Feasibility of magnetic resonance imaging-only rectum radiotherapy with a commercial synthetic computed tomography generation solution

Abstract

A B S T R A C TBackground and purpose: Synthetic computed tomography (sCT) images enable magnetic resonance (MR)-based dose calculations. This work investigated whether a commercially available sCT generation solution was suitable for accurate dose calculations and position verification on patients with rectal cancer. Material and methods: For twenty rectal cancer patients computed tomography (CT) images were rigidly registered to sCT images. Clinical volumetric modulated arc therapy plans were recalculated on registered CT and sCT images. Dose deviations were determined through gamma and voxelwise analysis. The impact on position verification was investigated by identifying differences in translations and rotation between cone-beam CT (CBCT) to CT and CBCT to sCT registrations. Results: Across twenty patients, within a threshold of 90% of the prescription dose, a gamma analysis (2%, 2 mm) mean pass rate of 95.2 ± 4.0% ( ± 1 ) and mean dose deviation of −0.3 ± 0.2% of prescription dose were obtained. The mean difference of translations and rotations over ten patients (76 CBCTs) was < 1 mm and < 0.5°in all directions. In the sole posterior-anterior direction a mean systematic shift of 0.7 ± 0.6 mm was found. Conclusions: Accurate MR-based dose calculations using a commercial sCT generation method were clinically feasible for treatment of rectal cancer patients. The accuracy of position verification was clinically acceptable. However, before clinical implementation future investigations will be performed to determine the origin of the systematic shift.

Assessment of dosimetric and positioning accuracy of a magnetic resonance imaging-only solution for external beam radiotherapy of pelvic anatomy

“…Wang et al [21] obtained median gamma-index pass-rate of 99.9% (99.4–100.0%) and medians of the dose difference averages were 0.21 Gy (0.2–0.3 Gy). In addition, Maspero et al [20] evaluated the feasibility of the same method used in this study (sCTb) for rectal cancer patients obtaining the mean gamma-index pass-rate of 95.2 (4.0)% and mean dose deviation of −0.3 (0.2)% of prescription dose. Liu et al [22] evaluated the sCT method for gynecological cancer patients obtaining the PTV dose deviation of 0.2 (0.4) Gy for D 0.5cc and 0.3 (0.3) Gy for D 99% .…”

“…The filling was equivalent to density override by water in the treatment planning system (TPS) corresponding to a clinical practice used with patients encompassing large air volumes at our institution. The same approach was used [20] or suggested to be used [29] in the dosimetric evaluations of MRI-only methods in order to avoid confounding dosimetric differences not related to the sCT methods.…”

“… [16] , [17] , [18] , [19] ). Two recent studies have evaluated the feasibility of MRI-only workflow for rectal cancers [20] , [21] . However, to the best of our knowledge, only the dosimetric accuracy has been evaluated for gynecological cancers [22] , [23] , [24] .…”

Clinical implementation of MRI-based organs-at-risk auto-segmentation with convolutional networks for prostate radiotherapy

“…Dixon images were generated as part of a proprietary solution (MRCAT, rev. 257, Philips Healthcare, Finland) that enabled MR-based dose calculation for patients with prostate cancer [36,37]. The imaging parameters, reported in Table 1, were locked by the vendor; therefore, they were stable through the whole study.…”

Imaging science and development in modern high-precision radiotherapy

“…MRI offers higher soft tissue contrast for tumor and organ definition but lacks information about electron density, which is a prerequisite for accurate dose calculation. To overcome this, several groups have proposed strategies to generate synthetic CT data sets derived solely from MRI data [53] , [54] , [55] , [56] . First dosimetric analysis of such MR-only workflow showed quite promising results for tumors in the pelvic region [57] .…”