ABSTRACT
Radiotherapy is an important modality used for the treat- ment of lung cancer. Seventy-seven percent of all patients with lung cancer have an evidence-based indication for radiotherapy, although it is often underutilized. Radiother- apy can be used as curative or palliative treatment across all stages of disease. Technological advances have allowed better radiotherapy targeting of tumours and reduced inci- dental irradiation of surrounding normal tissues. This has expanded the indications for radiotherapy in lung cancer and improved outcomes both in terms of increasing survival and reducing toxicity. This review examines the current role of radiotherapy in lung cancer, discusses the evidence behind this and identifies future directions in the radiotherapy treatment of lung cancer.
Keywords
lung neoplasms, non-small cell carcinoma, radio- therapy, small cell carcinoma, therapy.
INTRODUCTION
The treatment of lung cancer is complex often involv- ing multiple treatment modalities including surgery, radiotherapy, systemic therapies (chemotherapy, immunotherapy and targeted agents), interventional radiology and palliative care. Radiotherapy is the only treatment modality for which there are indica- tions in all stages of disease and across all categories of patient performance status. Modelling shows that 77% of all patients with lung cancer have an evidence-based indication for radiotherapy at some point in their cancer journey.1 However, radiotherapy remains underutilized in many parts of the world.2 At the population level, optimal use of radiotherapy could result in a 5-year local control gain of 8.3% and survival gain of 4%.3 Recent advances in radiotherapy have resulted in improved outcomes in lung cancer treatment.
ADVANCES IN RADIOTHERAPY TECHNOLOGIES
Radiotherapy technologies are rapidly evolving leading to more accurate and faster treatments with fewer side effects. One of the key factors in accuracy of radiotherapy delivery is imaging. The use of four-dimensional com- puted tomography (4DCT) is now routine for planning radiotherapy. This allows measurement of patient-specific tumour motion which can be incorporated into radio- therapy plans to ensure that the prescribed dose is deliv- ered to the tumour regardless of position. The standard configuration of cone beam computed tomography on linear accelerators also allows verification of the tumour position prior to and during treatment.
The advent of these imaging technologies combined with improved methods of patient immobilization has underpinned the ability to deliver stereotactic ablative body radiotherapy (SABR). SABR is the delivery of large ablative doses of radiotherapy in fewer fractions with geo- metric precision and accuracy. For conventional radio- therapy, improved imaging has allowed a reduction in the previously large margins given to account for tumour motion and uncertainties, thereby reducing incidental dose to surrounding normal tissues, and hence radiother- apy toxicities. Intensity-modulated radiotherapy (IMRT), where multiple beams of non-uniform intensity are directed towards the tumour, also allows increased con- formality of treatment and reduced normal tissue doses.
An alternative technology to account for tumour motion is respiratory gating, where the radiotherapy beam is only turned on when the tumour is in a spe- cific location.4 This may be useful for tumours with large respiratory excursion as can occur for lower lobe locations. Gating may be achieved using breathhold techniques, where the patient holds their breath at a particular point in the respiratory cycle and treatment is given in increments only during breathhold.5,6 How- ever, this is can be challenging for patients with underlying lung disease. Gating can also be performed by tracking tumour motion with the treatment only turned on when the tumour is in a predefined loca- tion.7,8 This generally requires either implantation of fiducial markers or specific tracking equipment. These technologies have expanded the role of modern radiotherapy in improving outcomes for all stages of lung cancer.
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