• Lorenzo Falcinelli, Isabella Palumbo, Valentina Radicchia, Fabio Arcidiacono, Valentina Lancellotta, Giampaolo Montesi, Fabio Matrone, Claudio Zucchetti, Marta Marcantonini, Vittorio Bini, and Cynthia Aristei.
• 1 Department of Onco-Haematological and Gastroenterological Science, Radiation Oncology Division, Perugia General Hospital, Perugia, Italy.
• Br J Radiol. 2015 Jan 1; 88 (1056): 20150509.

ObjectiveIn radiotherapy treatment, planning target volume and organs at risk are contoured on kilovoltage CT (kVCT) images. Unlike MR images, kVCT does not provide precise information on target volume extension. Since neither kVCT nor MRI may be suitable for contouring in patients with ferrous hip prostheses, this study evaluated whether megavoltage CT (MVCT) reduced interobserver variability.MethodsTwo patients without hip prostheses and one patient (Patient 3) with hip prostheses were enrolled. Six radiation oncologists contoured prostate, rectum and bladder on kVCT (Patients 1 and 3), MRI (Patient 2) and MVCT images (Patient 3). MVCT was acquired with fine, normal and coarse modalities. Interobserver variability for each organ was analysed using conformity index (CI) and coefficient of variation (CV).ResultsIn patients without hip prostheses, CIs were higher in prostate contouring with MRI than with kVCT, indicating lower interobserver variability with MRI. Very slight variations were seen in rectum and bladder contouring. In the patient with hip prostheses (Patient 3), contouring on kVCT lowered CI and increased CV in the prostate, bladder and rectum. The differences were more marked in the prostate. Only fine modality MVCT reduced interobserver variability and only for the prostate.ConclusionEven though greater noise and less soft-tissue contrast increase contouring variability with MVCT than with kVCT, lack of artefacts on MVCT could provide better image definition by this modality in hip prosthesis patients in whom MRI is precluded.Advances In KnowledgeWe recommend the fine modality MVCT for contouring hip prostheses patients.

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