A modified technique for RF-LCF interstitial hyperthermia.

To provide uniform heating of a tumour, it is necessary to establish sufficient volumetric control of power deposition. The interstitial Radio-Frequency Localized Current Field (RF-LCF) technique may provide such control when segmented electrodes are used. The length of segments is equal to 1-1.5 cm. Each segment is connected to a separate power source. However, this technique requires an additional implant for interstitial radiotherapy, because the lumen of segmented electrodes is filled with wires necessary to connect each segment to a separate power source. In this work, a modified method of implant that allows delivery of sequential and concomitant controlled thermoradiotherapy was investigated. In this method, each segmented electrode is surrounded by four continuous electrodes. Continuous electrodes pass through vertices of 1.5 x 1.5 cm square and a segmented electrode passes through the centre of the square. The distance between segmented and continuous electrodes is 1.06 cm. The electric field induced between an electrically interacting segment and continuous electrodes is concentrated primarily between this segment and its projection on continuous electrodes. Therefore, control of temperature distribution achieved with a modified implant is similar to that achieved with an implant containing only segmented electrodes. For temperature control during treatment, plastic catheters are inserted at a 0.5 cm distance from each segmented electrode. Temperature is monitored using multisensor temperature probes. The continuous electrodes are also used for placement of radioactive sources. The lateral distance between radioactive sources is equal to 1.5 cm. Besides allowing a sequential and concomitant thermoradiotherapy, the modified method is simpler to implement because it uses several fold less amount of segmented electrodes and power sources.