Esophageal cancer: Determination of internal target volume for conformal radiotherapy.
Résumé
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 20-40s 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 1cm. Cumulative distribution of GTV motion in absolute values showed that 95% of data ranged from 0 to 0.8cm. The correlation study demonstrated no specific relationship between respiratory and esophageal motions. CONCLUSION: The ITV margin for 3D conformal radiotherapy in esophageal cancer was 1cm 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.