Comparison of the normal range of standardized uptake values between 99mTc-MDP SPECT/CT and 18F-NaF PET/CT in breast cancer patient

Introduction: For many years, ^99mTc-MDP bone scans have been used to evaluate skeletal metastasis in oncology. In recent years, the ¹⁸F-NaF bone scan has also been used to identify skeletal metastases. Specifically, skeletal metastasis is qualitatively assessed in ^99mTc-MDP bone scans, whereas ¹⁸F-NaF bone scans have been evaluated qualitatively as well as quantitatively based on SUV values. With the recent introduction of ^99mTc-MDP SPECT SUV by many vendors, SPECT has been able to be quantitatively assessed based on SUV. Our study compares the normal axial bone SUVs measured by ^99mTc-MDP SPECT/CT to those measured by ¹⁸F-NaF PET/CT.

Methods: This study used 120 in carcinoma breast patients' data who underwent pretreatment ^99mTc-MDP SPECT/CT (60 patients) and ¹⁸F-NaF PET/CT (60 patients) with normal BMI and had no skeletal metastases. The ^99mTc MDP study was performed on the Discovery NM/CT 670 Pro SPECT/CT; GE Healthcare and the ¹⁸F-NaF scan was performed on the Gemini TF64 PET/CT, Philips Electronics. Volumetrix MI from GE Healthcare was used to perform quantitative reconstruction of SPECT images by applying scatter and attenuation corrections and collimator response corrections. SUV maximum (SUV_max) is measured at the normal site of the axial bones: skull, scapula, sternum, ribs, cervical spine, thoracic spine, lumbar spine, pelvis, humerus, and femur. Three ROIs (region of interest) of 2 cm diameter each were drawn on each normal bone to obtain three measurements. The mean and standard deviation of SUV_max was calculated for all normal bones for both modalities. To compare SUV_max obtained by PET and SPECT, the Wilcoxon signed-rank test was performed. A P-value <0.05 was considered significant.

Results: For most of the bone sites, the SUV_max were comparable for both modalities (table 1 & figure 1). For PET scans, the minimum and maximum SUV_max values were 12.56 (±3.54) (cervical spine) and 3,30(±1.30) (humerus), respectively. For SPECT, the values were 12.65 (±3.89) (Thoracic spine) and 2.98 (±1.28) (humerus). Six of the 10 boney sites did not have significant difference p-values>0.05 (table 1).

Table 1: This table presents the means and SD of normal bone SUV_max, along with the Wilcoxon signed-rank test p-values for each skeletal site.

Conclusions: 99mTc-MDP SPECT SUV measurements can be an effective way to assess skeletal metastasis quantitatively. Our study shows that SUVmax calculated by PET or SPECT for normal bone is comparable. We did not compare the SUV values for skeletal metastases assessed on SPECT and PET in this investigation, which is one of its limitations.

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