How PET is changing the management of cancer with radiotherapy

Information from PET scanning is transforming the management of many malignancies and the impact of PET is likely to increase further as new indications are recognised. PET is of particular value in patients treated with radiotherapy (RT) with curative intent. These patients rarely undergo invasive surgical staging and therefore imaging is crucial in determining the extent of disease before treatment. More accurate staging with PET means that futile aggressive RT or chcmoRT can be avoided in patients with incurable extensive disease. FDG-PET is of proven value in the staging of common metabolically-active malignancies treated with radiotherapy. These include lung cancer, head and neck cancer, lymphomas and oesophageal carcinoma. It has been shown that PET can improve the selection of patients for radical surgery or radiotherapy in lung cancer and that PET-based staging more accurately predicts survival than conventional staging. For those patients that remain eligible for definitive RT after PET. treatment can be more accurately targeted at the tumour and involved regional nodes. The value of PET for treatment planning is enhanced significantly when PET and CT scans are acquired on a combined PET/CT scanner. Fused PET-CT images can be imported into the radiotherapy planning computer and used to accurately target tumour with the best beam arrangement. After treatment, response may be hard to assess with structural imaging. PET-rcsponse to chemotherapy or radiotherapy in non-small cell lung cancer (NSCLC) predicts survival in NSCLC more accurately than CT response. However, PET has much more potential than imaging with FDG alone can realise. Markers such as FLT can be used to image proliferation in tumours, misonidazole or FAZA can be used to image hypoxia and labeled metabolites of anti-cancer drugs such as 5-FU can be used to study pharmacokinetics. New combinations of radiation and drugs may emerge that can be selected based on biological characteristics of tumours imaged by PET