Quality Assurance for a modern treatment planning

systemPeter Colley

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 Softw

are

User/D

ocs Data

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

Software

Considerations: Algorithm Inaccuracy

» 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

» 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

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

Acceptability

Additional Uncertainties: • tissue inhomogeneties?• under wedges and attenuators?• small fields?• electronic disequlibrium?

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

Test Min.Frequency

1. Input digitiser, output plot Square Contour

Weekley

2. CT Scan Transfer Quarterly3. Photon Beamsi) Point Doses (d = dmax, 5, 10) rectangular fields (5*30) irregular fieldii) Lateral Profiles Open (d = dmax, 10)(10*10, 35*35) Wedge (d = 10)(large field)iii) Inhomogeneities Single Beam (10*10) Air Slab in Water bone-like slab in water

Semi-annually

Semi-annually

Semi-annually

4. Summation Algorithmsi) Parallel pair-photons equally weighted unequally weighted wedged fieldsii) three field technique 30, 135 and 250 degreesiii) Two adjacent 180 degree arcs

Semi-annually

5. Machine Settings Semi-annually

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.