What should you know about a PET scan after radiotherapy?

A PET scan uses a tracer to show activity and CT to locate that activity. Radiotherapy can leave inflammation or tissue repair in the treated area, and these changes may take time to settle. For that reason, the oncology team chooses timing based on the body region, treatment plan and question being asked.

The report may compare the treated area with earlier images and describe whether activity has reduced, remains uncertain or needs investigation. An active area is not automatically recurrent cancer, and a quiet area is interpreted alongside examination, symptoms and other tests.

Follow the imaging centre’s guidance about food, fluids, exercise and medicines. Tell the team about recent infection, treatment side effects, diabetes, allergies and the date of your last radiotherapy session. During the scan, remain still when asked so the PET and CT images align.

Keep your treatment summary and earlier scan details available. Ask who will explain the report, whether the images will be compared with a baseline scan, and whether an uncertain result calls for observation, another test or a clinical review.

Alert staff promptly if you develop sudden swelling, a widespread rash, breathing difficulty or faintness after the tracer. Seek urgent care for severe breathing trouble or collapse. Contact your oncology team promptly for worsening pain, new neurological symptoms, trouble swallowing, heavy bleeding or a rapidly changing wound in the treated area.

Why is this scan being scheduled now? How could healing inflammation affect the treated area? Which earlier images will be compared? What symptoms should I report while waiting for the result? If the scan is unclear, what test or follow-up would clarify it?