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1.  Interim analyses in diagnostic versus treatment studies: differences and similarities 
The purpose of this paper was to contrast interim analyses in (randomized controlled) treatment studies with interim analyses in paired diagnostic studies of accuracy with respect to planning and conduct. The term ‘treatment study’ refers to a (randomized) clinical trial that aims to demonstrate the superiority or noninferiority of one treatment compared with another, and the term ‘diagnostic study’ to a clinical study that compares two diagnostic procedures, using a third diagnostic procedure as the gold standard. Though interim analyses in treatment studies and paired diagnostic studies show similarities in a priori planning of timing, decision rules, and the consequences of the analyses, they differ with respect to (1) the need for sample size adjustments, (2) the possibility of early decisions without early stopping, and (3) the impact of keeping results secret. These differences are due, respectively, to certain characteristics of paired diagnostic studies: the dependence of the sample size on the agreement rate between the modalities, multiple aims of diagnostic accuracy studies, and the advantages of early unblinding of results at the individual level. We exemplified our points by using a recent investigation at our institution on the detection of bone metastases from prostate cancer in patients with histologically confirmed prostate cancer in which 99mTc-MDP whole body bone scintigraphy was compared to positron emission tomography/computed tomography with 18F-fluorocholine as tracer, using magnetic resonance imaging as a reference.
PMCID: PMC3477734  PMID: 23133821
Study design; diagnostic imaging; PET/CT; efficacy studies; accuracy studies; sample size
2.  How to study optimal timing of PET/CT for monitoring of cancer treatment 
Purpose
The use of PET/CT for monitoring treatment response in cancer patients after chemo- or radiotherapy is a very promising approach to optimize cancer treatment. However, the timing of the PET/CT-based evaluation of reduction in viable tumor tissue is a crucial question. We investigated how to plan and analyze studies to optimize this timing.
Methods
General considerations about studying the optimal timing are given and four fundamental steps are illustrated using data from a published study.
Results
The optimal timing should be examined by optimizing the schedule with respect to predicting the overall individual time course we can observe in the case of dense measurements. The optimal timing needs not to and should not be studied by optimizing the association with the prognosis of the patient.
Conclusions
The optimal timing should be examined in specific ‘schedule optimizing studies’. These should be clearly distinguished from studies evaluating the prognostic value of a reduction in viable tumor tissue.
PMCID: PMC3477720  PMID: 23133795
cancer; response evaluation; prognostic value; optimal schedule

Results 1-2 (2)