<abstract xmlns="http://www.w3.org/1999/xhtml">

<sec><h3>Background</h3>
Hybrid MRI linear accelerators (MR-Linac) might enable individualized online adaptation of radiotherapy using quantitative MRI sequences as diffusion-weighted imaging (DWI). The purpose of this study was to investigate the dynamics of lesion apparent diffusion coefficient (ADC) in patients with prostate cancer undergoing MR-guided radiation therapy (MRgRT) on a 1.5T MR-Linac. The ADC values at a diagnostic 3T MRI scanner were used as the reference standard.
</sec>
<sec><h3>Patients and and methods</h3>
In this prospective single-center study, patients with biopsy-confirmed prostate cancer who underwent both an MRI exam at a 3T scanner (MRI3T) and an exam at a 1.5T MR-Linac (MRL) at baseline and during radiotherapy were included. Lesion ADC values were measured by a radiologist and a radiation oncologist on the slice with the largest lesion. ADC values were compared before <italic>vs</italic>. during radiotherapy (during the second week) on both systems via paired t-tests. Furthermore, Pearson correlation coefficient and inter-reader agreement were computed.
</sec>
<sec><h3>Results</h3>
A total of nine male patients aged 67 ± 6 years [range 60 – 67 years] were included. In seven patients, the cancerous lesion was in the peripheral zone, and in two patients the lesion was in the transition zone. Inter-reader reliability regarding lesion ADC measurement was excellent with an intraclass correlation coefficient of (ICC) > 0.90 both at baseline and during radiotherapy. Thus, the results of the first reader will be reported. In both systems, there was a statistically significant elevation of lesion ADC during radiotherapy (mean MRL-ADC at baseline was 0.97 ± 0.18 × 10−3 mm2/s <italic>vs</italic>. mean MRL-ADC during radiotherapy 1.38 ± 0.3 × 10−3 mm2/s, yielding a mean lesion ADC elevation of 0.41 ± 0.20 × 10−3 mm2/s, p &lt; 0.001). Mean MRI3T-ADC at baseline was 0.78 ± 0.165 × 10−3 mm2/s <italic>vs</italic>. mean MRI3T-ADC during radiotherapy 0.99 ± 0.175 × 10−3 mm2/s, yielding a mean lesion ADC elevation of 0.21 ± 0.96 × 10−3 mm2/s p &lt; 0.001). The absolute ADC values from MRL were consistently significantly higher than those from MRI3T at baseline and during radiotherapy (p &lt; = 0.001). However, there was a strong positive correlation between MRL-ADC and MRI3T-ADC at baseline (<italic>r</italic> = 0.798, p = 0.01) and during radiotherapy (<italic>r</italic> = 0.863, p = 0.003).
</sec>
<sec><h3>Conclusions</h3>
Lesion ADC as measured on MRL increased significantly during radiotherapy and ADC measurements of lesions on both systems showed similar dynamics. This indicates that lesion ADC as measured on the MRL may be used as a biomarker for evaluation of treatment response. In contrast, absolute ADC values as calculated by the algorithm of the manufacturer of the MRL showed systematic deviations from values obtained on a diagnostic 3T MRI system. These preliminary findings are promising but need large-scale validation. Once validated, lesion ADC on MRL might be used for real-time assessment of tumor response in patients with prostate cancer undergoing MR-guided radiation therapy.
</sec>
</abstract>

Background
Hybrid MRI linear accelerators (MR-Linac) might enable individualized online adaptation of radiotherapy using quantitative MRI sequences as diffusion-weighted imaging (DWI). The purpose of this study was to investigate the dynamics of lesion apparent diffusion coefficient (ADC) in patients with prostate cancer undergoing MR-guided radiation therapy (MRgRT) on a 1.5T MR-Linac. The ADC values at a diagnostic 3T MRI scanner were used as the reference standard.

Patients and and methods
In this prospective single-center study, patients with biopsy-confirmed prostate cancer who underwent both an MRI exam at a 3T scanner (MRI3T) and an exam at a 1.5T MR-Linac (MRL) at baseline and during radiotherapy were included. Lesion ADC values were measured by a radiologist and a radiation oncologist on the slice with the largest lesion. ADC values were compared before vs. during radiotherapy (during the second week) on both systems via paired t-tests. Furthermore, Pearson correlation coefficient and inter-reader agreement were computed.

Results
A total of nine male patients aged 67 ± 6 years [range 60 – 67 years] were included. In seven patients, the cancerous lesion was in the peripheral zone, and in two patients the lesion was in the transition zone. Inter-reader reliability regarding lesion ADC measurement was excellent with an intraclass correlation coefficient of (ICC) > 0.90 both at baseline and during radiotherapy. Thus, the results of the first reader will be reported. In both systems, there was a statistically significant elevation of lesion ADC during radiotherapy (mean MRL-ADC at baseline was 0.97 ± 0.18 × 10−3 mm2/s vs. mean MRL-ADC during radiotherapy 1.38 ± 0.3 × 10−3 mm2/s, yielding a mean lesion ADC elevation of 0.41 ± 0.20 × 10−3 mm2/s, p < 0.001). Mean MRI3T-ADC at baseline was 0.78 ± 0.165 × 10−3 mm2/s vs. mean MRI3T-ADC during radiotherapy 0.99 ± 0.175 × 10−3 mm2/s, yielding a mean lesion ADC elevation of 0.21 ± 0.96 × 10−3 mm2/s p < 0.001). The absolute ADC values from MRL were consistently significantly higher than those from MRI3T at baseline and during radiotherapy (p < = 0.001). However, there was a strong positive correlation between MRL-ADC and MRI3T-ADC at baseline (r = 0.798, p = 0.01) and during radiotherapy (r = 0.863, p = 0.003).

Conclusions
Lesion ADC as measured on MRL increased significantly during radiotherapy and ADC measurements of lesions on both systems showed similar dynamics. This indicates that lesion ADC as measured on the MRL may be used as a biomarker for evaluation of treatment response. In contrast, absolute ADC values as calculated by the algorithm of the manufacturer of the MRL showed systematic deviations from values obtained on a diagnostic 3T MRI system. These preliminary findings are promising but need large-scale validation. Once validated, lesion ADC on MRL might be used for real-time assessment of tumor response in patients with prostate cancer undergoing MR-guided radiation therapy.

Longitudinal monitoring of Apparent Diffusion Coefficient (ADC) in patients with prostate cancer undergoing MR-guided radiotherapy on an MR-Linac at 1.5 T: a prospective feasibility study

Department of Diagnostic and Interventional Radiology

Section for Experimental Radiology, Department of Radiology

Section for Biomedical Physics, Department of Radiation Oncology

Cluster of Excellence iFIT (EXC 2180) “Image Guided and Functionally Instructed Tumor Therapies”

Radiology and Oncology

This work is licensed under the Creative Commons Attribution 4.0 International License.

Background
Hybrid MRI linear accelerators (MR-Linac) might enable individualized online adaptation of radiotherapy using quantitative MRI sequences as...

Longitudinal monitoring of Apparent Diffusion Coefficient (ADC) in patients with prostate cancer undergoing MR-guided radiotherapy on an MR-Linac at 1.5 T: a prospective feasibility study

Article Category: Research Article

Publicado en línea: 21 jun 2023

Páginas: 184 - 190

Recibido: 20 ene 2023

Aceptado: 30 mar 2023

DOI: https://doi.org/10.2478/raon-2023-0020

Palabras clave
prostate carcinoma, MRI, adaptive radiotherapy, image guidance, MR-Linac, ADC

© 2023 Haidara Almansour et al., published by Sciendo

This work is licensed under the Creative Commons Attribution 4.0 International License.

FIGURE 1.

FIGURE 2.

FIGURE 3.

Longitudinal monitoring of Apparent Diffusion Coefficient (ADC) in patients with prostate cancer undergoing MR-guided radiotherapy on an MR-Linac at 1.5 T: a prospective feasibility study

Article Category: Research Article

Publicado en línea: 21 jun 2023

Páginas: 184 - 190

Recibido: 20 ene 2023

Aceptado: 30 mar 2023

DOI: https://doi.org/10.2478/raon-2023-0020

Palabras claveprostate carcinoma, MRI, adaptive radiotherapy, image guidance, MR-Linac, ADC

© 2023 Haidara Almansour et al., published by Sciendo

This work is licensed under the Creative Commons Attribution 4.0 International License.

FIGURE 1.

FIGURE 2.

FIGURE 3.

Palabras clave
prostate carcinoma, MRI, adaptive radiotherapy, image guidance, MR-Linac, ADC