New Imaging Modalities Reshape Radiotherapy Planning

At the 2014 Annual Scientific Meeting of the Canadian Organization of Medical Physicists in Banff, Alberta, the scientific programme examined The Impact of New Imaging Modalities on Radiotherapy Planning. Archived abstracts and presentations showed how imaging had moved beyond diagnosis to shape target definition, dose calculation and daily treatment decisions.

For Australian cancer centres, that shift is practical rather than abstract. Teams in Melbourne, Sydney, Brisbane and regional hospitals must choose suitable scans, interpret them within multidisciplinary meetings and build workflows that remain safe when equipment, staffing and patient travel vary. The strongest lesson is to treat multimodality imaging as a clinical service, not as a collection of impressive images.

Imaging now begins before the planning CT

Radiotherapy planning has long relied on CT to show bones, lungs and external contours. New imaging asks clinicians to define more: where tumour cells persist, which tissue is functioning, how anatomy changes with breathing, and how uncertainty should influence margins around gross and clinical target volumes.

Multimodality imaging separates two questions that CT often merges. MRI can sharpen soft-tissue boundaries, while PET or SPECT can map metabolism or tracer uptake. Combined with CT density data and motion records, these datasets create a more patient-specific description of both the target and organs at risk.

CT advances reveal motion and density

CT itself has advanced through iterative reconstruction, higher spatial resolution and four-dimensional imaging. Cone-beam CT on a linear accelerator can generate a low-dose image of the patient in the treatment position, showing setup errors and some respiratory motion without the machinery of a diagnostic scanner.

These developments support image-guided radiation therapy, but they do not remove discipline. Metal artefacts, motion streaks and inconsistent acquisition protocols can distort contours or dose estimates. A centre still needs agreed imaging parameters, matching criteria, tolerance limits and documentation explaining how any image change alters the approved plan.

MRI adds soft-tissue and biological contrast

MRI offers strong soft-tissue contrast and can reveal relationships hidden on CT, particularly in the brain, head and neck, pelvis and prostate. It may also provide functional information through diffusion, perfusion or spectroscopy, helping clinicians distinguish viable tumour from treatment response or surrounding healthy tissue.

Using MRI for planning requires more than importing a dataset. Magnetic-field artefacts, geometric distortion and organ motion must be checked, and MRI data usually need conversion, sometimes through a synthetic CT model, or fusion with CT electron-density information for dose calculation. MRI-guided linear accelerators may support online adaptation, where the treatment room becomes an imaging environment.

Molecular maps sharpen target definition

PET-CT, PET-MRI and SPECT add a biological layer to structural scans. Radiotracer uptake can expose metabolically active regions, help separate nearby structures and guide biopsy or target-volume decisions. Hypoxia-sensitive and receptor-targeted tracers may further characterise tumour heterogeneity when matched scanners, timing and reconstruction standards are available.

Functional signals must be interpreted cautiously. Partial-volume effects, inflammation and normal physiological uptake can mimic tumour, while differences between scanners can shift apparent boundaries. The practical value comes when nuclear medicine, radiology, radiation oncology and physics agree on how the image should influence contouring rather than simply adding colour to a CT.

Adaptive planning turns scans into decisions

Image-guided radiation therapy uses repeatable images to compare the planned geometry with the patient on each fraction. Daily cone-beam CT can reveal translation, rotation and deformation, allowing small corrections before beams are delivered and preventing unnecessary dose to normal tissue.

Adaptive planning extends that process. When anatomy or disease burden changes, deformable registration can map the original dose distribution onto a new image set, while replanning can revise beam angles, optimisation and margins. Gating and four-dimensional CT may be considered when respiratory motion is clinically important, particularly for lung and liver targets.

Each step needs validation. Automatic matching and contouring require commissioning, phantom testing and human review; clinicians should know when an automatic result is uncertain. A defensible pathway records who reviewed the images, what triggered adaptation and how the final plan was checked before delivery.

A Banff programme for multidisciplinary learning

The archived scientific programme offers a practical route into these subjects, with sessions and abstracts spanning imaging technology, planning methods and quality assurance. Readers can follow the subject from image acquisition through to contouring and delivery rather than treating each modality as an isolated topic.

That multidisciplinary sequence matters because most errors occur between disciplines. A radiologist may define anatomy differently from a radiation oncologist; a physicist may recognise a motion artefact that the planner overlooks; a therapist may see a reproducibility problem that never reaches the contouring session. Shared language and clear review points reduce those gaps.

Turning Australian insights into clinical action

Australian geography adds another layer. Major services in Melbourne, Sydney, Brisbane, Adelaide and Perth serve large populations, while patients from regional and remote areas may travel long distances or relocate temporarily for treatment. Imaging, planning and delivery appointments on different days can make image transfer and transport support as important as image quality.

The local market is a mixture of public hospitals, private radiation providers and private diagnostic imaging, with imaging funded through Medicare, public services or private insurance. A patient may complete a CT in a hospital, an MRI in a private centre and treatment in another facility, so electronic DICOM transfer, clear consent and a reconciled clinical history are essential daily practice.

Safety sits within the national framework overseen by the Australian Radiation Protection and Nuclear Safety Authority, or ARPANSA, and relevant state and territory regulators, including licensing requirements associated with the Australian Radiation Protection and Nuclear Safety Act 1999. The Canadian radiotherapy quality update in the COMP archive reinforces the value of shared indicators, peer review and evidence-based process changes across borders.

Use the archived programme to shortlist sessions on CT, MRI, PET and image guidance, share them with your multidisciplinary team and assign one local question for audit. Review image-matching tolerances, transfer procedures and adaptation triggers at your next department meeting, then record what changed and why.