Changes in Tumor Volume of Sacral Chordoma After Carbon Ion Radiotherapy

OBJECTIVE:: We evaluated changes in tumor volume in cases of sacral chordoma after carbon ion radiotherapy. METHODS:: Thirty-four patients with sacral chordoma underwent carbon ion radiotherapy between June 1996 and June 2003. We assessed 23 patients without previous surgery using T2-weighted magnetic resonance imaging. The tumor volume was calculated semiautomatically. RESULTS:: Two cases showed local recurrence. The median interval of this examination was 46 months. At the end of the treatment, the tumor showed an enlargement larger than 10% of its volume in 13 of the 23 cases, no change in 4 cases, and regression in 6 cases. At the last examination, 20 cases showed a reduction in tumor volume, and the median ratio, determined as the tumor volume at the last examination divided by that before the treatment, was 0.36. CONCLUSIONS:: An increase in tumor volume at the end of the treatment does not indicate the ineffectiveness of carbon ion radiotherapy.