Deep inspiration breath-hold (DIBH) for radiotherapy (RT) can mitigate breathing motion [Citation1–3], improve cone-beam computed tomography (CBCT) image quality [Citation4] and create a favorable anatomy regarding dose to organs at risk (OARs) [Citation1,Citation5–8]. Initial concerns about patient compliance [Citation9] have been reconsidered, as both spirometry based and voluntary, optical tracking based DIBH technique are tolerated by most patients [Citation3,Citation7,Citation10,Citation11]. However, reproducibility and dosimetric benefit vary between patients, so a method for individual assessment is warranted. It is desirable to supplement geometrical/anatomical evaluation of the reproducibility with an estimate of the dosimetric effect of an observed variation in DIBH level.

We provide a method to evaluate the dosimetric effect of intra-fractional variation in DIBH levels on a patient- and treatment plan specific level.