Catalog of Regulatory Science Tools to Help Assess New Medical Devices
This regulatory science tool presents a computer model that estimate the thermal effect produced in the vaginal wall by vaginal therapy devices. Please see appendix.
Technical Description
The Monopolar RF Thermal Dispersion Model for the Vaginal Wall provides VTT device designers with a first-pass estimation of the thermal effect produced in the vaginal wall by their device. Finite element analysis (FEA) was used to calculate the energy deposition due to radio frequency (RF) exposure and the bioheat transfer field simultaneously.
This tool should be used as a screening-level check on the depth of thermal dispersion for a device design and protocol, specifically that the device is only heating the target tissue and not heating deeper than the target tissue. If the device is heating past the target tissue, it could be unintentionally affecting sensitive adjacent tissue, such as the urethra. The device designer may use these data to inform their design process. This tool is meant to supplement in vivo or in vitro experiments and not as a stand-alone safety assessment tool.
The tool was originally implemented in COMSOL Multiphysics using the AC/DC and Heat Transfer Modules.
User inputs:
- Probe size and shape
- RF power
- Exposure time
- Probe tip cooling condition
Tool outputs:
- Area of thermal effect
- Depth of thermal dispersion marked by 43˚C isotherm
- Thermal field visualization in layered tissue section
- Comparison of deepest thermal extent to minimum vaginal wall boundary
Intended Purpose
This tool is designed to model a subset of vaginal thermotherapy devices which use monopolar radiofrequency (RF) only to heat the vaginal wall. This tool is not applicable to bipolar or multipolar RF devices or to laser-based vaginal heat therapy devices.
Ensuring the energy deposition and resultant heating is confined to the vaginal wall is intended to help ensure the safety of these devices. The purpose of this FEA-based tool is to provide device designers with an approximation of the depth of heating for their monopolar RF VTT devices. If the simulated area of thermal effect penetrates past the vaginal wall boundary, the device designers can iteratively change input parameters to address the issue.
FEA provides a rapid and flexible precursor to any follow-up benchtop experiments on ex vivo or in vivo tissue.
This tool should be implemented by a user with experience in FEA or similar numerical simulation techniques. The simulations were originally performed in COMSOL Multiphysics, but can be implemented in a number of FEA platforms using the simulation setup information provided in the Step-by-step user guide below.
This tool is meant to supplement in vivo or in vitro experiments and not as a stand-alone safety assessment tool.
Testing
This model is intended for screening-level usage, and not to be used in place of in vivo or in vitro models.
Validation details are provided in section 12 of the step-by-step user guide and in Ian A Carr et al 2021 Biomed. Phys. Eng. Express 7 065022. Depth of thermal dispersion of monopolar radiofrequency heating in the vaginal wall - IOPscience.
User-specific validation will be required based on the context of use (CoU) of the model and the associated model risk as defined by the user. Please refer to Sections 3 and 4 of ASME V&V40-2018, "Assessing Credibility of Computational Modeling through Verification and Validation: Application to Medical Devices" for additional details about CoU and model risk.
Limitations
Biological tissue has inherent inter- and intra-patient variation in material properties and geometry. As such, the results output by this tool should be considered a first-pass approximation of the area of thermal dispersion. The tool is designed to give a conservative estimate of the area of thermal effect. This tool is meant to supplement in vivo or in vitro experiments and not as a stand-alone safety assessment tool.
Supporting Documentation
See step-by-step user guide in Appendix below.
Contact
Tool Reference
- In addition to citing relevant publications please reference the use of this tool using RST24CV05.01