Abstract
Photon-based fractionated radiotherapy at a dose of 60 Gy has become the standard radiotherapy for malignant brain tumors, mainly gliomas. However, in most cases such treatment still does not provide a satisfactory clinical outcome. According to one large extended study, even with this standard radiotherapy the median survival time of patients with a glioblastoma after diagnosis is 9 to 12 months, and only 23% of patients achieve a glioblastoma size reduction of more than 50%. We therefore compared the effects of different advanced radiation modalities with those of standard radiotherapy. We introduce here four advanced radiation modalities, namely stereotactic conformal radiotherapy (SCRT) with micro multi-leaf collimator (mMLC), intensity modulated radiotherapy (IMRT), particle radiation therapy (carbon beam and proton beam), and boron neutron capture therapy (BNCT). SCRT with mMLC improved dosimetry remarkably even for relatively large tumors even though it is normally contraindicated in ordinary radiosurgery including that employing γ-and x-knives. IMRT is based on a clever concept of infiltrating tumors such as gliomas. The feature of this radiation modality is it applies a dose gradient for each planned target volume by a change in the shape and size of the collimator. It enables irradiation of different doses for contrast enhanced lesions and infiltration of a lesion separately. Particle radiation therapeutics has a very unique "Bragg peak" character. This modality provides a very sharp distribution of dosimetry behind the target compared to photon irradiation. Carbon and proton beams are utilized worldwide in particle radiation. So called "heavy particle radiation" employs carbon beams. Carbon beams have greater high-relative biological effects and a low oxygen enhancing ratio. These characteristics of carbon beams give them a theoretic advantage especially over radioresistant tumors. The three advanced radiation modalities share the concept of spatial targeting for tumors to obtain good tumor control with decreased damage to normal tissue. BNCT involves the unique concept of cell biological targeting. It employs a binary approach with boron compounds and neutron beams. It is based on the principle that if boron compounds were applied selectively to tumor tissue, then neutron α reactions that occur only within tumor cells would be followed by tumor cell death with minimal harm to normal tissue. All four advanced radiation modalities have been studied rigorously of late, and the publication of some promising results should not be too far away.
