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

https://doi.org/10.1016/S0360-3016(01)01766-7Get rights and content

Abstract

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.

Introduction

Optimization of three-dimensional conformal radiotherapy of intrathoracic tumors is based largely on improvement of the localization of target volumes. Radiotherapy beams are defined on the basis of static computed tomography (CT) acquisitions, by taking into account the patient’s predictable movements from one session to the next and organ/tumor motion during breathing (1). In the absence of precise data, the width of the margins is estimated arbitrarily, potentially resulting in either excessive exposure of normal tissues or insufficient target volume coverage 2, 3, 4, 5.

In the context of the lung, the estimated target volume comprises the clinical target volume (CTV), together with the uncertainties related to internal organ motion during breathing and uncertainties related to placement of irradiation fields and patient movements (6). For some authors, tumor movements correspond to a modification of the macroscopic tumor volume, whereas for others, they are an integral part of the definition of the estimated target volume. This controversy is purely theoretical, because as the final objective is to define a volume that is entirely included in the 95% isodose (5).

ICRU Report No. 62 distinguishes an internal target volume, taking into account movements of the CTV during breathing and a supplementary volume by addition of an external margin related to errors of irradiation beam positioning (6). Few data are available to define these volumes 4, 7, 8. The main objective of this study was to evaluate the amplitude of maximum intrathoracic organ motion during breathing. We also tried to determine whether the use of a personalized immobilization device had an impact on the amplitude of these respiratory movements.

Section snippets

Patients

Twenty patients treated for inoperable non-small-cell lung cancer were included in the study: 10 patients treated at the Institut Curie with a personalized alpha cradle immobilization and an armrest above the head, and 10 patients treated at Tenon Hospital, with the arms above the head held with a Posirest device below the arms. Table 1 presents the characteristics of these 20 patients.

Thirty-five measurements were performed per patient and per acquisition. The patients from the two centers

Measurement comparisons of thoracic displacements at deep inspiration and deep expiration

Table 2, Table 3, Table 4, Table 5 summarize the amplitudes of the various thoracic displacements at each institution. In the overall study population, the greatest displacements were observed for the diaphragm in the craniocaudal direction, with mean values between inspiration and expiration of 34.25 ± 20.4 mm and a maximum amplitude of 67.8 mm (Table 2).

The smallest displacements were observed for the lung apices (Table 3). The differences between inspiration and expiration in the three

Discussion

Movements of the tumor and intrathoracic organs during breathing are a potential cause of failure of radiotherapy for lung cancers 11, 12. These movements lead to uncertainty responsible for insufficient coverage of the limits of the CTV and, consequently, the delivery of an insufficient dose to destroy tumor cells 2, 4, 7.

Four approaches can be proposed to reduce the uncertainties related to respiratory movements (13):

  • Measure tumor movements, to take them into account in the final choice of

Conclusion

Movements of thoracic structures during extreme phases of breathing are considerable, particularly in regions close to the diaphragm. Identification and quantification of these movements are necessary to define the safety margin around the clinical target volume. A personalized immobilization device molded around the patient, combined with an armrest, appears to effectively reduce apical and lateral displacements, resulting in a reduction of the volume of healthy lung irradiated. Measurement

Acknowledgements

The authors thank Drs. F. Reboul, R. Garcia, and R. Oozeer at Clinique Sainte Catherine (Avignon, France) for their technical support in the conception of our immobilization device.

References (26)

  • J.W Wong et al.

    The use of active breathing control (ABC) to reduce margin for breathing motion

    Int J Radiat Oncol Biol Phys

    (1999)
  • I Rabinowitz et al.

    Accuracy of radiation field alignment in clinical practice

    Int J Radiat Oncol Biol Phys

    (1985)
  • P Munro

    Portal imaging technologyPast, present, and future

    Semin Radiat Oncol

    (1995)
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