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Esophageal cancer: determination of internal target volume for conformal radiotherapy
1Service de Radiothérapie, CHU Besançon, Bd Fleming, Besançon cedex, France. lorchel.fabrice@wanadoo.fr
Background And Purpose:
To evaluate esophageal tumor and OAR movement during the respiratory cycle in order to obtain optimal values for ITV and PRV. To correlate tumor motion with chest wall displacement - information of value in the free-breathing gating system.
Material And Method:
Inclusion criteria were: histologically proven squamous-cell carcinoma (SCC) or adenocarcinoma at stage T3 - T4 NX or TX N1 M0 according to the UICC 1997 classification. Two spiral scans were performed with breath-hold respiration under spirometric control: one at end expiration (EBH) and the other at end inspiration (IBH). Displacements between exhalation and inhalation were calculated according to ICRU report 42 recommendations. For the correlation study, CT-scan acquisition was performed at the isocenter over a 20 - 40 s period. After Fourier Transform, frequency spectra for amplitude and phase of tumor and chest wall motions were performed for each patient.
Results:
Cumulative distribution of CTV motion in absolute values showed that 95% of data ranged from 0 to 1 cm. Cumulative distribution of GTV motion in absolute values showed that 95% of data ranged from 0 to 0.8 cm. The correlation study demonstrated no specific relationship between respiratory and esophageal motions.
Conclusion:
The ITV margin for 3D conformal radiotherapy in esophageal cancer was 1 cm when 95% of motions were taken into account in this clinical study involving eight patients. Before using a free-breathing gating system, the correlation between external markers and target displacement during irradiation must be established for each patient.
