Regional Hyperthermia Therapy

A regional hyperthermia unit produces radiofrequency energy and delivers it through applicators, most often two capacitive electrodes placed opposite each other on the skin above and below the region to be treated, with a cooling water bolus between the electrode and the body to protect the skin and the fat layer. The energy passes through the tissue between them and is converted into heat. Systems differ: capacitive units heat a region between two plates, while phased array units surround the body with several antennas whose signals are combined so that the heating focus can be steered towards a deep target. The equipment includes thermometry, either through probes placed in accessible cavities or catheters, or by modelling, and a control system that adjusts power continuously. It is operated by a team that includes an oncologist and a physicist.

Tumours have disordered blood vessels and areas that are poorly oxygenated, and poorly oxygenated tissue is markedly less sensitive to radiotherapy. Warming the region opens vessels and increases perfusion, raising the oxygen available and improving the delivery of drugs to the tumour. At the same time, temperatures in the 40 to 44 degree range interfere with proteins involved in repairing breaks in DNA, so damage caused by radiation or by chemotherapy is less likely to be corrected before the cell divides. There is also evidence that heat stress exposes signals on the cell surface that make tumour cells more visible to the immune system. Because these effects are transient, timing matters: hyperthermia is given shortly before or after the radiotherapy fraction or the drug infusion it is intended to support, usually within an hour or so, according to the protocol in use.

The strongest evidence comes from randomised studies in soft tissue sarcoma treated with chemotherapy, in locally advanced cervical cancer treated with radiotherapy, and in recurrent breast cancer on the chest wall where reirradiation is limited by previous dose. It has also been studied in bladder cancer, head and neck tumours, melanoma nodules in the skin, rectal cancer and selected paediatric tumours. It is generally considered for tumours that are locally advanced, that have recurred within a previously irradiated area where the radiation dose that can be given again is restricted, or that respond poorly to standard treatment alone. It is not appropriate where a metal implant or an electronic device lies within the heating field, where sensation in the area is impaired so that overheating could go unnoticed, in pregnancy, or where the patient cannot lie still and communicate for an hour. A multidisciplinary team decides whether it adds to the plan.

The intended benefit is a better response to the radiotherapy or chemotherapy it accompanies, with improved local control reported in the settings where it has been tested, and without adding the systemic toxicity of another drug. During a session the patient lies on the treatment couch with the applicators positioned and a water bolus against the skin. Warmth builds gradually and is expected to feel like a comfortable heat; the operator adjusts the power in response to what the patient reports, and treatment is paused if any point becomes too hot. The most common problems are local: a superficial burn or blister, discomfort under the applicator, and painful induration of subcutaneous fat, which is more likely in people with a thicker fat layer. Some patients feel tired afterwards or notice a rise in body temperature and heart rate. Hyperthermia is a supportive technique whose availability and protocols vary between centres, and it should be discussed as part of the whole treatment plan rather than sought in isolation.