The first medical application of radiation to the medicine was performed immediately after the discovery of X-ray at 1985. Since then many kinds of the accelerator based radiations such as electron, neutron, proton, negative pion and heavy ion beams have been used to cure tumors. The technological development of the accelerator is deeply reflected in the modalities of the radiation therapy. In pursuit of a principle“higher dose to the tumor and less to the normal tissue” the pioneering researches in the proton and heavy ion therapy that utilize a Bragg peak are performed using cyclotron and synchrotron for physics researches. In the course of these studies many projects of the dedicated medical accelerator facilities have been planned and some of them are already in operation or are under construction. In this manuscript accelerators in the early years are reviewed briefly and most part is devoted to ones that are commonly used and newly built.
Beam delivery techniques for radiotherapy using heavy-charged-particle beam have been reviewed. The conventional techniques using fixed-modulation SOBP (Spread-Out Bragg Peak) are described. The double scattering methods and the wobbling methods are summarized as open systems. The newly-developed conformal techniques,3D spot scanning at PSI,3D raster scanning at GSI, and broad-beam 3D irradiation method at NIRS, are introduced as a method to improve the dose localization by using the variable modulation. It is pointed out that these new systems are the closed system since the dose for each beam configuration and some beam modifying devices should be controlled during the irradiation and that high-level security system is required for highdoserate techniques. Beam delivery techniques for charged particle therapy are rapidly evolving to improve the dose localization further.
A brief summary of the activities in the research and development of modern 3D treatment planning system both for conventional and particle radiotherapy will be described. Then, the current status of treatment planning for carbon beam radiotherapy at HIMAC, NIRS and a future plan will be presented.
Strategy for treatment of cancer by heavy ions beam, i. e., dose per fraction, total dose were discussed in this study. The survival curves from cell studies can be fitted to linear quadratic model, a nd survivingf ractionc an b e. calculateda t any doses. The simplem odel of fractionation makes linear survival curves as a function of number of fractions. The final surviving fraction after numberso f fractionsc an be calculateda t the final fraction. An approximaten umber of cells can be calculatedb y an averages ize of cells. To obtain “ cure”, tumor cells must be eradicated up to even the last cell, i. e., ∼1 X 10-10will be necessary to achieve “cure”. The fractionated calculationo f survivala fter 30th(the final) fraction of a conventional X-ray therapy for a resistant tumor cells showed only 0.0001, indicating far from the cure. Survivals after heavy ion beam were estimatedb y the same model, fitting survivalc urves of resistant cells against heavy ions. The results showedu singa ppropriated ose per fraction, t he final survivingf ractionr eached to a possible curability level. This study shows that the model using survival curves is a simple way to imagineh ow the radiationb eam eradicatest umor, a nd it wouldb e effectivet o help to be integrated into treatment planning.
Particle therapy, a clinical point of view. With the advent of the 3-D treatment planning system and new imaging modalities, particle therapy will open a new era of cancer treatment using ionizing radiation. A better spatial dose distribution and/or high biological effec ts, are the main properties of particle therapy. Too achieve a good clinical outcome using these properties, we shoud establish a high precision treatment system designed especially for particle therapy. A brief summary of treatment results of particle therapy and its indications were also described.
First, features of particle radiation therapy from the viewpoint of medical economics are pointed out. Then, relationship between effectiveness of particle radiation therapy and (time distance)cost is figured out, being expressed by a function, y=f(x). At the same plane of x-y coodinates, y=g(x) is defined to express relationship between urgent necessity x of particle radiotherapy for a patient and the capability of accepting such urgent necessity. The method of looking for the cross point by placing y=f(x)=g(x) in order to find economical significance of particle radiation therapy, and for the possibility of building up new facilities for the particle radiation therapy where and when and by what cost, are discussed. Moreover, the problems of non-profitable actions, redemption of generated cost and investment, and calculation of cost-effectiveness are raised. Especially, method of cost-effective analysis is proposed, and conclete proccedure for the measurement of cost, especially human cost which is considered to be very difficult to measure is presented. The method is according to the time study of medical stuffes for a certain patient. The experience of the author to carry out such study is reflected. Lastly, the advantage of constructing a databese for cost-effectiveness analysis and accumulation of measured data is stated.
The tissue-maximum ratio for extremely small X-ray beams was examined using a 4 MV linear accelerator applied to square fields and its usefulness in the output factor was investigated. Furthermore, measurements in a water phantom and the effects of a low density phantom (average electron density 0.30 relative to water) on the measured values were assessed. A cylindrical watertight ionization chamber was used and the sensitive volume with air cavity was 0.006cm3. Marked discrepancies were found between the measured values in water and low density phantoms for the depth of the maximum dose and the output factor of an extremely small field. The measurement in the low density phantom has no advantage in practical use; therefore, we used the small ionization chamber to obtain data for an extremely small field.