[Conformal radiotherapy of non-small-cell lung cancer]

[Gross tumor volume and clinical target volume in radiotherapy: lung cancer]

Radiotherapy plays a major role as a curative treatment of various stages non-small cell lung cancers (NSCLC): as an exclusive treatment in curative attempt for patients with unresectable stages I and II; as a preoperative treatment, which is often associated with chemotherapy, for patients with surgically stage IIIA NSCLC in clinical trials; in association with chemotherapy for unresectable stages IIIA and IIIB patients. Currently, three-dimensional conformal radiotherapy allows for some dose escalation, increasing radiation quality. However, the high inherent conformality of this radiotherapy technique requires a rigorous approach and an optimal quality of the preparation throughout the treatment procedure and specifically of the accurate definition of the safety margins (GTV, CTV...). Different questions remain specific to lung cancers: 1) Despite the absence of randomized trials, the irradiated lymph nodes volume should be only, for the majority of the authors, the visible macroscopically involved lymph nodal regions. However, local control remains low and solid arguments suggest the poor local control is due to an insufficient delivered dose. Therefore the goal of radiotherapy, in this particular location, is to improve local control by increasing the dose until the maximum normal tissue tolerance is achieved, which essentially depends on the dose to the organs at risk (OAR) and specifically for the lung, the esophagus and the spinal cord. For this reason, the irradiated volume should be as tiny as possible, leading to not including the macroscopically uninvolved lymph nodes regions in prophylactic view in the target volume; 2) The lung is one of the rare organs with extensive motion within the body, making lung tumors difficult to treat. This particular point is not specifically considered in the GTV and CTV definitions but it is important enough to be noted; 3) When radiation therapy starts after a good response to chemotherapy, the residual tumoral volume should be defined as the target volume in place of the initial tumor volume. These different elements are discussed in this paper.

[Immobilization devices in conformal radiotherapy for non-small cell lung cancer]

When considering three-dimensional conformal radiotherapy for non-small cell lung cancer, the uncertainties about treatment can be quite significant, due to set-up errors and organ or tumor motion. These can be important causes of treatment failure. Immobilization devices have only been studied recently in a scientific manner in the domain of chest tumors, presumably because other factors such as tumor motion were felt to be more important causes of treatment uncertainties. An international survey on immobilization devices in the treatment of non-small cell lung cancer has shown that about half of the centers are using three-dimensional conformal radiotherapy, and among these, only two-thirds use immobilization devices on a routine basis. Very few use internal fiducials. Current data on set-up errors show that the average discrepancy is about 5 mm, but in some cases it can be more than 15 mm. A recent study has demonstrated that less positioning corrections during treatments were needed for the patients who were immobilized. Another work indicates that there were no differences between a T-bar immobilization device and a system using chemical foams. Other works indicate that internal motion of bronchial tumors can vary greatly, depending on their location. A number of clinical groups are looking at minimizing the consequences of internal motion, but the currently proposed techniques appear to be cumbersome. New studies will be necessary in order to improve the knowledge of daily positioning and the effect of internal motion. Until then, it is essential to take care when considering narrow margins in conformal radiotherapy of non-small cell lung cancer.