An approach for retrospective measurements of thoron ((220)Rn) and radon ((222)Rn) by home-stored CDs/DVDs is proposed. It employs analysis of alpha tracks at two depths beneath the disk surface. The signal in the first one (69 µm) is due both to (220)Rn and (222)Rn, while the signal at the second (80 µm) is due only to (222)Rn. The second signal is used as to measure (222)Rn, as well as to determine and subtract 'the (222)Rn component' from the first signal. The remaining '(220)Rn component' is used to measure thoron. Numerical modelling is performed and the results show that simultaneous retrospective measurements of thoron and radon are possible over a wide range of environmental concentrations.