Purpose: Conformal radiotherapy beams are defined on the basis of static computed tomography acquisitions by taking into account setup errors and organ/tumor motion during breathing. In the absence of precise data, the size of the margins is estimated arbitrarily. The objective of this study was to evaluate the amplitude of maximum intrathoracic organ motion during breathing.
Methods and materials: Twenty patients treated for non-small-cell lung cancer were included in the study: 10 patients at the Institut Curie with a personalized alpha cradle immobilization and 10 patients at Tenon Hospital with just the Posirest device below their arms. Three computed tomography acquisitions were performed in the treatment position: the first during free breathing and the other two during deep breath-hold inspiration and expiration. For each acquisition, the displacements of the various intrathoracic structures were measured in three dimensions.
Results: Patients from the two centers were comparable in terms of age, weight, height, tumor site, and stage. In the overall population, the greatest displacements were observed for the diaphragm, and the smallest displacements were observed for the lung apices and carina. The relative amplitude of motion was comparable between the two centers. The use of a personalized immobilization device reduced lateral thoracic movements (p < 0.02) and lung apex movements (p < 0.02).
Conclusion: Intrathoracic organ movements during extreme phases of breathing are considerable. Quantification of organ motion is necessary for definition of the safety margins. A personalized immobilization device appears to effectively reduce apical and lateral displacement.