|Ahead of print publication
99mTc-PSMA SPECT/CT is superior to 99mTc-MDP SPECT/CT in the staging of prostatic cancer with osseous metastases after external beam radiotherapy
Knut Liepe, Marcel Baehr
Department of Nuclear Medicine, GH Klinikum Frankfurt (Oder), Frankfurt (Oder), Germany
|Date of Submission||06-Apr-2020|
|Date of Decision||24-Jun-2021|
|Date of Acceptance||22-Apr-2021|
Department of Nuclear Medicine, GH Klinikum Frankfurt (Oder), Muellroser Chaussee 7, 15236, Frankfurt (Oder)
Source of Support: None, Conflict of Interest: None
| Abstract|| |
In the reported patient with advanced prostate cancer, a bone scan showed false positive findings in the thoracic vertebrae after external beam radiotherapy two months ago. An additional 99mTc-PSMA SPECT/CT scan showed negative findings, although a non-irradiated iliac bone metastasis was concordantly positive in both scans. The decrease of PSA level from 154.6 ng/ml to 2.3 ng/ml indicates a strong effect of treatment, hence supporting that false positivity in bone scan is caused by the “flare phenomenon”.
Keywords: Bone metastases, external beam radiotherapy, prostate cancer, 99mTc-MDP, 99mTc-PSMA
|How to cite this URL:|
Liepe K, Baehr M. 99mTc-PSMA SPECT/CT is superior to 99mTc-MDP SPECT/CT in the staging of prostatic cancer with osseous metastases after external beam radiotherapy. World J Nucl Med [Epub ahead of print] [cited 2022 Jan 25]. Available from: http://www.wjnm.org/preprintarticle.asp?id=332242
| Introduction|| |
In prostate cancer, existence and number of bone and lymph node metastases substantially influence the overall survival. In the last decade, 68Ga prostate-specific membrane antigen (PSMA) positron emission tomography/computed tomography (PET/CT) has become the gold standard for diagnostics of prostate cancer before primary therapy and when prostate-specific antigen (PSA)-relapse occurs., Unfortunately, the costs for the 68Ge/68Ga generator are high and PET/CT systems are not available worldwide. Since 99mTc-PSMA single-photon emission computed tomography (SPECT)/CT is able to detect extraskeletal and skeletal metastases, it has the potential to replace 99mTc-methylene disphosphonate (99mTc-MDP) bone scan in standard staging, when 68Ga PSMA PET/CT is not available.
| Case Report|| |
A 65-year-old man with a PSA-level of 154.6 ng/ml had received the initial diagnosis of metastasized prostate cancer, cT4 cN0 (Gleason 4 + 5 = 9). A bone scan with 99mTc-MDP revealed three bone metastases in the left iliac body, right third rib, and thoracic vertebrae (T) 10 to T12 (not published). Systemic treatment with androgen deprivation and local treatment with external beam radiotherapy of T10 with 42.5 Gy and T11–T12 with 50 Gy was performed. The PSA-level decreased to 2.3 ng/ml. Re-staging was performed with SPECT/CT (GE NM/CT 850, GE Healthcare GmbH, Solingen, Germany), using 13.9 mCi (515 MBq) 99mTc-MDP (ROTOP Pharmaka GmbH, Dresden, Germany) and 17.0 mCi (629 MBq) 99mTc-PSMA (PSMA-Tc- API, Institute of Isotope, Budapest, Hungary). A 99mTc-MDP whole-body scan was performed 2 h post injection (p.i.), which showed strongly positive findings at the sites of the known metastases in the third rib, iliac body, T11 and T12 [Figure 1]a. A SPECT/CT (140 kV, 20 mA, 146 mGy × cm) added sclerosis and involvement of corpus and arcus vertebrae T12 [Figure 1]c and [Figure 1]e. A following 99mTc-PSMA scan with SPECT/CT (140 kV, 30 mA, 337 mGy × cm) revealed concordant positive findings in the third rib and iliac body, the prostate cancer and no lymphatic involvement [Figure 1]b. The sclerotic lesions in T11 and T12 were negative in the PSMA scan [Figure 1]d and [Figure 1]f. Quantification of uptake (Q.VMI Evolution, GE Healthcare GmbH, Solingen, Germany) was performed, including the comparison of irradiated and non-irradiated lesions. Since the iliac body was not included in the radiation field, it served as an internal positive control [Figure 1]g and [Figure 1]h. The uptake-ratio of T12/iliac body was 1.2 in MDP SPECT/CT and 0.2 in SPECT/CT, indicating a 6.0-fold lower uptake of T12 in 99mTc-PSMA SPECT/CT.
|Figure 1: Comparison of scans with 99mTc-MDP and 99mTc-PSMA after external beam radiotherapy of thoracic vertebrae 10-12. Within the third month after external beam radiotherapy, whole body scans with (a) 99mTc-MDP and (b) 99mTc-PSMA revealed concordant metastatic sites (a and b) in the third rib (blue) and the iliac body (pink). Within the radiation field, the bone scan (c) was strongly positive, whereas the PSMA scan (d) showed none (T11, green) to slightly (T12, red) increased uptake. 99mTc-MDP uptake involved the whole T12 (e), whereas PSMA uptake spared the left arcus vertebrae (f). The non-irradiated metastasis of the iliac body (g and h) served as internal positive control and showed uptake in both scans. MDP: Methylene diphosphonate; PSMA: Prostate specific membrane antigen; SPECT/CT: Single photon emission computed tomography/computed tomography|
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| Discussion|| |
Although androgen deprivation and external beam radiotherapy have led to a remarkable reduction of PSA-level, the uptake of 99mTc-PSMA and 99mTc-MDP in nonirradiated sites has remained high.
The high uptake of T12 in the bone scan suggests a false positive finding. The pathophysiological effect is called “flare phenomenon” and is caused by an enhanced turnover of hydroxyapatite as a part of the healing process after external beam radiotherapy. Therefore, the tumor-specific binding of 99mTc-PSMA is able to evaluate the therapeutic effect two months after external beam radiotherapy superior to 99mTc-MDP. Summarized, SPECT/CT with 99mTc-PSMA is able to reduce the frequency of false-positive findings in bone scans after external beam radiotherapy and hence after trauma, and in pronounced degenerative changes in the spine. Studies of patients with 99mTc-PSMA SPECT/CT before and after external beam radiotherapy will show that 99mTc-PSMA is able to assess response to external beam radiotherapy earlier and more specific than Tc-99m-MDP.
We thank Mr. Prof. Dr. R. Friebel and Mr. Bernd Kuhn for their valuable advice.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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