Biophysical characteristics of HIMAC clinical irradiation system for heavy-ion radiation therapy

Changes in the pharmacokinetics of Gd-DTPA in experimental tumors after charged particle radiation: comparison with gamma-ray radiation

We performed dynamic MRI to reveal the characteristic gadopentetate dimeglumine (Gd-DTPA) uptake in carbon-ion irradiated tumor and compare it with photon irradiation. Fibrosarcomas in C3H mice legs were irradiated with either 16 Gy of carbon ions (74 keV/mm) or an equivalent dose (30 Gy) of Cs-137 gamma-rays. Dynamic MRI was performed 1 or 6 days after irradiation when the tumors showed an initial growth delay or incipient regrowth, respectively. The enhancement pattern was visualized by mapping the maximum enhanced time (Tmax), relative signal intensity maximum (SImax), and time delay of starting enhancement (Td). Significantly larger Tmax and Td values were observed in the tumors 1 day after carbon-ion irradiation than in the nonradiated tumors (No-R) and tumors 1 day after gamma-ray irradiation. Among the selected pixels in the tumors 6 days after carbon irradiation, 77% had Tmax values of less than 120 sec, significantly more than in the No-R group. The Tmax maps for the tumors irradiated with gamma-rays showed a similar tendency to the carbon-irradiated ones, and only a significant difference was obtained between tumors 1 and 6 days after irradiation. Tmax and Td in the carbon-ion irradiated tumors were different from those in the gamma-ray-irradiated tumors. These treatment-specific kinetics may be useful in predicting the therapeutic efficacy of carbon-ion treatment.

Chromosomal aberrations in lymphocytes of lung cancer patients treated with carbon ions

The purpose of this study is to investigate the normal tissue damage caused by carbon-ion therapy. We measured chromosomal aberrations in peripheral blood lymphocytes before, during, and after radiotherapy, using the techniques of fluorescence in situ hybridization (FISH) and chemically induced premature chromosome condensation (PCC). Twenty-two lung cancer patients treated at HIMAC (Heavy Ion Medical Accelerator in Chiba) entered the study and signed an informed consent. Frequencies of lymphocytes with chromosomal aberrations at the end of carbon-ion therapy varied among the patients. This frequency was significantly correlated to the radiation field size and weakly correlated to the counts of white blood cells and lymphocytes during the treatment. As a result, we have found that chromosomal aberrations in peripheral blood lymphocytes from patients treated for lung cancer by carbon-ions were dependent on target volume, possibly reflecting the increased involvement of lymph nodes in the target field.

Ion beam transport in tissue-like media using the Monte Carlo code SHIELD-HIT

The development of the Monte Carlo code SHIELD-HIT (heavy ion transport) for the simulation of the transport of protons and heavier ions in tissue-like media is described. The code SHIELD-HIT, a spin-off of SHIELD (available as RSICC CCC-667), extends the transport of hadron cascades from standard targets to that of ions in arbitrary tissue-like materials, taking into account ionization energy-loss straggling and multiple Coulomb scattering effects. The consistency of the results obtained with SHIELD-HIT has been verified against experimental data and other existing Monte Carlo codes (PTRAN, PETRA), as well as with deterministic models for ion transport, comparing depth distributions of energy deposition by protons, 12C and 20Ne ions impinging on water. The SHIELD-HIT code yields distributions consistent with a proper treatment of nuclear inelastic collisions. Energy depositions up to and well beyond the Bragg peak due to nuclear fragmentations are well predicted. Satisfactory agreement is also found with experimental determinations of the number of fragments of a given type, as a function of depth in water, produced by 12C and 14N ions of 670 MeV u(-1), although less favourable agreement is observed for heavier projectiles such as 16O ions of the same energy. The calculated neutron spectra differential in energy and angle produced in a mimic of a Martian rock by irradiation with 12C ions of 290 MeV u(-1) also shows good agreement with experimental data. It is concluded that a careful analysis of stopping power data for different tissues is necessary for radiation therapy applications, since an incorrect estimation of the position of the Bragg peak might lead to a significant deviation from the prescribed dose in small target volumes. The results presented in this study indicate the usefulness of the SHIELD-HIT code for Monte Carlo simulations in the field of light ion radiation therapy.

Experimental evaluation of analytical penumbra calculation model for wobbled beams

The goal of radiotherapy is not only to apply a high radiation dose to a tumor, but also to avoid side effects in the surrounding healthy tissue. Therefore, it is important for carbon-ion treatment planning to calculate accurately the effects of the lateral penumbra. In this article, for wobbled beams under various irradiation conditions, we focus on the lateral penumbras at several aperture positions of one side leaf of the multileaf collimator. The penumbras predicted by an analytical penumbra calculation model were compared with the measured results. The results calculated by the model for various conditions agreed well with the experimental ones. In conclusion, we found that the analytical penumbra calculation model could predict accurately the measured results for wobbled beams and it was useful for carbon-ion treatment planning to apply the model.

A calibration procedure for beam monitors in a scanned beam of heavy charged particles

An international code of practice (CoP) for dosimetry based on standards of absorbed dose to water has recently been published by the IAEA [Technical Report Series No. 398, 2000] (TRS-398). This new CoP includes procedures for proton and heavy ion beams as well as all other beam qualities. In particular it defines reference conditions to which dose measurements should refer to. For proton and ion beams these conditions include dose measurements in the center of all possible modulated Bragg peaks. The recommended reference conditions in general are used also for the calibration of beam monitors. For a dynamic beam delivery system using beam scanning in combination with energy variation, like, e.g., at the German carbon ion radiotherapy facility, this calibration procedure is not appropriate. We have independently developed a different calibration procedure. Similar to the IAEA CoP this procedure is based on the measurement of absorbed dose to water. This is translated in terms of fluence which finally results in an energy-dependent calibration of the beam monitor in units of particle number per monitor unit, which is unique for all treatment fields. In contrast to the IAEA CoP, the reference depth is chosen to be very small. The procedure enables an accurate and reliable determination of calibration factors. In a second step, the calibration is verified by measurements of absorbed dose in various modulated Bragg peaks by comparing measured against calculated doses. The agreement between measured and calculated doses is usually better than 1% for homogeneous fields and the mean deviation for more inhomogeneous treatment fields, as they are used for patient treatments, is within 3%. It is proposed that the CoP in general, and in particular the IAEA TRS-398 should include explicit recommendations for the beam monitor calibration. These recommendations should then distinguish between systems using static and dynamic beams.

The potential application of β-delayed particle decay beam9C in cancer therapy

A radioactive ion beam like 9C serves as a double radiation source and may be useful in cancer treatment, where the essential irradiation comes from the external beam itself and the extra one is due to the low-energy particles emitted internally during the decay of 9C. Based on the microdosimetric specific energy spectrum in cell nuclei, a model to evaluate the biological effect induced by the internally emitted particles from a beta-delayed particle decay beam has been developed. In this paper, using this model the additional contributions to the cell-killing effect due to the emitted particles from stopping 9C ions were incorporated in the design of spread-out Bragg peaks (SOBP) for radioactive 9C beams. For this purpose, a simulated annealing algorithm was employed to optimize the superposing weighting fractions of all monoenergetic beams so that a uniform cell survival level could be realized across the SOBP within an acceptable deviation of 5%. SOBPs with different widths and at different cell survival levels were designed for both therapeutic 9C and 12C beams for comparison. The potential use of the 9C beam in radiotherapy compared to the 12C beam, which is commonly adopted in the practices of current heavy-ion therapy, is shown systematically in terms of the distributions of biological effective dose and cell survival along the beam penetration.

[11C]Methionine Positron Emission Tomography and Survival in Patients with Bone and Soft Tissue Sarcomas Treated by Carbon Ion Radiotherapy

PURPOSE

The development of the novel carbon ion radiotherapy (CIRT) in the treatment of refractory cancers has resulted in the need for a way to accurately evaluate patient prognosis. We evaluated whether L-[methyl-(11)C]-methionine (MET) uptake and its change after CIRT were the early survival predictors in patients with unresectable bone and soft tissue sarcomas.

EXPERIMENTAL DESIGN

MET positron emission tomography was prospectively performed in 62 patients with unresectable bone and soft tissue sarcomas before and within 1 month after CIRT. Tumor MET uptake was measured with the semiquantitative tumor:nontumor ratio (T/N ratio). The MET uptake in the tumor and relevant clinical parameters were entered into univariate and multivariate survival analysis.

RESULTS

The overall median survival time was 20 months. Patients with a baseline T/N ratio of <or=6 had a significant better survival than patients with a baseline T/N ratio >6 (2-year survival rate: 69.4% versus 32.3%; P = 0.01). Patients with a post-CIRT ratio of <or=4.4 had a better survival than that with a post-CIRT ratio >4.4 (2-year survival rate: 63.7% versus 41.3%; P = 0.01). A significant higher survival rate was observed in patients with post-therapeutic MET uptake change of >30% than patients in lower change group (2-year survival rate: 74.6% versus 41.6%; P = 0.049). The multivariate analysis showed that both baseline and post-CIRT T/N ratio were statistically significant independent predictors of patient survival. Tumors with larger T/N ratio had a significantly poorer prognosis.

CONCLUSIONS

MET uptake as measured by either baseline or post-CIRT T/N ratio was an independent predictor of survival in patients with bone and soft tissue sarcomas treated by carbon ion radiotherapy, whereas post-therapeutic MET uptake change might have potential value for the same purpose.

Effects of carbon-ion beams on human pancreatic cancer cell lines that differ in genetic status

The relative biologic effectiveness (RBE) of carbon-ion beams at 3 different linear energy transfer (LET) values (13, 50, and 80 keV/microm) accelerated by the Heavy Ion Medical Accelerator in Chiba on human pancreatic cancer cell lines differing in genetic status was determined. The RBE values were calculated as D10, the dose (Gy) required to reduce the surviving fraction to 10%, relative to X-rays. We also investigated apoptosis and the relationship between D10 and the cell cycle checkpoint using morphologic examination and flow cytometry analysis, respectively. The RBE values calculated by the D10 values ranged from 1.16 to 1.77 for the 13-keV/microm beam and from 1.83 to 2.46 for the 80-keV/microm beam. A correlation between the D10 values of each cell line and intensity of G2/M arrest was observed. In contrast, LET values did not clearly correlate with induction of apoptosis. These results suggest that carbon-ion beam therapy is a promising modality. Elucidation of the mechanisms of G2/M arrest and apoptosis may provide clues to enhancing the effects of radiation on pancreatic cancer.

Phase I/II clinical trials of carbon ion therapy for prostate cancer

BACKGROUND

Heavy ion beams possess high linear energy transfer components and a prominent Bragg peak in the human body, resulting in higher relative biological effectiveness and improved dose distribution. To establish heavy ion therapy techniques for the treatment of prostate cancer, phase I/II clinical trials were initiated.

METHODS

For 96 patients with T1b-T3 prostate cancer, three carbon ion beams were used to irradiate the prostate and seminal vesicles (20 times/5 weeks) with or without endocrine therapy. Radiation dose was expressed in GyE which was initially thought to be equivalent to photon dose. Total dose was gradually increased from 54 to 72 GyE.

RESULTS

Carbon ion therapy was completed in 20 cases of T1b/T1c/T2aN0M0 as monotherapy, in 8 cases of T2b/T3pN0M0 with neoadjuvant endocrine therapy, and in 68 cases of T2b/T3N0/pN1M0 with neoadjuvant and adjuvant endocrine therapy. Median observation period was 47 months. Grade 3 late radiation morbidity of rectum and/or bladder/urethra developed in one and five cases who received 66 and 72 GyE of radiation, respectively. After these adverse effects were observed, total dose was decreased to 66 GyE and the radiation field was coned down during the treatment course. At 5 years, overall, cause-specific, clinical recurrence-free, and biochemical recurrence-free survival rates were 87.7, 94.9, 90.0, and 82.6%, respectively. Local control was achieved in all patients except one patient who received 54 GyE of radiation.

CONCLUSIONS

The therapeutic techniques of carbon ion therapy have been established for patients with prostate cancer. Carbon ion therapy may exert excellent effect to the tissues of prostate cancer.

Experimental model for irradiating a restricted region of the rat brain using heavy-ion beams

Heavy-ion beams have the feature to administer a large radiation dose in the vicinity of the endpoint in the beam range, its irradiation system and biophysical characteristics are different from ordinary irradiation instruments like X-rays or gamma-rays. In order to get clarify characteristic effects of heavy-ion beams on the brain, we have developed an experimental system for irradiating a restricted region of the rat brain using heavy-ion beams. The left cerebral hemispheres of the adult rat brain were irradiated at dose of 50 Gy charged carbon particles (290 MeV/nucleon; 5 mm spread-out Bragg peak). After irradiation, the characteristics of the heavy-ion beams and the animal model were studied. Histological examination and measurement showed that extensive necrosis was observed between 2.5 mm and 7.5 mm depth from the surface of the rat head, suggesting a relatively high dose and uniform dose was delivered among designed depths and the spread-out Bragg peak used here successfully and satisfactorily retained its high-dose localization in the defined region. We believe that our experimental model for irradiating a restricted region of the rat brain using heavy-ion beams is a good model for analyzing regional radiation susceptibility of the brain.

Radiation Tolerance of the Rat Spinal Cord after Single and Split Doses of Photons and Carbon Ions1

The sensitivity of the rat spinal cord to single and split doses of radiation and the resulting relative biological effectiveness (RBE) were determined for carbon-ion irradiations (12C) in the plateau and Bragg-peak regions. The cranial part of the cervical and thoracic spinal cords of 180 rats were irradiated with one or two fractions of 12C ions or photons, respectively. Dose-response curves for the end point symptomatic myelopathy were established, and the resulting values for the ED50 (dose for 50% complication probability) were used to determine the RBEs. A median latency for myelopathy of 167 days (range, 121-288 days) was found. The ED50 values were 17.1 +/- 0.8 Gy, 24.9 +/- 0.7 Gy (one and two fractions, 12C plateau) and 13.9 +/- 0.8, 15.8 +/- 0.7 Gy (one and two fractions, 12C Bragg peak), respectively. For photons we obtained ED50 values of 24.5 +/- 0.8 Gy for single doses and 34.2 +/- 0.7 Gy when two fractions were applied. The corresponding RBEs were 1.43 +/- 0.08, 1.37 +/- 0.12 (one and two fractions, 12C plateau) and 1.76 +/- 0.05, 2.16 +/- 0.11 (one and two fractions, 12C Bragg peak), respectively. Hematoxylin and eosin staining revealed necrosis of the white matter in the spinal cord in all symptomatic animals. In summary, from one- and two-fraction photon, 12C plateau and Bragg-peak irradiation of the rat spinal cord, we have established RBEs as well as the individual ED50's. From the latter there is a clear indication of repair processes for fractionated photons and 12C plateau ions which are significantly reduced by using Bragg-peak ions. Additional studies are being carried with 6 and 18 fractions to further refine and define the RBE and ED50 values and estimate the alpha/beta ratios.

Ridge filter design for proton therapy at Hyogo Ion Beam Medical Center

At the Hyogo Ion Beam Medical Center (HIBMC) we have developed a new design method for the bar ridge filter used in proton therapy, taking into consideration the scattering and nuclear interaction effects within the filter itself, which are introduced in the design. In our beam delivery system, the bar ridge filter is employed as the range modulator. It is combined with the wobbler system, and produces a three-dimensionally uniform spread-out Bragg peak (SOBP). The design program predicts the three-dimensional dose distribution. Ridge filters of 3-12 cm SOBP in 1 cm increments were designed in the maximum radiation field for 150 MeV and 190 MeV proton beams so that a uniform physical dose area is obtained in the SOBP region three-dimensionally. Measurements were performed with the constructed ridge filters to verify the uniformity and these were compared with the predictions of the design program. The predictions and measurements were found to be in agreement except for the 12 cm SOBP. The uniformities were better than +/- 3.0% for all SOBPs produced. The ridge filters are now clinically in use.

Preoperative carbon ion radiotherapy for non-small cell lung cancer with chest wall invasion—pathological findings concerning tumor response and radiation induced lung injury in the resected organs

The purpose of this study was to make a pathological evaluation of the tumor response and the lung injury of non-small cell lung cancer (NSCLC) patients after carbon ion therapy. We enrolled four NSCLC patients with chest wall invasion but without nodal and distant metastasis (T3N0M0). Only primary lesions were irradiated with carbon ions, followed by surgical resection. The patients consisted of three males and one female varying by age from 54 to 73 (average 66.3). Total treatment dose was 59.4 and 64.8 GyE, respectively, administered in 18 fractions over 6 weeks, or 72.0 GyE in 16 fractions over 4 weeks. Resection after radiation therapy was performed as a combination of lobectomy, lymph node dissection and chest wall surgery. After fixation, the lung was sliced into thin sections to match the CT image. Each slice was anatomically identified and the slices were compared with each other subjected to pathological analysis. No tumor cells were observed in two cases. The other two cases exhibited only a few tumor cells sparsely distributed in the lung tissue. There was evidence of dense pulmonary fibrosis in the limited space surrounding primary tumors, but its density was found to rapidly decrease in the narrow area toward the outside. The rate at which its density subsided mirrored the rapid decrease in the planning CT dose distribution. Microscopy showed no evidence of fibrosis in any of the fields irradiated with less than 15 GyE. Microscopy confirmed an outstanding tumor response with limited pulmonary fibrosis. This substantiates the superior dose localization and strong biological effect of carbon ion beams with a Bragg peak in the lung. The pathological findings have thus provided evidence of the safety and effectiveness of carbon beam therapy in the treatment of NSCLC.

Biological effectiveness of accelerated particles for the induction of chromosome damage measured in metaphase and interphase human lymphocytes

Chromosome aberrations were investigated in human lymphocytes after in vitro exposure to 1H-, 3He-, 12C-, 40Ar-, 28Si-, 56Fe-, or 197Au-ion beams, with LET ranging from approximately 0.4-1393 keV/microm in the dose range of 0.075-3 Gy. Dose-response curves for chromosome exchanges, measured at the first mitosis postirradiation using fluorescence in situ hybridization (FISH) with whole-chromosome probes, were fitted with linear or linear-quadratic functions. The relative biological effectiveness (RBE) was estimated from the initial slope of the dose-response curve for chromosomal damage with respect to low- or high-dose-rate gamma rays. Estimates of RBEmax values for mitotic spreads, which ranged from near 0.7 to 11.1 for total exchanges, increased with LET, reaching a maximum at about 150 keV/microm, and decreased with further increase in LET. RBEs for complex aberrations are undefined due to the lack of an initial slope for gamma rays. Additionally, the effect of mitotic delay on RBE values was investigated by measuring chromosome aberrations in interphase after chemically induced premature chromosome condensation (PCC), and values were up to threefold higher than for metaphase analysis.

Influence of setup errors on spinal cord dose and treatment plan quality for cervical spine tumours: a phantom study for photon IMRT and heavy charged particle radiotherapy

Tumours partly surrounding the cervical spine may be treated by conformal radiotherapy (RT) using intensity-modulated RT (IMRT) with photons or heavy charged particle RT. For both, a high setup accuracy is required to spare the radiosensitive spinal cord, if a high dose is to be delivered. A phantom study was performed to determine the variation of the dose to the spinal cord surface by predefined setup errors. The measured doses were compared to those calculated by the treatment planning programme. The influence of systematic setup errors on characteristic parameters of the treatment plan quality was quantified. The largest variation of the mean and maximum doses to the spinal cord due to setup errors was significantly larger for carbon ions than for IMRT (mean: 11.9% versus 3.9%, max: 29.2% versus 10.8% of the prescribed dose). For the comparison of measured and calculated doses, mean deviations of 3% (IMRT) and 6% (carbon ions) of the prescribed dose were obtained. These deviations have to be considered, when the spinal cord dose is assessed from the treatment plan and they may also influence the dose prescription. Carbon ions yield better values for coverage (99.9% versus 93.1%) and conformality (110% versus 126%) of the PTV as compared to IMRT, while the spinal cord is better spared. Dose distributions produced with carbon ions, however, are more sensitive to setup errors, which have to be considered during treatment.

A model to evaluate the biological effect induced by the emitted particles from a -delayed particle decay beam

Due to their favourable properties such as high dose localization and high RBE heavy-ion beams have attracted increasing interest in cancer treatment. Efforts to exploit these advantages to the maximum extent in cancer therapy have never been given up. A new idea of applying a radioactive ion beam with beta-delayed particle decay such as 9C or 8B to cancer therapy is put forward in this paper. A model to evaluate the biological effect in terms of cell survival induced by the emitted particles from the decays of the stopped ions has been established. Because of the difference of the internally emitted particle irradiation from the external ion beam, the microdosimetric quantity such as specific energy is applied to evaluate the cell surviving effect induced by the emitted particles from the decays of the radioactive ions. Within the framework of this model, the cell-killing effects resulting from the emitted particles were calculated under different conditions. Finally, the potential application of the radioactive ion beam 9C in cancer therapy is demonstrated.

Primary malignant melanoma of the esophagus treated with heavy-ion radiotherapy

Primary malignant melanoma of the esophagus (PMME) is an uncommon but aggressive tumor with very poor prognosis. There is no established treatment plan for the disease, which may be attributed to its rarity and aggressiveness. Surgery is the choice of treatment in early cases. Radiotherapy follows surgery, and chemotherapy has an insignificant role in its treatment. Radiation with heavy ion beams is showing promising results in cancer therapy. Compared to conventional radiation, it permits selective irradiation with minimal injury to the surrounding normal tissue, and treatment with a low dose within a short interval of time is possible. We herein report a case of PMME treated with heavy ion radiation, the first case to be reported so far, and review the relevant literature.

Influence of fragment reaction of relativistic heavy charged particles on heavy-ion radiotherapy

The production of projectile fragments is one of the most important, but not yet perfectly understood, problems to be considered when planning for the utilization of high-energy heavy charged particles for radiotherapy. This paper reports our investigation of the fragments' fluence and linear energy transfer (LET) spectra produced from various incident ions using an experimental approach to reveal these physical qualities of the beams. Polymethyl methacrylate, as a substitute for the human body, was used as a target. A deltaE-E counter telescope with a plastic scintillator and a BGO scintillator made it possible to identify the species of fragments based on differences of various elements. By combining a gas-flow proportional counter with a counter telescope system, LET spectra as well as fluence spectra of the fragments were derived for each element down from the primary particles to hydrogen. Among them, the information on hydrogen and helium fragments was derived for the first time. The result revealed that the number of light fragments, such as hydrogen and helium, became larger than the number of primaries in the vicinity of the range end. However, the greater part of the dose delivered to a cell was still governed by the primaries. The calculated result of a simulation used for heavy-ion radiotherapy indicated room for improving the reaction model.

ESR spin trapping of hydroxyl radicals in aqueous solution irradiated with high-LET carbon-ion beams

The aim of this study was to quantify the hydroxyl radicals (*OH) produced when aqueous solutions are decomposed by high-linear energy transfer (LET) 290 MeV/nucleon carbon-ion beams using an electron spin resonance (ESR) spectrometer. Aerated cell culture medium containing 200 mM 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) was irradiated with doses of 0 to 20 Gy with an LET of 20 to 90 keV/ micro m. We were able to obtain ESR spectra 10 min after irradiation, and the formation of *OH and hydrogen atoms was confirmed by radiolysis of deuterium oxide and ethanol containing DMPO. Our results showed that the yield of *OH by carbon-ion radiolysis increased in proportion to the absorbed dose over the range of 0 to 20 Gy. Furthermore, we discovered that the yield of *OH decreased linearity as LET increased logarithmically from 20 to 90 keV/ micro m. The generation of *OH by carbon-ion radiolysis at LETs of 20, 40, 60, 80 and 90 keV/ micro m was 64, 58, 52, 49 and 50%, respectively, of that for low-LET X radiolysis. These unique findings provide a further understanding of the indirect effect of high-LET radiation.

Estimating uncertainties of the geometrical range of particle radiotherapy during respiration

PURPOSE

To propose a method for estimating uncertainties of the range calculation in particle radiotherapy associated with patient respiration.

MATERIALS AND METHODS

A set of sequential CT images at every 0.2 s was reconstructed from continuous X-ray projection data accumulated by dynamic helical scanning. At the same time that CT data was acquired, the respiratory signal of the patient and the X-ray on/off signal on CT scanner were recorded. Each CT image was timed according to the phase of respiration waveform. Conversion of the CT number to the water equivalent path length (WEL) was performed with our treatment planning system that included a conversion table. As an illustration, the CT images of a patient with liver cancer at the right upper lobe were analyzed. The geometric size of the liver and WELs from body surface to isocenter were measured in each CT image.

RESULTS

Variations of WEL from body surface to isocenter at the anterior-posterior and posterior-anterior direction were 6.2 mm and 18.9 mm, respectively. Liver size changed by 35.2 mm. However, these variations were shown to be considerably reduced by gated irradiation.

CONCLUSIONS

A method using sequential CT images with respiration waveform was proposed. It appeared to be useful in evaluating the uncertainties of the range calculation associated with patient breathing.

A CT calibration method based on the polybinary tissue model for radiotherapy treatment planning

A method to establish the relationship between CT number and effective density for therapeutic radiations is proposed. We approximated body tissues to mixtures of muscle, air, fat and bone. Consequently, the relationship can be calibrated only with a CT scan of their substitutes, for which we chose water, air, ethanol and potassium phosphate solution, respectively. With simple and specific corrections for non-equivalencies of the substitutes, a calibration accuracy of 1% will be achieved. We tested the calibration method with some biological materials to verify that the proposed method would offer the accuracy, simplicity and specificity required for a standard in radiotherapy treatment planning, in particular with heavy charged particles.

Carbon ion radiotherapy for stage I non-small cell lung cancer

BACKGROUND AND PURPOSE

Heavy ion radiotherapy is a promising modality because of its excellent dose localization and high biological effect on tumors. Using carbon beams, a dose escalation study was conducted for the treatment of stage I non-small cell lung cancer (NSCLC) to determine the optimal dose.

MATERIALS AND METHODS

The first stage phase I/II trial using 18 fractions over 6 weeks for 47 patients and the second one using nine fractions over 3 weeks for 34 patients were conducted by the dose escalation method from 59.4 to 95.4 Gray equivalents (GyE) in incremental steps of 10% and from 68.4 to 79.2 GyE in 5% increments, respectively. The local control and survival rates were obtained using the Kaplan-Meier method.

RESULTS

Radiation pneumonitis at grade III occurred in three of 81 patients, but they fully recovered. This was not a dose-limiting factor. The local control rates in the first and second trials were 64% and 84%, respectively. The total recurrence rate in both trials was 23.2%. The infield local recurrence in the first trial was significantly dependent on carbon dose. The doses greater than 86.4 GyE at 18 fractions and 72 GyE at nine fractions achieved a local control of 90% and 95%, respectively. The 5 year overall and cause-specific survivals in 81 patients were 42% and 60%, respectively.

CONCLUSIONS

With our dose escalation study, the optimum safety and efficacy dose of carbon beams was determined. Carbon beam therapy attained almost the same results as surgery for stage I NSCLC although this was a I/II study.

[The French project ETOILE: review of clinical data for light ion hadrontherapy]

The Lawrence Berkeley Laboratory was the pioneer in light ions hadrontherapy with almost 2500 patients treated between 1957 and 1993 with Helium and Neon. The NIRS (National Institute For Radiological Science, Chiba, Japan) was the first dedicated medical centre for cancer with more than 1200 patients exclusively treated with carbon ion from 1994. A three-year 70 to 100% local control was reported for radio-resistant cancers, supporting the use of high LET particles. Hypo-fractionation was particularly explored for lung cancers and hepatocarcinoma (4 sessions only). Dose escalation studies demonstrated a tumour dose-effect and permitted to precise dose constraints for healthy tissues especially for the rectum. More than 140 patients were treated with carbon ion exclusively or associated with photons since 1997 in the GSI laboratory Gesellschaft Für Schwerionenforschung, Darmstadt, Germany). A very high local control was also obtained for radioresistant cancer of the base of the skull. Preliminary clinical data seem to confirm the expected therapeutic gain with light ions, due to their ballistic and radio-biological properties, and justify the European projects for the construction of dedicated medical facilities for cancers. The French "Etoile" project will be integrated in the European hadrontherapy network "Enlight", with the objectives to coordinate technologic, medical and economic features.

Treatment planning for the layer-stacking irradiation system for three-dimensional conformal heavy-ion radiotherapy

We have upgraded a heavy-ion radiotherapy treatment-planning system to adapt for the layer-stacking irradiation method, which is to conform a variable spread-out Bragg peak to a target volume by means of dynamic control of the conventional beam-modifying devices. The biophysical model, the beam-setup logic, and the dose-calculation algorithm implemented for the layer-stacking method are described and the expected clinical usability is discussed. The layer-stacking method was integrated in perfect accordance with the ongoing conventional treatments so that the established protocols, which are the clinically optimized dose fractionation schemes, will still be valid. On the other hand, a simulation study indicated a substantial improvement of dose distribution with the layer-stacking method though the significance may depend on the size, shape, and location of the tumor. The completed treatment system will provide an option for improved conformal radiotherapy without interfering with the conventional method and we expect a gradual expansion of the clinical cases applicable to the layer-stacking method.

Effect of heavy-ion radiotherapy on pulmonary function in stage I non-small cell lung cancer patients

STUDY OBJECTIVES

The purpose of this study was to investigate the effect of heavy-ion radiotherapy on pulmonary function in patients with clinical stage I non-small cell lung cancer (NSCLC) patients.

DESIGN

Retrospective study.

SETTING

Research Center Hospital for Charged Particle Therapy, National Institute of Radiological Sciences, Chiba, Japan.

PATIENTS

From a total of 81 patients who were not candidates for surgical resection due to medical reasons or patient refusal, and who were treated with carbon beam radiotherapy from October 1994 to February 1999, the 52 patients who had completed the repeat overall pulmonary function tests at 6 and 12 months after undergoing heavy-ion radiotherapy were examined. The total heavy-ion irradiation dose ranged from 59.4 to 95.4 photon gray equivalents (GyE), with a mean dose of 76.2 GyE. INTERVENTIONS AND MEASUREMENT: Pulmonary function was evaluated prior to heavy-ion radiotherapy and at 6 and 12 months after heavy-ion radiotherapy. Comparisons of all pulmonary function indexes between, before, and at 6 and 12 months after heavy-ion radiotherapy were made using repeated-measures analysis of variance using the Dunnett test for post hoc comparison.

RESULTS

A statistically significant decrease in FEV(1) and total lung capacity was detected at both 6 and 12 months after the patient had undergone heavy-ion radiotherapy. No significant decreases in other pulmonary function indexes in patients were observed at either 6 or 12 months after heavy-ion radiotherapy. The magnitude of the decrease in all pulmonary function indexes was < 8% at both 6 and 12 months after heavy-ion radiotherapy.

CONCLUSIONS

These findings suggest that heavy-ion radiotherapy is feasible for stage I NSCLC patients without a severe loss of pulmonary function.

[Clinical dosimetry for heavy ion therapy]

Since December 1997, patients are treated with carbon ions at GSI (Gesellschaft für Schwerionenforschung). Dose delivery is performed with the intensity-controlled raster-scanning technique, which allows a highly conformal treatment of the tumor. To meet the special requirements of dosimetry with heavy ion beams, new dosimetric measurement techniques were developed and introduced into clinical application by the DKFZ (Deutsches Krebsforschungszentrum). The techniques comprise calibration of the irradiation monitor, checks of lateral and depth dose profiles, as well as verification of the beam delivery for complex three-dimensional dose distributions. The developed dosimetric methods are now integral part of clinical application and enable safe treatment with carbon ion therapy.

Efficacy and safety of carbon ion radiotherapy in bone and soft tissue sarcomas

PURPOSE

To evaluate the tolerance for and effectiveness of carbon ion radiotherapy in patients with unresectable bone and soft tissue sarcomas.

PATIENTS AND METHODS

We conducted a phase I/II dose escalation study of carbon ion radiotherapy. Fifty-seven patients with 64 sites of bone and soft tissue sarcomas not suited for resection received carbon ion radiotherapy. Tumors involved the spine or paraspinous soft tissues in 19 patients, pelvis in 32 patients, and extremities in six patients. The total dose ranged from 52.8 to 73.6 gray equivalent (GyE) and was administered in 16 fixed fractions over 4 weeks (3.3 to 4.6 GyE/fraction). The median tumor size was 559 cm(3) (range, 20 to 2,290 cm(3)). The minimum follow-up was 18 months.

RESULTS

Seven of 17 patients treated with the highest total dose of 73.6 GyE experienced Radiation Therapy Oncology Group grade 3 acute skin reactions. Dose escalation was then halted at this level. No other severe acute reactions (grade > 3) were observed in this series. The overall local control rates were 88% and 73% at 1 year and 3 years of follow-up, respectively. The median survival time was 31 months (range, 2 to 60 months), and the 1- and 3-year overall survival rates were 82% and 46%, respectively.

CONCLUSION

Carbon ion radiotherapy seems to be a safe and effective modality in the management of bone and soft tissue sarcomas not eligible for surgical resection, providing good local control and offering a survival advantage without unacceptable morbidity.

Preclinical biological assessment of proton and carbon ion beams at Hyogo Ion Beam Medical Center

PURPOSE

To assess the biologic effects of proton and carbon ion beams before clinical use.

METHODS AND MATERIALS

Cultured cells from human salivary gland cancer (HSG cells) were irradiated at 5 points along a 190 MeV per nucleon proton and a 320 MeV per nucleon carbon ion beam, with Bragg peaks modulated to 6 cm widths. A linac 4 MV X-ray was used as a reference. Relative biologic effectiveness (RBE) values at each point were calculated from survival curves. Cells were also irradiated in a cell-stack phantom to identify that localized cell deaths were observed at predefined depth. Total body irradiation of C3H/He mice was performed, and the number of regenerating crypts per jejunal section was compared to calculate intestinal RBE values. For carbon ion and referential 4 MV X-ray beams, mouse right legs were irradiated by four-fractional treatment and followed up for skin reaction scoring.

RESULTS

RBE values calculated from cell survival curves at the dose that would reduce cell survival to 10% (D10) ranged from 1.01 to 1.05 for protons and from 1.23 to 2.56 for carbon ions. The cell-stack phantom irradiation revealed localized cell deaths at predefined depth. The intestinal RBE values ranged from 1.01 to 1.08 for protons and from 1.15 to 1.88 for carbon ions. The skin RBE value was 2.16 at C320/6 cm spread-out Bragg peak (SOBP) center.

CONCLUSION

The radiobiologic measurements of proton and carbon ion beams at Hyogo Ion Beam Medical Center are consistent with previous reports using proton beams in clinical settings and carbon ion beams with similar linear energy transfer (LET) values.

Dose-response curves for late functional changes in the normal rat brain after single carbon-on doses evaluated by magnetic resonance imaging: influence of follow-up time and calculation of relative biological effectiveness

This study investigated late effects in the brain after irradiation with carbon ions using a rat model. Thirty-six animals were irradiated stereotactically at the right frontal lobe using an extended Bragg peak with maximum doses between 15.2 and 29.2 Gy. Dose-response curves for late changes in the normal brain were measured using T1- and T2-weighted magnetic resonance imaging (MRI). Tolerance doses were calculated at several effect probability levels and times after irradiation. The MRI changes were progressive in time up to 17 months and remained stationary after that time. At 20 months the tolerance doses at the 50% effect probability level were 20.3 +/- 2.0 Gy and 22.6 +/- 2.0 Gy for changes in T1- and T2-weighted MRI, respectively. The relative biological effectiveness (RBE) was calculated on the basis of a previous animal study with photons. Using tolerance doses at the 50% effect probability level, RBE values of 1.95 +/- 0.20 and 1.88 +/- 0.18 were obtained for T1- and T2-weighted MRI. A comparison with data in the literature for the spinal cord yielded good agreement, indicating that the RBE values for single-dose irradiations of the brain and the spinal cord are the same within the experimental uncertainty.

Relative biological effectiveness of 290 MeV/u carbon ions for the growth delay of a radioresistant murine fibrosarcoma

The relative biological effectiveness (RBE) for animal tumors treated with fractionated doses of 290 MeV/u carbon ions was studied. The growth delay of NFSa fibrosarcoma in mice was investigated following various daily doses given with carbon ions or those given with cesium gamma-rays, and the RBE was determined. Animal tumors were irradiated with carbon ions of various LET (linear energy transfer) in a 6-cm SOBP (spread-out Bragg peak), and the isoeffect doses; i.e. the dose necessary to induce a tumor growth delay of 15 days were studied. The iso-effect dose for carbon ions of 14 and 20 keV/microm increased with an increase in the number of fractions up to 4 fractions. The increase in the isoeffect dose with the fraction number was small for carbon ions of 44 keV/microm, and was not observed for 74 keV/microm. The alpha and beta values of the linear-quadratic model for the radiation dose-cell survival relationship were calculated by the Fe-plot analysis method. The alpha values increased linearly with an increase in the LET, while the beta values were independent of the LET. The alpha/beta ratio was 129 +/- 10 Gy for gamma-rays, and increased with an increase in the LET, reaching 475 +/- 168 Gy for 74 keV/microm carbon ions. The RBE for carbon ions relative to Cs-137 gamma-rays increased with the LET. The RBE values for 14 and 20 keV/microm carbon ions were 1.4 and independent of the number of fractions, while those for 44 and 74 keV/microm increased from 1.8 to 2.3 and from 2.4 to 3.0, respectively, when the number of fractions increased from 1 to 4. Increasing the number of fractions further from 4 to 6 was not associated with an increase in the RBE. These results together with our earlier study on the skin reaction support the use of an RBE of 3.0 in clinical trials of 80 keV/microm carbon beams. The RBE values for low doses of carbon beams were also considered.

Histological and elemental changes in the rat brain after local irradiation with carbon ion beams

The left cerebral hemispheres of adult Sprague-Dawley rat brains were irradiated at doses of 30, 50, or 100 Gy with charged carbon particles (290 MeV/nucleon; 5 mm spread-out Bragg peak). The spread-out Bragg peak used here successfully and satisfactorily retained its high-dose localization in the defined region. A histological examination showed that necrotic tissue damage, hemorrhage in the thalamus, and vasodilatations around the necrotic region were induced at 8 weeks after 100 Gy irradiation. The regions with tissue damage correlated well with those expected from the radiation-dose distribution, indicating an advantage of charged carbon particles for irradiating restricted brain regions. An X-ray fluorescent analysis demonstrated a decrease in the concentrations of K and P, and an increase in the concentrations of Cl, Fe, Zn in the damaged region at 8 weeks post-irradiation, though no significant changes were observed before 4 weeks of post-irradiation. This may indicate that even the very high radiation doses used here did not induce acute and immediate neuronal cell death, in contrast with ischemic brain injury where acute neuronal cell death occurred and the elemental concentrations changed within a day after the induction of ischemia.

Analysis of the calibration results obtained with Liulin-4J spectrometer-dosimeter on protons and heavy ions

We are developing a portable dosimeter (Liulin-4J) based on a silicon semiconductor detector for use in measuring the absorbed dose from primary or secondary cosmic rays to astronauts and airplane crews. The dosimeter can measure not only the flux and dose rate, but also the deposited energy spectrum for silicon in per unit time. In order to calibrate the dosimeter, we have carried out exposures at the NIRS cyclotron and HIMAC heavy ion synchrotron facilities. We obtained a detector response function for using in measuring energy deposition and LET.

High linear energy transfer carbon radiation effectively kills cultured glioma cells with either mutant or wild-type p53

PURPOSE

A mutation in the p53 gene is believed to play an important role in the radioresistance of many cancer cell lines. We studied cytotoxic effects of high linear energy transfer (LET) carbon beams on glioma cell lines with either mutant or wild-type p53.

METHODS AND MATERIALS

Cell lines U-87 and U-138 expressing wild-type p53 and U-251 and U-373 expressing mutant p53 were used. These cells were irradiated with 290 MeV/u carbon beams generated by the Heavy Ion Medical Accelerator in the National Institute of Radiologic Science or X-rays. A standard colony-forming assay and flow cytometric detection of apoptosis were performed. Cell cycle progression and the expression of p53, p21, and bax proteins were examined.

RESULTS

High LET carbon radiation was more cytotoxic than low LET X-ray treatment against glioma cells. The effects of the carbon beams were not dependent on the p53 gene status but were reduced by G(1) arrest, which was independent of p21 expression. The expression of bax remained unchanged in all four cell lines.

CONCLUSION

These results indicate that high LET charged particle radiation can induce cell death in glioma cells more effectively than X-rays and that cell death other than p53-dependent apoptosis may participate in the cytotoxicity of heavy charged particles. Thus, it might prove to be an effective alternative radiotherapy for patients with gliomas harboring mutated p53 gene.

Treatment planning for heavy ion radiotherapy: clinical implementation and application

The clinical implementation and application of a novel treatment planning system (TPS) for scanned ion beams is described, which is in clinical use for carbon ion treatments at the German heavy ion facility (GSI). All treatment plans are evaluated on the basis of biologically effective dose distributions. For therapy control, in-beam positron emission tomography (PET) and an online monitoring system for the beam intensity and position are used. The absence of a gantry restricts the treatment plans to horizontal beams. Most of the treatment plans consist of two nearly opposing lateral fields or sometimes orthogonal fields. In only a very few cases a single beam was used. For patients with very complex target volumes lateral and even distal field patching techniques were applied. Additional improvements can be achieved when the patient's head is fixed in a tilted position, in order to achieve sparing of the organs at risk. In order to test the stability of dose distributions in the case of patient misalignments we routinely simulate the effects of misalignments for patients with critical structures next to the target volume. The uncertainties in the range calculation are taken into account by a margin around the target volume of typically 2-3 mm, which can, however, be extended if the simulation demonstrates larger deviations. The novel TPS developed for scanned ion beams was introduced into clinical routine in December 1997 and was used for the treatment planning of 63 patients with head and neck tumours until July 2000. Planning strategies and methods were developed for this tumour location that facilitate the treatment of a larger number of patients with the scanned heavy ion beam in a clinical setting. Further developments aim towards a simultaneous optimization of the treatment field intensities and more effective procedures for the patient set-up. The results demonstrate that ion beams can be integrated into a clinical environment for treatment planning and delivery.

Treatment planning for heavy-ion radiotherapy: biological optimization of multiple beam ports

A crucial task in radiotherapy is dose conformation to the prescribed target volume whilst sparing the surrounding healthy tissue around as much as possible. One of the best approaches so far is active dose shaping in three dimensions using scanned beams of charged particles, like carbon ions. Besides their inverse dose profile and minimal lateral scattering, carbon ions have the advantage that their RBEs increase towards the end of their range. An active beam-delivery system for intensity-modulated carbon-ion beams has been operational at GSI since December, 1997. In order to ensure dose conformation, inverse treatment planning with respect to the biologically effective dose distribution must be applied. A typical patient irradiation comprises two singly optimized opposing fields. This paper discusses the superposition of biologically effective dose distributions for radiotherapy with 12C ions, which is non-trivial due to the nonlinear nature of the dose response of biological systems. Sum rules for the nonlinear addition of singly optimized fields are derived. This method is being used clinically, and has been successfully applied to more than 50 patients.

Treatment planning for heavy-ion radiotherapy: physical beam model and dose optimization

We describe a novel code system, TRiP, dedicated to the planning of radiotherapy with energetic ions, in particular 12C. The software is designed to cooperate with three-dimensional active dose shaping devices like the GSI raster scan system. This unique beam delivery system allows us to select any combination from a list of 253 individual beam energies, 7 different beam spot sizes and 15 intensity levels. The software includes a beam model adapted to and verified for carbon ions. Inverse planning techniques are implemented in order to obtain a uniform target dose distribution from clinical input data, i.e. CT images and patient contours. This implies the automatic generation of intensity modulated fields of heavy ions with as many as 40000 raster points, where each point corresponds to a specific beam position, energy and particle fluence. This set of data is directly passed to the beam delivery and control system. The treatment planning code has been in clinical use since the start of the GSI pilot project in December 1997. Forty-eight patients have been successfully planned and treated.

Relative biological effectiveness for cell-killing effect on various human cell lines irradiated with heavy-ion medical accelerator in Chiba (HIMAC) carbon-ion beams

PURPOSE

To clarify the relative biological effectiveness (RBE) values of various human cell lines for carbon-ion beams with 2 different linear energy transfer (LET) beams and to investigate the relationship between the cell-killing effect and the biophysical characters, such as the chromosome number and the area of the cell nucleus, using qualitatively different kinds of radiations.

METHODS AND MATERIALS

Sixteen different human cell lines were irradiated with carbon-ion beams, having 2 different LET values (LET(infinity) = 13.3 and approximately 77 keV/microm), accelerated by the Heavy Ion Medical Accelerator in Chiba (HIMAC) at National Institute of Radiological Sciences in Japan. Cell-killing effect was detected as reproductive cell death using a colony-formation assay. The number of chromosomes was observed in a metaphase spread using the conventional method. The area of the cell nucleus was calculated as an ellipse on photographs using a micrometer.

RESULTS

The RBE values calculated by the D(10), which is determined as the dose (Gy) required to reduce the surviving fraction to 10%, relative to X-rays, range from 1.06 to 1.33 for 13-keV/microm-beam and from 2.00 to 3. 01 for approximate 77-keV/microm-beam irradiation on each cell line. There was a good correlation in the D(10) values of each cell line between X-rays and carbon-ion beams. However, the D(10) values did not clearly depend on either the chromosome number or the area of the cell nuclei.

CONCLUSION

The RBE values for HIMAC carbon-ion beams are consistent with previous reports using carbon-ion beams with the similar LET values, and the cellular radiosensitivity of different cell lines well correlate among different types of radiation.

Change in radiosensitivity with fractionated-dose irradiation of carbon-ion beams in five different human cell lines

PURPOSE

To investigate the change in the surviving fractions by fractionated-dose irradiations with carbon ions, based on the recovery of potentially lethal damage (PLDR) and the change of radiosensitivity by every fractionated-dose irradiation.

METHODS AND MATERIALS

One normal human and four human-tumor cell lines were used. Cells were irradiated with carbon ions accelerated by the Heavy Ion Medical Accelerator in Chiba (HIMAC) at National Institute of Radiological Sciences in Japan. The LET values were estimated to be 13.18 keV/microm for low-LET beams and 76.92 +/- 0.20 keV/microm for high-LET beams. Fractionated-dose irradiations were carried out with 5 fractions within a 24-h interval.

RESULTS

The surviving fractions for the fractionated-dose irradiation with X-rays and carbon ions decreased exponentially with increasing the number of fractions in the tumor cell lines. In contrast, the surviving fractions for the carbon ions in normal human cells decreased exponentially as well as the tumor cell lines, while it tended to level off from the 3rd to the 5th fraction in the case of using X-rays.

CONCLUSION

The change in both the recovery ratio of the PLDR and radiosensitivity by every fractionated-dose irradiation depends on individual cell lines and the quality of radiations.

Respiratory gated irradiation system for heavy-ion radiotherapy

PURPOSE

In order to reduce the treatment margin of the moving target due to breathing, we developed a gated irradiation system for heavy-ion radiotherapy.

METHODS AND MATERIALS

The motion of a patient due to respiration is detected by the motion of the body surface around the chest wall. A respiratory sensor was developed using an infrared light spot and a position-sensitive detector. A timing signal to request a beam is generated in response to the respiration waveform, and a carbon beam is extracted from the synchrotron using a RF-knockout method. CT images for treatment planning are taken in synchronization with the respiratory motion. For patient positioning, digitized fluoroscopic images superimposed with the respiration waveform were used. The relation between the respiratory sensor signal and the organ motion was examined using digitized video images from fluoroscopy. The performance of our gated system was demonstrated by using the moving phantom, and dose profiles were measured in the direction of phantom motion.

RESULTS

The timing of gate-on is set at the end of the expiratory phase, because the motion of the diaphragm is slower and more reproducible than during the inspiratory phase. The signal of the respiratory sensor shows a phase difference of 120 milliseconds between lower and upper locations on the chest wall. The motion of diaphragm is delayed by 200 milliseconds from the respiration waveform at the lower location. The beam extraction system worked according to the beam on/off logic for gating, and the gated CT scanner performed well. The lateral penumbra size of the dose profile along the moving axis was distinguishably decreased by the gated irradiation. The ratio of the nongated to gated lateral fall-off was 4.3, 3.5, and 2. 0 under the stroke of 40.0, 29.0, and 13.0 mm respectively.

CONCLUSION

We developed a total treatment system of gated irradiation for heavy-ion radiotherapy. We found that with this system the target margin along the body axis could be decreased to 5-10 mm although the target moved twice or three times. Over 150 patients with lung or liver cancer had already been treated by this gated irradiation system by the end of July 1999.

X-rays vs. carbon-ion tumor therapy: cytogenetic damage in lymphocytes

PURPOSE

To measure chromosomal aberrations in peripheral blood lymphocytes from cancer patients treated with X-rays or carbon ions (C-ions).

METHODS AND MATERIALS

Blood samples from patients diagnosed for esophageal or uterine cervical cancer were obtained before, during, and at the end of the radiation treatment. The novel technique of interphase chromosome painting was used to detect aberrations in prematurely condensed chromosomes 2 and 4. The fraction of aberrant lymphocytes was measured as a function of the dose to the tumor volume. For comparison, blood samples were also exposed in vitro to X-rays or to carbon ions accelerated at the HIMAC.

RESULTS

C-ions were more efficient than X-rays in the induction of chromosomal aberrations in vitro. In patients with similar pathologies, tumor positions, and radiation field sizes, however, C-ions induced a lower fraction of aberrant lymphocytes than X-rays during the treatment. The initial slope of the dose-response curve for the induction of chromosomal aberrations during the treatment was correlated to the relative decrease in the number of white blood cells and lymphocytes during the treatment.

CONCLUSION

C-ions induce a lower level of cytogenetic damage in lymphocytes than X-rays, reducing the risk of bone marrow morbidity.

Electron paramagnetic resonance investigation of sucrose irradiated with heavy ions

We investigated the potential use of sucrose to estimate linear energy transfer (LET) for heavy-ion irradiation. We also made a quantitative comparison between heavy-ion and gamma irradiation in terms of spin concentration. Heavy-ion irradiation of sucrose produces stable free radicals. Based on the electron paramagnetic resonance (EPR) spectra obtained, the stable sucrose radicals are the same among helium ions, carbon ions and gamma rays. The EPR spectrum was approximately 70 G wide and was composed of several hyperfine structures. The total spin concentration obtained after the heavy-ion irradiation increased linearly as the absorbed dose increased and decreased logarithmically as LET increased. Production of the spin concentration of helium ions was two times more dependent on LET than that for carbon-ion irradiation. The empirical relationships obtained imply that LET at a certain dose can be determined by the spin concentration. Furthermore, the results of gamma irradiation of deuterated sucrose suggest that one of the persistent radicals is a carbon-centered radical.

Ridge filter design and optimization for the broad-beam three-dimensional irradiation system for heavy-ion radiotherapy

The broad-beam three-dimensional irradiation system under development at National Institute of Radiological Sciences (NIRS) requires a small ridge filter to spread the initially monoenergetic heavy-ion beam to a small spread-out Bragg peak (SOBP). A large SOBP covering the target volume is then achieved by a superposition of differently weighted and displaced small SOBPs. Two approaches were studied for the definition of a suitable ridge filter and experimental verifications were performed. Both approaches show a good agreement between the calculated and measured dose and lead to a good homogeneity of the biological dose in the target. However, the ridge filter design that produces a Gaussian-shaped spectrum of the particle ranges was found to be more robust to small errors and uncertainties in the beam application. Furthermore, an optimization procedure for two fields was applied to compensate for the missing dose from the fragmentation tail for the case of a simple-geometry target. The optimized biological dose distributions show that a very good homogeneity is achievable in the target.

Aspects of fast-ion dosimetry

A first step in the dosimetry of fast-ion beams is the determination of accurate Bragg (ionization) functions. Bragg functions for several substances have been measured and calculated for 3480 MeV carbon ions. In the measurements, the ions first traverse an absorber in which the energy is reduced to either 1900 or 1200 MeV, then a "range gauge" followed by a thin ionization chamber. Functions are calculated with an analytical method using convolutions of straggling functions. This approach gives results without the stochastic variations implicit in Monte Carlo methods. The comparison of measured and calculated functions shows how reliable the calculations are. An important part of the calculations is the determination of the total range of the ions. The range can be determined from the Bragg function. The measured range is given by the sum of the thickness of the absorber and the residual range measured with the range gauge. For water, the range is about 150 mm, and the precision of the measurements is +/-0.05 mm. Because the ion energy at the surface of the absorber fluctuates with time, measurements with water are used to define this energy. Thus the ranges (or average stopping powers) in absorbers are obtained relative to those in water. Measured ranges R(m) are compared with ranges R(0) calculated with a current version of the Bethe theory. For light absorbers (atomic number Z < 20), differences between R(m) and R(0) are less than +/-0.3 mm; for Z > 20 differences are between 0 and +/-0.6 mm. This agreement between calculated and measured ranges confirms the value I = 80 eV for water measured earlier for protons. The ionization by nuclear fragments is obtained from the difference between measured and calculated ionization functions, and has little influence on the ranges of the primary ions.