Comparison of Tc-99m MDP and Sm-153 EDTMP bone scan.

A 72-year-old male, a known case of carcinoma of prostate, had bilateral orchidectomy in 2002 and while on hormones developed multiple bone metastases in 2010. He was treated with (153)Samarium ethylene diamine tetra methylene phosphonate (EDTMP). The author compares the features of (99m)Tc methylene diphosphonate (MDP) scan and (153)Sm EDTMP bone scan, highlighting the similarities of skeletal uptake.

INTRODUCTION

Since mid-1930s, sodium phosphate (NaH2 32PO4), as a soluble orthophosphate, has been used for palliative treatment of multiple widespread painful metastases to bone. Advances in nuclear medicine have now added strontium chloride (89Sr), Samarium [153Sm ethylene diamine tetra methylene phosphonate (EDTMP)] and Rhenium hydroxyethylidene di phosphonate (186Re HEDP).

153Samarium

Samarium has a short physical half-life of 46.3 hours and is one of the shortest lived isotopes in current use for the palliation of bone pain from metastatic disease. 153Sm decays by a beta emission and gamma photon, allowing imaging of the therapeutic isotope. The beta particle has energies of 810 keV (20%), 710 keV (50%) and 640 keV (30%) which penetrate tissue over a relatively short distance (0.83 mm of water) and a gamma energy 103 keV (29.8% abundance) is suitable for standard scintigraphic imaging. 153Sm is complexed with EDTMP. The complex remains stable with no measurable breakdown during 48 hours.[1]

CASE REPORT

We report a case of a 72-year-old male patient with carcinoma prostrate, who had bilateral orchidectomy in 2002. In 2009, he had reactivation of bone pain and was detected to have cervical vertebral metastases. Radiation was given up to 30 Gy to the vertebrae. The patient was on hormone since then and had monthly Zolendronic acid injection i.v. (14 injections). Serum prostate specific antigen (PSA) was increased (58.8 ng/ml). In 2010, he developed diffuse body ache and 99mTc methylene diphosphonate (MDP) scan revealed multiple uptake in axial and appendicular skeleton [Figure 1]. Radiogram of chest revealed no pulmonary metastases [Figure 2].

Figure 1

Tc 99m MDP bone scan

Figure 2

Chest radiograph

The patient was given a dose of 40 mCi of 153Sm EDTMP intravenously. After 96 hours, whole body images were acquired (512×512 matrix) – anterior and posterior views. The scan was compared with 99mTc MDP bone scan. Both revealed abnormal concentration in dorsolumbar vertebrae and skull, besides pelvis and ribs [Figure 3]. The metastases concentrate 153Sm EDTMP – a prerequiirement for fixed pain relief. The patient had pain relief over a period of 1–2 weeks.

Figure 3

Sm 153 EDTMP post therapy scan

DISCUSSION

Eary[1] showed that the distribution of 153Sm EDTMP was similar to that of 99mTc MDP and had sensitivity equal to that of 99mTc MDP bone scanning (lesion to non-lesion bone localization ranged from 2.7 to 6.7). Likewise, 153Sm EDTMP was found to stay in the skeletal structures for approximately 42 hours and skeletal doses ranged from 20 to 32 rad/mCi with marrow doses ranging from 4.6 to 7.5 rad/mCi.

Another trial[2] also showed that lesion to normal ratios were 4.04±2.62 for 153Sm and 4.01±1.9 for 99mTc MDP. Likewise, ratios of lesion to soft tissue and normal bone to soft tissue were similar between the two agents and 53% of the dose was excreted by the kidneys in the first 8 hours. Clearance studies showed that 5% and 2% remained in the blood at 2 hours and at 4 hours, respectively, after injection.

Dose escalation trials[3] showed hematologic toxicity in the patients receiving higher doses and they determined a maximum tolerated dose level of 2.5 mCi/kg.

Pain relief typically occurred within 1–2 weeks after treatment, with about 12% showing a flare response after treatment. The lower dose regimen (1 mCi/kg) was compared with higher dose treatment (2.5 mCi/kg) and no definite dose–response relationship was found.[4] The duration of pain relief and survival was greater for the subgroup that received 153Sm re-treatment than for the group that received the single-dose treatment.

153Sm EDTMP holds great promise as a radiopharmaceutical agent for treating pain secondary to metastatic disease. With its imaging gamma photon, favorable beta energy particle, and short physical half-life, the care of patients can be optimized.