Room: ePoster Forums
Purpose: This study compared patient setup error on three different matching methods used in cone beam computed tomography (CBCT) during volumetric modulated arc therapy (VMAT) delivery for head and neck cancer.
Methods: For this study, twenty head and neck patients treated with 60 Gy in 30 fractions using VMAT technique were chosen. A total of 300 CBCT scans were acquired by institutional image guidance protocol for patient setup verification. Approved plan CT images were used as the reference image set in registration with the CBCT image set. Setup errors in mediolateral (ML), craniocaudal (CC) and anteroposterior (AP) direction were determined using manual matching (MM), bone matching (BM) and grey-scale matching (GM) between the reference CT images and onboard CBCT images. Patient setup verification was performed using clip-box registration (CBR). Considering the results from the GM method as the reference, two more matchings were performed using MM and BM in the offline mode. For comparison, systematic error (âˆ‘), random error (Ïƒ), mean displacement vector (R), mean setup error (M) and matching time (Mt) were analyzed. In addition, Post hoc Tukeyâ€™s honestly significant difference test was performed for multiple comparisons.
Results: The systematic and random errors were slightly less in MM as compared to BM and GM and no significant difference was observed (p>0.05). Similarly, maximum error, mean displacement error and mean setup errors were slightly less in MM as compared to BM and GM(p>0.05). In addition, the matching time was almost similar between MM, BM and GM and no significant time difference was observed (p>0.05). Moreover, multiple comparisons showed the insignificant difference in patient setup error (p>0.05).
Conclusion: For head and neck VMAT plan delivery, during CBCT, any of the three matching methods can be used for patient setup verification.