Automated replication of cone beam CT-guided treatments in the Pinnacle(3) treatment planning system for adaptive radiotherapy.

INTRODUCTION: Time-consuming manual methods have been required to register cone-beam computed tomography (CBCT) images with plans in the Pinnacle(3) treatment planning system in order to replicate delivered treatments for adaptive radiotherapy. These methods rely on fiducial marker (FM) placement during CBCT acquisition or the image mid-point to localise the image isocentre. A quality assurance study was conducted to validate an automated CBCT-plan registration method utilising the Digital Imaging and Communications in Medicine (DICOM) Structure Set (RS) and Spatial Registration (RE) files created during online image-guided radiotherapy (IGRT). METHODS: CBCTs of a phantom were acquired with FMs and predetermined setup errors using various online IGRT workflows. The CBCTs, DICOM RS and RE files were imported into Pinnacle(3) plans of the phantom and the resulting automated CBCT-plan registrations were compared to existing manual methods. A clinical protocol for the automated method was subsequently developed and tested retrospectively using CBCTs and plans for six bladder patients. RESULTS: The automated CBCT-plan registration method was successfully applied to thirty-four phantom CBCT images acquired with an online 0 mm action level workflow. Ten CBCTs acquired with other IGRT workflows required manual workarounds. This was addressed during the development and testing of the clinical protocol using twenty-eight patient CBCTs. The automated CBCT-plan registrations were instantaneous, replicating delivered treatments in Pinnacle(3) with errors of ±0.5 mm. These errors were comparable to mid-point-dependant manual registrations but superior to FM-dependant manual registrations. CONCLUSION: The automated CBCT-plan registration method quickly and reliably replicates delivered treatments in Pinnacle(3) for adaptive radiotherapy.

A prone technique for treatment of the breast, supraclavicular and axillary nodes.

Radiation therapy to women with large pendulous breasts presents dosimetric challenges when the whole breast (WB) and supraclavicular and axillary (SCF + AX) nodes need to be encompassed. The aim of this case study was to demonstrate the feasibility of planning and treating a pendulous breasted patient in the prone position. Computerised tomography (CT) images were acquired of the patient in both the prone and supine positions. A Perspex plate was added to the CDR Systems Inc. (Calgary, Canada) prone breastboard to minimize SCF + AX contour variations. Dosimetry was performed on both CT scans and the resultant treatment plans were evaluated for conformity, homogeneity, dose to the lung and maximum doses to the spinal cord (SC) and irradiated volume. The daily set-up in the prone position was monitored for stability and reproducibility. The patient completed her treatment course in the prone position. Minimal daily interventions were required to ensure the position was reproduced. Grade 3 skin toxicity was recorded in the SCF + AX region where the Perspex plate was added to the prone positioning device. There was minimal difference in dosimetry between prone and supine plans in the SCF + AX region. The prone WB plan showed improved homogeneity (prone 0.15; supine 0.22) and conformity (prone 0.90; supine 0.77). A simple addition to the breastboard has enabled a pendulous breasted woman with SC + AX involvement to be treated in the prone position. Set-up of this technique is achievable on a daily basis with minimal impact on workflow. It is a feasible alternative to supine treatment for this patient group.