Abstract
Background/Objectives: In patients with metastatic castration-resistant prostate cancer (mCRPC) and osseous metastases only, (223)Radium therapy represents a valuable therapeutic option. Bone scintigraphy (BS) is typically performed to assess metastasis load, with the BS-derived automated bone scan index (aBSI) used for response assessment. This study aimed to evaluate the prognostic value of aBSI in patients receiving three or six cycles of (223)Ra therapy. Methods: We included patients that were diagnosed with extensive osseous tumor load on BS, had no visceral or nodal metastases, had undergone (223)Ra therapy. The aBSI prior to and following three or six cycles of therapy, total tumor volume (TTV), SUV(max), and overall survival were analyzed. Results: This study included 49 mCRPC patients (mean age: 70 ± 9 years) with 42 (85.7%) receiving six and 7 (14.3%) receiving three cycles. After three cycles, the mean aBSI (p = 0.369), TTV (p = 0.902), and SUV(max) (p = 0.149) remained unchanged. After six cycles, the mean aBSI (p = 0.247) and TTV (p = 0.784) were unchanged, while SUV(max) decreased significantly (p = 0.001). The aBSI did not significantly correlate with the mean aBSI (six cycles: χ(2) = 1.823, p = 0.177; three cycles: χ(2) = 0.308, p = 0.579). Conclusions: Although quantitative changes in TTV and aBSI did not significantly correlate with each other, their respective absolute values consistently indicated stable disease burden under therapy. This highlights its potential as a useful tool for monitoring disease burden while indicating that aBSI alone is insufficient for predicting overall survival.