Fast, quantitative SPECT/CT acquisition following multiple therapy cycles of 177Lu-PSMA-617

Fast, quantitative SPECT/CT enables response assessment in Metastatic Prostate Cancer

By Andrés Ricaurte Fajardo, MD,1 Joseph Osborne, MD, PhD,1 Lady Sawoszczyk, BS, CNMT2
Data and images courtesy of New York-Presbyterian Hospital/Weill Cornell Medical Center, New York, New York, USA 

|03/13/2023

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. 

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.

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.

Treatment cycle

177Lu-PSMA-617 dose

Prostate-specific 
antigen (PSA) values

(ng/mL)

Absolute neutrophil 
count (ANC) (Normal 
ANC range: 2,500-6,000 
cells/μL)

1

203 mCi (7.5 GBq)

2,009

2,540

2

160 mCi (5.92 GBq)

1,514.29

1,000

3

193.5 mCi (7.1 GBq)

934.73

800

4

160.6 mCi (5.94 GBq)

658.83

1,220

5

156.9 mCi (5.8 GBq)

618.36

800

6

165.2 mCi (6.11 GBq)

374.46

1,300

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).

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.

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.

Scanners: Biograph mCT Flow PET/CT and Symbia Intevo Bold SPECT/CT

68Ga-PSMA-11 PET

 

Injected dose

3.76 mCi (139.12 MBq)

Post-injection delay

60 minutes

Acquisition

1.0 mm/s
FlowMotion™ continuous bed motion

Reconstruction

200 x 200 matrix

CT

Tube voltage

100 kV

Tube current

74 mAs

Slice collimation

3.0 mm

Slice thickness

3.0 mm

177Lu-PSMA-617 SPECT (Cycle 6) 

 

Injected dose

165.2 mCi (6.11 GBq)

Post-injection delay

7 days

Acquisition

3 bed positions/5 seconds per view, 60 views per detector
Total scan time: 15 minutes (5 minutes per bed) 

Reconstruction

256 x 256 matrix, xSPECT, Zoom 1.0

CT 

Tube voltage

110 kV

Tube current

12 mAs

Slice collimation

3.0 mm

Slice thickness

3.0 mm

1
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