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Factors Affecting Dose Calculation Accuracy Assessments of MRCAT-Based Prostate MR-Only Radiation Therapy

R Kemppainen1 , T Kiljunen2 , M Pesola3 , J Keyrilainen4*, (1) Philips MR Therapy, Vantaa, Finland,(2) Docrates Cancer Center, Helsinki, Finland, (3) Philips MR Therapy, Vantaa, Finland, (4) Department of Oncology and Radiotherapy, Turku University Hospital, Turku, Finland


(Tuesday, 7/31/2018) 9:30 AM - 10:00 AM

Room: Exhibit Hall | Forum 6

Purpose: To quantify the impact of factors affecting commissioning and dose accuracy assessment of MR-only radiation therapy.

Methods: Twenty prostate cancer (T1-3) patients treated with external beam radiation therapy (EBRT) were included in the study. The dose calculation accuracy assessment was performed by comparing the plans calculated with CT and MRCAT (Magnetic resonance for calculating attenuation) images for different treatment techniques (CRT, IMRT, VMAT) and beam energies (6-18 MV). In addition, the impact of HU-to density calibration based on different phantoms was evaluated. Assessment was based on dose-volume histogram and dose distribution metrics.

Results: The mean relative difference between CT and MRCAT dose calculation was between 0.60 (± 0.26) and 1.08 (± 0.42) being lowest for 10 MV VMAT and highest for 6 MV IMRT plans. For OARs, the mean dose differences were clinically acceptable being between 0.28 (± 2.10) to 2.06 (± 2.60) and -0.16 (±1.13) to 0.32 (±0.99) for bladder and rectum, respectively. The difference in mean relative difference was found to be significant only between VMAT and IMRT techniques (p=0.01). For all treatment techniques our analysis showed statistically significant difference in mean relative difference between different beam energies.

Conclusion: The MRCAT provided dosimetrically accurate pseudo-CT images and clinically feasible workflow which can be used instead of traditional CT-images for the EBRT planning of prostate cancer. The difference in mean dose for both PTV and OARs was clinically acceptable for all treatment techniques and energies when compared to CT-based planning. During commissioning, appropriateness of the HU-to-density conversion shall be verified with dosimetric measurements as different calibration phantoms might give differing results.


Not Applicable / None Entered.


IM/TH- MRI in Radiation Therapy: MRI for treatment planning

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