核医学と放射線治療

High Resolution Molecular Radiation Therapy and Tumor Imaging for the 21^st Century

Abstract

Anders Brahme

With the lightest ions beyond protons, i.e., Helium, Lithium and Beryllium ions, highly specific Molecular Bragg peak radiation therapy of malignant tumors is possible with minimal adverse normal tissue reactions elsewhere in the body. The Bragg peak ionization density is only elevated in a few mm wide spot at the end of the ion range with resultant increased local apoptosis and senescence. By only placing Bragg peaks in the tumor, an increased local therapeutic effect is obtained with only low ionization density and easily repairable damage in surrounding normal tissues. A geometrical accuracy in dose delivery of about 1 mm is possible with these ions, and high-resolution molecular tumor imaging is then needed to accurately delineate the target volume. It is proposed that ultra-sensitivity whole body PET cameras should be built to achieve mm resolution in the whole target region. With about 1 m axial field of view an almost 50-fold increased sensitivity and a reduced imaging time down to a few minutes should be in reach. To get sub mm resolution with whole body spectroscopic MR, about 15 Tesla to 20 Tesla is needed and will significantly increase the resolution with tumor specific metabolite imaging from the 10 mm to 15 mm available today. In the future, it should also be possible to achieve a resolution as high as 10 μm with Stereoscopic Phase Contrast X-ray imaging, or to reduce the dose and imaging time by using 2 projections instead of 400 to get 3D images, thanks to the significantly increased contrast in each projection. When these new methods are brought into clinical use together with light ion therapy a mean tumor cure as high as 80% should be possible, and even more if the new early tumor detection and malignancy estimation methods are brought into more regular clinical use.