Evaluation of Hybrid PET/MRI for Gross Tumor Volume (GTV) Delineation in Colorectal Cancer Liver Metastases Radiotherapy

Abstract

Hybrid PET/MRI has been increasingly incorporated into the practice of radiation oncologists since it contains both anatomical and biological data and may bring about personalized radiation plans for each patient. The objective of this study was to evaluate the feasibility of GTV delineation from hybrid PET/MRI compared with that from currentpractice MRI during radiotherapy planning in patients with colorectal liver metastases. Patients and Methods: Twenty-four patients (thirty lesions) with colorectal liver metastases were prospectively enrolled in this study. Three physicians delineated the target volume with the most popular delineating methods-the visual method. First of all, differences among the three observers were assessed. The difference and correlation of GTV values obtained by MRI, PET, and hybrid PET/MRI were subjected to statistical analysis afterwards. Finally, the dice similarity coefficient (DSC) was calculated to assess the spatial overlap. Based on the value of DSC, we also evaluate the correlation between DSC and tumor size. GTV-MRI was set as a reference. Results: There was no significant difference among observers in GTV-MRI (F=0.118, p=0.889), GTV-PET (F=0.070, p=0.933) and GTV-PET/MRI (F=0.40, p=0.961). 83.33% of GTV-PET/MRI and 63.33% of GTV-PET were larger than the reference GTV-MRI. Statistical analysis revealed that GTV-PET/MRI (p<0.001) and GTV-PET (p<0.05) diverged statistically significantly from GTV-MRI. GTV-PET (r=0.992, p<0.001) and GTV-PET/MRI (r=0.997, p<0.001) were significantly related to GTV-MRI. The average DSC value between GTV-MRI and GTV-PET was 0.51 (range 0-0.90) and that between GTV-MRI and GTV-PET/MRI was 0.72 (range 0.42-0.90). There was a positive correlation between the DSC and GTV-MRI (r=0.851, p<0.05). Conclusion:With the database used, there is good agreement among observers. Hybrid PET/MRI in colorectal liver metastases radiotherapy may affect the GTV delineation. Moreover, the overlap degree between GTV-MRI and GTV-PET/MRI is higher and increases with volume.

Gross tumor volume delineation in primary prostate cancer on 18F-PSMA-1007 PET/MRI and 68Ga-PSMA-11 PET/MRI

“…Gibson et al recommended that an enlarged GTV margin defined by mpMRI may support focus-enhancing or therapeutic PCa [ 22 ]. Several studies of different tumor sites have also shown that that GTV based on PET/MRI is larger than that obtained from GTV-MRI because of the additional biological information provided by PET, which can reduce the risk of locational errors and affect GTV variation during radiotherapy, thus influencing the radiation dose administered to normal tissue [ 17 , 23 , 24 ]. Therefore, we hypothesized that a larger GTV-PET/MRI may result in the acquisition of a more complete target, allowing adequate irradiation of the lesion, and, thus, affecting the therapeutic effect.…”

“…In the 68 Ga subgroup, only GTV-MRI was significantly correlated with DSC. As a previous study showed, the spatial overlap between GTV-MRI and GTV-PET/MRI increases as the tumor volume increases [ 23 ]. Draulans C et al investigated the effect of tracer variability on the GTV profile and found that the distribution of SUV% in the prostate was significantly altered in 18 F-PSMA-based images, resulting in increased interobserver variability [ 27 ].…”

The use of PET/MRI in radiotherapy

“…With the introduction of the IMRT, the significance of accurate tumor volumes is re-emphasized. Since [ 18 F]-FDG PET/MRI can concurrently capture both tissue morphology and tumor metabolism information, it can accurately distinguish tumor tissue from neighboring tissues, making it valuable for accurate target identification in radiotherapy [ 55 ].…”

“…The effect of PET/MRI on GTV has been studied through the observation of the differences among GTV-MRI, GTV-PET, and GTV-PET/MRI [ 55 , 58 , 59 ]. Using GTV-MRI as a reference, Zhang et al evaluated the differences between GTV-PET and GTV-[ 18 F]-FDG PET/MRI in the delineation of colorectal liver metastases and found that GTV-[ 18 F]-FDG PET/MRI had the highest tumor volume [ 55 ].…”

Gross Tumor Volume Delineation in Primary Prostate Cancer on 18 F-PSMA-1007 PET/MRI and 68 Ga-PSMA-11 PET/MRI

“…or therapeutic PCa(Gibson E et al 2016). Several studies of different tumor sites have also shown that GTV based on PET/MRI are larger than GTV-MRI because of the additional biological information of PET, which can reduce the risk of locational errors and affect GTV variation during radiotherapy, thus in uencing the radiation dose administered to normal tissue(Ma JT et al 2017;Zhang YN et al 2021;Muijs CT et al 2009…”