Action Levels on Dose and Anatomic Variation (ALDAV) for Adaptive Radiation Therapy using Daily Offline Plan Evaluation: Preliminary Results.

PURPOSE: To develop action levels for re-planning to accommodate dosimetric variations resulting from anatomic changes during the course of treatments, using daily cone-beam computed tomography (CBCT).

METHODS: Daily or weekly CBCT images of 20 patients (10 head and neck, 5 lung, and 5 prostate cancers) who underwent re-simulation by physicians' clinical decisions mainly from the comparison of CBCTs, were used to determine action levels. The first CBCT image acquired prior to the first treatment was used as the reference image to rule out the effects of dose inaccuracy from the CBCT. The Pearson correlation of clinical target volume (CTV) was used as a parameter of anatomic variation. Parameters for action levels on dose and anatomic variation (ALDAVs) were deduced by comparing the parameters and the clinical decisions made for re-planning. A software tool was developed to automatically perform all of the procedures, including dose calculations, using the CBCT and plan evaluations.

RESULTS: Re-plans were clinically decided based on either significant dose or anatomic changes in 13 cases. The 7 cases that did not require re-planning showed dose differences <5%, and the Pearson correlation of the CTV was >75% for all fractions. A difference in planning target volume dose >5% or a difference in the image correlation coefficient of the CTV < 0.75 proved to be indicators for re-planning. Once the results of the CBCT plan met the re-planning criteria, the software tool automatically alerted the attending physician and physicist by both e-mail and pager so that the case could be examined closely.

CONCLUSION: Our study shows that a dose difference of 5% and/or anatomy variation at 0.75 Pearson correlations are practical ALDAVs for re-planning for the given data sets.