Dose recalculation in megavoltage cone-beam CT for treatment evaluation: removal of cupping and truncation artefacts in scans of the thorax and abdomen.
OBJECTIVE
To correct megavoltage cone-beam CT (MVCBCT) images of the thorax and abdomen for cupping and truncation artefacts to reconstruct the 3D-delivered dose distribution for treatment evaluation.


METHODS
MVCBCT scans of three phantoms, three lung and two rectal cancer patients were acquired. The cone-beam projection images were iteratively corrected for cupping and truncation artefacts and the resulting primary transmission was used for cone-beam reconstruction. The reconstructed scans were merged into the planning CT scan (MVCBCT+). Dose distributions of clinical IMRT, stereotactic and conformal treatment plans were recalculated on the uncorrected and corrected MVCBCT+ scans using the treatment planning system and compared to the planned dose distribution.


RESULTS
The dose distributions on the corrected MVCBCT+ of the phantoms were accurate for 99% of the voxels within 2% or 2mm. Using this method the errors in mean GTV dose reduced from about 10% to 1% for the patients.


CONCLUSIONS
The method corrects cupping and truncation artefacts in cone-beam scans of the thorax and abdomen in addition to head-and-neck (demonstrated previously). The corrected scans can be used to calculate the influence of anatomical changes on the 3D-delivered dose distribution.
Petit
Steven F
SF
Department of Radiation Oncology (MAASTRO Clinic), Maastricht University Medical Center (MUMC+), Maastricht, The Netherlands. steven.petit@maastro.nl
van Elmpt
Wouter J C
WJ
Lambin
Philippe
P
Dekker
André L A J
AL
D000005:Abdomen / Q000000981:diagnostic imaging*; D000465:Algorithms; D016477:Artifacts; D054893:Cone-Beam Computed Tomography; D006801:Humans; D008175:Lung Neoplasms / Q000532:radiotherapy*; D019047:Phantoms, Imaging; D011879:Radiotherapy Dosage; D012004:Rectal Neoplasms / Q000532:radiotherapy*; D013909:Thorax / Q000000981:diagnostic imaging*; D016896:Treatment Outcome; D014463:Ultrasonography