Response evaluation criteria in PSMA PET/CT (RECIP 1.0) in metastatic castration-resistant prostate cancer.

Abstract

45 Background: Response Evaluation Criteria in Prostate-Specific Membrane Antigen (PSMA) PET/CT (RECIP 1.0) initially integrated software-based quantitative assessment of PSMA-positive total tumor volume (PSMA-VOL). Clinical implementation of such software is not expected soon, limiting the use of RECIP in practice. This study aimed to assess the agreement of RECIP determined using tumor segmentation software (quantitative RECIP) with RECIP determined by qualitative reads by nuclear medicine physicians (visual RECIP) for response evaluation in metastatic castration-resistant prostate cancer. Methods: This multicenter retrospective study at three academic centers included patients who received lutetium-177 (177Lu) PSMA treatment between December 2014 and July 2019. PSMA PET/CT images at baseline and 12 weeks were assessed qualitatively by five nuclear medicine physicians for changes in PSMA-VOL and for new lesions. Quantitative changes in PSMA-VOL were also measured using tumor segmentation software. The status of new lesions was combined with qualitative changes in PSMA-VOL to determine visual RECIP and with quantitative changes in PSMA-VOL to determine quantitative RECIP. The primary outcomes were the agreement between visual and quantitative RECIP and the interreader reliability of visual RECIP according to the Fleiss κ. The secondary outcome was the association of visual RECIP with overall survival according to Cox regression. Results: A total of 124 patients (median age, 73 years [IQR, 67–76 years]) were included. Forty (32%) and 84 (68%) patients had quantitative RECIP progressive disease (PD) and non-PD, respectively. Agreement between visual versus quantitative RECIP was excellent (κ=0.89; 118 of 124 patients [95%]). Agreement among readers in classifying visual RECIP PD versus non-PD was excellent (κ=0.81; 103 of 124 patients [83%]). RECIP-PD was associated with significantly shorter overall survival compared with RECIP-nonPD (hazard ratio, 2.6 [95%CI: 1.7, 3.8]; P <.001). Conclusions: Qualitatively assessed RECIP demonstrated excellent agreement with quantitative RECIP and excellent interreader reliability, and can be readily implemented in clinical practice for response evaluation in patients with metastatic castration-resistant prostate cancer undergoing 177Lu-PSMA therapy and possible other systemic therapies.