Role of tc-99m MIBI and tc-99m DMSA-V in evaluation of bone tumors

Abstract EN

Background : bone sarcomas are usually aggressive tumors treated by multimodality approaches.

Early detection of residual or recurrent tumor tissue after treatment is important in the management of these patients.

This is currently achieved by clinical examination, diagnostic radiological procedures, radionuclide imaging techniques and detailed histological examination.

Tumor response to preoperative chemotherapy in osteosarcoma as defined by the degree of tumor necrosis has been found to be one of the best prognostic indicators of disease control.

However, this information can be only obtained by detailed histologic examination after tumor resection.

Recently, there have been attempts to predict the tumor response to chemotherapy before surgical excision by radionuclide imaging techniques.

This enables the clinician to consider alternative chemo-therapeutic regimens or surgery at an earlier stage.

Purpose : evaluate and compare Tc-99m pentavalent DMSA to Tc-99m siesta MIBI and Tc-99m MDP blood pool image in patients with malignant bone tumors for the purpose of : 1- Detection of the primary lesion.

2- Evaluating treatment response of osteosarcoma after 4 cycles of preoperative chemotherapy.

3- Prediction of response of osteosarcoma after the first cycle only of preoperative chemotherapy.

4- Detection of residual or recurrent viable tumor after treatment.

Materials and Methods: Ninety-three patients with different types of bone sarcomas were studied.

They were divided into 3 groups: Group I: Newly diagnosed patients with different bone sarcomas (40cases) Group II: Fourteen patients from group I with definite pathological diagnosis of osteosarcoma were studied to evaluate the response of the primary lesion to preoperative chemotherapy (according to the treatment protocol adopted in NCI).

Group III : Patients with different types of bone sarcomas at different stages of treatment and under follow up (53 patients).

All patients were imaged following IV injection of 20 mCi (740 MBq) of 99mTc-MDP, 99mTc-MIBI and 99mTc (V) DMSA with time interval of 48 h between each scan.

Results: The sensitivity of 99mTc(V)DMSA for detection of primary lesion was nearly 100% versus 92% for BP and 85% for 99mTc-MIBI scanning in group I.

Regarding the assessment of response to preoperative chemotherapy, the patients were classified into 3 sub-groups according to percentage of tumor necrosis obtained from histopathologic examination when correlated with scintigraphic findings into partially responding disease, stable disease and progressive disease.

Quantitative analysis revealed cut off values of tumor to background ratios (to differentiate between viable and non-viable tumor tissue) for 99mTc(V)DMSA, 99mTc-MIBI and BP of 1.7, 1.5 and 1.5 respectively.

Nineteen patients in group 3 had equivocal findings for local tumor recurrence on CT and/or MRI and the sensitivity for detection of tumor recurrence by 99mTc-DMSA, BP and 99mTc-MIBI was 94 %, 73 % and 68 % respectively.

Conclusions : Tc-99m (V) DMSA has high avidity for primary malignant bone tumors with no false negative results.

The evaluation of response to preoperative chemotherapy in osteosarcoma after the first cycle may predict the final response where partial responders with significant declining ratios should continue the same treatment while those with progressive disease and rising ratios should change their chemotherapy regimen or do surgery at an earlier stage saving their time and money.

This issue needs confirmation with large number of patients and multi-center trials.

The higher sensitivity of Tc-DMSA compared to Tc-MIBI in the detection of primary lesions as well as recurrent tumors suggests that Tc-99m pentavalent DMSA is not affected by multi-drug resistance.

Further studies using both tracers and confirmed with immuno-histochemical staining of P-glycoprotein from tumor samples are recommended to confirm this issue.