Output-limiting symptoms induced by radiofrequency hyperthermia. Are they predictable?

During radiofrequency (RF) hyperthermia treatment, hot-spot phenomena may occur and prevent treatment continuation if the output is not lowered. We previously reported a significant correlation between the initial energy output at which output-limiting symptoms occurred and patient status. Patients with a complete clinical response had significantly increased temperature, while some patients with partial clinical response and stable disease had increased temperature, depending on the occurrence of output-limiting symptoms. To predict the initial energy output at which output-limiting symptoms occur, we performed multiple regression analysis with the parameters of patients' physical status.

Hyperthermia alone or concomitant with chemotherapy and/or radiotherapy was applied in 62 patients with malignant disease for a total of 310 treatments with a Thermotron RF-8 between December 2011 and April 2014.

No output-limiting symptoms were shown in 65.5% of 310 treatments. Pain (29.7%), micturition desire (1.9%), skin discomfort (0.6%), subcutaneous induration (1.6%), cold sensation (0.6%), and nausea (0.3%) were reported in the 310 treatments. A good predictive equation for initial energy output at which output-limiting symptoms occur was determined with two parameters, initial time of an output-limiting symptom onset, and thickness of the fat of the abdominal wall. Multiple regression analysis showed an adjusted R(2 )= 0.99 and variance inflation factor < 2.

We present a good predictive equation for initial energy output at which output-limiting symptoms occur. It is critical to prevent RF hyperthermia-induced output-limiting symptoms and establish new prevention strategies.