**4. Other imaging modalities**

240 12 Chapters on Nuclear Medicine

Hung et al. conducted different protocol, RxWBS on the third to fourth day, fifth to sixth day and tenth to eleventh day post-therapy (Hung et al., 2009). They reported that there is a trend of decreasing visualization of I-131 uptake in sequential images and that 17% of lung metastasis and 16% of bone metastases were missed on the tenth to eleventh day scans. Lee et al. conducted RxWBS on the third and tenth day post-therapy (Lee et al., 2011). They also reported significant reduction in visual analysis scores and uptake ratios of I-131 avid

In addition, diagnostic accuracy of RxWBS is related to the past-history of previous I-131 therapy. Oh et al. reported the sensitivity of RxWBS in detecting distant metastasis after first I-131 therapy is 75% (Oh et al., 2011). In contrast, in patients with history of multiple radioiodine therapy, sensitivity of RxWBS in detecting distant metastasis is only 35%. The sensitivity of RxWBS and SPECT/CT is reported to be similar. However, the specificity of RxWBS is lower than SPECT/CT (Table 1). The sensitivity of FDG PET/CT is lower than RxWBS in detecting distant metastasis and the specificity of FDG PET/CT is much higher

WBS 65 55 59 42 76 SPECT/CT 65 95 85 86 85 PET/CT 61 98 86 93 84

WBS 90 56 63 35 6 SPECT/CT 90 96 95 86 97 PET/CT 48 100 89 100 88

WBS 44 50 46 30 33 SPECT/CT 44 86 59 85 46 PET/CT 72 86 77 90 63 Table 1. Diagnostic performance of WBS, SPECT/CT and PET/CT in detecting distant metastasis (patient-based analysis) (adapted and modified from Oh et al., 2011).

*Sens*, Sensitivity; *Spec*, Specificity; *DA,* diagnostic accuracy; *PPV,* positive predictive value;

Previous radioiodine scanning might be the reason of decreased sensitivity (Rawson et al., 1951). Thyroid stunning has been reported as the temporary impairment of thyroid tissue after a 111 MBq (3 mCi) or greater diagnostic I-131 dose that decreases the final absorbed dose in ablative therapy. However, Rosario et al. reported that diagnostic scanning using a 185 MBq (5 mCi) of I-131 dose does not interfere with uptake of the ablative dose or with treatment efficacy when ablation is performed within 72 hours (Rosario et al., 2005). Dam et al. reported that even though, stunning might occur but there was no significant difference

Sens(%) Spec(%) DA(%) PPV(%) NPV(%)

lesions on the delayed RxWBS.

than RxWBS or SPECT/CT.

All patients (n=140)

Single therapy (n=101)

Multiple therapies (n=39)

*NPV,* negative predictive value

in treatment success rates (Dam et al., 2004).
