Comparison of Different Registration Methods on Patient Set-Up Error During Volumetric Modulated Arc Therapy Using Cone-Beam CT Imaging for Lung Cancer

Background: The three-dimensional image-guided radiation therapy is very important in volumetric modulated arc therapy (VMAT) to enhance accuracy throughout the course of a patient's radiation treatment. The image guidance can ensure the safe administration of prescribed radiation dose to the patient. Aim: This study investigated patient set-up uncertainties based on three different registration methods in cone bean CT (CBCT) using volumetric modulated arc therapy (VMAT) for different clinical sites. Methods: A total of 396 CBCT performed for lung VMAT plan for patient set-up verification as per institution image guidance protocol. The approved CT images were transferred from treatment planning system (TPS) to x-ray volumetric imaging system (XVI) for reference image registration. The set-up errors in mediolateral (ML), craniocaudal (CC) and anterioposterior (AP) direction were determined using grayscale matching between the reference CT image and onboard CBCT images. For the current study, patient set-up verification was performed based on clip-box registration (CBR) for image matching. By considering clip-box registration as a reference, other two registration methods of mask registration (MR) and dual registration (DR) (clip-box and mask) were performed for comparison. To compare three registration methods, systematic error (∑), random error (σ), mean displacement, mean set-up error and maximum error were analyzed. Results: The systemic and random errors were less in clip-box registration as compared with other two registration ( P > 0.05). Similarly, maximum error, mean displacement error and mean set-up errors were observed less in clip-box registration as compared with mask and dual registration ( P > 0.05). However, statically no significant difference was observed between three different registration methods ( P > 0.05). Conclusion: All three registration methods can be used for patient set-up accuracy for lung VMAT plan. However, the current study suggested that clip-box method will be more efficient as compared with mask and dual registration methods.

Study to Compare the Effect of Different Registration Methods on Patient Setup Uncertainties in Cone-beam Computed Tomography during Volumetric Modulated Arc Therapy for Breast Cancer Patients

PURPOSE

This study compared three different methods used in registering cone-beam computed tomography (CBCT) image set with planning CT image set for determining patient setup uncertainties during volumetric modulated arc therapy (VMAT) for breast cancer patients.

MATERIALS AND METHODS

Seven breast cancer patients treated with 50 Gy in 25 fractions using VMAT technique were chosen for this study. A total of 105 CBCT scans were acquired by image guidance protocol for patient setup verification. Approved plans' CT images were used as the reference image sets for registration with their corresponding CBCT image sets. Setup errors in mediolateral, craniocaudal, and anteroposterior direction were determined using gray-scale matching between the reference CT images and onboard CBCT images. Patient setup verification was performed using clip-box registration (CBR) method during online imaging. Considering the CBR method as the reference, two more registrations were performed using mask registration (MR) method and dual registration (DR) (CBR + MR) method in the offline mode. For comparison, systematic error (∑), random error (σ), mean displacement vector (R), mean setup error (M), and registration time (R t) were analyzed. Post hoc Tukey's honest significant difference test was performed for multiple comparisons.

RESULTS

Systematic and random errors were less in CBR as compared to MR and DR (P > 0.05). The mean displacement error and mean setup errors were less in CBR as compared to MR and DR (P > 0.05). Increased R t was observed in DR as compared to CBR and MR (P < 0.05). In addition, multiple comparisons did not show any significant difference in patient setup error (P > 0.05).

CONCLUSION

For breast VMAT plan delivery, all three registration methods show insignificant variation in patient setup error. One can use any of the three registration methods for patient setup verification.