Details of calculations and results of the decision analysis for a cohort of 1000 men comparing TRUS-guided biopsy with mpMRI and MRI-targeted biopsy
| TRUS-guided biopsy for all | mpMRI then MRI-targeted biopsy | |
|---|---|---|
| Number of biopsies | 1000 (all men) | 600 = P(MRI+|D+)+P(MRI+|D−) = (MRIsens*prev*no_in_cohort)+ ((1-MRIspec)*(1-prev)*no_in_cohort)) = (0.8*0.5*1000)+((1−0.6)*(1−0.5)*1000) |
| Patients with clinically significant cancer and correctly identified (true positive) | 250 =P(TRUS+|D+) =TRUSsens*prev*no_in_cohort =0.5*0.5*1000 | 320 =P(MRI+|D+).P(MRITB+|D+) =MRIsens*MRITBsens*prev*no_in_cohort =0.8*0.8*0.5*1000 |
| Patients with clinically significant cancer and wrongly identified (false negative) | 250 =p(TRUS−|D+) =(1-TRUSsens)*prev*no_in_cohort =(1−0.5)*0.5*1000 | 180 =P(MRI−|D+)+P(MRI+|D+).P(MRITB−|D+) =((1-MRIsens)*prev*no_in_cohort) + (MRIsens*(1-MRITBsens)*prev*no_in_cohort) =((1−0.8)*0.5*1000)+(0.8*(1−0.8)*0.5*1000) |
| Patients with insignificant prostate cancer or no prostate cancer and correctly identified (true negative) | 450 =P(TRUS−|D−) =TRUSspec *(1-prev)*no_in_cohort =0.9*(1−0.5)*1000 | 480 =P(MRI−|D−)+P(MRI+|D−).P(MRITB−|D−) =(MRIspec*(1-prev)*no_in_cohort) + ((1-MRIspec)*MRITBspec*(1-prev)*no_in_cohort) =(0.6*(1−0.5)*1000)+((1−0.6)*0.9*(1−0.5)*1000) |
| Patients with insignificant prostate cancer or no prostate cancer and wrongly identified (false positive) | 50 =P(TRUS+|D−) =(1-TRUSspec)*(1-prev)* no_in_cohort =(1−0.9)*0.5*1000 | 20 =P(MRI+|D−).P(MRITB+|D−) =(1-MRIspec)*(1-MRITBspec)*(1-prev)*no_in_cohort =(1−0.6)*(1−0.9)*(1−0.5)*1000 |
‘prev’ – prevalence; ‘no_in_cohort’ – number of men in cohort; ‘TRUSsens’ – sensitivity of TRUS-guided biopsy; ‘TRUSspec’ – specificity of TRUS-guided biopsy; ‘MRIsens’ – sensitivity of mpMRI; ‘MRIspec’ – specificity of mpMRI; ‘MRITBsens’ – sensitivity of MRI-targeted biopsy; ‘MRITBspec’ – specificity of MRI-targeted biopsy.