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

Accuracy of methionine-PET in predicting the efficacy of heavy-particle therapy on primary adenoid cystic carcinomas of the head and neck

BACKGROUND

We evaluated whether or not PET or PET/CT using L-methyl-[11C]-methionine (MET) can allow for the early prediction of local recurrence and metastasis, as well as the prognosis (disease-specific survival), in patients with adenoid cystic carcinoma of the head and neck treated by carbon ion beam radiotherapy.

METHODS

This was a retrospective cohort study of sixty-seven patients who underwent a MET-PET or PET/CT study prior to and one month after the completion of carbon ion radiotherapy (CIRT). The minimum follow-up period for survivors was 12 months. The MET accumulation of the tumor was evaluated using the semiquantitative tumor to normal tissue ratio (TNR). A univariate analysis was conducted using the log-rank method, and the Cox model was used in a multivariate survival regression analysis.

RESULTS

The average TNR prior to and following treatment was 4.8 (±1.5) and 3.0 (±1.3), respectively, showing a significant decrease following treatment. In the univariate analysis, a high TNR prior to treatment (TNRpre) was a significant factor for predicting the occurrence of metastasis and the disease-specific survival. A high TNR following treatment (TNRpost) was a significant factor for predicting the development of local recurrence. The residual ratio of TNR changes (TNRratio) seemed to be less useful than the TNRpre. In the multivariate analysis, the TNRpost and tumor size were the factors found to significantly influence the risk of local recurrence. The TNRpre, TNRratio and tumor size were all significant factors influencing the occurrence of metastasis. Regarding the disease-specific survival, the TNRpre and age were the only factors with a significant influence on the outcome.

CONCLUSIONS

The TNRpre was a factor that was significantly related to the occurrence of metastasis and the disease-specific survival after CIRT for adenoid cystic carcinoma of the head and neck. The TNRpost was a factor that was significantly related to the development of local recurrence. Thus, MET-PET or PET/CT can be useful for predicting or determining the therapeutic efficacy of CIRT.

Effects of low-dose heavy ions on embryonic development in mice and on melanocyte differentiation in the epidermis and hair bulb

The effects of prenatal low-dose irradiation with heavy ions on embryonic development in mice and on melanocyte differentiation are not well understood. We performed whole-body irradiation of pregnant C57BL/10J mice at embryonic Day 9 (E9) with a single dose of γ-rays, silicon, argon or iron ions. The number of living embryos and embryonic body weight at E18 decreased after exposure to heavy ions at high doses. Malformations such as small eyes and limb anomalies were observed in heavy-ion-treated embryos, but not in γ-ray-treated embryos. The frequency of abnormally curved tails was increased by exposure to γ-rays and argon and iron ions even at a dose of 0.1 Gy (P < 0.05). In contrast, a dose-dependent decrease in the number of epidermal melanoblasts/melanocytes and hair bulb melanocytes was observed after 0.1 Gy irradiation with γ-rays or heavy ions (P < 0.01). The decrease in the number of dorsal hair bulb melanocytes, dorsal and ventral epidermal melanoblasts/melanocytes and ventral hair bulb melanocytes was not necessarily correlated with the linear energy transfer of the radiation tested. Moreover, the effects of heavy ions were larger on the ventral skin than on the dorsal skin, indicating that the sensitivity of melanocytes to heavy ions differs between the dorsal and ventral skin. Taken together, these results suggest that the effects of the low-dose heavy ions differ between cell types and tissues, and the effects on the prenatal development of mice and melanocyte development are not necessarily greater than those of γ-rays.

Microdosimetric calculation of relative biological effectiveness for design of therapeutic proton beams

The authors attempt to establish the relative biological effectiveness (RBE) calculation for designing therapeutic proton beams on the basis of microdosimetry. The tissue-equivalent proportional counter (TEPC) was used to measure microdosimetric lineal energy spectra for proton beams at various depths in a water phantom. An RBE-weighted absorbed dose is defined as an absorbed dose multiplied by an RBE for cell death of human salivary gland (HSG) tumor cells in this study. The RBE values were calculated by a modified microdosimetric kinetic model using the biological parameters for HSG tumor cells. The calculated RBE distributions showed a gradual increase to about 1cm short of a beam range and a steep increase around the beam range for both the mono-energetic and spread-out Bragg peak (SOBP) proton beams. The calculated RBE values were partially compared with a biological experiment in which the HSG tumor cells were irradiated by the SOBP beam except around the distal end. The RBE-weighted absorbed dose distribution for the SOBP beam was derived from the measured spectra for the mono-energetic beam by a mixing calculation, and it was confirmed that it agreed well with that directly derived from the microdosimetric spectra measured in the SOBP beam. The absorbed dose distributions to planarize the RBE-weighted absorbed dose were calculated in consideration of the RBE dependence on the prescribed absorbed dose and cellular radio-sensitivity. The results show that the microdosimetric measurement for the mono-energetic proton beam is also useful for designing RBE-weighted absorbed dose distributions for range-modulated proton beams.

Comparison of human chordoma cell-kill for 290 MeV/n carbon ions versus 70 MeV protons in vitro

BACKGROUND

While the pace of commissioning of new charged particle radiation therapy facilities is accelerating worldwide, biological data pertaining to chordomas, theoretically and clinically optimally suited targets for particle radiotherapy, are still lacking. In spite of the numerous clinical reports of successful treatment of these malignancies with this modality, the characterization of this malignancy remains hampered by its characteristic slow cell growth, particularly in vitro.

METHODS

Cellular lethality of U-CH1-N cells in response to different qualities of radiation was compared with immediate plating after radiation or as previously reported using the multilayered OptiCell™ system. The OptiCell™ system was used to evaluate cellular lethality over a broad dose-depth deposition range of particle radiation to anatomically mimic the clinical setting. Cells were irradiated with either 290 MeV/n accelerated carbon ions or 70 MeV accelerated protons and photons and evaluated through colony formation assays at a single position or at each depth, depending on the system.

RESULTS

There was a cell killing of approximately 20-40% for all radiation qualities in the OptiCell™ system in which chordoma cells are herein described as more radiation sensitive than regular colony formation assay. The relative biological effectiveness values were, however, similar in both in vitro systems for any given radiation quality. Relative biological effectiveness values of proton was 0.89, of 13-20 keV/μm carbon ions was 0.85, of 20-30 keV/μm carbon ions was 1.27, and >30 keV/μm carbon ions was 1.69. Carbon-ions killed cells depending on both the dose and the LET, while protons depended on the dose alone in the condition of our study. This is the first report and characterization of a direct comparison between the effects of charged particle carbon ions versus protons for a chordoma cell line in vitro. Our results support a potentially superior therapeutic value of carbon particle irradiation in chordoma patients.

CONCLUSION

Carbon ion therapy may have an advantage for chordoma radiotherapy because of higher cell-killing effect with high LET doses from biological observation in this study.

Comparison of the bromodeoxyuridine-mediated sensitization effects between low-LET and high-LET ionizing radiation on DNA double-strand breaks

The incorporation of halogenated pyrmidines such as bromo- and iodo-deoxyuridines (BrdU, IdU) into DNA as thymidine analogs enhances cellular radiosensitivity when high-linear energy transfer (LET) radiation is not used. Although it is known that high-LET ionizing radiation confers fewer biological effects resulting from halogenated pyrimidine incorporation, the exact mechanisms of reduced radiosensitivity with high-LET radiation are not clear. We investigated the radiosensitization effects of halogenated pyrimidines with high-LET radiation using accelerated carbon and iron ions. Cells synchronized into the G1 phase after unifilar (1 cell cycle) and bifilar (2 cell cycles) substitution with 10 µM BrdU were exposed to various degrees of LET with heavy ions and X-rays. We then carried out a colony formation assay to measure cell survival. The γ-H2AX focus formation assay provided a measure of DNA double-strand break (DSB) formation and repair kinetics. Chromosomal aberration formations for the first post-irradiation metaphase were also scored. For both low-LET X-rays and carbon ions (13 keV/µm), BrdU incorporation led to impaired DNA repair kinetics, a larger initial number of DNA DSBs more frequent chromosomal aberrations at the first post-irradiated metaphase, and increased radiosensitivity for cell lethality. The enhancement ratio was higher after bifilar substitution. In contrast, no such synergistic enhancements were observed after high-LET irradiation with carbon and iron ions (70 and 200 keV/µm, respectively), even after bifilar substitution. Our results suggest that BrdU substitution did not modify the number and quality of DNA DSBs produced by high-LET radiation. The incorporation of halogenated pyrimidines may produce more complex/clustered DNA damage along with radicals formed by low-LET ionizing radiation. In contrast, the severity of damage produced by high-LET radiation may undermine the effects of BrdU and account for the observed minimal radiosensitization effects.

Characteristics of myeloid differentiation and maturation pathway derived from human hematopoietic stem cells exposed to different linear energy transfer radiation types

Exposure of hematopoietic stem/progenitor cells (HSPCs) to ionizing radiation causes a marked suppression of mature functional blood cell production in a linear energy transfer (LET)- and/or dose-dependent manner. However, little information about LET effects on the proliferation and differentiation of HSPCs has been reported. With the aim of characterizing the effects of different types of LET radiations on human myeloid hematopoiesis, in vitro hematopoiesis in Human CD34⁺ cells exposed to carbon-ion beams or X-rays was compared. Highly purified CD34⁺ cells exposed to each form of radiation were plated onto semi-solid culture for a myeloid progenitor assay. The surviving fractions of total myeloid progenitors, colony-forming cells (CFC), exposed to carbon-ion beams were significantly lower than of those exposed to X-rays, indicating that CFCs are more sensitive to carbon-ion beams (D₀ = 0.65) than to X-rays (D₀ = 1.07). Similar sensitivities were observed in granulocyte-macrophage and erythroid progenitors, respectively. However, the sensitivities of mixed-type progenitors to both radiation types were similar.

In liquid culture for 14 days, no significant difference in total numbers of mononuclear cells was observed between non-irradiated control culture and cells exposed to 0.5 Gy X-rays, whereas 0.5 Gy carbon-ion beams suppressed cell proliferation to 4.9% of the control, a level similar to that for cells exposed to 1.5 Gy X-rays. Cell surface antigens associated with terminal maturation, such as CD13, CD14, and CD15, on harvest from the culture of X-ray-exposed cells were almost the same as those from the non-irradiated control culture. X-rays increased the CD235a⁺ erythroid-related fraction, whereas carbon-ion beams increased the CD34⁺CD38⁻ primitive cell fraction and the CD13⁺CD14^+/−CD15⁻ fraction. These results suggest that carbon-ion beams inflict severe damage on the clonal growth of myeloid HSPCs, although the intensity of cell surface antigen expression by mature myeloid cells derived from HSPCs exposed to each type of radiation was similar to that by controls.

Particle radiotherapy with carbon ion beams

Carbon ion radiotherapy offers superior dose conformity in the treatment of deep-seated malignant tumours compared with conventional X-ray therapy. In addition, carbon ion beams have a higher relative biological effectiveness compared with protons or X-ray beams. The algorithm of treatment planning and beam delivery system is tailored to the individual parameters of the patient. The present article reviews the available literatures for various disease sites including the head and neck, skull base, lung, liver, prostate, bone and soft tissues and pelvic recurrence of rectal cancer as well as physical and biological properties.

Influence of track directions on the biological consequences in cells irradiated with high LET heavy ions

PURPOSE

The impact of the damage distribution to cellular survival and chromosomal aberrations following high Linear Energy Transfer (LET) radiation was investigated.

MATERIALS AND METHODS

High LET iron-ions (500 MeV/n, LET 200 keV/μm) were delivered to G1-phase synchronized Chinese Hamster Ovary (CHO) cells located at a vertical or horizontal angle relative to the ion beam in order to give same dose but different fluence and damage distribution.

RESULTS

Horizontal irradiation produced DNA double-strand break (DSB) along each ion track represented as clustered lines, and vertical irradiation produced a greater fluence. The initial damages measured by premature chromosome condensation were equal per dose in both irradiation types. Horizontal irradiation proved to be less effective in cell killing than vertical at doses of more than 3 Gy. Vertical irradiation produced a higher number of metaphase chromosomal aberrations compared to horizontally irradiated samples. In particular, formation of exchange-type aberrations was the same, but that of deletion-type aberrations were significantly higher after vertical irradiation than horizontal irradiation.

CONCLUSIONS

Therefore, we concluded that high fluence per dose is more effective than low fluence per dose to produce radiation-induced chromosomal aberrations and to kill exposed cells following high LET heavy-ion exposure.

Adaptive radiotherapy based on the daily regression of a tumor in carbon-ion beam irradiation

We propose a new application of adaptive radiotherapy using a scanning beam, taking into account the daily regression of a tumor. No patient-specific hardware (such as collimators and compensating filters) is needed for the scanning technique; thus, it allows re-planning immediately before each fractional irradiation using the sophisticated conformations of dose distributions. We retrospectively modeled the tumor volume regression curves as a function of the dose from the CT images which were taken three times during the treatment course. The daily shape of the tumor was mathematically interpolated assuming constant continuity of the tumor deformation. We simulated the adaptive radiotherapy by optimizing the dose distribution on the estimated daily tumor volume for every fraction. The dose-volume histogram (DVH) for the organ at risk in the adaptive radiotherapy was compared with that of the current clinical protocol. We performed analysis using the CT images of cervical cancer patients who received carbon-ion radiotherapy in broad-beam irradiation. The DVH for the rectum and the sigmoid colon was improved by adaptive radiotherapy considering the inter-fractional tumor regression. The result shows that this approach has possible advantages.

Physical interactions of charged particles for radiotherapy and space applications

In this paper, the basic physics by which energetic charged particles deposit energy in matter is reviewed. Energetic charged particles are used for radiotherapy and are encountered in spaceflight, where they pose a health risk to astronauts. They interact with matter through nuclear and electromagnetic forces. Deposition of energy occurs mostly along the trajectory of the incoming particle, but depending on the type of incident particle and its energy, there is some nonzero probability for energy deposition relatively far from the nominal trajectory, either due to long-ranged knock-on electrons (sometimes called delta rays) or from the products of nuclear fragmentation, including neutrons. In the therapy setting, dose localization is of paramount importance, and the deposition of energy outside nominal treatment volumes complicates planning and increases the risk of secondary cancers as well as noncancer effects in normal tissue. Statistical effects are also important and will be discussed. In contrast to radiation therapy patients, astronauts in space receive comparatively small whole-body radiation doses from energetic charged particles and associated secondary radiation. A unique aspect of space radiation exposures is the high-energy heavy-ion component of the dose. This is not present in terrestrial exposures except in carbon-ion radiotherapy. Designers of space missions must limit exposures to keep risk within acceptable limits. These limits are, at present, defined for low-Earth orbit, but not for deep-space missions outside the geomagnetosphere. Most of the uncertainty in risk assessment for such missions comes from the lack of understanding of the biological effectiveness of the heavy-ion component, with a smaller component due to uncertainties in transport physics and dosimetry. These same uncertainties are also critical in the therapy setting.

Impact of enhancements in the local effect model (LEM) on the predicted RBE-weighted target dose distribution in carbon ion therapy

Biological optimization for treatment planning in carbon ion therapy is currently based on the first version of the local effect model (LEM I). Further developments implemented in the latest version (LEM IV) allowed to predict more accurately the Relative Biological Effectiveness (RBE) in-vitro. The main goal of this study is to compare the LEM IV against LEM I under treatment-like conditions for idealized target geometries. Therefore, physical dose distributions resulting from the biological optimization with LEM I were used to recalculate the RBE-weighted dose distribution based on LEM IV. Input parameters representing the clinical endpoints late toxicity in the central nervous system and the tumor control for chordoma were chosen to investigate the impact of changes on the predicted isoeffective dose levels. The recalculated RBE-weighted dose distributions show an increase within the target region, and the mean RBE-weighted dose values are dependent on the geometry and decrease with increasing target dimension. The differences between predictions of LEM IV and LEM I are less than 10% for typical tumor volumes treated in the pilot project at GSI. Median RBE-weighted doses predicted by LEM IV in the target region are consistent with clinically observed dose-response behavior as demonstrated by comparison to the 5-year local control curve for skull base chordoma.

Carbon ion radiotherapy for localized primary sarcoma of the extremities: results of a phase I/II trial

PURPOSE

To determine the effectiveness of carbon ion radiotherapy (CIRT) for localized primary sarcomas of the extremities in a prospective study.

PATIENTS AND MATERIALS

From April 2000 to May 2010, 17 (male/female: 12/5) patients with localized primary sarcoma of the extremities received CIRT. The median age was 53 years (range: 14-87 years). Nine patients had primary diseases and eight had recurrent diseases. Of the 17 patients, eight refused amputation, and the remaining nine refused surgical resection. Tumors were located in the upper limbs in four patients and lower limbs in 13. Histological diagnosis was osteosarcoma in three patients, liposarcoma in two, synovial sarcoma in two, rhabdomyosarcoma in two, pleomorphic sarcoma in two, and miscellaneous in six. The CIRT dose to the limb was 52.8 GyE for one patient, 64 GyE for three, 70.4 GyE for 13 in 16 fixed fractions over 4 weeks. Records were reviewed and outcomes including radiologic response, local control (progression-free), and survival were analyzed.

RESULTS

The median follow-up was 37 months (range: 11-97 months). Radiological response rate was 65% (PR in 11, SD in 5, and PD in 1). The local control rate at 5 years was 76%. The overall survival rate at 5 years was 56%. Of the 17 patients, 10 survived without disease progression. Four patients had local recurrences, one was salvaged by repeated CIRT and the other three died due to systemic diseases. Distant failure was observed in six patients. One patient suffered from femoral fracture (grade 3) and received surgical fixation 27 months after CIRT. No other severe reactions (grade 3) were observed.

CONCLUSIONS

CIRT is suggested to be an effective and safe treatment for patients who refuse surgery for localized primary sarcomas of the extremities.

Efficacy of carbon-ion radiotherapy and high-dose chemotherapy for patients with unresectable Ewing's sarcoma family of tumors

BACKGROUND

Treatment for unresectable Ewing's sarcoma family of tumors (ESFT) is a formidable challenge because of its high tendency for local and distant failure. Recently, carbon-ion radiotherapy (CIRT) has been applied to unresectable bone and soft tissue sarcoma. Additionally, high-dose chemotherapy (HDC) with stem cell rescue has been used to improve the survival of patients with relapsed ESFT. Here we report our experience with CIRT and HDC in the treatment of unresectable ESFT.

METHODS

Five unresectable ESFT patients including 4 who underwent CIRT and HDC and one who underwent CIRT from 1999-2009 were retrospectively studied. After neoadjuvant chemotherapy, CIRT was conducted at the National Institute of Radiological Sciences in Chiba as local therapy. Consecutively, we employed HDC including busulfan, melphalan, and thiotepa with stem cell rescue.

RESULTS

Two patients showed tumor shrinkage after CIRT, including 1 patient who achieved partial response. No severe acute toxicity related to CIRT was observed. Local failure was observed in only 1 patient at 22 months after CIRT. Four patients conducted HDC with stem cell rescue after CIRT and 1 patient suffered from veno-occlusive disease just after HDC. Distant failure was observed in 3 patients after completion of the treatment.

CONCLUSIONS

CIRT and HDC for unresectable ESFT patients show favorable local control, with unsatisfactory results for distant control.

Design of ridge filters for spread-out Bragg peaks with Monte Carlo simulation in carbon ion therapy

Spread-out Bragg peaks made by ridge filters or wheel range modulators are used in charged particle therapy with passive methods to achieve uniform biological responses in irradiated tumors. Following the biological responses needed to design the ridge filters, which were developed at the National Institute of Radiological Sciences in Japan, new ridge filters were designed using recent developments in heavy-ion reactions and dosimetry. The Monte Carlo code of Geant4 was used to calculate the qualities of carbon ion beams in a water phantom. The results obtained from the simulation were corrected so that they agreed with the measurements of depth dose distributions. The calculations of biological responses to fragments other than carbon ions were assumed to be for helium ions. The measured dose distributions with the designed ridge filters were compared to the calculated distributions. A beam modifying system using this adaptable method was successively applied to carbon ion therapy at Gunma University.

Homologous recombination in Arabidopsis seeds along the track of energetic carbon ions

Heavy ion irradiation has been used as radiotherapy of deep-seated tumors, and is also an inevitable health concern for astronauts in space mission. Unlike photons such as X-rays and γ-rays, a high linear energy transfer (LET) heavy ion has a varying energy distribution along its track. Therefore, it is important to determine the correlation of biological effects with the Bragg curve energy distribution of heavy ions. In this study, a continuous biological tissue equivalent was constructed using a layered cylinder of Arabidopsis seeds, which was irradiated with carbon ions of 87.5MeV/nucleon. The position of energy loss peak in the seed pool was determined with CR-39 track detectors. The mutagenic effect in vivo along the path of carbon ions was investigated with the seeds in each layer as an assay unit, which corresponded to a given position in physical Bragg curve. Homologous recombination frequency (HRF), expression level of AtRAD54 gene, germination rate of seeds, and survival rate of young seedlings were used as checking endpoints, respectively. Our results showed that Arabidopsis S0 and S1 plants exhibited significant increases in HRF compared to their controls, and the expression level of AtRAD54 gene in S0 plants was significantly up-regulated. The depth-biological effect curves for HRF and the expression of AtRAD54 gene were not consistent with the physical Bragg curve. Differently, the depth-biological effect curves for the developmental endpoints matched generally with the physical Bragg curve. The results suggested a different response pattern of various types of biological events to heavy ion irradiation. It is also interesting that except for HRF in S0 plants, the depth-biological effect curves for each biological endpoint were similar for 5Gy and 30Gy of carbon irradiation.

Phase 1 trial of preoperative, short-course carbon-ion radiotherapy for patients with resectable pancreatic cancer

BACKGROUND

The authors evaluated the tolerance and efficacy of carbon-ion radiotherapy (CIRT) as a short-course, preoperative treatment and determined the recommended dose needed to reduce the risk of postoperative local recurrence without excess injury to normal tissue.

METHODS

Patients radiographically defined with potentially resectable pancreatic cancer were eligible. A preoperative, short-course, dose-escalation study was performed with fixed 8 fractions in 2 weeks. The dose of irradiation was increased by 5% increments from 30 grays equivalents (GyE) to 36.8 GyE. Surgery was to be performed 2 to 4 weeks after the completion of CIRT.

RESULTS

The study enrolled 26 patients. At the time of restaging after CIRT, disease progression with distant metastasis or refusal ruled out 5 patients from surgery. Twenty-one of 26 patients (81%) patients underwent surgery. The pattern of initial disease progression was distant metastasis in 17 patients (65%) and regional recurrence in 2 patients (8%). No patients experienced local recurrence. The 5-year survival rates for all 26 patients and for those who underwent surgery were 42% and 52%, respectively.

CONCLUSIONS

Preoperative, short-course CIRT followed by surgery is feasible and tolerable without unacceptable morbidity.

Sinonasal malignancies and charged particle radiation treatment: a systematic literature review

Background. Paranasal and nasal cavity malignancies are rare tumors that frequently present at advanced stages. Tumor extension and anatomic complexity pose a challenge for their treatment. Due to their peculiar physical and biological properties particle radiation therapy, i.e. protons and ions can have a role in their management. We performed a systematic literature review to gather clinical evidence about their use to treat sinonasal malignancies. Materials and Methods. We searched the browsers PubMed and Medline as well as specific journals and conference proceedings. Inclusion criteria were: at least 10 patients, English language, reporting outcome and/or toxicity data. Results. We found six studies with data on clinical outcome. Carbon and helium ions were each used in one study, protons in four. Toxicity was specifically described in five studies. One reported acute toxicity of carbon ions, one dealt with brain toxicity from both carbon ions and protons. Three papers reported on visual toxicity: one from carbon ions, one from protons and one from both. Specific data were extracted and compared with the most pertinent literature. Conclusion. Particle radiation therapy is in its early phase of development. Promising results achieved so far must be confirmed in further studies.

Heavy-Particle Radiotherapy: System Design and Application

The requirements for an accelerator and a beam-delivery system for medical application are described (pointing out terms of heavy-particle radiotherapy), based on 15 years of experience with carbon-ion radiotherapy at HIMAC. The present heavy-particle radiotherapy and system are reviewed here. With a view to further development of carbon-ion radiotherapy, recent progress in heavy-particle radiotherapy and a new system are also described. Finally, the clinical applications are summarized.

Carbon ion radiotherapy for recurrent malignant transformation from mature cystic teratoma of the ovary

Mature cystic teratoma (MCT) is the most common tumor of the ovary; malignant transformation (MT) of squamous cell carcinoma is a rare disorder. A 78-year-old woman with stage IIc MT-MCT (squamous cell carcinoma [SCC]) underwent a total abdominal hysterectomy and bilateral salpingo-oophorectomy; there was residual tumor in the pelvis. The patient was treated with six courses of paclitaxel and carboplatin, but the recurrent tumor grew. The patient was then treated with carbon ion radiotherapy (CIRT). The recurrent tumor shrank and the patient has been free of clinical disease for 53 months. CIRT can be considered as a treatment for recurrent MT-MCT.

Optimizing normal tissue sparing in ion therapy using calculated isoeffective dose for ion selection

PURPOSE

To investigate how the selection of ion type affects the calculated isoeffective dose to the surrounding normal tissue as a function of both normal tissue and target tissue α/β ratios.

METHODS AND MATERIALS

A microdosimetric biologic dose model was incorporated into a Geant4 simulation of parallel opposed beams of protons, helium, lithium, beryllium, carbon, and neon ions. The beams were constructed to give a homogeneous isoeffective dose to a volume in the center of a water phantom for target tissues covering a range of cobalt equivalent α/β ratios of 1-20 Gy. Concomitant normal tissue isoeffective doses in the plateau of the ion beam were then compared for different ions across the range of normal tissue and target tissue radiosensitivities for a fixed isoeffective dose to the target tissue.

RESULTS

The ion type yielding the optimal normal tissue sparing was highly dependent on the α/β ratio of both the normal and the target tissue. For carbon ions, the calculated isoeffective dose to normal tissue at a 5-cm depth varied by almost a factor of 5, depending on the α/β ratios of the normal and target tissue. This ranges from a factor of 2 less than the isoeffective dose of a similar proton treatment to a factor of 2 greater.

CONCLUSIONS

No single ion is optimal for all treatment scenarios. The heavier ions are superior in cases in which the α/β ratio of the target tissue is low and the α/β ratio of normal tissue is high, and protons are superior in the opposite circumstances. Lithium and beryllium appear to offer dose advantages similar to carbon, with a considerably lower normal tissue dose when the α/β ratio in the target tissue is high and the α/β ratio in the normal tissue is low.

Basics of particle therapy II: relative biological effectiveness

In the previous review, the physical aspect of heavy particles, with a focus on the carbon beam was introduced. Particle beam therapy has many potential advantages for cancer treatment without increasing severe side effects in normal tissue, these kinds of radiation have different biologic characteristics and have advantages over using conventional photon beam radiation during treatment. The relative biological effectiveness (RBE) is used for many biological, clinical endpoints among different radiation types and is the only convenient way to transfer the clinical experience in radiotherapy with photons to another type of radiation therapy. However, the RBE varies dependent on the energy of the beam, the fractionation, cell types, oxygenation status, and the biological endpoint studied. Thus this review describes the concerns about RBE related to particle beam to increase interests of the Korean radiation oncologists' society.

Carbon-ion radiation therapy for prostate cancer

In 1994, carbon-ion radiotherapy was started at the National Institute of Radiological Sciences using the Heavy-Ion Medical Accelerator in Chiba. Between June 1995 and March 2000, two phase I/II dose escalation studies (protocols 9402 and 9703) of hypofractionated carbon-ion radiotherapy for both early- and advance-stage prostate cancer patients had been carried out to establish radiotherapy technique and to determine the optimal radiation dose. To validate the feasibility and efficacy of hypofractionated carbon-ion radiotherapy, a phase II study (9904) was initiated in April 2000 using the shrinking field technique and the recommended dose fractionation (66 gray equivalents in 20 fractions over 5 weeks) obtained from the phase I/II studies, and was successfully completed in October 2003. The data from 175 patients in the phase II study showed the importance of an appropriate use of androgen deprivation therapy according to tumor risk group. Since November 2003, carbon-ion radiotherapy for prostate cancer was approved as "Highly Advanced Medical Technology" from the Ministry of Health, Labor, and Welfare, and since then approximately 1100 patients have received carbon-ion radiotherapy as of July 2011. In this review, we introduce our steps thorough three clinical trials carried out at National Institute of Radiological Sciences, and show the updated data of carbon-ion radiotherapy obtained from approximately 1000 prostate cancer patients. In addition, our recent challenge and future direction will be also described.

Carbon Ion Radiotherapy at the Gunma University Heavy Ion Medical Center: New Facility Set-up

Carbon ion radiotherapy (C-ion RT) offers superior dose conformity in the treatment of deep-seated tumors compared with conventional X-ray therapy. In addition, carbon ion beams have a higher relative biological effectiveness compared with protons or X-ray beams. C-ion RT for the first patient at Gunma University Heavy Ion Medical Center (GHMC) was initiated in March of 2010. The major specifications of the facility were determined based on the experience of clinical treatments at the National Institute of Radiological Sciences (NIRS), with the size and cost being reduced to one-third of those at NIRS. The currently indicated sites of cancer treatment at GHMC are lung, prostate, head and neck, liver, rectum, bone and soft tissue. Between March 2010 and July 2011, a total of 177 patients were treated at GHMC although a total of 100 patients was the design specification during the period in considering the optimal machine performance. In the present article, we introduce the facility set-up of GHMC, including the facility design, treatment planning systems, and clinical preparations.

Preliminary calculation of RBE-weighted dose distribution for cerebral radionecrosis in carbon-ion treatment planning

Cerebral radionecrosis is a significant side effect in radiotherapy for brain cancer. The purpose of this study is to calculate the relative biological effectiveness (RBE) of carbon-ion beams on brain cells and to show RBE-weighted dose distributions for cerebral radionecrosis speculation in a carbon-ion treatment planning system. The RBE value of the radionecrosis for the carbon-ion beam is calculated by the modified microdosimetric kinetic model on the assumption of a typical clinical α/β ratio of 2 Gy for cerebral radionecrosis in X-rays. This calculation method for the RBE-weighted dose is built into the treatment planning system for the carbon-ion radiotherapy. The RBE-weighted dose distributions are calculated on computed tomography (CT) images of four patients who had been treated by carbon-ion radiotherapy for astrocytoma (WHO grade 2) and who suffered from necrosis around the target areas. The necrotic areas were detected by brain scans via magnetic resonance imaging (MRI) after the treatment irradiation. The detected necrotic areas are easily found near high RBE-weighted dose regions. The visual comparison between the RBE-weighted dose distribution and the necrosis region indicates that the RBE-weighted dose distribution will be helpful information for the prediction of radionecrosis areas after carbon-ion radiotherapy.

In vitro characterization of cells derived from chordoma cell line U-CH1 following treatment with X-rays, heavy ions and chemotherapeutic drugs

Background

Chordoma, a rare cancer, is usually treated with surgery and/or radiation. However, very limited characterizations of chordoma cells are available due to a minimal availability (only two lines validated by now) and the extremely long doubling time. In order to overcome this situation, we successfully derived a cell line with a shorter doubling time from the first validated chordoma line U-CH1 and obtained invaluable cell biological data.

Method

After isolating a subpopulation of U-CH1 cells with a short doubling time (U-CH1-N), cell growth, cell cycle distribution, DNA content, chromosome number, p53 status, and cell survival were examined after exposure to X-rays, heavy ions, camptothecin, mitomycin C, cisplatin and bleocin. These data were compared with those of HeLa (cervical cancer) and U87-MG (glioblastoma) cells.

Results

The cell doubling times for HeLa, U87-MG and U-CH1-N were approximately 18 h, 24 h and 3 days respectively. Heavy ion irradiation resulted in more efficient cell killing than x-rays in all three cell lines. Relative biological effectiveness (RBE) at 10% survival for U-CH1-N was about 2.45 for 70 keV/μm carbon and 3.86 for 200 keV/μm iron ions. Of the four chemicals, bleocin showed the most marked cytotoxic effect on U-CH1-N.

Conclusion

Our data provide the first comprehensive cellular characterization using cells of chordoma origin and furnish the biological basis for successful clinical results of chordoma treatment by heavy ions.

Detection of chromosomal instability in bystander cells after Si490-ion irradiation

There is increasing evidence that two of the biological effects associated with low-dose ionizing radiation, genomic instability and bystander responses, may be linked. To verify and validate the link between the two phenomena, the ability of Si490 ions (high-energy particles associated with radiation risk in space) to induce bystander responses and chromosomal instability in human bronchial epithelial (HBEC-3kt) cells was investigated. These studies were conducted at both the population and single cell level in irradiated and nonirradiated bystander cells receiving medium from the irradiated cultures. At the general population level, transfer of medium from silicon-ion (Si490)-irradiated cultures (at doses of 0.073 Gy, 1.2 Gy and 2 Gy) to nonirradiated bystander cells resulted in small increases in the levels of chromosomal aberrations at the first division. Subsequently, single cell clones isolated from irradiated and bystander populations were analyzed for the appearance of de novo chromosome-type aberrations after ∼50 population doublings using mFISH. Both irradiated and bystander clones demonstrated chromosomal instability (as seen by the de novo appearance of translocations and chromosomal fragments), albeit to different degrees, whereas sham-treated controls showed relatively stable chromosomal patterns. The results presented here highlight the importance of nontargeted effects of radiation on chromosomal instability in human epithelial cells and their potential relevance to human health.

Carbon ion radiotherapy for skull base chordoma

OBJECTIVE

To present the results of the clinical study of carbon ion radiotherapy (CIRT) for skull base and paracervical spine tumors at the National Institute of Radiological Sciences in Chiba, Japan.

METHODS

The study is comprised of three protocols: a pilot study, a phase I/II dose escalation study, and a phase II study. All the patients were treated by 16 fractions for 4 weeks with total doses of 48.0, 52.8, 57.6, and 60.8 Gy equivalents (GyE).

RESULTS

As a result of the dose escalation study of CIRT for skull base tumors, a dose fractionation of 60.8 GyE/16 fractions for 4 weeks was decided as the recommended dose because of acceptable normal tissue reactions and good local tumor control.

CONCLUSIONS

Preliminary results of the phase II clinical study of CIRT for skull base chordoma showed local control at 5 years at 100%, and normal tissues showed a mild reaction without any severe morbidity of important organs.

Mutagenic adaptive response to high-LET radiation in human lymphoblastoid cells exposed to low doses of heavy-ion radiation

Adaptive response (AR) and bystander effect are two important phenomena involved in biological responses to low doses of ionizing radiation (IR). Furthermore, there is a strong interest in better understanding the biological effects of high-LET radiation. We previously demonstrated the ability of low doses of X-rays to induce an AR to challenging heavy-ion radiation [8]. In this study, we assessed in vitro the ability of priming low doses (0.01Gy) of heavy-ion radiation to induce a similar AR to a subsequent challenging dose (1-4Gy) of high-LET IR (carbon-ion: 20 and 40keV/μm, neon-ion: 150keV/μm) in TK6, AHH-1 and NH32 cells. Our results showed that low doses of high-LET radiation can induce an AR characterized by lower mutation frequencies at hypoxanthine-guanine phosphoribosyl transferase locus and faster DNA repair kinetics, in cells expressing p53.

Effects of carbon ion beam on putative colon cancer stem cells and its comparison with X-rays

Although carbon ion therapy facilities are expensive, the biological effects of carbon ion beam treatment may be better against cancer (and cancer stem cells) than the effects of a photon beam. To investigate whether a carbon ion beam may have a biological advantage over X-rays by targeting cancer stem-like cells, human colon cancer cells were used in vitro and in vivo. The in vitro relative biological effectiveness (RBE) values of a carbon ion beam relative to X-rays at the D10 values were from 1.63 to 1.74. Cancer stem-like CD133(+), CD44(+)/ESA(+) cells had a greater ability for colony and spheroid formation, as well as in vivo tumorigenicity compared with the CD133(-), CD44(-)/ESA(-) cells. FACS (fluorescence-activated cell sorting) data showed that cancer stem-like cells were more highly enriched after irradiation with X-rays than carbon ion at doses that produced the same level of biological efficacy. A colony assay for cancer stem-like cells showed that RBE values calculated by the D10 levels were from 2.05 to 2.28 for the carbon ion beam relative to X-rays. The in vivo xenotransplant assay showed an RBE of 3.05 to 3.25, calculated from the slope of the dose-response curve for tumor growth suppression. Carbon ion irradiation with 15 Gy induced more severe xenograft tumor cell cavitation and fibrosis without significant enhancement of cells with putative cancer stem cell markers, CD133, ESA, and CD44, compared with 30 Gy X-rays, and marker positive cells were significantly decreased following 30 Gy carbon ion irradiation. Taken together, carbon ion beam therapy may have an advantage over photon beam therapy by improved targeting of putative colon cancer stem-like cells.

Carbon ion radiotherapy for sacral chordoma

The National Institute of Radiological Sciences in Chiba, Japan has offered carbon ion radiotherapy (CIRT) since 1994 using carbon ion beams generated by the heavy ion medical accelerator in Chiba (HIMAC). The total number of cases treated with the HIMAC exceeded 5000 in July 2009. Here, we present a retrospective analysis of CIRT for sacral chordoma. The study included 95 patients with medically unresectable sacral chordomas treated between 1996 and 2007. The median age of the patients was 66 years. Of all the patients, 84 had not been treated previously and 11 had a locally recurrent tumour following previous resection. The carbon ion dose ranged from 52.8 to 73.6 GyE (median 70.4 GyE) in a total of 16 fixed fractions over 4 weeks. The median clinical target volume was 370 cm(3). The overall survival rate at 5 years for all 95 patients was 86%, and follow-up survival time was 42 months (range, 13-112 months). The 5-year local control rate was 88% and median time to local failure was 35 months (range, 13-60 months). Of the 95 patients, 91% remained ambulatory with or without a supportive device. Two patients experienced severe skin or soft tissue complications requiring skin grafts. 15 patients experienced severe sciatic nerve complications requiring continuing medication. CIRT appears effective and safe in the management of patients with sacral chordoma and offers a promising alternative to surgery.

Effects of low-dose heavy ions on the postnatal development of mice and the yield of white spots in the mid-ventrum and tail-tips

Effects of prenatal low-dose irradiations of heavy ions on the postnatal development of mice and of melanocytes have not been well studied. Pregnant females of C57BL/10J mice were irradiated whole-body at 9 days of gestation with a single acute dose of γ-rays, silicon (Si, 57 keV/µm), argon (Ar, 100 keV/µm) and iron (Fe, 220 keV/µm) ions. The effects were studied by scoring changes in the postnatal development of mice as well as in the pigmentation of cutaneous coats and tail-tips of their offspring 22 days after birth. The survival to day 22 decreased from the offspring exposed to 0.4 Gy of argon and iron ions and to 0.75 Gy of silicon ions. White spots were found in the mid-ventrum and tail-tips of irradiated offspring. The frequency and size of the white spots in the mid-ventrum in mice exposed to silicon, argon and iron ions were greater than those of γ-rays. Even in the low dose (0.1 Gy), γ-rays and heavy ions increased the frequency of the ventral spots. The RBE estimated by the frequency of the ventral spots was 2.3 (Si), 3.1 (Ar) and 4.5 (Fe). These results suggest that prenatal exposure to heavy ions possesses a greater effect on the postnatal development of mice as well as melanocyte development than does exposure to γ-rays.

Radiation-induced ICAM-1 expression via TGF-β1 pathway on human umbilical vein endothelial cells; comparison between X-ray and carbon-ion beam irradiation

Adhesion of inflammatory cells to endothelial cells is considered to be involved in the process of radiation-induced damage and fibrosis. Intercellular adhesion molecule-1 (ICAM-1) and transforming growth factor-beta1 (TGF-β1) are thought to play important roles in this process. In this study, radiation-induced ICAM-1 expression on endothelial cells was investigated with the use of an inhibitor of TGF-β1 receptor kinase (SB431542) and the effects of X-ray and carbon-ion beam were compared. Cell cultures of human umbilical vein endothelial cells (HUVE cells) were incubated with TGF-β1 and irradiated with 140 KV X-ray. Next, HUVE cells were irradiated with X-ray and 220 MeV carbon-ion beam with or without SB431542. Immunofluorescence analysis was used to quantify ICAM-1 expression. The expression of ICAM-1 on HUVE cells was significantly increased by the stimulation with TGF-β1. Expression of ICAM-1 was increased by X-ray and carbon-ion beam irradiation and decreased significantly with SB431542 after both irradiations. The expression of ICAM-1 by 2 Gy of carbon-ion beam irradiation was 6.7 fold higher than that of non-irradiated cells, while 5 Gy of X-ray irradiation increased the expression of ICAM-1 by 2.5 fold. According to ICAM-1 expression, the effect of carbon-ion beam irradiation was about 2.2, 4.4 and 5.0 times greater than that of the same doses of X-ray irradiation (1, 2 and 5 Gy, respectively). The present results suggested that radiation-induced ICAM-1 expression on HUVE cells was, at least partially, regulated by TGF-β1. Carbon-ion beam induced significantly higher ICAM-1 expression than X-ray.