T-20 ), minimum/maximum tumor temperatures, cumulative minutes T-90 greater than or equal to 43 degrees C, and 43 degrees C-equivalent min T-90. Radiation dose, treatment time, and chemotherapy regiment are also con sidered. A response parameter is defined using the pre- and posttherap eutic tumor volumes. A multivariate variance analysis is performed for the dependent variables power density, thermal parameters, and respon se. Results: A significant correlation exists between power density an d absorption, presence of a fat layer, and applicator illumination. Th e maximum depth is 5 cm, where SAR of greater than or equal to 10 mW/g are registered. Achieved temperatures at individual measurement point s are dependent on the SAR, and to a lesser extent, the perfusion-depe ndent cooling coefficients, but the index temperature T-90 is only sig nificantly related to intratumorally achieved SAR. The thermal gradien t (T-20-T-50) and temperature peak (T-20) are significantly influenced by the tumor volume. The response is directly related to the index te mperature T-90, equivalent minute T-90 43 degrees C, and cumulative mi nutes T-90 greater than or equal to 40.5 degrees C, and inversely rela ted to the tumor volume. Conclusions: Local hyperthermia using microwa ve and radiowave applicators in the head and neck region is a tolerabl e and clinically practical supplementary therapy used as part of multi modal regimens, and has already been proven to be effective. However, the analyses also demonstrated the limits of currently available techn ology, and confirm the need for continued methodical research.