Global dose prescription variances exemplified through oropharynx cancer: when is 70 Gray 70 Gray?

PURPOSE/OBJECTIVES: Radiotherapy treatment planning hinges on a critical factor: the prescribed dose. Surprisingly, there is no consistent, standardised global approach to evaluating the dosimetry of this prescription across different centres treating head and neck cancer (HNC). This study aimed to quantify global dose variations for identical prescriptions across international centres treating oropharyngeal cancer, to establish the foundation for future outcome-based studies and improve consistency of interpretation worldwide.

MATERIALS AND METHODS: The study included patients with oropharyngeal cancer who were consecutively treated from 2017 onwards with intensity-modulated radiotherapy (IMRT) or volumetric modulated arc therapy (VMAT) at eight globally recognised radiotherapy departments. These centres were categorised into four categories: North American, North European, Oceanic, and Asian.

RESULTS: The study included 1,514 patients from eight centres and revealed 40 different dose prescriptions, ranging from 55 Gy in 20 to 70 Gy in 35 fractions. When normalised to a 70 Gy prescription, the mean CTV dose showed a 4% median difference across centres. European and Oceania centres deviated by 0.4%, while North American and Asian centres had 2% variability. Near-minimum CTV doses (D98%) ranged from 68.7 Gy to 71.4 Gy.

CONCLUSIONS: The study underscores the wide-ranging implementation of dose prescriptions in HNC. The lack of a standardised global approach to HNC treatment dose prescription carries potential implications for patient care, collaborative research, and treatment de-escalation or radiotherapy dose-painting strategies. This study highlights the need for careful interpretation of dose prescription standards across international centres, to analyse radiotherapy outcomes more accurately in light of their varied implementation.