Abstract
Purpose: Preclinical studies and clinical observations suggest that amplitude modulation (AM) below 100 kHz may enhance the intratumoral power absorption of radiofrequency hyperthermia at 13.56 MHz; however, it remains unclear whether AM induces temperature-dependent effects.Methods: We established tumor models assuming typical tumor architectures or cell suspensions to analyze the effects of additional power dissipation. The preconditions for demodulation at cell membranes in situ were outlined. The bioheat transfer equation was solved analytically for the selected models and the possibility of circumscribed temperature increases (point heating) with dependency on the specific absorption rate (SAR) peaks was estimated for centimeter down to nanometer scales.Results: Very-low-frequency (VLF) AM radiofrequency can increase the SAR in the extracellular space or necrosis of tumors as compared to radiofrequencies alone. Such modulation-derived SAR peaks can induce higher temperatures (hot spots) in tumors with necrotic areas of millimeter to centimeter size. However, for lesions <1 cm, excessive (unrealistic) SAR > 1000, 10,000 and 1014 W/kg for diameters of ∼5 mm, ∼1 mm and ∼10 nm (nanoheating), respectively, would be required to explain the cell kill observed in pre-clinical and clinical data, even with VLF modulation.Conclusion: Our analysis suggests that VLF AM of radiofrequency hyperthermia for a theoretical tumor model cannot induce relevant temperature-dependent effects, as the associated temperature increases caused by the resultant SAR peaks are too small. Further investigation of possible non-temperature-dependent effects is recommended.
Highlights
Radiofrequency (RF) hyperthermia using annular phased array (APA) techniques (70–140 MHz), capacitive systems (8–13.5 MHz) or local applicators (200–1000 MHz) has been validated for various tumor entities [1,2,3,4,5]
The power deposition patterns (SAR) in Watts per kilogram can be estimated on a microscopic level for nanotherapy or various electromagnetic techniques
In the case of mEHT, we employ simple three-dimensional models and assume arbitrarily high specific absorption rate (SAR) in the extracellular fluid (ECF), which is deposited by currents at low frequencies (Figures 1 and 2)
Summary
Radiofrequency (RF) hyperthermia using annular phased array (APA) techniques (70–140 MHz), capacitive systems (8–13.5 MHz) or local applicators (200–1000 MHz) has been validated for various tumor entities [1,2,3,4,5]. The steady-state temperature increase h [C] in extended tumors is influenced by the tumor perfusion w [ml/100 g/min] and can be estimated using a simple equation involving the SAR: h 1⁄4 1.5 Â SAR/w. Based on successful clinical trials (e.g., for cervical cancer), we can assume a typical total power >600 W for APA systems [6,9] and an even higher total power >800 W for capacitive techniques [10,11]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
