History
A male in his 70s with a history of prostate-specific membrane antigen (PSMA)-positive metastatic castration-resistant prostate cancer (mCRPC) underwent 177Lu-PSMA-617 treatment 14 years after his initial diagnosis. When prostate-specific antigen (PSA) levels began to rise, the patient was unsuccessfully treated with androgen deprivation therapy (ADT) and multiple lines of systemic chemotherapy. As the disease progressed, the patient received treatment with 223Ra-dichloride, docetaxel, and cabazitaxel with no significant improvement. The patient also completed a palliative course of radiotherapy (30 Gy in 10 fractions) without any treatment complications.
Findings
A routine 68Ga-PSMA-11 PET/CT was performed to qualify the patient for 177Lu-PSMA-617 treatment. PET/CT findings confirmed PSMA expression in the tumors. The patient was administered with 3.76 mCi (139.12 MBq) intravenous (IV) injection of 68Ga-PSMA-11, and approximately 1 hour later, a single-scan, whole-body acquisition was conducted on Biograph mCT Flow™ PET/CT.
Figure 1: Coronal CT, 68Ga-PSMA-11 PET, and PET/CT images confirm PSMA expression in metastatic disease and qualify the patient for 177Lu-PSMA-617 treatment.
As observed in Figures 1-3, 68Ga-PSMA-11 PET/CT images demonstrate an increased extent of PSMA-avid osseous metastasis within the T3-T7 vertebrae with extension into the neural foramen and ventral epidural space suspected at the T4-T6 levels. There is an overall increased extent of PSMA-avid cervical, thoracic, and abdominopelvic nodal metastasis.
The patient underwent 6 cycles of 177Lu-PSMA-617 therapy; each cycle was delivered every 6-8 weeks. Multi-bed, quantitative SPECT/CT imaging was conducted on Symbia Intevo Bold™ with xSPECT Quant™ after each treatment cycle. The 3-bed, quantitative SPECT/CT study was acquired at 60 stops per detector with 5 seconds per stop. Total scan time was 15 minutes. Following CT attenuation correction (CTAC), the corrected SPECT data was fused with CT data for visual interpretation.
Due to the patient’s neutropenia, which was based on absolute neutrophil count (ANC) values in between cycles, the recommended dose of 200 mCi (7.4 GBq) was modified by 20% to 160 mCi (5.9 GBq). Therapy response continued to be monitored via PSA values and quantitative SPECT/CT imaging.
Figure 4: Sagittal CT through the thoracic and lumbar spine shows extensive sclerosis in the vertebral bodies reflecting metastatic disease with particularly dense sclerosis in the T5 vertebral body. Cycle 2 image shows significant decrease in mid-thoracic vertebral uptake compared to that of low thoracic and lumbar vertebrae, which can be explained by additional mid-thoracic external beam radiation delivered throughout the 177Lu-PSMA therapy regimen. Cycle 3 images acquired 7 days post injection demonstrate lower bladder uptake when increasing time lapse post injection. High uptake in the lower thoracic and lumbar vertebrae is visualized after cycles 2 and 3 but shows considerable decrease after cycles 4 and 6, which clearly demonstrates tumor response.
As observed in Figures 4 and 5, the SPECT/CT with xSPECT Quant images demonstrate a normal biodistribution of 177Lu-PSMA-617 and foci of increased uptake compatible with the expected distribution of targeted PSMA in concordance with findings from the preceding PSMA PET (Figures 1 and 2).
Discussion
This case demonstrates the clinical advantage of using quantitative SPECT/CT with 177Lu-PSMA-617 treatment for therapy monitoring. The confirmation of positive or negative treatment response plays a critical role in disease management, and SPECT/CT with xSPECT Quant images helped confirm that the tumors visualized on the 68Ga-PSMA-11 PET/CT were the same tumors being treated with 177Lu-PSMA-617. The large field of view available on Symbia Intevo Bold SPECT/CT enabled a 15-minute, 3-bed-position imaging protocol, which covered vertex to thigh and allowed the routine use of post-treatment, image-based 177Lu-PSMA-617 uptake assessment. As shown in Figure 5, a progressive reduction of 177Lu-PSMA-617 uptake demonstrated the efficacy of this treatment. Furthermore, the method of imaging after each treatment cycle enabled quality control checks that helped ensure that the treatment was irradiating the tumors as expected.
Conclusion
177Lu-PSMA-617 treatment plays a critical role in patients with mCRPC who have a history of unsuccessful response to hormone therapy and chemotherapy. The ability to perform fast, multi-bed, quantitative SPECT/CT imaging on Symbia Intevo Bold with xSPECT Quant provides high sensitivity to assess 177Lu-PSMA-617 therapy response. Thus, post-treatment imaging is critical for quality control evaluation to confirm PSMA-avid tumors are being treated properly.
Examination protocol
Scanners: Biograph mCT Flow PET/CT and Symbia Intevo Bold SPECT/CT
The outcomes achieved by the Siemens Healthineers customers described herein were achieved in the customer’s unique setting. Since there is no “typical” hospital and many variables exist (eg, hospital size, case mix, level of IT adoption) there can be no guarantee that others will achieve the same results.
