Reply to Tonghu Liu, Congcong Zhu, and Zechen Yan's Letter to the Editor re: Heidi Fettke, Louise Kostos, Maria Docanto, et al. Baseline and Early On-treatment Circulating Tumour DNA Fraction Are a Key Prognostic Biomarker in Metastatic Castration-resistant Prostate Cancer Treated with [177Lu]Lu-PSMA-617. Eur Urol. In press. https://doi.org/10.