“One approach to satisfy two sets of rules”

As stated in the last blog post, there are two sets of rules for SW regulation—twice the rules, twice the confusion. My recommendation is to base your software development procedures on the IEC 62304 Standard, which is easier to understand, and then include any additional adjustments needed to meet all the FDA requirements. Here I will go into more detail about exactly what that entails and how best to ensure your SW development project checks all the boxes.

IEC 62304 Medical Device Software Standard

The IEC 62304 medical device software standard (“Medical device software—Software life cycle processes”) is comprised of five processes in five chapters (5-9):

  • 5 – Software Development Process = this is the main process that SW groups are focused on and includes all the key aspects of development from planning and requirements to testing and release
  • 6 – Software Maintenance Process = this is an abridged form of the main software development process and is intended to quickly release patches for SW bugs and security risks
  • 7 – Software Risk Management Process = risk assessment of SW failures as well as management of SW safety features which serve as risk controls for HW failures, for use error, and for other system failures
  • 8 – Software Configuration Management Process = source code control system/ development environment and how to manage builds and releases
  • 9 – Software Problem Resolution Process = bug tracking system and how your organization evaluates bugs and related activities to resolve issues

The diagram below shows 4 of these 5 processes (numbered 5-9, but missing 6) and their relationship to overall system validation. Note that the 62304 standard does not cover system validation or other system development activities—it only covers up to “SW System Testing.” FDA SW Guidances have a much broader scope, including system validation and development of non-product software.

IEC 62304 Software Standard

The Software Development Process (#5) consists of 8 key activities:

  1. SW Development Planning – defining the scope of the SW development project
  2. SW Requirements Analysis – decomposing system/product requirements into software requirements within the context of the system architecture design (identifying the system functions that are to be implemented in software)
  3. SW Architectural Design – high level design of the software, including partitioning/segregation of high-risk software, as appropriate
  4. SW Detailed Design – defining the SW units and their interfaces, including state diagrams, data structures, and risk controls (the software engineer’s view of how the SW will function)
  5. SW Unit Implementation & Verification – the core of SW development; coding and testing
  6. SW Integration & Integration Testing – merge software units and demonstrate that multiple software components work properly together and with the system hardware
  7. SW System Testing –verification of software against the SW requirements in a system environment
  8. SW Release – deploying a controlled, verified version of SW

These activities are described in the 62304 standard and in this diagram as a linear sequence, however, there is nothing in the standard that prevents SW teams from utilizing iterative (agile) approaches for SW development.

Note that processes 7, 8 and 9 in the diagram above occur concurrently. The intent of the 62304 standard is that the SW team sets up configuration management and bug tracking systems at the beginning of the project and are performing risk management continually throughout development.

How these requirements of the 62304 standard are translated into specific procedures can vary considerably from company to company depending on the complexity of the software and the safety risks associated with it. For example, the appropriate methods to manage development of a small amount of firmware in a simple, low risk device would be quite different than the methods to manage software in a complex, safety-critical system.

One of the challenges in understanding the 62304 standard is that it has its own language. For example, here are some terms from it that often confuse newcomers:

  • Anomaly = software bug
  • SOUP = Software Of Unknown Provenance; basically Off-the-Shelf (OTS) software but can also include legacy software that was not documented
  • Software Item = a software component or module (a part of a complete “software system”)
  • Software Unit = the smallest software item
  • Configuration Item = a software item that can be identified and tracked in the build system (e.g., a SW library from a 3rd party that is tracked by its own version number)
  • Problem Resolution = bug tracking and evaluating bugs and documenting the resolution of bugs

Now that we’ve pulled the curtain back on the 62304 standard, let’s dive into software regulation from the viewpoint of FDA Guidances.

FDA Software Guidances

The FDA issued its first Software Guidance over 20 years ago, responding to issues and problems with software-controlled medical devices. The reasoning was to clearly explain FDA expectations around software development and documentation for medical device manufacturers. Over the years, they’ve updated and added more Guidances as other issues arose.

This list of Guidance documents is current as of SEP 2018 but be sure to check the FDA CDRH website (https://www.fda.gov/RegulatoryInformation/Guidances/ucm214106.htm ) for any newly released or draft guidances. Note that the term “guidance” here does not mean optional—the FDA expects you to follow their guidances exactly or have solid rationale for deviating from them. And, of course, the general FDA regulations for design controls (21 CFR 820.30) apply to all medical device (product) software. These FDA Guidances describe how to interpret those regulations for different aspects of software.

  1. General Principles of Software Validation; Final Guidance for Industry and FDA Staff (2002)
  2. Guidance for the Content of Premarket Submissions for Software Contained in Medical Devices (2005)
  3. Guidance for Industry, FDA Reviewers and Compliance on Off-The-Shelf Software Use in Medical Devices (1999)
  4. Cybersecurity For Networked Medical Devices Containing Off-The Shelf (OTS) Software (2005)
  5. Content Of Premarket Submissions For Management Of Cybersecurity In Medical Devices (2014)
  6. Mobile Medical Applications: Guidance for Industry and FDA Staff (2015)
  7. Medical Device Data Systems (MDDS): Guidance for Industry and FDA Staff (2015)
  8. Postmarket Management of Cybersecurity in Medical Devices (2016)
  9. Software as a Medical Device (SAMD): Clinical Evaluation (2017)

The first 3 are what I consider the ‘main’ software Guidances (also the oldest); the remaining Guidances have been written to clarify more recent issues with medical device software like mobile apps, networked devices, and cybersecurity.

General Principles of Software Validation (GPSV)

This guidance, published 16 years ago, is a general discussion of good practices for software development. It does not provide specific instructions on what must be done and since it covers a very broad scope, beyond product software, it can be difficult to translate it into specific quality system procedures. Some parts of this guidance appear to be written for an audience that is unfamiliar with software (explaining for example how software is different from hardware and describing standard practices for software testing). However, there are some particular points that stand out in the guidance:

  • One of the most important points: “software testing by itself is not sufficient to establish confidence that the software is fit for its intended use.” In other words, detailed software test reports alone are not sufficient to claim that medical device software is safe and effective.
  • “Because of its complexity, the development process for software should be even more tightly controlled than for hardware, in order to prevent problems that cannot be easily detected later in the development process.” Translation: you will need additional procedures and documentation for software development
  • The importance of risk analysis throughout development and particular practices for safety-critical software, such as defining risk controls in the software requirements

Note that Section 6 of the guidance (Validation of Automated Process Equipment and Quality System Software) does not apply to medical device software. For validation of these types of non-product software, I recommend using the AAMI TIR36 guidance instead, which is more focused than this guidance and has a handy set of examples in its appendix.

Content of Premarket Submissions

This guidance is important for understanding the required software documentation for regulatory submissions to the FDA. The requirements depend on the “Level of Concern” of the software, which is based on the potential worst case result of a software failure. There are three defined levels of safety risk:

  • Major – can result in serious injury or death
  • Moderate – can result in minor injury
  • Minor – no injury

The guidance has a set of questions to determine the Level of Concern of your product’s software and a table showing which software documents are required for each level. The rest of the guidance explains the expected contents of each type of software documentation (Software Requirements Specification, Architectural Design Chart, etc.).

Off-The-Shelf Software Use in Medical Devices

The basic message of this guidance is that medical device companies are responsible for all of the software in their products, including software libraries and other off-the-shelf (OTS) software components that were bought instead of developed.  Responsibility in this case entails defining (documenting) what OTS software you are incorporating into your product software, analyzing the safety risks associated with the OTS software, and managing changes and bugs that are discovered in the OTS software.  The guidance describes the documentation to be included in submissions to the FDA as “basic documentation” for all OTS software and “special documentation” for OTS software with safety risks.  The latter depends on the software Level of Concern (Major / Moderate / Minor), analogous to what is required for the software you’ve developed yourself. Cybersecurity, which was not much of a concern for medical devices when this guidance was published in 1999, is now an important part of risk analysis of OTS software incorporated into medical devices.

Typical software documentation

So what documents does your SW team need to produce?  The answer, unfortunately, is rarely a simple list. The required documents, document names, and approaches all vary depending on the company, its quality system, and its products. But they  all seek to answer these essential questions:

  1. What are our goals for this SW project?
  2. How are we organizing the project for success?
  3. What does the SW need to do?
  4. How can the SW hurt someone?
  5. How have we designed the SW?
  6. What is the test evidence that the SW does what it needs to do?
  7. What are the remaining bugs and are any of them a safety risk?
  8. What SW was tested?
  9. What changes were made between tests?
  10. How do we make sure the right SW is installed in the product?

(For example, the Software Requirements Specification document answers question #3)

Now, how much documentation is enough? How detailed do these documents need to be? These questions need to be asked for every SW development project and the answer is inherently linked to the safety risks associated with the software, which will be covered in the next blog post.

About the Author

Aaron Joseph, Lean & Compliant Medical Device Development Consultant

Aaron Joseph has 20 years of experience in medical device development over a wide range of products: surgical robotics system, digital x-ray fluoroscopy system, drug inhaler devices, robotic catheter system, x-ray catheter for brachytherapy, laser eye surgery system, heart-lung bypass machine, and endoscopy instruments with RF ablation.

Aaron helps clients to efficiently comply with regulatory requirements for software and hardware development. He works closely with product development teams in performing risk analyses, designing test plans, managing product requirements, refining design control procedures, making efficient use of SW tools, and training R&D staff. Aaron is an expert at medical device design verification and validation, including software, hardware, and system testing. He is able to apply design controls efficiently and rigorously to a broad range of products and adapt them to small and large organizations.

Aaron has a BS in Electrical Engineering from Rice University and a MS in Bioengineering from University of Washington.