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Annual Scientific Meeting of the Canadian Organization of Medical Physicists — July 9–12, 2014, The Banff Centre, Banff, Alberta, Canada

Commissioning a Treatment Planning System for Safe Clinical Use

Every linear accelerator treatment pathway rests on the quiet confidence that a planning system will compute dose accurately, model beams faithfully, and export data without distortion. Comprehensive commissioning converts that confidence from assumption into evidence. The process carries extra weight in countries such as Australia, where a single TPS often supports radiotherapy delivery across geographically dispersed centres and where every miscalculation travels a long way from source to patient.

The 2014 COMP Annual Scientific Meeting in Banff placed patient safety at the centre of its scientific programme, and the patient safety discussions reinforced how commissioning failures cascade directly into clinical risk. The presidential address at COMP similarly called for tighter expectations in equipment acceptance and routine audit. Those themes align closely with Australasian practice, where ARPANSA, state regulators such as the NSW Environment Protection Authority and the Victorian Department of Health, and the Australasian College of Physical Scientists and Engineers in Medicine coordinate the standards applied to new treatment technology.

This article walks through the full sequence of a thorough TPS commissioning, from project scoping and beam data acquisition through to advanced technique validation and clinical handover. It draws on the working knowledge of physicists in public hospitals and private networks such as Icon Cancer Centre and GenesisCare, who commission platforms for metropolitan and regional Australian departments alike. Sharing commissioning data across the wider community is part of the discipline, and departments that document their work well can contribute meaningfully to peer-reviewed conferences and benchmarking studies.

Defining Scope and Governance

A commissioning project should begin with a written scope that names the algorithms, treatment techniques, and machine configurations to be brought into clinical service. The scope must align with local regulatory obligations, including ARPANSA codes, the Therapeutic Goods Administration's framework for software as a medical device, and state-level licensing. Including procurement, clinical, and information technology stakeholders in early governance meetings reduces the risk of late surprises, particularly when the new platform must interface with record and verify systems already in use across Sydney, Melbourne, and regional sites.

The scope document should also set tolerance thresholds for every test, drawn from references such as the IAEA TRS-430 commissioning protocol, the AAPM TG-53 report, and the eviQ cancer treatment protocols widely used in Australian radiotherapy. Tolerances are usually expressed as percentage dose deviation, distance-to-agreement in millimetres, or pass-rate thresholds for gamma evaluation. Recording these thresholds early prevents disputes when a borderline test result emerges.

Acquiring and Preparing Beam Data

Beam data is the foundation of every commissioned model, so its collection deserves a carefully designed measurement campaign. Measurements should be taken with calibrated detectors in a known geometry, using a water tank or solid water equivalent and following consistent scanning conventions. Output factors, percentage depth dose curves, profiles at multiple depths, and off-axis factors for open, wedged, and MLC-shaped fields all need to be captured across the energy range planned for clinical use.

Once measured, the data should be reviewed for consistency before being passed to the modeling engine. Cross-checking against published reference datasets and prior commissioned beam data helps identify outliers. Australian physicists frequently compare their measurements against benchmark libraries produced at collaborating centres in Brisbane and Adelaide, an approach that catches subtle errors introduced by detector drift, chamber polarity, or water tank setup.

Configuring the Dose Calculation Engine

With clean data in hand, the next step is configuration of the dose calculation engine, whether a pencil beam, collapsed cone, or Monte Carlo algorithm. Model parameters such as effective source size, mean energy, focal spot position, MLC offset, leaf transmission, and tongue-and-groove parameters must be set using vendor-recommended starting values and then refined iteratively. Iterative refinement typically involves running calculation versus measurement comparisons at a wide range of field sizes, depths, and source-to-surface distances until residual deviations sit within tolerance.

For dynamic delivery, the configuration should also cover the parameters that govern leaf motion, dose rate variation, and gantry speed. Many Australian centres assign a single physicist to drive this stage, with peer review by an independent colleague before locking parameters. Independent review catches confirmation bias, which is otherwise easy to fall into when a model converges nicely on the dataset used to build it.

Validating Calculations in Homogeneous Media

Before the system touches patient anatomy, dose calculations must be validated in homogeneous water-like media. This stage involves recalculating the full suite of reference fields used during commissioning and comparing the results against measured data using absolute dose differences and gamma analysis. A pass-rate of at least ninety-five percent at a three percent, three millimetre gamma criterion is a common benchmark, with tighter criteria applied for stereotactic work.

This is also the moment to test oblique incidence, asymmetric fields, and the behaviour of the model at the extremes of the clinical range, including very small fields used for cranial radiosurgery and very large fields used for total body irradiation. Outliers found here are easier to diagnose than those discovered later in heterogeneous or patient geometries.

Testing in Heterogeneous Geometry and Clinical Cases

Heterogeneity validation introduces air gaps, lung, bone, and soft tissue equivalents that stress the calculation algorithm in different ways. Anthropomorphic phantoms such as the CIRS thorax or the IROC head and neck phantom are useful tools, and several Australian centres also rely on locally constructed slab phantoms containing cork and aluminium inserts. Dose calculated by the TPS should be compared with measured dose or with independent Monte Carlo recalculation, because algorithm-specific weaknesses often emerge only once the model meets heterogeneous layers.

A small library of representative clinical cases should also be recalculated and reviewed against historical plans created on the previous TPS. This comparison does not validate the new system on its own, but it provides confidence that dose distributions have not shifted unexpectedly across the transition. Clinicians should review the recalculated cases to confirm that plan quality, target coverage, and organ-at-risk sparing remain clinically acceptable.

Commissioning Advanced Techniques

Advanced technique commissioning covers IMRT step-and-shoot, dynamic MLC IMRT, and VMAT, each of which carries its own validation burden. The process typically includes commissioning the delivery system parameters, validating the optimiser on representative cases, and confirming that the post-optimisation fluence translates faithfully to measured dose on the treatment couch. Patient-specific pretreatment QA, often performed with a portal dosimetry array or a cylindrical diode array, is part of this stage rather than a substitute for it.

Rotational therapy deserves particular attention to leaf speed, gantry acceleration, and the interplay between dose rate and motion that defines VMAT delivery. Centres in Sydney and Melbourne that run stereotactic programmes routinely extend this stage to include flattening-filter-free beams, non-coplanar arcs, and dynamic couch motions. Documenting the reference baselines here makes ongoing QA simpler once clinical use begins.

Documentation, Training and Clinical Handover

The final stage of commissioning converts test data and procedures into a controlled document library. A commissioning report should describe every measurement, every model parameter, every tolerance test, and every deviation, with references to national and international standards. Standard operating procedures for routine QA, plan checking, and fault response should be drafted in parallel with the report, and the new system should not be released clinically until these documents are signed off.

Radiation therapists, dosimetrists, and oncologists need hands-on time with the new platform before the first patient is planned. Walk-through rehearsals using real patient data from Brisbane, Perth, or Hobart catch workflow issues that pure bench testing misses. When the first real patient plan is created, an experienced physicist should review every step, and an independent dose calculation should be performed before approval.

Practical recommendations

  • Build the commissioning scope around national standards such as ARPANSA guidance, the IAEA TRS-430 protocol, and AAPM task group reports rather than around vendor checklists.
  • Acquire beam data with calibrated, traceable detectors and review the dataset for consistency before any modeling work begins.
  • Engage an independent physicist to peer review model configuration and calculation validation results.
  • Use a graded set of test cases, from homogeneous reference fields through heterogeneous phantoms to representative clinical plans, with explicit tolerance thresholds at each stage.
  • Document every parameter, test, and deviation in a single commissioning report and back it with signed standard operating procedures.
  • Carry out supervised clinical use of the first patient plans, with independent dose calculation and dual physicist sign-off.

Physics departments planning a new TPS commissioning are encouraged to register the work as a quality improvement project and share the resulting dataset with their state radiation health branch. Past commissioning abstracts and benchmark exchanges from conferences such as COMP help lift the standards of the whole field. Teams intending to publish their findings should review the abstract submission workflow before the deadline, and reach out to the organising committee for template documents, benchmark data exchange opportunities, and peer review contacts.