To study the dose evaluation parameter and assess the therapeutic effect of prostate brachytherapy based on SPECT/CT detection.

A patient with prostate cancer underwent ¹²⁵I seed implantation was scanned by SPECT/CT. The images of SPECT and CT were fused and adjusted the radioactivity concentration region to match 145Gy and 217.5Gy isodose line. The two-radioactivity density count values were recorded. The relationship between target, the organ at risk and region in the two count value lines was observed. Counted the ratio between the volume in the two count value lines and the target volume. After 4 years follow up, the patient showed a good tumor control and no complication. Then, evaluated a second patient with the count value line and the ratio used before and followed up.

The count value matched 145Gy isodose line in the first patient was 200. The ratio between the volume in this count value line and target volume was 106%. A little part of the anterior wall of the rectum was involved. The count value matched 217.5Gy isodose line in the first patient was 300. The ratio between the volume in this count value line and target volume was 58%. The urethra was avoided. The 200-count value line in the second patient covered the target completely and part of the anterior wall of the rectum was involved. The ratio between the volume in this count value line and target volume was 176%. The 300-count value line in the second patient covered part of the urethra. The ratio between the volume in this count value line and target volume was 74%. The second patient was followed up for three months till now. PSA declined to normal and no complications of rectum and urethra were observed.

The dose distribution of ¹²⁵I seed in the prostate cancer can be detected and imaged by SPECT/CT. SPECT/CT based dose verification may be a new method to access the therapeutic effect of prostate cancer brachytherapy if the radioactive count value and the dose were related.