Quality Assurance for a modern treatment planning system Peter Colley

This talk will concentrate on the QA of the computer system used in the treatment planning process. As can be seen from the diagram the accuracy and quality of information produced by the computer system and its associated inputs will have major effects on the patient treatment plan.

What is QA ? QA - systematic procedures necessary to ensure that a product or process performs to specification little published data for QA of treatment planning computers ICRU Report 42 Hardware Software User/Docs Data QA is defined as the systematic procedures necessary to ensure that a product or procedure conforms to the design specifications, and is performed in three ways: (a) measurement of current performance (b) comparison of current performance with existing standards (c) corresponding actions necessary to maintain or regain agreement with the standard. Consideration of a treatment planning system will reveal that the Quality Assurance Aspects fall in 4 categories: Hardware, Software, User/Documentation and Data. For the remaining 6.5 minutes we will discuss these areas. Quality System

Documentation and User Training Considerations: ICRU 42 user must be “informed” about procedures implemented by the software and hardware users’ ability to enter correct information into the system Adequate staff training Physicist should validate the performance of the algorithms Documented System (Dahlin et al) Actions: Patient Dose Calculations - Experimental Check Absolute Dose Rate for reference conditions Considerations: Dahlin et al - 10 points for comprehensive system documentation including data file formats text files containing communication descriptors algorithm descriptions program source code software libraries (including device handlers) description of data entry requirements test example plans Actions: The treatment planning computer calculates the dose at points within the patient relative to a reference point. Experimental check of this calculation involves measurement at points of interest, and the reference point (using the same instrument). If the TPS performs absolute calculations (MU or beam on time) additional information requires verification - absolute dose rate for a set of reference conditions.

Software Considerations: Algorithm Inaccuracy Actions: complex physical problems = approximations Implementation Inaccuracies dose grid spacing interpolation schemes Actions: Test Algorithm in Routine and Extreme conditions

Data Considerations: Inaccuracies in measured data Data Consistency measurement of beam parameters measurement of patient data Data Consistency data corruption defragmentation / media failure virus intentional modification Inaccuracies in data entry USER TRAINING HARDWARE Inaccuracies in data output

Hardware Considerations: Input and Output Device Accuracy and Resolution Digitizer Calibration test and recalibration Pen Plotters / Printer accuracy ( > 1mm) resolution Video Display distortion free consistent with hard copy Processor and Memory tests Video Display will be used for decision making during planning and must therefore be consistent with the hard copy.

Acceptability Additional Uncertainties: tissue inhomogeneties? under wedges and attenuators? small fields? electronic disequlibrium? Inaccuracies in the Data and Hardware are perhaps the hardest ones top control for. Different levels of acceptance have been proposed in the literature along with very many test criteria, which cannot be covered in detail within this talk. The two tables shown represent the test scenarios for photon beams proposed by Van Dyk, taken as an example from the literature, which are considered to be achievable at the 67% confidence interval by modern TPS. The tests consist of comparing measured values with those calculated by the TPS, but the limits do not represent levels beyond which no further improvements are necessary, rather the minimum which should be achieved. Uncertainties which require careful consideration within these limits are: tissue inhomogeneities in photon beams uncertainties under wedges and attenuators small field uncertainties (stereotatic surgery) regions of electronic disequlibrium (tissue interfaces) Van Dyk also recommends that basic radiation beam data from other institutions should not be used.

QA Systems Initial Testing / Acceptance Testing Basis of a Quality System Provides an operational “bench mark” validates data coms and registration with other equipment Reproducibility / Regular QA Testing Uses similar tests to Initial Testing Stipulates minimum frequency for testing to be performed Input to corrective action stage if equipment does not meet the benchmark standards

Finally... Quote from the literature: “No complex computer system can be made completely error free - careful daily examination of the treatment plans should be performed.” References: Van Dyk et al. Commissioning and Quality Assurance of Treatment Planning Computers. IJROBP, Vol26. pp261-273 Fraass et al. AAPM, Radiation Therapy Committee Task Group 53: Quality assurance for clinical radiotherapy treatment planning. Med. Phys. (10) 1998. Mayles et al. Physics Aspects of Quality Control in Radiotherapy. Report 81. Shaw JE. A Guide to Commissioning and Quality Control of Treatment Planning Systems. IPEM Report 68.