Good Timing Matters: The Spatially Fractionated High Dose Rate Boost Should Come First

Abstract

Monoplanar microbeam irradiation (MBI) and pencilbeam irradiation (PBI) are two new concepts of high dose rate radiotherapy, combined with spatial dose fractionation at the micrometre range. In a small animal model, we have explored the concept of integrating MBI or PBI as a simultaneously integrated boost (SIB), either at the beginning or at the end of a conventional, low-dose rate schedule of 5x4 Gy broad beam (BB) whole brain radiotherapy (WBRT). MBI was administered as array of 50 µm wide, quasi-parallel microbeams. For PBI, the target was covered with an array of 50 µm × 50 µm pencilbeams. In both techniques, the centre-to-centre distance was 400 µm. To assure that the entire brain received a dose of at least 4 Gy in all irradiated animals, the peak doses were calculated based on the daily BB fraction to approximate the valley dose. The results of our study have shown that the sequence of the BB irradiation fractions and the microbeam SIB is important to limit the risk of acute adverse effects, including epileptic seizures and death. The microbeam SIB should be integrated early rather than late in the irradiation schedule.

The Spinal Cord as Organ of Risk: Assessment for Acute and Subacute Neurological Adverse Effects after Microbeam Radiotherapy in a Rodent Model

“…A good therapeutic efficacy even in malignant tumours which are extremely difficult to control with conventional, already clinically established radiotherapy techniques has been shown in small animal models of malignant brain tumour [2][3][4][5] and lung carcinoma [6]. At the same time, the preservation of normal tissue function was excellent even after irradiation with high MRT peak doses [6][7][8]. The high flux needed to provide the high dose rates of several hundred Gy/s required for MRT can currently only be obtained at synchrotron facilities.…”