Cone beam CT for QA of synthetic CT in MRI only for prostate patients

Emilia Palmér; Emilia Persson; Petra Ambolt; Christian Gustafsson; Adalsteinn Gunnlaugsson; Lars E Olsson

doi:10.1002/acm2.12429

Cone beam CT for QA of synthetic CT in MRI only for prostate patients

J Appl Clin Med Phys. 2018 Nov;19(6):44-52. doi: 10.1002/acm2.12429. Epub 2018 Sep 4.

Authors

Emilia Palmér¹, Emilia Persson^{1

2}, Petra Ambolt¹, Christian Gustafsson^{1

2}, Adalsteinn Gunnlaugsson¹, Lars E Olsson^{1

2}

Affiliations

¹ Department of Hematology, Oncology, and Radiation Physics, Skåne University Hospital, Lund, Sweden.
² Department of Translational Medicine, Medical Radiation Physics, Lund University, Malmö, Sweden.

Abstract

Purpose: Magnetic resonance imaging (MRI)-only radiotherapy is performed without computed tomography (CT). A synthetic CT (sCT) is used for treatment planning. The aim of this study was to develop a clinically feasible quality assurance (QA) procedure for sCT using the kV-cone beam CT (CBCT), in an MRI-only workflow for prostate cancer patients.

Material and method: Three criteria were addressed; stability in Hounsfield Units (HUs), deviations in HUs between the CT and CBCT, and validation of the QA procedure. For the two first criteria, weekly phantom measurements were performed. For the third criteria, sCT, CT, and CBCT for ten patients were used. Treatment plans were created based on the sCT (MriPlanner^TM ). CT and CBCT images were registered to the sCT. The treatment plan was copied to the CT and CBCT and recalculated. Dose-volume histogram (DVH) metrics were used to evaluate dosimetric differences between the sCT plan and the recalculated CT and CBCT plans. HU distributions in sCT, CT, and CBCT were compared. Well-defined errors were introduced in the sCT for one patient to evaluate efficacy of the QA procedure.

Results: The kV-CBCT system was stable in HU over time (standard deviation <40 HU). Variation in HUs between CT and CBCT was <60 HU. The differences between sCT-CT and sCT-CBCT dose distributions were below or equal to 1.0%. The highest mean dose difference for the CT and CBCT dose distribution was 0.6%. No statistically significant difference was found between total mean dose deviations from recalculated CT and CBCT plans, except for femoral head. Comparing HU distributions, the CBCT appeared to be similar to the CT. All introduced errors were identified by the proposed QA procedure, except all tissue compartments assigned as water.

Conclusion: The results in this study shows that CBCT can be used as a clinically feasible QA procedure for MRI-only radiotherapy of prostate cancer patients.

Keywords: MRI, MRI only; cone beam CT; prostate cancer; quality assurance; synthetic CT.

MeSH terms

Aged
Aged, 80 and over
Cone-Beam Computed Tomography / methods*
Feasibility Studies
Follow-Up Studies
Humans
Image Processing, Computer-Assisted / methods
Magnetic Resonance Imaging / methods*
Male
Middle Aged
Phantoms, Imaging*
Prognosis
Prostatic Neoplasms / diagnostic imaging
Prostatic Neoplasms / pathology
Prostatic Neoplasms / radiotherapy*
Quality Assurance, Health Care / standards*
Radiotherapy Dosage
Radiotherapy Planning, Computer-Assisted / methods*
Radiotherapy, Intensity-Modulated / methods

Grants and funding

Gentle Radiotherapy