Room: Pins Room | Hall 2
Purpose: to analyze the frequency and efficiency on the use of 6DOF couch during HN radiation treatment
Methods: Daily setup data of 128 HN patients who were previously treated on truebeam platform with 6DOF couch correction was retrieved from Record and Verification system and analyzed. On average each patient received 34 fractions. These patients were initially set up with laser marks on the masks and verified by orthogonal KV pairs or CBCT prior to their daily treatments. Frequency of image modalities was noted on prescription. Half of these treatment fractions were verified by CBCT, mostly based on bony anatomies. In addition to translational shift, rotational correction was performed whenever CBCT indicated angle correction. The statistics of shifts based on CBCT and KVs were reported and compared. Correlation between couch rotational corrections and translational shift was calculated.
Results: The translational shifts from KV were similar to CBCT, although range was larger with CBCT(-1.9-1.4 cm) compared with KV(-1.1-0.9 cm). For fractions imaged with CBCT, angle corrections were applied on 72% of fractions. The average angle correction with CBCT is around zero with a standard deviation of 0.67-0.94Â°(range -3.0-3.0Â°), where 1-4.5% of fractions with over 2Â° and 7.4-22% over 1Â°. Among all angles, pitch was most often to be corrected. Group analysis did not indicate any dependence of shifts on number of fractions. Correlations between angles and translational shifts are relatively small, except that between pitch and Anterior-Posterior (AP) shift (r=0.47, p<0.005). For fraction with AP translational shift over 5 mm, the pitch correction is 1.21oÂ±1.04Â°.
Conclusion: 6DOF couch are frequently used in HN radiation with CBCT. There is moderate correlation between pitch and AP shift. This suggests that therapists should apply pitch with caution. Guideline needs to be set in terms of re-verification in case of large angle correction.