Acute esophagitis results in esophageal swelling. Here we evaluate the effect of this response on DVH metrics calculated throughout the course of radiation therapy.
Twenty-nine NSCLC patients were identified who received weekly CT imaging, and varying esophagitis grades (11 grade0 patients, 12 grade2 patients, 6 grade3 patients), using CTCAE scoring criteria. Deformable image registration was used to map the planning esophagus contour to the weekly CT images. Treatment plans were recalculated on each weekly 4DCT and DVH metrics for the esophagus were compared to the delivered treatment plan. DVH metrics were also extracted for esophagus planning-at-risk volumes (PRV) with 1-3mm uniform expansions.
The esophagus V50 increased as the treatment progressed by 2.3±0.7cc and 9.0±1.1cc, for the grade 0 and grade 2/3 patients, respectively. The mean esophageal dose (MED) increased by 3.5±0.9Gy, and 8.0±1.1Gy for the grade 0 and grade 2/3 patients, respectively. In some cases where the planned V50 was similar, it remained the same at the end of treatment for grade 0 cases, but increased for higher grade cases. These apparent changes in delivered dose, as expressed by the DVH, are mostly attributed to volume changes in the regions of esophagitis. In addition, portions of the esophagus of some patients moved into highdose regions. The 2mm PRV was able to account for these differences in all but 1 of the 18 G2/3 patients. The 1mm PRV produced the closest DVH metrics calculated from the average weekly plans compared to the true treatment plan.
Esophagus radiation response affects DVH parameters throughout treatment, especially patients with high toxicity. This effect must be considered when comparing DVHs calculated using daily IGRT CT images with those from the original planning CT (e.g. for adaptive planning). Adding a margin to the esophagus can account for variation in DVH metrics.
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