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Improving Health Through Medical Physics

AAPM Statement to FDA’s Public Meeting on Incorporation of New Science Into Regulatory Decision making within the Center for Devices and Radiological Health

Presented by Mahadevappa Mahesh for Maryellen Giger, Chairman of the Board (due to weather)
American Association of Physicists in Medicine (AAPM)

Tuesday, February 9, 2010
Gaithersburg, Maryland

This statement is being given on behalf of the American Association of Physicists in Medicine (AAPM), which represents over 7,000 medical physicists. AAPM aims to advance the practice of physics in medicine and biology by encouraging innovative research and development, disseminating scientific and technical information, fostering the education and professional development of medical physicists, and promoting the highest quality medical services for patients. Medical physicists contribute to the effectiveness of radiological imaging procedures by assuring radiation safety and helping to develop improved imaging techniques (e.g., mammography, CT, MRI, ultrasound). Medical physicists contribute to the development of therapeutic techniques (e.g., IMRT, prostate implants, stereotactic radiosurgery), collaborate with radiation oncologists to design treatment plans, and monitor equipment and procedures to insure that cancer patients receive the prescribed dose of radiation to the correct location.

This statement addresses Case Study 1*.

Case Study 1 would benefit from the independent assessment of the particular product or type of product, i.e., Devices X, Y, Z, and Q.  Such assessments could be performed with technology assessment studies

Means to perform such comparative assessment studies may include clinical evidence-based outcomes evaluations that require expensive and sometimes lengthy clinical trials involving a substantial number of patients to achieve statistical certainty.  However, when well-defined physical or engineering differences exist between products, which do not rely on different anatomic or physiological phenomenon, comparative effectiveness can be determined by assessing technology using quantitative metrics. This will be particularly useful and cost effective in situations where simple modifications of an existing medical technology are introduced or a new technology is available that is changing rapidly in its potential for proving efficacy.  In those cases and at those times, relatively inexpensive physical measurements or observer-based diagnostic accuracy studies may be most appropriate. 

The AAPM is proposing that it collaborate with other scientific organizations and federal agencies in developing an independent TAI – technology assessment institute, that would further evaluate, e.g., imaging and therapeutic devices of the type in Case Study 1.  Such evaluations could include either pre-market or post-market evaluations.  For the specific Case Study, a TAI could conduct the evaluations of Devices X, Y, Z, and Q.  The “minimum bar” could be recommended and applied to all the devices, and the FDA could base their decision on performances.  The FDA could use the results to allow the use of a predicate, determine the need for a 510(k) or PMA, issue a recall, or agree with/counter “a compelling peer-reviewed publication”.

An example includes the optimization of radiation dose in computed tomography (CT). Image quality can be assessed quantitatively between different computed tomography (CT) scanners at the same radiation dose levels, providing an objective measure of comparative effectiveness that may not require a clinical trial.  These comparisons could also include the analysis of safety mechanisms involved in order to avoid accidental over doses as well as a review of quality control procedures.

Another example is the comparative evaluation of mammography, breast CT, and breast tomosynthesis in detecting and assessing the extent of breast cancer by using various metrics of physical and psychophysical image quality (e.g., spatial resolution, noise, or conspicuity) and balancing the results in terms of cost and radiation dose level.

Examples of devices in radiation therapy include the assessment of photon therapy versus proton therapy in the treatment of prostate cancer by measuring the dose to the tumor target compared to the rest of the patient’s (normal) tissues. 

A TAI could also be the secure holder of databases.  For example, for the independent test of a new CAD system, the TAI could have the system run on randomly selected mammograms from its database based on the type of population requested.  The TAI would give the sensitivity and specificity of the system, without informing the company of the exact cases which did well (or poorly).  In later testings, another distribution of cases would be selected for the examination.  This would preserve the integrity of the testing cases and also allow testing across applicable populations.

Other databases maintained by a TAI could include error registries based on a usable, national event reporting mechanism from which users, vendors, and government agencies could benefit.  Such a database could allow reporting by medical staff and manufacturers and others in a complete and consistent manner, be searchable to identify patterns, risks and corrective actions and to provide education, and require a partnership between all involved (federal and state government, manufacturers, users, patient advocates).

The AAPM is well positioned to lead the establishment of a technology assessment institute since it already participates in the development of procedures and guidelines for the safe, efficacious implementation and utilization of existing, new and advanced technologies. Currently, the AAPM produces many detailed scientific, educational and practical reports for technology and procedures for medical imaging and radiation therapy. These reports include specific processes for radiation dose measurement and calibration, quality assurance and peer review. These reports are presented in educational forums at national and regional meetings and are also publicly available.

An TAI could initially be virtual and “without walls allowing the AAPM and others to determine the extent of evaluations necessary.  It also could be supported by federal and industry funding.

In summary, it is important to realize that technology assessment studies of both diagnostic and therapeutic procedures and systems could benefit the FDA decision making process via the establishment of a technology assessment institute, and that medical physicists would serve a vital role in conducting such studies.

* Case Study 1:
Scenario A: CDRH clears Device X for marketing through the 510(k) process. Device X is cleared for a specific intended use. Several years later, a pattern of Medical Device Reports (MDRs) that have been submitted to CDRH calls into question the safety of the device when used in the long term for its cleared use. A number of other devices of the same type and with the same intended use as Device X are on the market when this new safety information comes to light. There is also a device of the same type, Device Y, under review through the 510(k) process. The 510(k) submission for Device Y cites Device X as a predicate.

Scenario B: CDRH approves Device Z for marketing through the PMA process on the basis of favorable results in a pivotal clinical trial. Several years later, a compelling peer-reviewed publication reports that an attempt to replicate these clinical trial results was unsuccessful. A number of other devices of the same type and with the same intended use as Device Z are PMA-approved and on the market when this article comes to light. There is also a device of the same type and for the same intended use, Device Q, under review through the PMA process.

Questions of Interest:
(A)(1) When CDRH gains new scientific information about a particular product or type of product, what should the criteria be for changing CDRH’s expectations of the evidence necessary for pre- or postmarket regulatory decisions, keeping in mind our mission to protect and promote the public health, as well as our statutory and regulatory framework?
(A)(3) When such changes are warranted, how should CDRH apply them to devices currently under review?
(A)(4) When such changes are warranted, how should CDRH apply them to products currently on the market?