Esophageal cancer: Determination of internal target volume for conformal radiotherapy

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. 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. 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. 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.