PHYSICS

  1. The Effect of Target Fragmentation on the Autoactivity Induced by Heavy Ion Therapy
  2. Effects of Nuclear Fragmentation Reactions at Relativistic Energies
  3. Measurements of Nuclear Tracks on CR-39 with Atomic Force Microcopy
  4. Measurements of Bulk Etch Rate of CR-39 with Atomic Force Microcopy
  5. An Experiment on Remote Action against Man in Sensory-Shielding Condition (PartU)
  6. An experiment on Extrasensory Information Transfer with Electroencephalogram Measurement
  7. Dosimetry of Particle Beams with Diffferent Walled Ionization Chambers
  8. Small-scale Dosimetry Comparison for Therapeutic Carbon Beam at HIMAC
  9. Estimation of the Exposure and a Risk-Benefit Analysis for a CT System Designed for a Lung Cancer Mass Screening Unit
  10. A Prescribed Diffusion Model to Estimate G-value of Fricke Dosimeter Irradiated by Photons of 100 eV-10 Mev
  11. Status of the HIMAC Injector
  12. A Respiration-Gated Beam Control System for Patient Treatment
  13. Development of the Gated Irradiation System Synchronized with Respiratory Motion for Heavy Ion Therapy
  14. Distribution of Fragment Particles in Heavy Ion Therapeutic Beam
  15. Development of 3D Irradiation System for Heavy Ion Radiotherapy at HIMAC
  16. The Local Noise Property in a Reconstructed Image of a Uniform-activity Sphere for 3D Positron Emission Tomography



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1. The Effect of Target Fragmentation on the Autoactivity Induced by Heavy Ion Therapy

Takehiro Tomitani, Mitsutaka Kanazawa, Kyosan Yoshikawa, Yasuhiro Wada*, Ikuhiro Shinoda*
(* Siemens-Asahi Medical Technology Inc.)

keywords: positron, target fragmentation, heavy ion therapy

In 12C heavy ion therapy, some 12C heavy ion beams transform themselves to 11C through fragmentation reaction with target material. Hence this phenomenon is referred t as autoactivation of the projectiles. Likewise some target nuclei also become radioactive through fragmentation reaction of the target nuclei, which is referred to as target fragmentation hereafter. 11C autoactivity is useful for checking heavy ion treatment, since 11C is a positron emitter and the distribution can be measured by positron emission tomography(PET). After physical experiments with phantoms and experiments on animals, the technique was applied to patients. Each trial underwent inspection by the comittee on clinical trials. In the physical and animal studies, we observed 11C activity peak attributed to the projectile fragentation of 12C promary beams and 11C activity due to target fragmentation that distributes uniformly and forms a pedestal. The calculations based on the semi-empirical fragmentation cross-section formula(L. Sihver, T. Kanai et al: Phys. Rev. 47(3):1225-1236, 1993) indicated that the 11C activity induced by target fragmentation distributes almost uniformly over the entrance region to the and-points of projectiles. In these cases, the media were assumed uniform. On the other hand, 11C activity induced from projectile fragmentatio concentrates mainly near the end-points of the promary beams and is reasonably higher than that due to target fragmentation.
11C activity in the patient undergone 12C heavy ion therapy was measured. (The images are not shown here as they are best seen by using color display.) The patient had a metastatic brain tumor induced from lung cancer. In the PET image, 11C accumulates around the target region. In addition, an unexpected accumulation of activity is observed in the region near the head surface. The purpose of this report is to explore the source of the latter activity. Activity induced in the target region may be partly washed away by blood flow and recirculated to the surface of the head. However, the activity in the blood would be faurly low and distributed almost uniformly over the whole body, so that this possibility can be ruled out. Another possibiity is positron emitters induced through target fragmentation reaction. Typical atomic constituents of various organs are shown in Fig. 1. Possible positron emitters are 11C(t1/220.39 min.), 38K(t1/27.636 min.). Potassium isotopes can be exclided because of relatively short half-lives. 38K may be induced from 40Ca. The density of the bone(P`1.82) is almost twice as high as densities of other organs(P`1) and the atomic fraction of C is higher thatn in other organs except adipose tissure. To explore these two possibilities, we performed three experiments. In the first experiment, a polyethylene cylinder (15 cm diameter, 10 cm height) was attached in front of the cylinder. In the third experiment, a stack of three lenses made of CaF2 (3 cm diameter, 1.5 cm thick in total) was attached in front of the cylinder. Fluorine in CaF2 might induce 18F, but its half-life (109.77 min.) is longer than that of 11C, so that 18F can be distinguished from 11C activity by time-activity analysis. The results are shown in Fig. 2, from which we conclude that the activity in the skull region can be attributed to 11C induced from target fragmentation of 12C in the skull and not to 38K from 40Ca. This result indicates that fat tissue will also contribute to the generation of 11C through target fragmentation, since C fraction in fat is about 1.5 times higher than that of bone, even though its density (P`0.92) is 0.5 of that of bone. In fact, we observed high activity accumulation near the surface in the PET image taken of a patient with a liver tumor, in which rib bone may be another source.

Publications:
1) Yoshikawa, K., Tomitani, T., Kanazawa, M., Wada, Y. Kanai, T., Imai, Y., Suhara, T., Kato, H., Koga, M., Kandatsu, S., Yoshioka, H. and Tsuji H.,J. Nucl. Med. Technol. 24, 167-168, 1996.
2) Tomiaki, T., Yoshikawa, K., Kanazawa, M. et al.: in Advances in Hadrontherapy, U. Amaidi, B. Larsson and Y. Lemoigne, editors, Elsevier, Amsterdam, pp.339-345, 1997.

Figure captions
Fig. 1. Atomic constituents of human organs. Data were cited from ICRU report 37, pp.27-29.
Fig. 2. Positron emitter distribution induced from 12C heavy ion beams. Left: Psitron emitter distribution in the polyethylene cylinder; middle: that in the polyethylene cylinder with a graphite slab in the upstream positron; right: that in the polyethylene cylinder with CaF2 lenses in the upstream positron.


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2. Effects of Nuclear Fragmentation Reactions at Relativistic Energies

Susumu Kinpara

Keywords: nuclear fragmentation reaction, cross section, 12C

One interesting dynamical phenomenon in physics is heavy ion nuclear reactions, which yield mass number distribution. Various experimental data have been accumulated, but now, it is necessary to look at the reactions systematically through a theoretical investigation in order to comprehend nuclear interactions and structure of atomic nuclei. In particular, recent developments of the nuclear many-body problem allow nuclear structure to be described using the meson exchange interaction expressed in terms of the meson degrees of freedom explicitly. Such results encourage study of nuclear interactions by means of a microscopic treatment. Knowledge of reaction processes considerably affects studies in fields other than nuclear physics. For example, the use of heavy ions has become feasible recently in the field of radiotherapy treatment for cancer diseases utilizing ionization by the particle beam. It is necessary to study the nuclear reaction processes in order to evaluate microscopically the energy loss in matter or the biological effects on cells. When a radiation beam passes through matter, the kinetic energy of the radiation is usually lost by transferring the energy to the electrons in the atom. In addition to this scattering process, the kinetic energy of the heavy ion also possibly transfers to the matter through nuclear fragmentation reactions.
As another example, atomic nuclei are known to propagate in a galaxy with high kinetic energies as cosmic rays. Knowledge of the cross section of the spallation is experimentally and theoretically important for understanding the creation of elements from the beginning of the universe to the present.

In this work, fragmentation reaction cross sections at relativistic energies are investigated using phenomenological approach. Equations are obtained by a geometrical treatment in the framework of classical dynamics, in which the impact parameters is introduced. A numerical solution is obtained for the 56Fe + 12C system at 600 MeV/nucleon incident energy and shown in Fig. 3. The predicted mass number distribution of fragmentation reproduces well the experimental data. The coulomb energy term in the mass formula affects the nuclide dependence of cross sections in a favorable direction.

Publication: Kinpara, S.:J. Phys. Soc. Jpn, 66 522-524, 1997.

Fig.3 Mass yield cross sections (units, millibarn (mb)) fr the mass number A of the fragments. The data are connected by guidelines. The experimental data are from the literature.


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3. Measurements of Nuclear Tracks on CR-39 with Atomic Force Microscopy

Mikio Yamamoto, Nakahiro Yasuda, Minori Yamagishi1, Youji Kaizuka2, Mieko Kurano, Tatuaki Kanai, Akira Furukawa, Nobuhito Ishigure, Masaharu Nakazawa2, Hiroyuki Takahashi2, Tadayoshi Doke3 and Koichi Ogura4 (1Toho Univ., 2Univ.of Tokyo, 3Nihon Univ., 4Waseda Univ.)

Keywords: track detector, CR-39, etch pit, heavy ion cancer treatment, atomic force microscope

Recently, some demonstrations of an atomic force microscope (AFM) have been made taking images of the track etch pits of the solid state detector (SSNTD), but reports on quantitative analysis of track etch pits using the AFM technique are limited.

Object sizes for AFM measurements are about 1/100 - 1/1000 of those for OPT measurements. Therefore, AFM is a very useful tool to study the track formation and etching mechanism of the track detector. This method makes it possible to observe high density etch pits produced by heavy ions of more than 107 ions/cm2. It is applicable to in vivo measurements of LET and has been used to measure dose for carbon ion cancer treatments at NIRS, which use an ion density of 106 ions/cm2 (Table 1).

The feasibility of applying AFM to the quantitative analysis of minute etch pits on CR-39 was studied in comparison with observations using an optical microscope (OPT).
The CR-39 detectors were irradiated by 490 MeV/u silicon ions and 290 MeV/u carbon ions at NIRS-HIMAC with a density of about 107 ions/cm2, each. The chemical etching was carried out in a solution of 7N NaOH at 70, using a water bath incubator at a constant temperature. The etching time was varied from 10 to 900 minutes. Etched silicon and carbon tracks with diameters ranging from 0.1-2m were measured with the AFM and 2-10m with the OPT. Some samples were observed using both AFM and OPT.

The diameter (D) of etch pits as a funtion of etching time for silicon and carbon trradiated samples is shown in Fig. 4. In order to chack the cnsistency between the two techniques, some samples were measured by both OPT and AFM. The data obtained by the two methods are connected smoothly without any inconsistency. While the track diameter is almost constant for the layer of 0.5-9.0 m, it decreases a little in the surface layer under 0.5m. The result of this study will be useful for understanding the track formation mechanism of SSTD. Moreover this AFM technique makes it possible to analyze the high track density of 106 - 108 tracks/cm2.

Table.1 Comparison of measuring methods.
OPTAFMRef. Cancer treatment
Density (ions/cm2)104108106
Etching (hours)240.1

Fig.4. Variations of diameter of etch pit obtained by AFM (white points) and OPT (black points) are shown as a function of etching time.

Publication:
M. Yamamoto, N. Yasuda, et al., Radiation Measurements, 28(1997)227.


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4. Measurements of Bulk Etch Rate of CR-39 with Atomic Force Microscopy

Nakahiro Yasuda, Mikio Yamamoto, Nobuyuki Miyahara, Nobuhito Ishigure, Tatuaki Kanai and Koichi Ogura* (*Nihon Univ.)

Keywords: atomic force microscope, track detector, CR-39, bulk etch rate

For the atomic force microscope (AFM) observation of minute tracks (1m) in CR=39 track detectors, an accurate method for the measurement of the extremely small amount of bulk etch is required. A simple method for the direct measurements of the bulk etch using AFM was developed.

The bulk etch, B, is the amount of material removed from each surface of a solid state track detector (SSTD) during its chemical etching. The B is an important parameter for determining the track sensitivity of SSTD. The traditional methods for measuring B are through the measurement of 1) the change in the detector thickness, 2) the mass change of the detector, 3) the diameter of high-LET particle tracks such as fission tracks. In the case of the short etching time required for the AFM observations, the thickness and the mass changes of the etched detector are extremely small. Therefore, the methods 1) and 2) are not applicable to determine B for these samples. Method 3) was chosen for comparison to the developed method.

The small CR-39 samples (1x1 cm2) were irradiated to 252Cf fission fragments in air. After the irradiation, a part of the CR-39 surface exposed to fission fragments was masked with epoxy resin adhesive. The partially masked samples were etched in 7N NaOH solution at 70 using a water bath incubator. The etching time was varied from 3 to 60 minutes. The mask was easily peeled off from the CR-39 surface of CR-39 after etching. The surface of the detector were imaged directly by AFM.

Since the part of the surface masked by epoxy resin was not etched, a step appeared on the CR-39 surface as shown in the AFM image of Fig.5. Then the amount of bulk etch, B, of the detector was directly measured as a level difference of this step.
These results were compared with those by the conventional measuring method described as the method 3) in which, diameters of fission tracks on the etched surfaces of the same samples were also measured by AFM. It is well known that the average radius of fission tracks corresponds to the amount of B of the etched sample. The comparison for the two methods is shown in Fig.6. The measured amounts of B for CR-39 are in good agreement between each other within the statistical errors.

By using AFM, it is expected that precise analysis for the minute tracks in CR-39 can be made to get the etching properties, the etch induction time and the track sensitivities for various ions including low velocity ions. The results of those studies will be useful for understanding the track formation mechanism of SSTD.

Fig. 5. An AFM image (153x153 m2) of masked-atched surface. The CR-39 was etched in 7N NaOH at 70 for 10 minutes. This image is displayed as a viewer 30above the surface would see it. The level difference shows the amount of bulk etch (B).

Fig. 6. The radius of etch pits vs. amount of bulk etch.

Publications:
M. Yamamoto, N. Yasuda, et al., Radiation Measurements, 28(1997)227.


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5. An Experiment on Remote Action against Man in Sensory-Shielding Condition (Part II)

Mikio Yamamoto, Masahiko Hirasawa, Hideyuki Kokubo,
Kimiko Kawano1, Tsuyoshi Hirata2, Tomoko Kokado, Hideaki Sakaida,
Nakahiro Yasuda, Akira Furukawa and Nobuo Fukuda
(1 Nippon Medical School, 2 NEC Corporation)

Keywords: qigong, tohate, sense shielding, suggestion, extrasensory, remote action, EEG

"Tohate" is a term from traditional Japanese martial arts. When tohate is performed, the receiver feels a sensory shock and steps back rapidly when a master of the martial arts (the sender) emits "qi" to the receiver without any touching. Tohate is seen as a signal translation by qi. However, we do not have complete theories explaining tohate or qi. In our earlier experimental studies, we reported that the phenomenon of tohate when performed by a qigong master is not caused only by the master's suggestion.
This report examines our earlier results by new experiments which were done under randomized and double blind conditions.
The sender (qigong master) and the receiver (his pupil) were separated in two rooms of a sensory-shielded building, with the receiver on the 1st floor and the sender on the 4th. The sender performed one "qi-emission" action during each 80 sec trial at a random time indicated by the experimenter. When the sender performed a remote action, the sender's qi-emitting motion time and the receiver's response motion time (start of the step back) were recorded. The coincidence frequency within }5.5 sec was 16 (expected value was 7.88) for the 49 trials. It is statistically significant and the p-value is 0.0008 (post hoc analysis).
This suggests that there is an unknown communication mechanism between the sender and receiver. The coincidence frequency is very high in the range from -5.5 to +5.5 sec. It is especially high in the range from -1 to +1 sec in our earlier experiments. However, there was no remarkable }1 sec peak in the new experiments. The reason for the difference between the previous and new results may be due to the change of experimental conditions.
In more experiments using the same sender and receiver, electroencephalograms (EEGs) of the receiver were recorded. The qi-emission was performed at a random time selected within a minute period by the experimenter. For 57 trials there is a statistically significant difference between the emitting and non-emitting times in the alpha wave mean amplitudes of the EEGs for the right frontal part of the brain for the receiver. This suggests that extrasensory information transfer may take place and that it may be related to the right frontal part of the brain.

Publications:
1) Yamamoto, M., Hirasawa, M., Kawano, K., Yasuda, N. and Furukawa, A.: J. Intl. Soc. Life Info. Sci., 14, 97-101, 1996.
2) Yamamoto, M., Hirasawa, M., Kawano, K., Kokubo, H., Kokado, T., Hirata, T., Yasuda, N., Furukawa, A. and Fukuda, N.: J. Intl. Soc. Life Info. Sci., 14, 228-248, 1996.


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6. An Experiment on Extrasensory Information Transfer with Electroencephalogram Measurements

Masahiko Hirasawa, Mikio Yamamoto, Kimiko Kawano*, Akira Furukawa and Nakahiro Yasuda (*Nippon Medical School)

Keywords: subconscious, extrasensory, information transfer, EEG, alpha wave amplitude, right frontal region

A sender and a receiver were located in two separate, sensory-shielded rooms. Their electroencephalograms (EEGs) were measured at 12 points (Fp1, Fp2, F7, F8, C3, C4, T5, T6, O1, O2, Fz, Pz) with monopolar leads both while sending and not sending extrasensory information.

To transmit extrasensory information, an experimenter showed the sender a card for a few seconds that was randomly selected from forty non-picture cards. The sender then concentrated on that card with the eyes closed for one minute. The receiver was previously informed that the information to be transmitted consisted of one of forty non-picture cards. During the non-sending period, the sender thought nothing for one minute with the eyes closed.
The sending and non-sending of extrasensory information were each carried out for one minute in a two-minute period. The experimenter randomly decided and notified the sender whether the first or second half were to be used for sending. The receiver was only informed of the start time and one and two minutes later with phoneticsigns and was not informed which half was used for sending. The receiver guessed both the sending information and sending time period, with the eyes closed during the two-minute trial. This trial was repeated 20 times.
The experiment was carried out for two pairs of subjects (A and B) using two rooms separated by a corridor on the fifth floor of the First Research Building at NIRS on the 11th of October, 1995.
Conscious recognition by the receivers in guessing the time when information was sent was not significant at the 5% level of significance (one-tailed) for either pairs. Thus, extrasensory transfer of information between the subjects' consciousness was not demonstrated. On the other hand, there was a difference in the wave mean amplitudes calculated from Pair A receiver's EEGs between the sending and non-sending tome zones that was judged significant at the 5 % level of significance (one-tailed) at one point (O2) in the period 20 to 25 seconds after the start of the sending and non-sending times. Likewise, there was a difference for Pair B at one point (Pz) in the 20 nto 25 second period from the start, at three points (Fp2, F7, F8) in the 30 to 35 second period and at one point (O2) in the 50 to 55 second period. These results suggest that extrasensory information is transferred between the subjects' subconscious.
The reactions for this extrasensory transfer of information occur first in the occipital to parietal regions and next in the right frontal regions of the receivers. The occipital is a visual region, while the frontal region is concerned with integration. Since the extrasensory transfer of visual onformation was attempted in this experiment, one hypotesis is that the visual regions react first and compose visual information. This is followed by the integration regions reacting to the information. However, the wave differences were 10 seconds or more between the reactions in the visual and frontal regions. Thus, these reactions are different from those of ordinary conscious recognition.

Comparisons of the significant changes in the receivers and senders of the differences of the wave mean amplitudes obtained from the EEGs between the sending and non-sending times indicate that there is no correlation between the senders and receivers. This shows that the extrasensory transfer of information in the subject's subconscious suggested in this experiment is not completed instantaneously.

Publication:
Hirasawa, M., Yamamoto, M., Kawano, K., Furukawa, A., and Yasuda, N.: J. Int. Soc. Life Info. Sci., 14: 185-195, 1996.


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7. Dosimetry of Particle Beams with Different Walled Ionization Chambers

Takeshi Hiraoka, Kaname Omata, Akifumi Fukumura and Mitsue Takeshita

Keywords: ionization chamber, absorbed dose, wall material, absorbed dose comparison

In Japan, absorbed dose for radiotherapy beams must be determined@according to the protocol for the dosimetry of high-energy photon and electron beams in radiotherapy which is published by the Japanese Association of Radiological Physicists (JARP). The protocol requires to use of the JARP-type ionization chamber which is basically a Farmer ionization chamber made of PMMA for both the wall and build-up cap. Several types of Farmer ionization chambers are commercially available. Then, for this investigation we determined the absorbed dose to water for heavy ion beams were by using several types of Farmer ionization chambers with different wall and build-up cap materials.
We prepared five different wall and build-up cap combinations PMMA-PMMA, Nylon-PMMA, Carbon-Delrin, A-150-Lucentine and C-552-Polystyrene. All ionization chambers had the same geometrical conditions with very small differences of length and diameter of the outer and central electrodes. The chamber readings were calibrated by 60Co gamma rays whose intensity had been calibrated by a chamber traceable to the national standard.
Absorbed dose measurements were carried out for 290 MeV/u carbon ion beams from HIMAC(Heavy Ion Medical Accelerator in Chiba). Measurements were also made for 70 MeV proton beams from NIRS AVF cyclotron. Irradiations were made at the entrance plateau for a mono-energetic beam and at the center of the Spread Out Bragg Peak(SOBP). Irradiations were carried out in air without a build-up cap.
Ionization charges were measured by an electrometer, Keithley model 6517, which has built into a 1000V high voltage source. We used 500V as the polarizing voltage for the measurement of heavy ion and proton beams, except for the chamber made by A-150 wall which used 400 V.
One of the most important problems in the experiment of dose comparison is the stability of beam monitor. In the HIMAC irradiation facilities, three beam monitor system are installed, two ionization chamber monitors and a secondary emission monitor. In order to check the stability of the beam monitor, measurements were repeated regularly using a reference ionization chamber. Then, the stability was estimated within 0.2% for both heavy ion and proton beams.
Before the measurements, we examined the physical constants appearance in the dose evaluation formulae, especially for the 60Co calibration beam. The values were taken form the data of Andreo and the values used for the IAEA protocol.
For all chamber irradiations, measurements were made for both positive and negative polarities. The polarity effect for all chambers was less than 1%, and the largest value was 0.61%. So the effect was very small for the chambers investigated, especially for the charged particle beams. Actually, absorbed dose was calculated using the average value for both polarities.
The ionization chamber readings were converted to absorbed dose to water according to the JARP protocol. The dose was expressed in Gy for appropriate monitor counts. No corrections were made for the very small differences in ionization chamber geometry. The range of variation of the absorbed dose estimated for all chambers was within 0.8% for both particle beams. The maximum standard deviation was 0.45% for SOBP at 117mm.
We concluded that the absorbed dose to water for heavy ion beams, which was determined with several Farmer-type ionization chambers, showed good agreement, within 0.8% according to the JARP protocol. The small difference of the absorbed doses may depend on inaccuracy of physical constants used for the chamber calibration.


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8. Small-scale Dosimetry Comparison for Therapeutic Carbon Beam at HIMAC

Akifumi Fukumura, Takeshi Hiraoka, Kaname Omata, Mitsue Takeshita, Kiyomitsu Kawachi, Tatsuaki Kanai, Naruhito Matsufuji, Hiromi Tomura, Yasuyuki Futami and Guenther Hartmann*
(*DKFZ, Germany)

Keywords: absorbed dose, carbon beam, dosimetry intercomparison, HIMAC

The traceability for the absorbed dose of proton and heavier ion beams has not been established by national standard laboratories so far. Therefore it is important for heavy ion therapy facilities to compare the absorbed dose evaluated by their own dosimetry system with others and to establish a standardized base for the dosimetry. The dosimetry comaparison experimant between Japanese and German heavy-ion therapy dacilities was carried out with the 290 MeV/u carbon beam at HIMAC in December 1996, following the comparison held at GSI in March 1996(G. Hartmann et al.,Advances in Hadrontherapy, 346-350, 1997).
The dosimeters which each dacility used were Farmer-type air-filled ionization chambers manufactured by PTW. Each chamber was installed behind the binary filters made of polymethylmethacrylate and irradiated with the carbon beam for which quantity had been preset by the beam monitor. The measurement of the carbon beam was carried out under three conditions as follows:
1. at 0 cm depth for the monoenergetic 290 MeV/u carbon beam;
2. at the depth equivalent to 12 cm in water for the monoenergetic 290 MeV/u carbon beam; and
3. at the depth equivalent to 12.1 cm in water for the carbon beam which has the range of about 15 cm and the Bragg Peak spread out to a 6 cm width, both in water.
Each facility individually evaluiated the absorbed dose in water from electrical charge collected by its own chamber, according to the dosimetry protocol adopted by the facility. The protocol of the Japanese group is based on the European proton dosimetry protocol(S. Vynckier, et al., Radioth. Oncol., 20, 53, 1991;S. Vynckier, et al., Radioth. Oncol., 32, 174, 1994)and uses the stopping power ratio of water-to-air for the carbon beam(T. Hiraoka and H. Bichsel, Jpn. J. Med. Phys 15-2, 91, 1995). On the other hand, the German group adapts the newest ICRU report for clinical proton dosimetry without modifications. The difference between the two proton dosimetry protocols is described elsewhere(J. Medin, et al., Phys. Med. Biol. 40, 1161, 1995).
Under the first condition, fluence measurements were also performed with CR-39 track detectors, which were processed independently at both institutes. In addition, a plastic scintillator was used for fluence measurements. The measured fluence was multiplied by the stopping power of the 290 MeV/u carbon beam t evaluate the absorbed dose in water.
Table 2 summarizes the results of this dosimetry comparison. The values in each condition are normalized to the mean value obtained with the ionization chambers. In spite of different dosimetry protocols, the values obtained by the ionization chambers are in very good agreement within experimantal errors for all conditions.Therefore, this comparison establiches a relatively standardized base between Japanese and German heavy-ion facilities for the ionization chamber dosimetry of the carbon beam. The values obtained by fluence methods are, however, lower than those using ionization chambers. This is partly because the fluence measurements miss the contribution of the low LET particles such as fragments or secondary electrons. On the other hand, both groups substitute the differencial W-value of the low-energy proton beam, because of the lack of data on the differencial W-value for a high energy carbon beam. If the differencial W-value for the high energy carbon beam is lower or close to the W-value for an electron beam, the doses obtained with the ionization chamber would be overestimated. To establish an absolutely standardized base with high accuracy, dosimetry with a water calorimater is also required.

Table 2. Results of dosimetry comparison for carbon beam at HIMAC
InstituteMethodRatio of evaluated dose to mean value obtaned by ionization chambers
Condition 1condition 2Condition 3
NIRSIon. chamber0.996}0.0010.999}0.0021.000}0.001
DKFSIon. chamber1.004}0.0081.001}0.0021.000}0.002
NIRSCR-390.945}0.023
DKFSCR-390.908}0.027
NIRSScintillator0.942}0.037


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