Conformal radiotherapy (CRT) planning for lung cancer: Analysis of intrathoracic organ motion during extreme phases of breathing

Purpose: Conformal radiotherapy beams are defined on the basis of static co mputed tomography acquisitions by taking into account setup errors and orga n/tumor motion during breathing. In the absence of precise data, the size o f the margins is estimated arbitrarily. The objective of this study was to evaluate the amplitude of maximum intrathoracic organ motion during breathi ng. Methods and Materials: Twenty patients treated for non-small-cell lung canc er were included in the study: 10 patients at the Institut Curie with a per sonalized alpha cradle immobilization and 10 patients at Tenon Hospital wit h just the Posirest device below their arms. Three computed tomography acqu isitions were performed in the treatment position: the first during free br eathing and the other two during deep breath-hold inspiration and expiratio n. For each acquisition, the displacements of the various intrathoracic str uctures were measured in three dimensions. Results: Patients from the two centers were comparable in terms of age, wei ght, height, tumor site, and stage. In the overall population, the greatest displacements were observed for the diaphragm, and the smallest displaceme nts were observed for the lung apices and carina. The relative amplitude of motion was comparable between the two centers. The use of a personalized i mmobilization device reduced lateral thoracic movements (p < 0.02) and lung apex movements (p < 0.02). Conclusion: Intrathoracic organ movements during extreme phases of breathin g are considerable. Quantification of organ motion is necessary for definit ion of the safety margins. A personalized immobilization device appears to effectively reduce apical and lateral displacement. <(c)> 2001 Elsevier Sci ence Inc.