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

Abstract

Background We aimed to assess the clinical value of 18F-PSMA-1007 and 68Ga-PSMA-11 PET/MRI in the gross tumor volume (GTV) delineation of radiotherapy for prostate cancer (PCa). Methods Sixty-nine patients were retrospectively enrolled (57 in the 18F subgroup and 12 in the 68Ga subgroup). Three physicians delineated the GTV and tumor length by the visual method and threshold method with thresholds of 30%, 40%, 50%, and 60% SUVmax. The volume correlation and differences in GTVs were assessed. The dice similarity coefficient (DSC) was applied to estimate the spatial overlap between GTVs. For 51 patients undergoing radical prostatectomy, the tumor length (Lpath) of the maximum area was measured, and compared with the longest tumor length obtained based on the images (LMRI, LPET/MRI, LPET, LPET30%, LPET40%, LPET50%, LPET60%) to determine the best delineation method. Results In the 18F subgroup, (1) GTV-PET/MRI (p < 0.001) was significantly different from the reference GTV-MRI. DSC between them was > 0.7. (2) GTV-MRI (R2 = 0.462, p < 0.05) was the influencing factor of DSC. In the 68Ga subgroup, (1) GTV-PET/MRI (p < 0.05) was significantly different from the reference GTV-MRI. DSC between them was > 0.7. (2) There was a significant correlation between GTV-MRI (r = 0.580, p < 0.05) and DSC. The longest tumor length measured by PET/MRI was in good agreement with that measured by histopathological analysis in both subgroups. Conclusion It is feasible to visually delineate GTV on PSMA PET/MRI in PCa radiotherapy, and we emphasize the utility of PET/MRI fusion images in GTV delineation. In addition, the overlap degree was the highest between GTV-MRI and GTV-PET/MRI, and it increased with increasing volume.

Key learnings from concordant systematic biopsies in prostate‐specific membrane antigen positron emission tomography/computed tomography‐guided prostate biopsies: Enhancing targeting accuracy

“…PSMA‐PET/CT imaging suffers from relatively limited spatial resolution, which can lead to blurring and volume artifacts due to technical constraints. In addition, fusion of PSMA‐PET/CT images with transrectal ultrasound may introduce inaccuracies due to factors such as patient positioning and the use of transrectal ultrasound probes, as noted by Zhang et al 24 As a result, the accurate delineation of ROIs, prostate margins, and zone separations becomes an even more difficult task with PSMA‐PET/CT imaging compared to MRI 25 . To overcome these issues, recent studies have reported encouraging results for prebiopsy PSMA‐PET/MRI, suggesting that this hybrid imaging modality may have the potential to improve spatial resolution 26,27 .…”

Variability of radiotherapy volume delineation: PSMA PET/MRI and MRI based clinical target volume and lymph node target volume for high-risk prostate cancer

“…The spatial analysis index indicated that the overlap between the two GTVn was low, and when combined with the analysis of sensitivity and specificity for lymph nodes, we confidently concluded that the GTVn contouring on PSMA PET/MRI is more accurate and may help to reduce lymph node recurrence. In combination with a recent research effort conducted by our group, which showed that it was feasible to visually delineate GTV on PSMA PET/MRI in PCa radiotherapy [ 21 ]. Our investigation has shown that it is feasible to delineate GTVn and CTV on PSMA PET/MRI.…”

“…The above target areas were outlined manually on MRI and PET/MR fusion images based on axial T2-weighted MRI. The method of image acquisition and the sequence selected for target delineation is similar to a previous research project done by our group, which was based on assessing the clinical value of 18F-PSMA-1007 and 68 Ga-PSMA-11 PET/MRI in the gross tumour volume (GTV) delineation of radiotherapy for prostate cancer [ 21 ].…”

The use of PET/MRI in radiotherapy

“…This discrepancy may be attributed to the utilization of specific tracers in PET, which enable the detection of microscopic tumor activity even in the absence of morphological changes. As a result, the obtained GTV will expand [ 59 , 60 ]. Conversely, [ 68 Ga]-DOTATOC PET/MRI allows for the visualization of the boundary between the tumor and normal tissue, as well as the necrotic parts of the tumor resulting from adjuvant treatment, which can lead to a reduced estimation of GTV [ 61 ].…”

“…Moreover, the pathological analysis also confirmed the advantage of PET/MRI in the target delineation, Zhang et al proposed that PET/MRI is more adept at mapping GTV by comparing the Dice Similarity Coefficient (DSC) of PET/MRI and PET. Additionally, they demonstrated that the longest tumor length measured by PET/MRI correlated well with the longest tumor length measured by histopathological analysis, providing robust evidence for the superior accuracy of GTV delineation by PET/MRI [ 60 , 62 ]. Figure 3 illustrates the difference between [ 18 F]-FDG PET/MRI and other traditional imaging methods for GTV delineation.…”