Maximum tumor diameter and renal function can predict the declining surface dose rate after 177Lu-Dotatate: preliminary results of single institution in Japan

Abstract Purpose This study aimed to develop a user-friendly prediction formula for dose rate adjustment after initial 177 Lu-Dotatate therapy from a prospective observational study of patients. Materials and methods This study included consenting patients in a prospective observational study who underwent their first treatment in four cycles of 177 Lu-Dotatate treatment at our hospital between January 2022 and February 2024. All patients received 7.4 GBq of 177 Lu-Dotatate. The prediction formula was derived from the regression analysis of tumor-related factors and renal function. Creatinine clearance was estimated using the Cockcroft–Gault equation in this study for renal function. Results Among the 13 patients (seven males, six females, median age: 59 years), logarithmically transformed total tumor volume (cc) and maximum tumor diameter (mm) of primary tumors or metastases showed strong correlations ( p < 0.001, R 2 = 0.897). As such, the maximum tumor diameter was used as the tumor parameter in the prediction formula. Additionally, maximum tumor diameter and creatinine clearance showed strong ( p < 0.001, R 2 = 0.768) and moderate ( p = 0.013, R 2 = 445) correlations, respectively, with the ratio of the dose rate 5.5-h post-administration to the dose rate immediately post-administration (%) at 1 m from the body surface. The resulting formula, 51.4 + 0.360 × maximum tumor diameter (mm) − 0.212 × creatinine clearance (ml/min), demonstrated an extremely strong correlation ( p < 0.001, R 2 = 0.937). Conclusion The present study showed that the maximum tumor diameter and renal function affected the declining the dose rate of patients surface after 177 Lu-Dotatate, which can inform post-administration dose rate management and potentially facilitate outpatient treatment in Japan.