Status quo and directions in deep head and neck hyperthermia

Abstract

The benefit of hyperthermia as a potent modifier of radiotherapy has been well established and more recently also the combination with chemotherapy was shown beneficial. Also for head and neck cancer, the impact of hyperthermia has been clinically demonstrated by a number of clinical trials. Unfortunately, the technology applied in these studies provided only limited thermal dose control, and the devices used only allowed treatment of target regions close to the skin. Over the last decade, we developed the technology for deep and controlled hyperthermia that allows treatment of the entire head and neck region. Our strategy involves focused microwave heating combined with 3D patient-specific electromagnetic and thermal simulations for conformal, reproducible and adaptive hyperthermia application. Validation of our strategy has been performed by 3D thermal dose assessment based on invasively placed temperature sensors combined with the 3D patient specific simulations. In this paper, we review the phase III clinical evidence for hyperthermia in head and neck tumors, as well as the heating and dosimetry technology applied in these studies. Next, we describe the development, clinical implementation and validation of 3D guided deep hyperthermia with the HYPERcollar, and its second generation, i.e. the HYPERcollar3D. Lastly, we discuss early clinical results and provide an outlook for this technology.

Fig. 1

The HYPERcollar applicator, as it was used until 2014, surrounding the 1^st author. This applicator features twelve antennas fed by a high power system with twelve channels with independent power and phase control for focusing the heat at the target region

Fig. 2

a Design and (b) clinical prototype of the HYPERcollar3D applicator. Twenty antennas are arranged in three rings to allow more precise longitudinal steering, as compared to the HYPERcollar applicator. In addition, positioning reproducibility and waterbolus shape stability was improved to improve the focusing ability and reproducibility of the applicator, and hence the treatment. Note that still a high power system with twelve channels is used and hence a dedicated antenna selection procedure was developed

Fig. 3

VEDO interface displaying the predicted SAR (or temperature) distribution on top of the planning CT in all Cartesian directions. VEDO also provides an implementation of the complaint adaptive steering approach. In addition, VEDO provides indicators to assess treatment quality based on the simulated SAR as well as to assess the risk of overtreatment

Fig. 4

Coronal views in VEDO of the predicted normalized cubic-filtered SAR (%) and temperature (°C) distributions displayed as overlay over the CT scan. This figure shows the effectiveness of real-time adaptive treatment by adjusting the pre-optimized power absorption distributions. Re-optimization reduced the SAR at the hotspot (Region 3, yellow contour) by 2.3-fold and the maximum temperature by 2.2 °C, while the predicted temperature in the entire clinical target volume (CTV, red contour) was virtually unaffected, i.e. T90 reduced from 39.6 °C to 39.5 °C. Note that, following this effective re-optimization, increase in power can be used to increase the temperatures in the target region