- However if ≥ 2 in 6 patients experience a DLT then the maximum administered dose (MAD)will have been reached and the previous dosing level should be used for the expansion phase. If the MAD is reached at dose level 1 the combination therapy of pembrolizumab, cisplatin and radiotherapy will not be considered possible and the trial discontinued. Once the MTD has been determined the trial enters the expansion cohort whereby a further 14 patients are treated with the determined dosage of pembrolizumab in combination with radiotherapy, brachytherapy and cisplatin. For this study the dose limiting toxicities will be assessed by the presence of: