Personalized volume-deescalated elective nodal irradiation in oropharyngeal squamous cell carcinoma (DeEscO): a study protocol

BackgroundDefinitive (chemo)radiotherapy of oropharyngeal squamous cell carcinoma (SCC) consists of treatment of the macroscopic tumor and prophylactic irradiation of large parts of the lymphatic drainage system: the elective clinical target volume (CTV). There is limited data and quantification of (occult) lymphatic spread and the required extent of the elective CTV. De-escalation of the irradiated volume could result in less early and late toxicity and less affection of the immune system. In this study, we reduce the elective CTV based on the personalized factors T-stage, clinical lymphatic involvement, and lateralization of the primary tumor. MethodsThe primary objective is to evaluate the efficacy and safety of an individualized de-escalation of elective node irradiation volumes. We collected a multi-institutional dataset of 598 oropharyngeal SCC patients in whom detailed lymph node involvement was reported. The data can be explored on the publicly available online platform LyProX.org. Based on the data, we developed a model of lymphatic tumor progression to estimate the probability of occult metastases in the clinically negative lymph node levels (LNLs). Metastatic lymphatic progression is described via a hidden Markov model. The patients state of lymph node involvement is described by hidden binary random variables, and the transition matrix describes the probabilities of lymphatic spread. Based on this model and clinical judgement, we created tables that define the personalized elective CTV for different combinations of T-stage, midline extension and clinical LNL involvement. The elective CTV is defined such that the cumulative risk of occult metastases in all non-irradiated LNLs is below 10%. The primary endpoint of this multicentric, prospective, single-arm trial is the rate of out-of-field nodal recurrences after 2 years. The study will be conducted in 6 centers across Switzerland and 120 patients will be enrolled. DiscussionThis study sets out to personalize the elective CTV in oropharyngeal SCC patients, with the goal to de-escalate radiotherapy for patients and herewith improve therapy-associated toxicity and quality of life. The results of this study may be used to personalize treatment in oropharyngeal SCC patients. Trial RegistrationThis study sets out to personalize the elective CTV in oropharyngeal SCC patients, with the goal to de-escalate radiotherapy for patients and herewith improve therapy-associated toxicity and quality of life. The results of this study may be used to personalize treatment in oropharyngeal SCC patients.