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

This study aimed to develop a user-friendly prediction formula for dose rate adjustment after initial ¹⁷⁷Lu-Dotatate therapy from a prospective observational study of patients.

This study included consenting patients in a prospective observational study who underwent their first treatment in four cycles of ¹⁷⁷Lu-Dotatate treatment at our hospital between January 2022 and February 2024. All patients received 7.4 GBq of ¹⁷⁷Lu-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.

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, R² = 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, R² = 0.768) and moderate (p = 0.013, R² = 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, R² = 0.937).

The present study showed that the maximum tumor diameter and renal function affected the declining the dose rate of patients surface after ¹⁷⁷Lu-Dotatate, which can inform post-administration dose rate management and potentially facilitate outpatient treatment in Japan.