^{99   m} Tc-antigranulocyte scintigraphy for estimation of bone marrow reserve prior to PSMA-radioligand therapy

Ziel/Aim PSMA-directed radioligand-therapy (RLT) is gaining increasing clinical importance for the treatment of metastasic, castration-resistant prostate cancer (mCRPC). However, RLT can affect remaining viable bone marrow, especially in patients with extensive osseous tumor load and prior myelotoxic treatment. We assessed the value of ^99 mTc-antigranulocyte scintigraphy for estimation of bone marrow reserve prior to RLT.

Methodik/Methods 7 mCRPC patients with extensive osseous tumour load on ¹⁸ F-PSMA PET/CT were included. ^99 mTc-antigranulocyte scintigraphy was performed prior to subsequent RLT. Both modalities were compared with regards to spatial overlap of tumor burden and bone marrow. In case of low spatial overlap, the patient was deemed available for PSMA-RLT. In those patients subsequently undergoing RLT, blood samples (haemoglobin, leucocytes, platelets, neutrophils) and PSA were assessed 4 and 8 weeks after RLT.

Ergebnisse/Results There was no relevant spatial correlation of bone marrow and tumor load in 6/7 patients. 4/6 patients underwent PSMA-RLT with ¹⁷⁷Lu (2/4) or ²²⁵Ac (2/4). In 1/6 patient, bone marrow and PSMA-positive tumor load were congruent; the dosimetry simulation using population-based time activity curves revealed a 3-fold higher bone marrow dose compared to those with non-congruent findings. 2/6 patients were not treated due to acute contraindications. Blood samples were stable after 4 and 8 weeks (haemoglobin: 8.5 ± 1.5 vs. 8.4 ± 1.0 vs. 8.9 ± 0.4 g/dl, p < 0.05; leucocytes: 4.3 ± 0.9 vs. 4.3 ± 1.5 vs. 4.3 ± 0.4 G/I, p < 0.05; platelets: 187.8 ± 98.5 vs. 167.3 ± 58.7 vs. 151.0 ± 61.5 G/I, p < 0.05; neutrophils: 3.0 ± 0.8 vs. 3.3 ± 1.5 vs. 3.4 ± 1.0 G/I, p < 0.05), whereas PSA increased (210.8 ± 162.1 vs. 290.0 ± 264.6 vs. 535.3 ± 395.6 mg/ml, p < 0.05).

Schlussfolgerungen/Conclusions In case of spatial mismatch of viable bone marrow and osseous tumour load RLT seems feasible without major risk of bone marrow affection, whereas congruent findings on ^99 mTc-antigranulocyte scintigraphy and PSMA-PET indicate significantly higher bone marrow doses.