Heavy element enhanced synchrotron stereotactic radiotherapy as a promising brain tumour treatment.

Synchrotron stereotactic radiotherapy (SSR) is a treatment that involves selective accumulation of high-Z elements in tumours followed by stereotactic irradiation, in CT mode, with monochromatic X-rays from a synchrotron source, tuned at an optimal energy. The irradiation geometry, characteristic X-rays, photoelectrons, and Auger electrons generated on high-Z atoms by kilovoltage X-rays produce a localized dose enhancement. Two complimentary SSR approaches have been successfully developed in the past 5 years in our team, and may be promising in high-grade glioma management: iodine-enhanced SSR, with an iodinated contrast agent; and Pt-enhanced SSR; a concomitant radio-chemotherapy treatment with locoregional injection of platinated chemotherapy drugs. The results for iodine-enhanced SSR using contrast agents are presented in this paper. IUdR-enhanced SSR was also tested in this study. Up to 15 Gy, intracarotid infusion of iodine significantly improved the rats' survival compared to irradiation alone. SSR provides the most protracted survivals of F98 glioma-bearing rats. The technique is currently transferred to clinical trials. Iodine-enhanced SSR will be implemented first, because of its simplicity; and pave the way for Pt-enhanced SSR, the most efficient technique, but still needing to be improved in terms of intrinsic toxicity.

Polymer gel dosimetry for synchrotron stereotactic radiotherapy and iodine dose-enhancement measurements.

Synchrotron stereotactic radiotherapy (SSR) is a radiotherapy technique that makes use of the interactions of monochromatic low energy x-rays with high atomic number (Z) elements. An important dose-enhancement can be obtained if the target volume has been loaded with a sufficient amount of a high-Z element, such as iodine. In this study, we compare experimental dose measurements, obtained with normoxic polymer gel (nPAG), with Monte Carlo computations. Gels were irradiated within an anthropomorphic head phantom and were read out by magnetic resonance imaging. The dose-enhancement due to the presence of iodine in the gel (iodine concentration: 5 and 10 mg ml(-1)) was measured at two radiation energies (35 and 80 keV) and was compared to the calculated factors. nPAG dosimetry was shown to be efficient for measuring the sharp dose gradients produced by SSR. The agreement between 3D gel dosimetry and calculated dose distributions was found to be within 4% of the dose difference criterion and a distance to agreement of 2.1 mm for 80% of the voxels. Polymer gel doped with iodine exhibited higher sensitivity, in good agreement with the calculated iodine-dose enhancement. We demonstrate in this preliminary study that iodine-doped nPAG could be used for measuring in situ dose distributions for iodine-enhanced SSR treatment.