CASE OF THE WEEK – “Comparing 99mTc-MDP Whole body hybrid SPECT CT scan with Whole body Ga68 PSMA PET CT scan in Prostate Cancer Staging of the Skeletal System ” by Dr. Shekhar Shikare, HOD & Consultant, Nuclear Medicine & Dr. Mohammed Istrabadi Consultant Urology Surgery & General Surgery at NMC Royal Hospital Sharjah

CASE OF THE WEEK – “Comparing 99mTc-MDP Whole body hybrid SPECT CT scan with Whole body Ga68 PSMA PET CT scan in Prostate Cancer Staging of the Skeletal System ” by Dr. Shekhar Shikare, HOD & Consultant, Nuclear Medicine  & Dr. Mohammed Istrabadi Consultant Urology Surgery & General Surgery at NMC Royal Hospital Sharjah

Introduction

Prostate cancer (PCa) is the most common non cutaneous cancer in men with a lifetime risk of 12.5%. Although only 6% of men with PCa have metastatic disease at diagnosis, 90% of men who die of PCa have metastatic disease to bone. The high rate of bone metastases has led to the incorporation of bone imaging in most published national and international treatment guidelines. Imaging of bone metastases in PCa has traditionally involved the use of the bone-seeking 99mTc-MDP, which is highly sensitive for detection of bone lesions.99mTc/Ga68 labeled prostate-specific membrane antigen (PSMA) used for imaging in PCa. It has the advantage of being able to demonstrate both visceral and bone lesions.

Case

66 years old gentleman with histopathology diagnosis of acinar adenocarcinoma with Gleason score of 8 and elevated PSA fraction free 15.026 ng/ml (4-10) & PSA total 116.802 ng/ml (0.-4.0).

99m Tc-MDP whole body Hybrid SPECT CT scan

It shows areas of abnormally increased tracer uptakes in

Facet joints of C3 vertebra (lt) and C7 vertebra

(rt)- figure 1

Left 1st rib medially- figure 2

Spinous process of D3 vertebra- figure 3

Spinous process of L5 vertebra figure 3

Suspiciously 7th rib right anteriorly-figure 2

Body of L4/L5 vertebra (lt) and Body of L5/S1 (rt) due to degenerative pathology -figure 4.

Figure 1 99mTc MDP hybrid SPECT CT IMAGES OF THE NECK
Figure 2 99mTc MDP hybrid SPECT CT IMAGES OF THE CHEST
Figure 3 99mTc MDP hybrid SPECT CT IMAGES OF THORASIC & LUMABR

Figure 4 99mTc MDP hybrid SPECT CT IMAGES OF LUMABR

Whole body Ga68 PSMA PECT CT SCAN

Multiple hypermetabolic predominantly sclerotic bone lesions seen in C3 vertebral body (SUV 7.65), C7 vertebral body (right posterolateral aspect (SUV 7.41), c) D3 junction (right lamina and spinous process (SUV 25.81), left 1st rib rib medially (SUV 25.81), d) L5 spinous process, (SUV 30.14).

Hypermetabolic mass lesion in prostate, predominantly in right lobe (SUV 33.74), No scintigraphy evidence of ga 68 PSMA lymphadenopathy. Rest of the whole-body images were unremarkable.

Discussion

99mTc-MDP bone scintigraphy is the cornerstone of skeletal nuclear medicine imaging and has been regarded as the standard of reference in detection of bone metastases in PCa patients. It is highly sensitive, readily available, and cost-effective, and it has been the standard method for nuclear imaging of the skeletal system for decades. There is a need to affordably improve imaging of metastases in PCa as scintigraphy with 99mTc-MDP is associated with limited sensitivity in patients with low prostate-specific antigen (PSA), long PSA doubling time, lytic bone lesions, and in assessing biochemical progression after radical prostatectomy. Modern clinical management of PCa increasingly relies on exploiting the PSMA as a molecular target both for imaging and for treatment of PCa.

PSMA is a type II integral membrane glycoprotein with an intracellular component, a transmembrane component, and a large extracellular domain.99mTc-PSMA/Ga 68 PSMA can detect both soft tissue and skeletal metastases.

99mTc-MDP bone to Ga68-PSMA scintigraphy is comparable in detection of bone metastases. Hybrid SPECT CT images were also useful in picking up additional benign degenerative pathology, which were negative on Ga68 PSMA imaging.

99mTc PSMA / Ga68 PSMA demonstrated an additional benefit of providing information on visceral disease.

PSMA imaging may be a better alternative to 99mTc-MDP in staging, restaging, and assessment of patients with biochemical progression after radical therapy of PCa.

Therefore, in patients who can afford an only single scan,99mTc-PSMA SPECT CT / Ga68 PSMA PET CT scan would be a better choice. With regards to therapy, PMSA scan might have utility to select candidates for PSMA radioligand therapy such as 177Lu-PSMA, whereas 99mTc-bone scan may have similar utility in palliative radioligand bone therapy with bisphosphonates.