A theoretical study to focus a polychromatic synchrotron X-ray beam for microbeam radiation therapy

Abstract

Microbeam radiotherapy (MRT) appears to target tumour cells while sparing normal healthy cells. However, it is in its preclinical stage at present. Clinical trials of MRT can be done in the Imaging and Medical Beamline (IMBL) of the Australian Synchrotron provided that the dose rate deliverable by the X-ray beam in Hutch 3B of the IMBL, where the required patient positioning equipment is located, is sufficiently high for MRT. At present the deliverable dose rate there is only 75Gys−1. However, a deliverable dose rate of between and including 375Gys−1 and 750Gys−1 is required for doing MRT clinical trials in Hutch 3B due to the irradiation profile inherent to MRT. The height of the focused beam in Hutch 3B must also be between and including 1.0 mm and 10 mm. A kinoform compound refractive lens (kinoform CRL) made of [3.5×1018Patomscm−3]-doped Si is proposed to be used in the Scenario where the X-ray beam, produced by a superconducting multipole wiggler source (SCMPW) operating at a maximum magnetic field of 4.000 T, is filtered by 0.6 mm of diamond before reaching the kinoform CRL. This is the Diamond-Optic Scenario. In this Scenario, the dose rate deliverable in Hutch 3B using the optic ranges from 380Gys−1 to 1300Gys−1 with beam heights ranging from 3.55 mm down to 1.0 mm, respectively. Also, the weighted average photon energies of the beam in Hutch 3B in this Scenario are almost entirely suitable for MRT in the IMBL. The X-ray beam in this Scenario can heat the P-doped Si optic to a few hundred degrees Kelvin above the hypothesised melting point of the P-doped Si due to its high power density. Therefore, the optic must be cooled lest it melt. The Diamond-Optic Scenario is not used routinely in the IMBL due to its excessive power. A variation of the Diamond-Optic Scenario, namely that the kinoform CRL be placed before sensitive components instead of after them is proposed for the routine use of this Scenario.