Developing Secure Medical Device Software with Design Controls

Developing medical device software means to formalize a development process with a multitude of design controls and follow it during software construction.

What are ISO 13485 design controls exactly?

Design controls are a structured approach to ensure medical device software meets regulatory standards, quality, and user needs. They include identifying requirements, architecture and design elements, documenting inputs and outputs, conducting reviews, verifying specifications, and validating the product’s intended use. In addition, elements of risk management, usability design and cybersecurity testing provide additional controls. These controls ensure compliance with ISO 13485 and FDA regulations, emphasizing safety and efficacy. As design controls are not intended only for software, “substandards” describe further details.

Extending design controls in IEC 62304 and 81001-5-1

IEC 62304 emphasizes a lifecycle approach to software development for medical devices, focusing on risk management and software safety. The standards requires detailed unit testing, traceability matrices linking requirements to test cases, and independent code reviews to ensure compliance.

Meanwhile, ISO/IEC 81001-5-1 expands this scope to include cybersecurity controls, essential in modern medical environments. An example would be implementing a threat model to identify vulnerabilities in communication protocols or applying encryption techniques for secure patient data exchange. In addition some controls are operations-oriented and maybe satisfied by existing ISO 27001 certifications.

Combined, these controls create a robust software framework, also called an SPDF (secure product development framework), tailored to the complexities of medical device and health software development.

How can we trace requirements, apply the V-model and finally do verification and validation?

Developing medical device software involves requirements tracing, the V-model, and verification and validation (V&V) to ensure regulatory compliance, safety, and efficacy.

Requirements Tracing

·  Document requirements in a Software Requirements Specification (SRS).

·  Use a traceability matrix to map requirements to design outputs, tests, and validation results.

·  Maintain bi-directional traceability between requirements, design, and testing.

·  Integrate risk management and cybersecurity considerations (ISO 14971, CSRMP).

The V-Model

·  Align left-side phases (requirements, design) with right-side testing phases (verification, validation).

·  Use the Software Development Plan (SDP) to coordinate milestones and outputs like SRS and Software Design Description (SDD).

·  Conduct reviews and approvals at each phase.

·  Incorporate risk-driven testing and usability engineering.

Risk, Threat Modeling, and Cybersecurity

·  All elements from the risk file should be included in the tracability database.

·  Tools used for threat modeling, such as Microsofts Threat Modeler, can export elements needed for further tracing.

·  Dependencies from vulnerability management systems (e.g. dep-track) should be used with all assessments documented.

Verification and Validation (V&V)

·  Verification: Unit testing, integration testing, code reviews, and static/dynamic analysis.

·  Validation: System testing, real-world scenario simulations, and formal reporting.

·  Continuous testing with agile methods and regression testing.

Tools

·  Tools such as Jira, IBM DOORS, or Polarion ALM can automate and maintain the traceability matrix.

·  Enhanced inline comments using tools like Doxygen can be utilized to generate Software Design Descriptions (SDD), particularly for IEC 62304 Class C software.

Implementing requirements tracing, the V-model, and formal V&V builds a compliant framework for developing safe and effective medical device software. Putting all elements in a formal database and maintaining relationships between them, allows for instant generation of up-to-date traceability matrices.

What do fast innovation cycles and agile development methods  mean for software development of medical devices and health software?

Fast innovation cycles and agile development methods bring both opportunities and challenges to the software development of medical devices and health software. On the positive side, these approaches enable teams to respond quickly to market demands, technological advancements, and regulatory updates. Agile methodologies allow for iterative development and deployment, fostering continuous improvement and adaptability, which is especially critical in the rapidly evolving healthcare industry.

However, adopting these methods within the stringent regulatory frameworks governing medical software requires careful planning and execution. Incorporating recommendations from AAMI TIR45, which advocates for the integration of agile principles into regulated environments, provides a pathway to balance innovation with compliance. For instance, TIR45 emphasizes the use of iterative planning, risk-based decision-making, and frequent and automated verification activities to ensure alignment with standards like IEC 62304 and ISO 14971 while maintaining agility.

Moreover, fast innovation cycles can pressure development teams to prioritize speed over thorough risk management and robust testing. To counteract this, leveraging requirement management tools for maintaining traceability matrices and automated documentation can help ensure compliance without sacrificing agility. Additionally, adopting TIR45’s focus on continuous testing and early involvement of stakeholders, aligned with agile iterations, enhances the validation of software performance in real-world scenarios.

Ultimately, the key lies in blending the flexibility of agile methods with the rigor of regulatory compliance to achieve a framework that supports both innovation and patient safety. By following TIR45’s recommendations, development teams can create medical device software that is not only cutting-edge but also reliable, secure, and compliant with regulatory expectations.

Effective testing methods (V&V) for medical device software

Effective Testing Methods for Medical Device Software ensuring safety and compliance include:

·  Unit Testing: Verifies individual components in isolation using tools like JUnit.

Example: Testing a dosage calculation function for adherence to safety constraints.

·  Integration Testing: Tests interactions between software modules.

Example: Ensuring accurate communication between a device’s interface and a control system.

·  System Testing: Validates the complete software against requirements.

Example: Testing a patient monitoring device for accurate vital sign logging.

·  Risk-Based Testing: Targets high-risk areas identified in the Risk Management File.

Example: Testing an infusion pump’s alarm functionality for system failure alerts.

·  Validation Testing: Evaluates software under real-world conditions for its intended use and purpose.

Example: Usability testing with healthcare professionals for safe operation.

·  Regression Testing: Ensures updates do not introduce defects.

Example: Retesting diagnostic imaging software after algorithm updates.

·  Security Testing: Focuses on cybersecurity risks with penetration tests and network scans.

Example: Testing vulnerabilities in wearable health tracker communication or scanning IoT-backend services in the cloud.

·  Performance Testing: Assesses speed, responsiveness, and stability.

Example: Testing a telemedicine platform under high user loads.

·  Fuzz Testing, Random Inputs, Invalid Inputs and Bounds Checking: Ensures requirements are thoroughly tested, error cases and edge cases are included.

Example: Creating protocol data units with invalid commands and values for a blood glucose monitoring sensor.

·  Simulation Testing: Tests software in simulated real-world scenarios.

Example: Simulating an implantable cardiac device under varying heart rhythms. Test data maybe from patients or artificially generated.

These methods collectively enhance software safety, reliability, and regulatory compliance. Modern test tools and environments help to structure and generate these tests.  As testing time and devices are limited, a risk-weighted approach to the more expensive, explorative methods is recommended.

Software Documentation for Submissions

Derived from above considerations the following important documents are used in an FDA submission using the latest eSTAR forms:

·  Software Development Plan (SDP): Strategy outlining milestones, deliverables, and timelines.

·  Risk Management File: Evaluates hazards, mitigation strategies, and residual risks (ISO 14971). Hazards may arise from cybersecurity incidents and need to be covered with a CSRMP (cyber security risk management plan), comprehensive threat model based on the security architecture, and the reporting including all assessments.

·  Software Requirements Specification (SRS): Defines functional/non-functional requirements and ensures traceability.

·  Software Design Description (SDD): Details architecture and design aligned with requirements. This is mandatory only for IEC 62304 Class C software. In practice, we recommend to provide at least a comprehensive software architecture for all classes (SAD), the SDD itself is often close to code and can be generated from enhanced inline comments using tools such as doxygen.

·  Verification and Validation (V&V): Includes test plans and reports to confirm performance and safety. Tracing from requirements to design, risks, threats, mitigations, verification, and validation activities . Part of security validation is covered by including penetration tests.

·  Usability Engineering File: Analyzes and mitigates user risks for safe and effective use (refer to IEC 62366-1).

·  Cybersecurity Documentation: Addresses data privacy, data security, threats and risks. It includes a cybersecurity management plan (CSMP) covering operational aspects, such as vulnerability disclosure.

·  Remaining Software Problem Resolution Documentation for each release: Tracks issues and demonstrates risk assessment and resolution practices.

·  Summary of Safety and Effectiveness Data: Compiles findings proving software safety and efficacy.