SU-E-J-194: The Impact of Different Imaging Measures on Treatment Response Assessment of Bone Metastases

Several treatment response metrics, such as RECIST and PERCIST, have been established for assessing individual solid tumors. However, metastatic prostate cancer poses a unique challenge to these metrics because bone lesions are often numerous and non-measureable. This study investigated the impact of using different imaging measures for treatment response assessment in patients with metastatic prostate cancer.

Six patients with metastatic prostate cancer were treated with molecular targeted therapy and received whole body [₁₈ F]NaF PET/CT scans pre-, mid-, and post-treatment. Lesions were segmented using a threshold of 20% the maximum SUV in bone and then manually adjusted with physician guidance. For each patient, SUVmax, SUVmean, SUVpeak, SUVtotal, number of lesions, and total volume of bone lesions were determined. For each measure, treatment response was calculated as the percent change relative to pre-treatment. The range of the different responses was calculated for each patient at each response time point. The population average of the patient ranges was calculated.

The patient responses varied greatly for different imaging measures. The population-averaged range for all response measures was 50%. In general, SUVmax, SUVmean, and SUVpeak responses were negative, indicating good response to treatment, but the number of lesions, volume, and SUVtotal responses were positive, indicating disease progression. When the measures were separated into these two groups, the population-averaged range was only 25% among the number of lesions, volume, and SUVtotal responses and 10% among the SUVmax, SUVmean, and SUVpeak responses.

Several treatment response metrics, such as RECIST and PERCIST, have been established for assessing individual solid tumors. However, metastatic prostate cancer poses a unique challenge to these metrics because bone lesions are often numerous and non-measureable. This study investigated the impact of using different imaging measures for treatment response assessment in patients with metastatic prostate cancer.