Comparison of 68 Ga-PSMA ligand PET/CT versus conventional cross-sectional imaging for target volume delineation for metastasis-directed radiotherapy for metachronous lymph node metastases from prostate cancer.

PURPOSE: To assess the differences in the target volume (TV) delineation of metachronous lymph node metastases between 68 Ga-PSMA ligand PET/CT and conventional imaging in a comparative retrospective contouring study. PATIENTS AND METHODS: Twenty-five patients with biochemical prostate cancer recurrence after primary prostatectomy underwent 68 Ga-PSMA ligand PET/CT in addition to conventional imaging techniques such as CT and/or MR imaging for restaging. All patients were diagnosed with at least one lymph node metastasis. TVs were manually delineated in two different ways: (a) based on conventional imaging (CT/MRI) and (b) based on conventional imaging (CT/MRI) plus 68 Ga-PSMA ligand PET/CT. The size of TVs, overlap rates, and subjective assessment of the difficulty of TV delineation reported by the radiation oncologist (easy/moderate/difficult) were compared. RESULTS: With the additional information from PSMA ligand PET, 47 lymph node metastases were identified and included in the gross tumor volume (GTV). The median clinical target volume (CTV) of non-PET-based TV delineation was statistically larger than the CTV based on PET imaging (134.8 ml [range 6.9-565.2] versus 44.9 ml [range 4.9-481.3; p = 0.001]). The CTV based on CT/MRI enclosed only 81.3% (39/48) of PET-positive lymph nodes. The CT/MRI-based CTV did not enclose all PET-positive lymph nodes in 24% (6/25) of patients. In 12% (3/25) of patients, all PET-positive lymph nodes were outside of the CT/MRI-based CTV. The median overlap rates (TVPET/TVCT/MRIâ€¯× 100) were 45.7% (range 0-96.9) for the GTV and 71.7% (range 9.8-98.2) for the CTV. The assessment of difficulty of contouring revealed that contouring with the additional imaging information of the PET was categorized as easy/moderate in 92% (23/25) and as difficult in 8% (2/25) of the cases, whereas contouring based on CT/MRI without PET was categorized as difficult in 56% (14/25) and as easy/moderate in 44% of the cases (11/25; p = 0.003). CONCLUSION: 68 Ga-PSMA ligand PET/CT is superior to conventional cross-sectional imaging for the delineation of lymph node metastases from prostate cancer. PET-based TV delineation allows for smaller target volumes and should be considered the standard for irradiation of metachronous lymph node metastases in recurrent prostate cancer. Conventional imaging is not sufficiently sensitive for radio-oncological treatment concepts in oligometastatic prostate cancer.

Patterns of Progression After 68Ga-PSMA-Ligand PET/CT-Guided Radiation Therapy for Recurrent Prostate Cancer.

PURPOSE: To determine the patterns of progression after 68Ga prostate-specific membrane antigen (PSMA)-ligand positron emission tomography (PET)/computed tomography (CT)-guided radiation therapy (RT) for recurrent oligometastatic prostate cancer (PCa). METHODS AND MATERIALS: One hundred and eight patients with increased prostate-specific antigen levels, who received 68Ga-PSMA-ligand PET/CT-guided RT for recurrent oligometastatic disease after primary therapy for PCa were included. The biochemical progression-free survival and distant disease-free survival after PSMA-ligand PET/CT-guided RT were determined. The patterns of progression were determined using renewed 68Ga-PSMA-ligand PET/CT in patients with biochemical progression and compared with the clinical target volume of the 68Ga-PSMA-ligand PET/CT-guided RT. The frequency of infield and outfield relapses was recorded. RESULTS: A total of 97.2% (105 of 108) of patients showed a decrease in prostate-specific antigen levels after RT and were classified as biochemical responders. After the median follow-up of 18 months, 43.5% (47 of 108) of the patients experienced biochemical progression, resulting in an estimated biochemical progression-free survival of 16 months. Renewed 68Ga-PSMA-ligand PET/CT allowed localization of recurrent disease in 91.7% (33 of 36) of patients. Analysis of the patterns of progression resulted in a cumulative infield relapse rate of 12.1% (4 of 33) and a cumulative outfield relapse rate of 87.9% (29 of 33). The resultant median disease-free survival was 11 months. In terms of the pattern of progression, we observed a shift in the pattern of metastases toward skeletal involvement and distant lymph node metastases. Of these patients, 45.5% (15 of 33) were treated with further RT to delay initiation or escalation of systemic therapies. CONCLUSION: PSMA-ligand PET/CT-guided RT for relapsed PCa with limited tumor burden allowed individualization of treatment approaches, provided effective local control, and resulted in considerably prolonged biochemical progression-free survival. As indicated by the PSMA-ligand PET/CT-based patterns of progression, repeated PET/CT-guided RT may represent a treatment option in well-selected patients with relapse after RT for oligometastatic disease.

Comparison of relative and absolute rectal dose-volume parameters and clinical correlation with acute and late radiation proctitis in prostate cancer patients.

PURPOSE: To compare relative and absolute dose-volume parameters (DV) of the rectum and their clinical correlation with acute and late radiation proctitis (RP) after radiotherapy (RT) for prostate cancer (PCa). PATIENTS AND METHODS: 366 patients received RT for PCa. In total, 49.2% received definitive RT, 20.2% received postoperative RT and 30.6% received salvage RT for biochemical recurrence. In 77.9% of patients, RT was delivered to the prostate or prostate bed, and additional whole pelvic RT was performed in 22.1%. 33.9% received 3D-RT, and 66.1% received IMRT. The median follow-up was 59.5 months (18.0-84.0 months). The relative (in %) and absolute (in ccm) rectal doses from 20-75 Gy including the receiver operating characteristics curves (rAUC) from 30-65 Gy (in % and ccm) and several other clinical parameters were analyzed in univariate and multivariate analyses. We performed the statistical analyses separately for the entire cohort (n = 366), patients with (n = 81) and without (n = 285) pelvic RT, comparing RP vs. RP ≥ grade I. RESULTS: With the exception of the V50Gyccm (p = 0.02) in the univariate analyses for acute RP in the entire patient cohort, no absolute DV parameter (in ccm) was statistically significant associated with either acute or late RP. In the multivariate analyses, 3D-RT (p < 0.008) and rAUCV30-50 Gy% (p = 0.006) were significant parameters for acute RP for the entire cohort, and the V50Gy% (p = 0.01) was the significant parameter for patients with pelvic RT. The rAUCV40-50 Gy% (p = 0.004) was significant for RT to the prostate/prostate bed. Regarding the statistical analysis for late RP, the rAUCV30-65 Gy% (p = 0.001) was significant for the entire cohort, and rAUCV30-50 Gy% (p = 0.001) was significant for RT of the prostate/prostate bed. No parameter was significant in patients with pelvic RT. CONCLUSION: Absolute DV parameters in ccm are not required for RT in PCa patients.