Short communication: Intracavitary hyperthermia applicators for treating nasopharyngeal and cervical cancers

Abstract

Many intracavitary microwave applicators have been designed to heat tissues along the side of an antenna. For tumours in nearly closed-end cavities such as the nasopharynx and cervix, heating near the tip of the applicators is necessary for effective treatment. A nasopharyngeal applicator made of Micro Coax UT-250A and a cervical applicator made of RG-9/U cables were designed to provide heating at the tip. Return losses of 8–12 dB were obtained at 915 MHz by varying the size of two metal sleeves and adjusting the distance between these sleeves and the reflectors at the applicator tips. Heating patterns were evaluated on a muscle phantom with a thermograph. At 915 MHz, maximum heating rates of 1·3 and 0·85°C/W-min, respectively, were observed near the tip of the nasopharyngeal applicator and at its first sleeve opening. When operated at 915 MHz the cervical applicator has a maximum heating rate of 0·25°C/W-min at the tip. Clinically, both applicators require a maximum power of 30 W to provide effective heating. This makes it possible to provide intracavitary hyperthermia at rural hospitals and small clinics with a small portable system.

Key Words:

• intracavitary
• hyperthermia
• applicator
• nasopharyngeal
• cervical