PubMed · 11022727
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S Morita, H Tsuji, S Matsuoka, H Tsujii. 2000. [Heavy ion radiotherapy].. https://pubmed.ncbi.nlm.nih.gov/11022727/
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This paper summarises the conclusions of a working group established jointly by the International Atomic Energy Agency (IAEA) and the International Commission on Radiation Units and Measurements (ICRU) to address some of the relative biological effectiveness (RBE) issues encountered in ion-beam therapy. Special emphasis is put on the selection and definition of the involved quantities and units. The isoeffective dose, as introduced here for radiation therapy applications, is the dose that delivered under reference conditions would produce the same clinical effects as the actual treatment in a given system, all other conditions being identical. It is expressed in Gy. The reference treatment conditions are: photon irradiation, 2 Gy per fraction, 5 daily fractions a week. The isoeffective dose D(IsoE) is the product of the physical quantity absorbed dose D and a weighting factor W(IsoE). W(IsoE) is an inclusive weighting factor that takes into account all factors that could influence the clinical effects like dose per fraction, overall time, radiation quality (RQ), biological system and effects. The numerical value of W(IsoE) is selected by the radiation-oncology team for a given patient (or treatment protocol). It is part of the treatment prescription. Evaluation of the influence of RQ on W(IsoE) raises complex problems because of the clinically significant RBE variations with biological effect (late vs. early) and position in depth in the tissues which is a problem specific to ion-beam therapy. Comparison of the isoeffective dose with the equivalent dose frequently used in proton- and ion-beam therapy is discussed.
Exchange of clinical information is essential for the development and progress in radiation oncology. This goal can be achieved only through a general harmonization on methods of reporting. The ICRU has been involved for several decades in a continuous effort to harmonize reporting of dose and to standardize methods used to determine the doses and points or volumes where these doses are delivered. Requirements for reporting proton and ion beam therapy should, in principle, be as similar as possible to reporting the current radiation therapy modalities. However, proton and ion therapy have their own clinical and technical uniqueness: in particular, they require definition of new clinical, radiobiological and technical concepts, and strict quality assurance programmes for efficient and safe clinical application. The current ICRU definitions of volumes are reviewed: Gross Tumour Volume (GTV), Clinical Target Volume (CTV), Planning Target Volume (PTV), Organs At Risk (OAR), Planning organ at Risk Volume (PRV), treated volume and reference volume. The irradiation conditions and the absorbed dose should always be reported together with the point(s) and/or volume(s) where the dose is delivered. In addition, the weighting factor W(RBE) introduced to take into account the RBE, and the related weighted dose D(RBE) have to be reported.
Research in the field of biological effects of heavy charged particles is needed for both heavy-ion therapy (hadrontherapy) and protection from the exposure to galactic cosmic radiation in long-term manned space missions. Although the exposure conditions (e.g. high- vs. low-dose rate) and relevant endpoints (e.g. cell killing vs. neoplastic transformation) are different in the two fields, it is clear that a substantial overlap exists in several research topics. Three such topics are discussed in this short review: individual radiosensitivity, mixed radiation fields, and late stochastic effects of heavy ions. In addition, researchers involved either in experimental studies on space radiation protection or heavy-ion therapy will basically use the same accelerator facilities. It seems to be important that novel accelerator facilities planned (or under construction) for heavy-ion therapy reserve a substantial amount of beamtime to basic studies of heavy-ion radiobiology and its applications in space radiation research.