Volume definition in radiotherapy planning for lung cancer: how the radiologist can help

Effective treatment for carcinoma of the lung remains one of the biggest challenges in oncology. Radical radiotherapy may be a curative option for patients who are unsuitable for radical surgery either because of disease stage or because of co-morbidity. Long-term disease control with radical radiotherapy is disappointing with only about 6% of patients treated being alive at 5 years. Technological advances involved in the planning and delivery of radiotherapy may improve this. The advent of conformal radiotherapy, utilizing computed tomography and three-dimensional planning systems, allows much more accurate shaping of the radiation fields. This greater accuracy of target volume definition facilitates a reduction in the radiation dose to normal tissues, allowing for dose escalation to the tumour. Delineation of the target volume can be problematic. Conventional CT has limitations in term of distinguishing between benign and malignant tissues, e.g. the size criteria for involved lymph nodes. The oncologist uses a combination of radiological and clinical information when defining the target volume but their radiological interpretation of imaging is inferior to that of a radiologist. The Royal College of Radiologists (RCR) issued guidance in 2004 on the optimal imaging strategies for common cancers. These guidelines address issues regarding the localisation and staging of cancers and treatment planning, and also reporting and training. They recommend the development of closer links between radiologists and oncologists to optimise the interpretation of imaging and target volume definition. This article aims to briefly explain the planning process involved in irradiating lung cancers, highlight problematic areas and suggest ways in which co-operation with radiologists may improve the delivery of radiotherapy and therefore the treatment outcomes for this group of patients.