1. Quality Assurance for a modern treatment planning system
Peter Colley

2. 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.

3. 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

4. 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.

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

6. 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

7. 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.

8. 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.

9. 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

10. 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. pp
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.