Analysis of which local set-up errors can be covered by a 5-mm margin for cone beam CT-guided radiotherapy for nasopharyngeal carcinoma.

OBJECTIVE

To analyse which local set-up errors can be covered by a 5-mm margin for cone beam computed tomography (CBCT)-guided radiotherapy in nasopharyngeal carcinoma (NPC).

METHODS

11 regions of interest (ROIs) were registered for 24 NPC patients, with a total of 323 CBCT scans. According to the registration results, clinical target volume-planning target volume (CTV-PTV)/organs at risk-planning risk volume (OAR-PRV) margin analysis; Pearson correlation analysis; Bland-Altman plots; and a receiver operating characteristic (ROC) analysis were used to investigate which local set-up errors of substructure can be represented by the PTV.

RESULTS

The clinical target volume-PTV/OAR-planning risk volume margins were less than 5 mm for C1-C4, mandible (M), and sphenoid sinus (S) with respect to PTV. C1-C4, M, and S exhibited significant correlations and consistencies in the mediolateral, superior-inferior, and anteroposterior (AP) directions and significant receiver operating characteristic analysis results in the anteroposterior direction.

CONCLUSION

Only the upper local set-up error of C1-C4, M, and S can be covered by a 5-mm margin for CBCT-guided NPC radiotherapy with a large ROI. Using these ROIs as an integral reference ROI is better than individual bony landmark. Advances in knowledge: This report is helpful to CBCT registration for NPC radiotherapy in clinical practice.