PhysioDose: A Shortwave Diathermy Dose Calculator for Clinical, Academic, and Scientific Use in Musculoskeletal Conditions

Introduction

Shortwave diathermy (SWD), operating at a standard carrier frequency of 27.12 MHz, is widely employed in physical rehabilitation to manage musculoskeletal conditions. In its inductive application, the alternating current generates a magnetic field that induces eddy currents primarily within low-impedance tissues. Depending on the selected emission—mode continuous (cSWD) or pulsed (pSWD)—the energy delivery dictates the net thermal load and the subsequent biological response, often resulting in varying thermal profiles that influence clinical outcomes [1, 2].

Despite the clinical efficacy of SWD, the existing physical therapy literature suffers from severe methodological shortcomings: the incomplete reporting of technical parameters and the widespread omission of precise dosimetric calculations. Studies in related fields involving electromagnetic energy, such as radiobiology and radiation therapy, have demonstrated that the lack of detailed technical data prevents the safe and robust replication of trial procedures, significantly contributing to a broader reproducibility crisis [3, 4]. Within SWD literature specifically, systematic reviews continually highlight that the lack of standardization in treatment parameters, such as peak power, pulse width, and pulse frequency, leads to inconsistent temperature changes in tissues. This variability directly restricts the synthesis of evidence, complicates cross-protocol comparisons, and hinders the development of robust clinical guidelines [1, 2, 5, 6].

Although calculating the Specific Absorption Rate (SAR) represents the theoretical gold standard for quantifying actual tissue absorption, it remains clinically unfeasible due to applicator variability, inadequate estimation methods, and patient-specific anatomical factors [7]. Consequently, calculating the mean power and total emitted energy from the machine is currently recommended as a practical, standardized alternative that correlates effectively with tissue exposure without the complexities of direct SAR measurement [7].

To accurately compute the actual thermal load delivered to the tissue during pSWD, researchers must calculate the mean power:

This mathematical conversion is critical for translating raw machine settings into an estimated clinical dosage (e.g., from athermal to vigorous heating). However, because interventions often rely solely on the subjective thermal sensation of the patient rather than objective dosimetric calculations, crucial data regarding the total energy delivered is frequently lost in scientific reporting.

To address this critical gap, we developed PhysioDose, an open-source, offline-ready HTML application designed to standardize emitted energy reporting in SWD interventions. PhysioDose automates the computation of the duty cycle, mean power, and total delivered energy based on standard machine settings. While other physical therapy domains possess dosimetric calculators, there is a notable absence of dedicated, accessible software for SWD dosimetry. By automatically categorizing the clinical dosage and generating standardized scientific intervention reports, PhysioDose provides researchers and clinicians with a rigorous tool to enhance dosimetric documentation, effectively bridging theoretical physics and applied musculoskeletal rehabilitation.

Implementation and Architecture

PhysioDose is implemented as a lightweight, single-page HTML application featuring a strict zero-dependency architecture. This design choice ensures that the software is entirely offline-ready, requiring no external libraries, frameworks, server-side processing, or internet connection to function. The application is universally compatible with any standard web browser and incorporates a responsive design, allowing the user interface to scale seamlessly across desktop computers, tablets, and mobile smartphones. This cross-platform and mobile adaptability is particularly advantageous for point-of-care clinical environments, enabling practitioners to compute dosimetric data directly at the patient’s bedside.

The software’s architecture is structured around three primary sequential modules, representing a linear workflow (Figure 1):

Figure 1

1. Input module: The user interface captures the selected emission mode—cSWD or pSWD—along with standard machine parameters: peak power (W), pulse width (s), pulse repetition frequency (Hz), and total treatment duration (minutes).

2. Processing core: The computational engine executes the dosimetric conversions. For pSWD, the algorithm first automatically converts the pulse width from microseconds to seconds (1 μs = 0.000001 s) and then applies the fundamental physics formula to compute the mean power (mean power = peak power × pulse width × frequency). In the cSWD algorithm branch, the mean power is programmed to equal the input peak power. Following this, the core computes the duty cycle and the total delivered energy in kilojoules (kJ). Based on the resulting mean power, the system categorizes the estimated clinical effect into four evidence-based tiers (I: Athermal; II: Mild Thermal; III: Moderate; IV: Vigorous) and correlates it with clinical safety guidelines based on patient thermal perception.

3. Output module: The application dynamically generates a standardized, ready-to-copy ‘Intervention Report.’ This text output encapsulates all raw parameters and calculated dosimetric data, designed to be directly pasted into electronic health records or the methodology sections of scientific manuscripts.

Regarding implementation variants, the software does not require separate builds for different operating systems due to its universal browser-based nature. The primary internal variant relies on the algorithmic branching between the cSWD and pSWD modes, which dictates the specific mathematical models applied to the user’s input data.

To address the need for asynchronous documentation in electronic health records, PhysioDose incorporates a dedicated ‘Save PDF’ feature alongside the instant copy function. Technically, this is achieved through a custom printToPDF() JavaScript function paired with specific CSS media queries (@media print). When triggered, the visual calculator interface is automatically hidden, and dosimetric data is dynamically mapped into structured HTML tables, generating a standardized medical printout. This allows clinicians to safely export a professional clinical record without relying on external servers, ensuring 100% patient data privacy. Furthermore, to maximize international accessibility and usability, the architecture now includes a dynamic bilingual toggle (English/Spanish), which instantly translates the entire user interface and the generated intervention reports without requiring page reloads.

Quality Control

Functional testing of the PhysioDose core algorithm was rigorously conducted by cross-validating the software’s JavaScript computational outputs against manual physical calculations to ensure absolute dosimetric accuracy. Given its zero-dependency HTML architecture, environment testing focused on cross-browser compatibility and responsive scaling. The application was successfully tested across major modern desktop web browsers (Google Chrome, Mozilla Firefox, Apple Safari, and Microsoft Edge) as well as mobile operating systems (iOS and Android), ensuring consistent performance without visual or computational errors.

To quickly verify that the software is functioning correctly, a new user or peer reviewer can run a test using a standardized sample dataset derived from typical clinical parameters designed to generate a moderate therapeutic thermal response. The following sample data should first be input:

• Emission mode: Pulsed (pSWD)

• Peak power: 200 W

• Pulse width: 400

• Frequency: 400 Hz

• Treatment duration: 20 minutes

Upon interaction, the processing core should instantaneously calculate and display the following outputs:

• Mean power: 32.0 W (calculated internally as 200 × 0.0004 × 400)

• Duty cycle: 16.0%

• Total energy: 38,400 Joules or 38.4 kJ (calculated as 32 W × 1,200 seconds)

• Net thermal load: Categorized as ‘Moderate (Therapeutic)’ (falling within the 20–40 W clinical tier based on the reference ranges proposed by Laufer and Dar [8] and Masiero et al. [9])

If the interface outputs these exact dosimetric values and dynamically generates the corresponding standardized intervention report, the user can be confident that the application’s underlying mathematical conversions and clinical categorization logic are functioning perfectly.

Operating system

PhysioDose is platform-agnostic. As a browser-based application, it is fully compatible with any desktop or mobile operating system that supports a modern web browser. Minimum recommended operating systems include Windows 10, macOS 10.15 (Catalina), Linux (Ubuntu 18.04+ or equivalent), iOS 12, and Android 8.0.

Programming language

The application supports the use of HTML5, CSS3, and JavaScript (ECMAScript 6 / ES6). No server-side processing language is required.

Additional system requirements

These could be memory, disk space, processor, input devices, or output devices. Due to its highly lightweight nature (the core executable file is under 40 kB), the system requirements are negligible:

• Memory: <10 MB RAM

• Disk space: <100 KB of local storage

• Processor: Any standard processor capable of running a modern web browser

• Input devices: Mouse and keyboard (desktop) or touchscreen interface (mobile/tablet)

• Output devices: Any standard monitor or mobile screen

Dependencies

There are no dependencies. PhysioDose features a strict zero-dependency architecture. It does not rely on any external libraries, frameworks (e.g., React, Angular), or APIs. This ensures it remains entirely offline-ready and immune to external software deprecation.

Software location

Language

• Software interface: Bilingual (English and Spanish)

• Repository metadata and supporting documentation: English and supporting files

Scientific and research use cases

The software directly addresses the widespread methodological limitation of incomplete dosimetric reporting in electrotherapy research. Researchers can use the application to calculate the exact mean power and total delivered energy, ensuring that clinical trials involving shortwave diathermy SWD are fully reproducible from a technical standpoint. The tool’s ability to generate a standardized, ready-to-copy ‘Intervention Report’ allows authors to directly paste comprehensive dosimetric data into the methodology sections of scientific manuscripts. This standardization is crucial to facilitate future meta-analyses, enhance evidence synthesis, and clarify dose-response relationships.

Clinical use cases

In daily clinical practice, the application serves as an offline, point-of-care decision-support tool. Practitioners often struggle to translate raw machine parameters (peak power, frequency, pulse width) into safe biological effects. PhysioDose bridges this gap by instantaneously categorizing the calculated thermal load into evidence-based clinical tiers (Athermal, Mild, Moderate, or Vigorous) based on the current literature. By integrating objective dosimetric calculations with patient thermal perception guidelines, clinicians can maximize therapeutic efficacy while strictly avoiding tissue overexposure.

Academic and educational use cases

For university professors and physical therapy students, the software acts as an interactive educational simulator. It visually demonstrates the fundamental physics of electrotherapy, allowing students to experiment with variables and intuitively understand how altering a single parameter (e.g., increasing pulse repetition frequency) directly and exponentially impacts the mean power and total energy. Furthermore, it actively instills rigorous documentation habits in future professionals.

Modification, extension, and support

Released under the open-source MIT license and built with a zero-dependency HTML/JS architecture, the software is highly accessible and adaptable. Researchers and developers from other fields can easily inspect the raw source code to translate the user interface into other languages, adjust the dosimetric thresholds as new literature emerges, or use the core algorithmic structure as a foundation to develop dosimetric calculators for other physical agents (e.g., microwave diathermy, therapeutic ultrasound, or high-intensity laser therapy).

Given its lightweight and standalone nature, the software does not require active server maintenance. Support is community-driven and managed directly by the authors. Users, researchers, or developers wishing to propose modifications, report issues, or collaborate on extensions are encouraged to contact the corresponding author via email at jserrano@euses.cat.