Reply to the letter “Choline PET/CT compared with bone scintigraphy in the detection of bone metastases in prostate cancer patients”

Abstract

Dear Sir, We thank Beheshti and Langsteger [1] for their interest in our paper “[C]Choline PET/CT detection of bone metastases in patients with PSA progression after primary treatment for prostate cancer: comparison with bone scintigraphy” [2] and for raising important issues; we would like to reply to the comments presented. We agree that the comparison between tomographic and planar modalities has an intrinsic bias due to the different potentials of the two techniques. Knowing that it has already been demonstrated that single photon emission computed tomography (SPECT) and/or SPECT/CT significantly improve the specificity of bone scintigraphy (BS) [3, 4], in the present paper the clinical advantages and limitations of one technique over the other have been described exclusively based on a clinical point of view, and the comparison between the two modalities to evaluate the potential benefits that PET/CT could offer over BS have been performed. We are aware that the comparison of bone metastases may be of limited value because [C]choline PET/CTstudies were performed from the base of the skull. This limitation is due to the retrospective nature of the study; thus, [C]choline PET/ CT scans were acquired according to a standard protocol. In particular, only two lesions, one at the skull, and categorized at BS as malignant, and one at an arm, and categorized at BS as equivocal, could not be validated because the anatomical localizations were outside the field of view of PET/CT and thus excluded from lesion-based analysis. Regarding the low choline uptake in sclerotic bone lesions, our opinion is that further studies are required to clarify the meaning of this phenomenon. At present we cannot distinguish between the low uptake due to a regression of bone disease in response to therapy or due to a false-negative [C] choline PET/CT finding. Until this crucial concept has been clarified, the monitoring of bone metastatic disease should be based on a conventional bone scan. At present the low choline uptake in sclerotic bone lesions can be considered a limitation of [C]choline PET/CT but, once the metabolic meaning of this finding is clarified, it could potentially become a prognostic tool with significant clinical relevance. In our series, there were 24 of 78 patients with bone metastases on [C]choline PET/CT and 19 of 78 patients on BS. In our opinion the relevance of these results is the following: if a patient undergoes [C]choline PET/CT for biochemical recurrence for restaging his disease and a pathological bone uptake occurs, due to the high positive predictive value of [C]choline PET/CT, the clinician may be confident in considering that pathological uptake as a bone metastatic lesion. Moreover, the absence of [C]choline uptake in degenerative changes of the skeleton is another issue that emphasizes the potential superiority of this technique over BS. In response to the comment of Beheshti and Langsteger [1], we would also like to remark that [C]choline PET/CT, being a whole-body modality, presents the great advantage M. Picchio (*) : F. Fallanca Nuclear Medicine Department, Scientific Institute San Raffaele, Milan, Italy e-mail: picchio.maria@hsr.it