198 Part II Chapter 8 Both BTMs and Na[18F]F PET-CT showed concordant no improvement in FD burden until March 2018. From early 2019 onwards, patient was able to tolerate trimonthly 120mg subcutaneous denosumab. This last regimen resulted in both visual and quantitative decrease on Na[18F]F PET-CT, of which the volume-based-parameter FTV and FAS correlated best with both BTMs, especially P1NP (Figure 6). Figure 6. Follow-up of FD burden in a patient with MFD (male, 59 yo at baseline BS) at start of denosumab undergoing baseline bone scintigraphy and SBS and subsequent 4 consecutive Na[18F]F PET-CT scans. This exceptional amount of scans was related to coinciding Inflammatory Bowel Disease needing treatment and subsequent suboptimal dosage of denosumab and recurring pain complaints. Percentage change in serum biomarkers is given around the date of Na[18F]F PET-CT, with change relative to the direct previous scan. After bisphosphonates treatment starting in 2013, in May 2016 patient received 60 mg of denosumab every three months, no other interventions. FD burden for this patient was low as measured with SBS and at baseline Na[18F]F PET-CT moderately increased when measured with FTV. On consecutive follow-up Na[18F]F PET-CT scan No 2, a clear increase in disease activity is measured with both SUVpeak and FTV and this is reflected by simultaneous increase in both serum alkaline phosphatase and P1NP. Na[18F]F PET-CT scan No 3 interestingly shows further increase in FTV on Na[18F]F PET-CT in accordance with increased serum P1NP, but decrease of SUVpeak on Na[ 18F]F PET-CT and serum alkaline phosphatase. Na[18F]F PET-CT scan No 4 is to our knowledge the first ever to visualize clear decrease in FD burden using molecular imaging and this is reflected by both Na[18F]F PET-CT-parameters and is in accordance with both serum bone formation biomarkers. Upper limit of normal 98 IU/L for ALP and 59 ng/mL for P1NP in [#] in men and premenopausal women and [*] 76 ng/mL for P1NP in postmenopausal patients.