Intermittent radiotherapy as alternative treatment for recurrent high grade glioma: A modelling study based on longitudinal tumor measurements

Recurrent high grade glioma patients face a poor prognosis for which no curative treatment option currently exists. In contrast to prescribing high dose hypofractionated stereotactic radiotherapy (HFSRT, [≥] 6 Gyx5 in daily fractions) with debulking intent, we suggest a personalized treatment strategy to improve tumor control by delivering intermittent high dose treatment (iRT, [≥] 6 Gyx1 every six weeks). We performed a simulation analysis to compare HFSRT, iRT and iRT plus boost ([≥] 6 Gyx3 in daily fractions at time of progression) based on a mathematical model of tumour growth, radiation response and patient-specific evolution of resistance to additional treatments (pembrolizumab and bevacizumab). Model parameters were fitted from tumour growth curves of 16 patients enrolled in the phase 1 NCT02313272 trial that combined HFSRT with bevacizumab and pembrolizumab. Then, iRT +/-boost treatments were simulated and compared to HFSRT based on time to tumor regrowth. The modelling results demonstrated that iRT+boost(-boost) treatment was equal or superior to HFSRT in 15(11) out of 16 cases and that patients that remained responsive to pembrolizumab and bevacizumab would benefit most from iRT. Time to progression could be prolonged through the application of additional, intermittently delivered fractions. iRT hence provides a promising treatment option for recurrent high grade glioma patients.