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. 2023 Jan 4;23(1):1.
doi: 10.1186/s40644-022-00518-7.

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

Lin-Lin Liu #  1 , Lei-Lei Zhu #  1 , Zhen-Guo Lu  1 , Jun-Die Sun  1 , Jun Zhao  2 , Hai-Feng Wang  3 , Zuo-Lin Xiang  4   5
Affiliations

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

Lin-Lin Liu et al. Cancer Imaging. .

Abstract

Purpose: A comparative retrospective study to assess the impact of PSMA Ligand PET/MRI ([68 Ga]-Ga-PSMA-11 and [18F]-F-PSMA-1007 PET/MRI) as a new method of target delineation compared to conventional imaging on whole-pelvis radiotherapy for high-risk prostate cancer (PCa).

Patients and methods: Forty-nine patients with primary high-risk PCa completed the whole-pelvis radiotherapy plan based on PSMA PET/MRI and MRI. The primary endpoint compared the size and overlap of clinical target volume (CTV) and nodal gross tumour volume (GTVn) based on PSMA PET/MRI and MRI. The diagnostic performance of two methods for pelvic lymph node metastasis (PLNM) was evaluated.

Results: In the radiotherapy planning for high-risk PCa patients, there was a significant correlation between MRI-CTV and PET/MRI-CTV (P = 0.005), as well as between MRI-GTVn and PET/MRI-GTVn (P < 0.001). There are non-significant differences in the CTV and GTVn based on MRI and PET/MRI images (P = 0.660, P = 0.650, respectively). The conformity index (CI), lesion coverage factor (LCF) and Dice similarity coefficient (DSC) of CTVs were 0.999, 0.953 and 0.954. The CI, LCF and DSC of GTVns were 0.927, 0.284, and 0.32. Based on pathological lymph node analysis of 463 lymph nodes from 37 patients, the sensitivity, specificity of PET/MRI in the diagnosis of PLNM were 77.78% and 99.76%, respectively, which were higher than those of MRI (P = 0.011). Eight high-risk PCa patients who finished PSMA PET/MRI changed their N or M stage.

Conclusion: The CTV delineated based on PET/MRI and MRI differ little. The GTVn delineated based on PET/MRI encompasses metastatic pelvic lymph nodes more accurately than MRI and avoids covering pelvic lymph nodes without metastasis. We emphasize the utility of PET/MRI fusion images in GTVn delineation in whole pelvic radiotherapy for PCa. The use of PSMA PET/MRI aids in the realization of more individual and precise radiotherapy for PCa.

Keywords: CTV; GTVn; PET/MRI; PSMA; Prostate cancer; Radiotherapy.

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Conflict of interest statement

The authors declare that there are no conflicts of interest regarding the publication of this article.

Figures

Fig. 1
Fig. 1
Patient enrollment process
Fig. 2
Fig. 2
Target volume delineation for a 68-year-old man with high-risk PCa who was assumed three lymph node metastases based on PSMA Ligand PET/MRI (T2-weighted) leading to three GTVs (green line)(A). Target volume delineation based on MRI (T2-weighted) assuming two lymph node metastases leading to two GTVs (pink line) (B)
Fig. 3
Fig. 3
Target volume delineation for a 68-year-old man with high-risk PCa who was assumed two lymph node metastases based on PET/MRI (T2-weighted), leading to two GTVs (green line), resulting CTV in blue line (A). Target volume delineation based on MRI (T2-weighted) assuming two lymph node metastases leading to two GTVs (pink line), resulting CTV in pink line (B). Target volume delineation for a 67-year-old man with high-risk PCa who was assumed one lymph node metastasis based on PET/MRI (T2-weighted), leading to one GTV (green line), resulting CTV in blue line (C). Target volume delineation based on MRI (T2-weighted) assuming no lymph node metastasis, resulting CTV in pink line (D)
Fig. 4
Fig. 4
Bland–Altman analysis between volumes delineated on the two modalities for CTV(A) and for GTVn (B)
Fig. 5
Fig. 5
PSMA PET/MRI-CTV versus MRI-CTV (A); PSMA PET/MRI-GTVn versus MRI-GTVn (B)
Fig. 6
Fig. 6
Confusion matrix results of MRI and PET/MRI for lymph node-based analysis (A) and for patient-based analysis (B)
See this image and copyright information in PMC

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