Lung cancer



Both small cell and non-small lung cancer is sensitive to radiotherapy with the effect being more dependent on the dose which is able to be delivered than on the histology of the tumour. The thorax contains many vital organs which are themselves sensitive to radiation. This limits the doses of radiotherapy which can be delivered to tours. Many tumours, particularly unresectable tumours, are sited near the hilum making it difficult to plan effective irradiation while avoiding the heart, spinal cord and parenchymal lung tissue.

Radical radiotherapy

A tumouricidal dose of radiation is approximately 60 Gy (delivered in 18 to 30 fractions) for NSCLC. In addition to the tumour itself it is necessary to deliver this dose to a margin of 2 cm. This limits the size of tumours which can be treated with curative intent to approximately 3 cm in maximum diameter. Therefore only a small percentage of tumours in patients unfit for resection or who refuse surgery can be treated radically. 5 year survival has been reported in 15-20% of this highly selected group.

Palliative radiotherapy

In patients unfit even for high risk palliative radiotherapy, single fractions of 5-10Gy are effective for specific symptoms such as haemoptysis or pain.

High dose palliative radiotherapy

Most patients therefore receive radiotherapy for palliation. Delivering doses in the region of 30 Gy allows much larger tumours to be treated. While cure is rare relief of symptoms. Obstructed bronchi can be opened up in some circumstances relieving breathlessness. In patients with minimal symptoms it is not clear whether such palliative therapy prolongs survival or quality of life. A more effective strategy may be to withhold treatment so that a full dose may be applied to relieve symptoms when they do arise in a particular site. Treatment of painful bony metastases is particularly effective.

Newer techniques for delivering radiotherapy have been developed. The latest spiral CT scanners allow more accurate three dimensional planning. Delivery of conformal radiation fields which follow the contour of the tumour more closely and avoid irradiating contiguous radiosensitive structures translates into a tumourocidal dose as high as 80 Gy to tumours which at present can only be palliated. Continuous hyper-fractionated radiotherapy (CHART) has been shown to increase the response rate of tumours treated radically. There is also early evidence of increased survival. It is very resource-intensive requiring 54 Gy to be delivered in 36 fractions over 12 days. The radiation effect is believed to be enhanced by delivering tumourocidal radiation to cells at diffent times in the cell cycle. A number of chemotherapeutic agents including cisplatin and the taxanes are radiosensitizers. In addition to their effect on metastatic disease they enhance the effect of radiation on the primary tumour. In NSCLC the combination has been shown to have better survival than either modality on its own.

Late effects of radiation include lung fibrosis, neo-vacularisation and carcinogenesis. Non-malignant recurrent laryngeal nerve, phrenic nerve and spinal cord paresis can also occur when they have been included in the radiation field.