| Complete metabolic response | Uptake less than or equal to liver activity in BM sites and FLs previously involved, including PSD and EMD (DS 1-3) | RAC1 | Highly likely to be responding:Return of normal fat containing marrow in areas previously infiltrated by FLs or DD; Unequivocal decrease in number or size of FLs; Conversion of a packed BM infiltrate into discrete nodules, with unequivocal decrease in tumor load in the respective BM space; Decreasing soft tissue associated with bone disease; Emergence of intra- or peritumoral fat within/around FLs (fat dot or halo sign); Previously evident lesion shows increase in ADC from ≤1400 μm2/s to >1400 μm2/s; ≥40% increase in ADC from baseline, with corresponding decrease in normalized high b-value signal intensity, and morphologic findings consistent with stable or responding disease; For soft-tissue disease, RECIST version 1.1 criteria for CR (disappearance of all TLs)/PR (≥30% decrease in the sum of L-Di of TLs, taking as reference the baseline sum L-Di)
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| Partial metabolic response | Decrease in number and/or activity of BM/FLs present at baseline, but persistence of lesion(s) with uptake more than liver activity (DS 4-5) | RAC2 | Likely to be responding:Evidence of improvement but not enough to fulfill criteria for RAC1, for example, slight decrease in number/size of FLs, previously evident lesions showing increases in ADC from ≤1000 μm2/s to <1400 μm2/s, a 25% to 40% increase in ADC from baseline with corresponding decrease in b-value signal intensity, and morphologic findings consistent with stable or responding disease; For soft-tissue disease, RECIST version 1.1 criteria not meeting requirements for PR
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| Stable metabolic disease | No significant change in BM/FLs compared with baseline | RAC3 | No change: |
| Progressive metabolic disease | New FLs consistent with MM compared with baseline | RAC4 | Likely to be progressing:Evidence of worsening disease, but not enough to fulfill criteria for RAC5; Equivocal appearance of new lesion(s); No change in size but increasing signal intensity on high b-value images (with ADC values <1400 μm2/s) consistent with possible disease progression; Relapsed disease: reemergence of lesion(s) that previously disappeared or enlargement of lesion(s) that had partially regressed/stabilized with prior treatments; Soft tissue in spinal canal causing narrowing not associated with neurologic findings and not requiring radiation therapy; For soft-tissue disease, RECIST version 1.1 criteria not meeting requirements for PD
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| | | RAC5 | Highly likely to be progressing:New critical fracture(s)/cord compression requiring radiation therapy/surgical intervention; only if confirmed as malignant with MRI signal characteristics; Unequivocal new focal (5-10 mm)/diffuse area(s) of infiltration in regions of previously normal marrow; Unequivocal increase in number/size of FLs; Evolution of FLs to diffuse neoplastic pattern; Appearance/increasing soft tissue associated with bone disease; New lesions/regions of high signal intensity on high b-value images with ADC value between 600 and 1000 μm2/s; For soft-tissue disease, RECIST version 1.1 criteria meeting requirements for PD (≥ 20% increase in the sum of L-Di of TLs, taking as reference the smallest sum L-Di recorded since the treatment started, or the appearance of ≥1 new lesion(s))
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