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

The proangiogenic factor ephrin-A1 is up-regulated in radioresistant murine tumor by irradiation

While the pre-treatment status of cancer is generally correlated with outcome, little is known about microenvironmental change caused by anti-cancer treatment and how it may affect outcome. For example, treatment may lead to induction of gene expression that promotes resistance to therapy. In the present study, we attempted to find a gene that was both induced by irradiation and associated with radioresistance in tumors. Using single-color oligo-microarrays, we analyzed the gene expression profiles of two murine squamous cell carcinomas, NR-S1, which is highly radioresistant, and SCCVII, which is radiosensitive, after irradiation with 137-Cs gamma rays or carbon ions. Candidate genes were those differentially regulated between NR-S1 and SCCVII after any kind of irradiation. Four genes, Efna1 (Ephrin-A1), Sprr1a (small proline-rich protein 1A), Srgap3 (SLIT-ROBO Rho GTPase activating protein 3) and Xrra1 [RIKEN 2 days neonate thymus thymic cells (NOD) cDNA clone E430023D08 3'], were selected as candidate genes associated with radiotherapy-induced radioresistance. We focused on Efna1, which encodes a ligand for the Eph receptor tyrosine kinase known to be involved in the vascular endothelial growth factor (VEGF) pathway. We used immunohistochemical methods to detect expression of Ephrin-A1, VEGF, and the microvascular marker CD31 in radioresistant NR-S1 tumor cells. Ephrin-A1 was detected in the cytoplasm of NR-S1 tumor cells after irradiation, but not in SCCVII tumor cells. Irradiation of NR-S1 tumor cells also led to significant increases in microvascular density, and up-regulation of VEGF expression. Our results suggest that radiotherapy-induced changes in gene expression related with angiogenesis might also modulate microenvironment and influence responsiveness of tumors.

Effectiveness of monoenergetic and spread-out bragg peak carbon-ions for inactivation of various normal and tumour human cell lines

This work aimed at measuring cell-killing effectiveness of monoenergetic and Spread-Out Bragg Peak (SOBP) carbon-ion beams in normal and tumour cells with different radiation sensitivity. Clonogenic survival was assayed in normal and tumour human cell lines exhibiting different radiosensitivity to X- or gamma-rays following exposure to monoenergetic carbon-ion beams (incident LET 13-303 keV/microm) and at various positions along the ionization curve of a therapeutic carbon-ion beam, corresponding to three dose-averaged LET (LET(d)) values (40, 50 and 75 keV/microm). Chinese hamster V79 cells were also used. Carbon-ion effectiveness for cell inactivation generally increased with LET for monoenergetic beams, with the largest gain in cell-killing obtained in the cells most radioresistant to X- or gamma-rays. Such an increased effectiveness in cells less responsive to low LET radiation was found also for SOBP irradiation, but the latter was less effective compared with monoenergetic ion beams of the same LET. Our data show the superior effectiveness for cell-killing exhibited by carbon-ion beams compared to lower LET radiation, particularly in tumour cells radioresistant to X- or gamma-rays, hence the advantage of using such beams in radiotherapy. The observed lower effectiveness of SOBP irradiation compared to monoenergetic carbon beam irradiation argues against the radiobiological equivalence between dose-averaged LET in a point in the SOBP and the corresponding monoenergetic beams.

The difference in LET and ion species dependence for induction of initially measured and non-rejoined chromatin breaks in normal human fibroblasts

We studied the LET and ion species dependence of the induction of chromatin breaks measured immediately after irradiation as initially measured breaks and after 24 h postirradiation incubation (37 degrees C) as non-rejoined breaks in normal human fibroblasts with different heavy ions, such as carbon, neon, silicon and iron, generated by the Heavy Ion Medical Accelerator in Chiba (HIMAC) at the National Institute of Radiological Science (NIRS). Chromatin breaks were measured as an excess number of fragments of prematurely condensed chromosomes using premature chromosome condensation (PCC). The results showed that the number of excess fragments per cell per Gy for initially measured chromatin breaks was dependent on LET in the range from 13.3 to 113.1 keV/mum but was not dependent on ion species. On the other hand, the number of non-rejoined chromatin breaks detected after 24 h postirradiation incubation was clearly dependent on both LET and ion species. No significant difference was observed in the cross section for initially measured breaks, but a statistically significant difference was observed in the cross section for non-rejoined breaks among carbon, neon, silicon and iron ions. This suggests that the LET-dependent structure in the biological effects is reflected in biological consequences of repair processes.

Comparative study of dose distribution between carbon ion radiotherapy and photon radiotherapy for head and neck tumor

PURPOSE

A comparative treatment planning study has been performed between carbon ion radiotherapy (CIRT) and photon radiotherapy [three-dimensional conformal radiotherapy (3D-CRT) and intensity-modulated radiotherapy (IMRT)] to assess the potential improvements and limitations that could result for locally advanced, nonresectable head and neck tumors.

MATERIALS AND METHODS

Seven patients, originally treated with CIRT, were randomly selected for the comparative study. The evaluations analyzed using dose-volume histogram parameters, conformity index, inhomogeneity coefficient, and dose to the organs at risk (OARs).

RESULTS

The mean conformity index was 1.46, 1.43, and 1.22 for 3D-CRT, IMRT, and CIRT, respectively. The mean inhomogeneity coefficient was 0.05, 0.07, and 0.02 for 3D-CRT, IMRT, and CIRT respectively. Photon plans resulted in greater volumes of normal tissues at 10% to 95% isodose levels compared with the corresponding carbon ion plans where the volumes increased by a factor of 1.2 to 2.7 for 3D-CRT and 1.2 to 2.0 for IMRT.

CONCLUSION

CIRT has the potential to improve the target dose conformity, inhomogeneity coefficient, and OAR sparing when compared with 3D-CRT and IMRT. Compared with 3D-CRT, normal tissue exposure was reduced mainly in the mid-to low-isodose levels using IMRT. Additional improvement was obtained using CIRT.

Comparison of the radiobiological effect of carbon ion beam therapy and conventional radiation therapy on cervical cancer

Little clinical evidence has been provided to show the minimization of radiation resistance of tumors using high linear energy transfer radiation. We therefore investigated the radiobiological and molecular pathological aspects of carbon beam therapy. A total of 27 patients with squamous cell carcinoma (SCC) of the cervix were treated using a carbon beam and 50 control patients with SCC of the cervix using a photon beam. The expression of Ki-67, p53, and p27 proteins before radiotherapy and 5 and 15 days after therapy initiation were investigated using immunohistochemistry. Similar changes were observed in Ki-67 labeling index (LI) and p53 LI during carbon and photon beam therapies. However, for carbon beam therapy, the mean p27 LI significantly decreased from 25.2% before treatment to 18.6% on the 5th day after treatment initiation, followed by a significant increase to 36.1% on the 15th day. In contrast, for photon beam therapy, the p27 LI consistently decreased from the initial 19.9% to 13.7% on the 15th day. Histological effects were observably stronger under carbon than photon beam therapy, though no statistically significant difference was observed (p = 0.07 on the 5th day and p = 0.10 on the 15th day). The changes in p27 LI under carbon beam therapy were significantly different from those under photon beam therapy, which suggests important molecular differences in the radio-biological response between therapies. Further investigation is required to elucidate the clinical relevance of these putative changes and optimize the relative biological effectiveness of carbon beam to X-ray.

Carbon ion radiotherapy for elderly patients 80 years and older with stage I non-small cell lung cancer

Surgical resection is the standard treatment for stage I non-small cell lung cancer (NSCLC). However, elderly patients with NSCLC often suffer from other conditions, such as chronic obstructive pulmonary disease (COPD) or cardiovascular disease, and are not suitable candidates for surgery. Different modalities to treat stage I NSCLC have been developed, such as stereotactic radiotherapy (SRT), proton beam radiotherapy and carbon ion radiotherapy (CIRT). Between April 1999 and November 2003, we treated 129 patients with stage I NSCLC using CIRT. In this study, we focused on 28 patients aged 80 years and older who underwent CIRT, and analyzed the effectiveness of CIRT in treating their lung cancer and the impact on their activity of daily life (ADL). The 5-year local control rate for these patients was 95.8%, and the 5-year overall survival rate was 30.7%, but there were no patients who started home oxygen therapy or had decreased ADL. Our data demonstrate that CIRT was effective in treating elderly patients with stage I NSCLC.

Effects of a 2-step culture with cytokine combinations on megakaryocytopoiesis and thrombopoiesis from carbon-ion beam-irradiated human hematopoietic stem/progenitor cells

To evaluate whether the continuous treatment of two cytokine combinations is effective in megakaryocytopoiesis and thrombopoiesis in hematopoietic stem/progenitor cells exposed to heavy ion beams, the effects of a 2-step culture by a combination of recombinant human interleukin-3 (IL-3) + stem cell factor (SCF) + thrombopoietin (TPO), which just slightly protected against carbon-ion beam-induced damages, and a combination of IL-3 + TPO, which selectively stimulated the differentiation of the hematopoietic stem/progenitor cells to megakaryocytes and platelets, were examined. CD34(+)-hematopoietic stem/progenitor cells isolated from the human placental and umbilical cord blood were exposed to carbon-ion beams (LET = 50 keV/microm) at 2 Gy. These cells were cultured under three cytokine conditions. The number of megakaryocytes, platelets and hematopoietic progenitors were assessed using a flow cytometer and a clonogenic assay at 14 and 21 days after irradiation, respectively. However, the efficacy of each 2-step culture was equal or lower than that of using the IL-3 + SCF + TPO combination alone and the 2-step culture could not induce megakaryocytes and platelets from hematopoietic stem/progenitor cells exposed to high LET-radiation such as carbon-ion beams. Therefore, additional cytokines and/or hematopoietic promoting compounds might be required to overcome damage to hematopoietic cells by high LET radiation.

High yields of isochromatid breaks and successive formation of chromosome exchanges may lead to reproductive cell death following high-LET irradiation

To clarify the relationship between cell death and chromosomal aberrations following exposure to heavy-charged ion particles beams, exponentially growing Human Salivary Gland Tumor cells (HSG cells) were irradiated with various kinds of high energy heavy ions; 13 keV/μm carbon ions as a low-LET charged particle radiation source, 120 keV/μm carbon ions and 440 keV/μm iron ions as high-LET charged particle radiation sources. X-rays (200 kVp) were used as a reference. Reproductive cell death was evaluated by clonogenic assays, and the chromatid aberrations in G2/M phase and their repairing kinetics were analyzed by the calyculin A induced premature chromosome condensation (PCC) method. High-LET heavy-ion beams introduced much more severe and un-repairable chromatid breaks and isochromatid breaks in HSG cells than low-LET irradiation. In addition, the continuous increase of exchange aberrations after irradiation occurred in the high-LET irradiated cells. The cell death, initial production of isochromatid breaks and subsequent formation of chromosome exchange seemed to be depend similarly on LET with a maximum RBE peak around 100–200 keV/μm of LET value. Conversely, un-rejoined isochromatid breaks or chromatid breaks/gaps seemed to be less effective in reproductive cell death. These results suggest that the continuous yield of chromosome exchange aberrations induced by high-LET ionizing particles is a possible reason for the high RBE for cell death following high-LET irradiation, alongside other chromosomal aberrations additively or synergistically.

Evaluation of beam wobbling methods for heavy-ion radiotherapy

The National Institute of Radiological Sciences (NIRS) has extensively studied carbon-ion radiotherapy at the Heavy-Ion Medical Accelerator in Chiba (HIMAC) with some positive outcomes, and has established its efficacy. Therefore, efforts to distribute the therapy to the general public should be made, for which it is essential to enable direct application of clinical and technological experiences obtained at NIRS. For widespread use, it is very important to reduce the cost through facility downsizing with minimal acceleration energy to deliver the HIMAC-equivalent clinical beams. For the beam delivery system, the requirement of miniaturization is translated to reduction in length while maintaining the clinically available field size and penetration range for range-modulated uniform broad beams of regular fields that are either circular or square for simplicity. In this paper, we evaluate the various wobbling methods including original improvements, especially for application to the compact facilities through the experimental and computational studies. The single-ring wobbling method used at HIMAC is the best one including a lot of experience at HIMAC but the residual range is a fatal problem in the case of a compact facility. On the other hand, uniform wobbling methods such as the spiral and zigzag wobbling methods are effective and suitable for a compact facility. Furthermore, these methods can be applied for treatment with passive range modulation including respiratory gated irradiation. In theory, the choice between the spiral and zigzag wobbling methods depends on the shape of the required irradiation field. However, we found that it is better to use the zigzag wobbling method with transformation of the wobbling pattern even when a circular uniform irradiation field is required, because it is difficult to maintain the stability of the wobbler magnet due to the rapid change of the wobbler current in the spiral wobbling method. The regulated wobbling method, which is our improvement, can well expand the uniform irradiation field and lead to reducing the power requirement of the wobbler magnets. Our evaluations showed that the regulated zigzag wobbling method is the most suitable method for use in currently designed compact carbon-therapy facilities.

The grid-dose-spreading algorithm for dose distribution calculation in heavy charged particle radiotherapy

A new variant of the pencil-beam (PB) algorithm for dose distribution calculation for radiotherapy with protons and heavier ions, the grid-dose spreading (GDS) algorithm, is proposed. The GDS algorithm is intrinsically faster than conventional PB algorithms due to approximations in convolution integral, where physical calculations are decoupled from simple grid-to-grid energy transfer. It was effortlessly implemented to a carbon-ion radiotherapy treatment planning system to enable realistic beam blurring in the field, which was absent with the broad-beam (BB) algorithm. For a typical prostate treatment, the slowing factor of the GDS algorithm relative to the BB algorithm was 1.4, which is a great improvement over the conventional PB algorithms with a typical slowing factor of several tens. The GDS algorithm is mathematically equivalent to the PB algorithm for horizontal and vertical coplanar beams commonly used in carbon-ion radiotherapy while dose deformation within the size of the pristine spread occurs for angled beams, which was within 3 mm for a single 150-MeV proton pencil beam of 30 degrees incidence, and needs to be assessed against the clinical requirements and tolerances in practical situations.

Accuracy of the local effect model for the prediction of biologic effects of carbon ion beams in vitro and in vivo

PURPOSE

To analyze the accuracy of relative biologic effectiveness (RBE) values for treatment planning in carbon ion radiotherapy based on the local effect model (LEM) and to discuss the implications on the clinically relevant depth dose profiles.

METHODS AND MATERIALS

Predictions of the LEM are compared with a broad panel of experimental data in vitro and to the tolerance of the rat spinal cord in vivo. To improve the accuracy of the LEM, the description of track structure is modified by taking into account a velocity-dependent extension of the inner part of the track.

RESULTS

The original version of the LEM (LEM I) underestimates the therapeutic ratio of carbon ions (i.e., the ratio of RBE in the Bragg peak region as compared with the RBE in the entrance channel). Although significantly reduced, the cluster extension of the LEM (LEM II) still shows the same tendency. Implementation of the modified track structure (LEM III) almost completely compensates these systematic deviations, and predictions of RBE by LEM III for high and low energetic carbon ions show good agreement for a wide panel of different cell lines, as well as for the tolerance of the rat spinal cord. As a consequence, the expected RBE in the normal tissue surrounding the tumor becomes significantly lower than estimated with the LEM in its original version (LEM I).

CONCLUSIONS

The modified track structure description represents an empiric approach to improve the accuracy of the LEM for treatment planning. This will be particularly useful for further optimization of carbon ion therapy in general and with respect to comparison with other treatment modalities, such as protons or intensity-modulated radiotherapy.

Radiobiologic parameters and local effect model predictions for head-and-neck squamous cell carcinomas exposed to high linear energy transfer ions

PURPOSE

To establish the radiobiologic parameters of head-and-neck squamous cell carcinomas (HNSCC) in response to ion irradiation with various linear energy transfer (LET) values and to evaluate the relevance of the local effect model (LEM) in HNSCC.

METHODS AND MATERIALS

Cell survival curves were established in radiosensitive SCC61 and radioresistant SQ20B cell lines irradiated with [33.6 and 184 keV/n] carbon, [302 keV/n] argon, and X-rays. The results of ion experiments were confronted to LEM predictions.

RESULTS

The relative biologic efficiency ranged from 1.5 to 4.2 for SCC61 and 2.1 to 2.8 for SQ20B cells. Fixing an arbitrary D(0) parameter, which characterized survival to X-ray at high doses (>10 Gy), gave unsatisfying LEM predictions for both cell lines. For D(0) = 10 Gy, the error on survival fraction at 2 Gy amounted to a factor of 10 for [184 keV/n] carbon in SCC61 cells. We showed that the slope (s(max)) of the survival curve at high doses was much more reliable than D(0). Fitting s(max) to 2.5 Gy(-1) gave better predictions for both cell lines. Nevertheless, LEM could not predict the responses to fast and slow ions with the same accuracy.

CONCLUSIONS

The LEM could predict the main trends of these experimental data with correct orders of magnitude while s(max) was optimized. Thus the efficiency of carbon ions cannot be simply extracted from the clinical response of a patient to X-rays. LEM should help to optimize planning for hadrontherapy if a set of experimental data is available for high-LET radiations in various types of tumors.

Monitoring the irradiation field of 12C and 16O SOBP beams using positron emitters produced through projectile fragmentation reactions

In order to effectively utilize the prominent properties of heavy ions in radiotherapy, it is important to evaluate both the position of the field irradiated with incident ions and the absorbed dose distribution in a patient's body. One of the methods for this purpose is the utilization of the positron emitters produced through the projectile fragmentation reactions of stable heavy ions with target nuclei. In heavy-ion therapy, spread-out Bragg peak (SOBP) beams are used to achieve uniform biological dose distributions in the whole tumor volume. Therefore, in this study, we designed SOBP beams of 30 and 50 mm water-equivalent length (mmWEL) in width for (12)C and (16)O, and carried out irradiation experiments using them. Water, polyethylene and polymethyl methacrylate were selected as targets to simulate a human body. Pairs of annihilation gamma rays were detected by means of a limited-angle positron camera for 500 s, and annihilation gamma-ray distributions were obtained. The maximum likelihood estimation (MLE) method was applied to the detected distributions for evaluating the positions of the distal and proximal edges of the SOBP in a target. The differences between the positions evaluated with the MLE method and those derived from the measured dose distributions were less than 1.7 mm and 2.5 mm for the distal and the proximal edge, respectively, in all irradiation conditions. When the positions of both edges are determined with the MLE method, the most probable shape of the dose distribution in a target can be estimated simultaneously. The close agreement between the estimated and the measured distributions implied that the shape of the dose distribution in an irradiated target could be evaluated from the detected annihilation gamma-ray distribution.

Dosimetric factors used for thoracic X-ray radiotherapy are not predictive of the occurrence of radiation pneumonitis after carbon-ion radiotherapy

Radiation pneumonitis (RP) is one of the most common dose-limiting toxicities in thoracic X-ray radiotherapy (XRT). Dosimetric factors are used for prediction of the occurrence of RP after XRT. Carbon-ion radiotherapy (CRT) is a promising modality because of its excellent dose localization and high biological effect on tumors. This study aims to analyze the relationship between dosimetric factors developed for XRT and the incidence of RP in patients with stage I non-small cell lung cancer (NSCLC) after CRT. We examined 80 inoperable patients with NSCLC. The ranges of the daily fraction sizes and the total doses were from 3.3 to 8.8 GyE and from 59.4 to 95.4 GyE, respectively. These doses were successfully delivered with acceptable toxicity; >or= grade 2 RP was observed in 8 patients (10%). The severity of RP was graded within 6 months of the initiation of CRT using the Radiation Therapy Oncology Group criteria. These results indicate the excellent dose distribution of CRT. We then compared the dosimetric data of the 8 patients developed >or= grade 2 RP with those of 72 patients developed <or= grade 1 RP. Dosimetric factors useful for predicting RP in XRT, such as the percentage of the computed tomography-defined total lung volume receiving > 5, > 20, and > 30 GyE, and mean lung dose, were not predictive factors for RP after CRT. The dosimetric factors used for XRT are not applicable for CRT in patients with NSCLC. The dosimetric factors for CRT remain to be developed.

Design of a compensating bolus by use of exhalation CT data for covering residual motion in respiratory-gated charged-particle lung therapy: four-dimensional carbon beam dose calculation

We developed an algorithm which we used to design a compensating bolus by using respiratory-gated CT data for respiratory-gated carbon beam lung therapy and evaluated it by calculating dose distributions as a function of time. Four-dimensional CT (4DCT) images were obtained for seven lung cancer patients under free breathing conditions. The internal target volume (ITV) was calculated by maximum intensity projection processing which use of three types of gross tumor volumes (GTVs): at peak exhalation and with a 5 mm shift of the GTV to both superior and inferior sides. Then a compensating bolus was designed which use of the ITV and applied to 4DCT data at the gating window (around exhalation phase). The carbon beam distribution was calculated by a pencil-beam algorithm as a function of time. The compensating bolus provides a sufficient prescribed dose to the target in the gating window and minimizes any excessive dose to the normal tissues. The metric of dosimetric assessment metrics of D95 in all patients is greater than 96% of the prescribed dose in the gating window. Our results will be beneficial for improving the accuracy of charged-particle radiotherapy for hospitals where 4DCT cannot be used.

Carbon ion radiotherapy for stage I non-small cell lung cancer using a regimen of four fractions during 1 week

BACKGROUND

A phase I/II study was first conducted for the treatment of stage I non-small cell lung cancer (NSCLC) from 1994 to 1999 to determine the optimal dose. On the basis on the results, a phase II study using a regimen of four fractions during 1 week was performed. The purpose of the present study was to determine the local control and 5-year survival rates.

METHODS

From December 2000 to November 2003, 79 patients with 80 primary lesions were treated. Using a fixed dose of 52.8 GyE for stage IA NSCLC and 60.0 GyE for stage IB NSCLC in four fractions during 1 week, the primary tumors were irradiated with carbon beams alone. The average age of the patients was 74.8 years. Sixty-two (78.5%) of these patients were medically inoperable. Local control and survival were determined using the Kaplan-Meier method. The data were statistically processed using the log-rank test.

RESULTS

All patients were observed for a minimum of 3 years or until death, with a median follow-up time of 38.6 months, ranging from 2.5 to 72.2 months. The local control rate for all patients was 90% (T1: 98%, T2: 80%). The patients' 5-year lung cancer-specific survival rate was 68% (IA: 87%, IB: 42%). The overall survival was 45% (IA: 62%, IB: 25%). Half of the deaths were attributable to intercurrent diseases. No toxic reactions in the lung greater than grade 3 were detected.

CONCLUSION

Carbon ion beam radiotherapy with a regimen of four fractions during 1 week has been proven as a valid alternative to surgery for stage I NSCLC and to offer particular benefits, especially for elderly and inoperable patients.

Heavy-ion conformal irradiation in the shallow-seated tumor therapy terminal at HIRFL

Basic research related to heavy-ion cancer therapy has been done at the Institute of Modern Physics (IMP), Chinese Academy of Sciences since 1995. Now a plan of clinical trial with heavy ions has been launched at IMP. First, superficially placed tumor treatment with heavy ions is expected in the therapy terminal at the Heavy Ion Research Facility in Lanzhou (HIRFL), where carbon ion beams with energy up to 100 MeV/u can be supplied. The shallow-seated tumor therapy terminal at HIRFL is equipped with a passive beam delivery system including two orthogonal dipole magnets, which continuously scan pencil beams laterally and generate a broad and uniform irradiation field, a motor-driven energy degrader and a multi-leaf collimator. Two different types of range modulator, ripple filter and ridge filter with which Guassian-shaped physical dose and uniform biological effective dose Bragg peaks can be shaped for therapeutic ion beams respectively, have been designed and manufactured. Therefore, two-dimensional and three-dimensional conformal irradiations to tumors can be performed with the passive beam delivery system at the earlier therapy terminal. Both the conformal irradiation methods have been verified experimentally and carbon-ion conformal irradiations to patients with superficially placed tumors have been carried out at HIRFL since November 2006.

Microdosimetric evaluation of secondary particles in a phantom produced by carbon 290 MeV/nucleon ions at HIMAC

Microdosimetric single event spectra as a function of depth in a phantom for the 290 MeV/nucleon therapeutic carbon beam at HIMAC were measured by using a tissue equivalent proportional counter (TEPC). Two types of geometries were used: one is a fragment particle identification measurement (PID-mode) with time of flight (TOF) method without a backward phantom, and the other is an in-phantom measurement (IPM-mode) with a backward phantom. On the PID-mode geometry, fragments produced by carbon beam in a phantom are identified by the DeltaE-TOF distribution between two scintillation counters positioned up- and down-stream relative to the tissue equivalent proportional counter (TEPC). Lineal energy distributions for carbon and five ion fragments (proton, helium, lithium, beryllium and boron) were obtained in the lineal-energy range of 0.1-1000 keV/microm at eight depths (7.9-147.9 mm) in an acrylic phantom. In the IPM-mode geometry, the total lineal energy distributions measured at eight depths (61.9-322.9 mm) were compared with the distributions in the PID-mode. Both spectra are consistent with each other. This shows that the PID-mode measurement can be discussed as the equivalent of the phantom measurement. The dose distribution of the carbon beam and fragments were obtained separately. In the depth dose curve, the Bragg peak was observed. Relative biological effectiveness (RBE) for the carbon beam in the acrylic phantom was obtained based on a biological response function as a lineal-energy. The RBE of carbon beam had a maximum of 4.5 at the Bragg peak. Downstream of the Bragg peak, the RBE rapidly decreases. The RBE of fragments is dominated by Boron particles around the Bragg peak region.

Carbon ion radiotherapy for vaginal malignant melanoma: a case report

Malignant melanoma of the vagina is a very rare neoplasm and resistant to conventional radiotherapy. We report a case of vaginal malignant melanoma that was locally well controlled by carbon ion radiotherapy. A 55-year-old postmenopausal woman presented with abnormal vaginal bleeding. On pelvic and imaging examinations, an irregular mass of the posterior vaginal wall sized 7.5 x 5 x 5 cm, an enlarged right inguinal lymph node, and two lung metastases were observed. Histologic diagnosis based on positive immunostaining for HMB-45 was malignant melanoma. She received dacarbazine-based chemotherapy and carbon ion radiotherapy for vaginal and inguinal tumor sites with 57.6 Gy equivalent dose per 16 fractions using five ports. Six months later, she was also given carbon ion radiotherapy for regrowing lung metastasis with 52.8 Gy equivalent dose per four fractions using four ports. She died 19 months after initial treatment due to brain metastases. The primary irradiated tumor disappeared completely 12 months after initial treatment. The vaginal tumor, right inguinal lymph node, and lung tumor treated with carbon ion radiotherapy did not show any evidence of recurrence until her death. Carbon ion radiotherapy may be of value for vaginal malignant melanoma as a conservative approach.

Secondary range shifting with range compensator for reduction of beam data library in heavy-ion radiotherapy

We report our experience with extended usage of range compensators in heavy-ion radiotherapy with broad beams to lighten the management task of the beam data library, which is a collection of the standard beams to be referenced in treatment planning. Partly due to interference between lateral spreading and range shifting, as many as hundreds of beam entries may be necessary to cover all the possible clinical situations. We have introduced downstream secondary range shifting with a range compensator to reduce the interference and consequently to simplify the library. In our case, 30% reduction in beam entries is achieved without significantly degrading the beam quality nor increasing the material consumption by more than 3%, which is experimentally verified with carbon-ion beams or statistically estimated from the clinical records.

Carbon ion therapy for ocular melanoma: planning orthogonal two-port treatment

We recently started orthogonal two-port carbon ion therapy for choroidal melanoma with the intent to reduce the incidence of radiation complications that occur with mono-port therapy. Treatment planning techniques involving therapeutic beam characteristics are described here. The vertical (140 MeV/u) and horizontal (170 MeV/u) carbon ion beams from the synchrotron at the NIRS were shaped, using the passive beam delivery system, to irradiate the target volume. The range modulating ridge filters were designed to produce spread-out Bragg peaks (SOBPs) with a region of uniform HMV-I cell killing. The apertures and range compensators were designed for individual patients. A commercial treatment planning system, which was customized to our general carbon ion therapy, was tested for applicability to this treatment. Dose distributions were calculated with either a broad beam or a pencil beam algorithm using parameters determined by measurements and calculations. We evaluated the accuracy of the system software features, and replaced or added some other features to the software. The system was used for 12 patients during the past year. For nine patients two-port treatment was assessed to be more effective than mono-port therapy and these patients were treated with two fractions of vertical beams and three fractions of horizontal beams.

Assessment of the homogeneous efficacy of carbon ions in the spread-out Bragg peak for human lung cancer cell lines

PURPOSE

The aim of this study was to assess the radiosensitivities and homogeneous efficacy in the spread-out Bragg peak (SOBP) for lung cancer cell lines exposed to carbon ions.

MATERIALS AND METHODS

The dose-dependent survival rates of seven cell lines exposed to carbon ions, fast neutrons, and photons were obtained using colony-forming assays in vitro. The relative biological effectiveness (RBE) of carbon ions and fast neutrons to photons was determined by comparing the doses at the 10% and 1% survival levels.

RESULTS

The RBEs at 13, 40, 50, and 80 keV/microm were 1.20-1.29, 1.55-1.80, 1.57-2.00, and 1.69-2.58, respectively, at the 10% survival level. The RBE of 290 MeV carbon ions increased with increasing linear energy transfer. The biological dose (relative physical dose x RBE) distributions in the SOBP did not statistically differ at the proximal, mid, or distal points at the 10% (p = 0.945) and 1% (p = 0.211) survival levels, respectively; however, deviation of the biological dose at 10% and 1% survival were 3%-16% and 6%-24%, respectively. Furthermore, 290 MeV carbon ions at 80 keV/microm in the SOBP were nearly equivalent to 30 MeV fast neutrons.

CONCLUSION

Our results demonstrate nearly homogeneous effectiveness in the SOBP, although we are aware of the deviation in some cell lines.

Phase I/II clinical trial of carbon ion radiotherapy for malignant gliomas: combined X-ray radiotherapy, chemotherapy, and carbon ion radiotherapy

PURPOSE

To report the results of a Phase I/II clinical trial for patients with malignant gliomas, treated with combined X-ray radiotherapy (XRT), chemotherapy, and carbon ion radiotherapy (CRT).

METHODS AND MATERIALS

Between October 1994 and February 2002, 48 patients with histologically confirmed malignant gliomas (16 anaplastic astrocytoma (AA) and 32 glioblastoma multiforme (GBM) were enrolled in a Phase I/II clinical study. The treatment involved the application of 50 Gy/25 fractions/5 weeks of XRT, followed by CRT at 8 fractions/2 weeks. Nimustine hydrochloride (ACNU) were administered at a dose of 100 mg/m(2) concurrently in weeks 1, 4, or 5 of XRT. The carbon ion dose was increased from 16.8 to 24.8 Gray equivalent (GyE) in 10% incremental steps (16.8, 18.4, 20.0, 22.4, and 24.8 GyE, respectively).

RESULTS

There was no Grade 3 or higher acute reaction in the brain. The late reactions included four cases of Grade 2 brain morbidity and four cases of Grade 2 brain reaction among 48 cases. The median survival time (MST) of AA patients was 35 months and that of GBM patients 17 months (p = 0.0035). The median progression-free survival and MST of GBM showed 4 and 7 months for the low-dose group, 7 and 19 months for the middle-dose group, and 14 and 26 months for the high-dose group.

CONCLUSION

The results of combined therapy using XRT, ACNU chemotherapy, and CRT showed the potential efficacy of CRT for malignant gliomas in terms of the improved survival rate in those patients who received higher carbon doses.

Cell killing, nuclear damage and apoptosis in Chinese hamster V79 cells after irradiation with heavy-ion beams of (16)O, (12)C and (7)Li

Chinese hamster V79 cells were exposed to high LET (linear energy transfer) (16)O-beam (625keV/mum) radiation in the dose range of 0-9.83Gy. Cell survival, micronuclei (MN), chromosomal aberrations (CA) and induction of apoptosis were studied as a follow up of our earlier study on high LET radiations ((7)Li-beam of 60keV/mum and (12)C-beam of 295keV/mum) as well as (60)Co gamma-rays. Dose dependent decline in surviving fraction was noticed along with the increase of MN frequency, CA frequency as well as percentage of apoptosis as detected by nuclear fragmentation assay. The relative intensity of DNA ladder, which is a useful marker for the determination of the extent of apoptosis induction, was also increased in a dose dependent manner. Additionally, expression of tyrosine kinase lck-1 gene, which plays an important role in response to ionizing radiation induced apoptosis, was increased with the increase of radiation doses and also with incubation time. The present study showed that all the high LET radiations were generally more effective in cell killing and inflicting other cytogenetic damages than that of low LET gamma-rays. The dose response curves revealed that (7)Li-beam was most effective in cell killing as well as inducing other nuclear damages followed by (12)C, (16)O and (60)Co gamma-rays, in that order. The result of this study may have some application in biological dosimetry for assessment of genotoxicity in heavy ion exposed subjects and in determining suitable doses for radiotherapy in cancer patients where various species of heavy ions are now being generally used.

Curative treatment of Stage I non-small-cell lung cancer with carbon ion beams using a hypofractionated regimen

PURPOSE

A phase I/II study on carbon ion radiotherapy for Stage I non-small-cell lung cancer (NSCLC) was first conducted between 1994 and 1999 and determined the optimal dose. Second, a Phase II study using the optimal dose was performed. The purpose of the present study was to clarify the local control and 5-year survival rates.

METHODS AND MATERIALS

Between April 1999 and December 2000, 50 patients with 51 primary lesions were treated. Using a fixed dose of 72 GyE in nine fractions over 3 weeks, the primary tumors were irradiated with carbon ion beams alone. The average age of the patients was 74.5 years. Thirty-three (66%) of these were medically inoperable. Local control and survival were determined by using the Kaplan-Meier method and the data were statistically processed by using the log-rank test.

RESULTS

All patients were observed for a minimum of 5 years or until death with a median follow-up time of 59.2 months (range, 6.0-83.0 months). The local control rate for all patients was 94.7%. The patients' 5-year cause-specific survival rate was 75.7% (IA: 89.4; IB: 55.1), and overall survival 50.0% (IA: 55.2; IB: 42.9). No toxic reactions in the lung greater than Grade 3 were detected.

CONCLUSIONS

Carbon ion radiotherapy, a new treatment modality with superior benefits in terms of quality of life and activity of daily living, has been proven as a valid alternative to surgery for Stage I NSCLC and to offer particular benefits, especially for elderly and inoperable patients.

Comparison of the Methods of Specifying Carbon Ion Doses at NIRS and GSI

Due to the RBE variations, the carbon-ion doses (in Gy) are no longer sufficient to monitor adequately the biological effect of these radiations. Therefore, "RBE dose weighting factors" - W(RBE) - allowing for the RBE variations with energy, dose and biological system have to be introduced in the treatment plans in order to provide the physician with interpretable information. This paper compares the methods employed for this purpose at NIRS and GSI, which are specific of the beam delivery system of these institutions. NIRS has a "passive" beam delivery system where the dose distribution in the SOBP is determined by a Ridge filter. The dose distribution - and thus, the shaping of the filter - is chosen according to the clinical situation and determined with respect to W(RBE) factors in order to yield a biologically iso-effective SOBP. W(RBE )factors in the SOBP are at first derived from a RBE/LET function for HSG cells, then normalized to 3 at a LET of 80 keV/mum. The latter value of 3 corresponds to the clinical RBE of NIRS-neutrons, which were found to exhibit the same radiobiological properties as 80 keV/mum carbon-ions. GSI has a "dynamic" beam delivery system ("spot" or "voxel" scanning) making it possible to irradiate irregular volumes and to modulate the radiation intensity according to the radiosensitivity of different tissues and/or different sub-volumes. Due to the "power" and the resulting complexity of the system, W(RBE )factors are determined through an integrated calculation code allowing iterative interaction of both physical and radiobiological parameters. The "Local Effect Model" (LEM) was developed in this view with the aim of deriving carbon-ion W(RBE )factors from the parameters determining the response to photons. Advantages and weaknesses of the respective methods will be discussed.

Specification of Carbon Ion Dose at the National Institute of Radiological Sciences (NIRS)

The clinical dose distributions of therapeutic carbon beams, currently used at NIRS HIMAC, are based on in-vitro Human Salivary Gland (HSG) cell survival response and clinical experience from fast neutron radiotherapy. Moderate radiosensitivity of HSG cells is expected to be a typical response of tumours to carbon beams. At first, the biological dose distribution is designed so as to cause a flat biological effect on HSG cells in the spread-out Bragg peak (SOBP) region. Then, the entire biological dose distribution is evenly raised in order to attain a RBE (relative biological effectiveness) = 3.0 at a depth where dose-averaged LET (linear energy transfer) is 80 keV/mum. At that point, biological experiments have shown that carbon ions can be expected to have a biological effect identical to fast neutrons, which showed a clinical RBE of 3.0 for fast neutron radiotherapy at NIRS. The resulting clinical dose distribution in this approximation is not dependent on dose level, tumour type or fractionation scheme and thus reduces the unknown parameters in the analysis of the clinical results. The width SOBP and the clinical / physical dose at the center of SOBP specify the dose distribution. The clinical results analysed in terms of TCP were found to show good agreement with the expected RBE value at higher TCP levels. The TCP analysis method was applied for the prospective dose estimation of hypofractionation.

Clinical Results of Carbon Ion Radiotherapy at NIRS

In 1994 a Phase I/II clinical study on carbon ion radiotherapy was begun at NIRS using HIMAC, which was then the world's only heavy ion accelerator complex dedicated to medical use in a hospital environment. Among several types of ion species, we have chosen carbon ions for cancer therapy because they had the most optimal properties in terms of possessing, both physically and biologically, the most effective dose-localization in the body. The purpose of the clinical study was to investigate the efficacy of carbon ion radiotherapy against a variety of tumors as well as to develop effective techniques for delivering an efficient dose to the tumor. The RBE of carbon ions was estimated to be 2.0 to 3.0 along the SOBP for acute skin reactions. As of August 2006, a total of 2,867 patients had been entered into Phase I/II or Phase II studies and analyzed for toxicity and local tumor response. The results have shown that carbon ion radiotherapy has the potential ability to provide a sufficient dose to the tumor with acceptable morbidity in the surrounding normal tissues. Tumors that appear to respond favorably to carbon ions include locally advanced tumors and those with histologically non-squamous cell type of tumors such as adenocarcinoma, adenoid cystic carcinoma, malignant melanoma, hepatoma, and bone/soft tissue sarcoma. By taking advantage of the biological and physical properties of high-LET radiation, the efficacy of treatment regimens with small fractions in short treatment times has been confirmed for almost all types of tumors in carbon ion radiotherapy.

Specifying carbon ion doses for radiotherapy: the heidelberg approach

There are currently no guidelines for prescribing and reporting radiation therapy (RT) with ion beams. In this paper an overview over some technical aspects and their implication on ion RT are reported. This includes a discussion of the difference in the treatment planning systems currently used for active and passive beam shaping systems, aspects of patient positioning and target definition and dose prescription. Special emphasis is put on the questions arising from the use of the beam scanning methods in combination with biological treatment plan optimization, which is used in the German heavy ion therapy facility at GSI and will also be introduced at the hospital based facility in Heidelberg. Furthermore, the Heidelberg approach for the clinical dose prescription is compared with the methods developed at HIMAC in Chiba, Japan.

Biological intercomparison using gut crypt survivals for proton and carbon-ion beams

Charged particle therapy depends on biological information for the dose prescription. Relative biological effectiveness or RBE for this requirement could basically be provided by experimental data. As RBE values of protons and carbon ions depend on several factors such as cell/tissue type, biological endpoint, dose and fractionation schedule, a single RBE value could not deal with all different radiosensitivities. However, any biological model with accurate reproducibility is useful for comparing biological effectiveness between different facilities. We used mouse gut crypt survivals as endpoint, and compared the cell killing efficiency of proton beams at three Japanese facilities. Three Linac X-ray machines with 4 and 6 MeV were used as reference beams, and there was only a small variation (coefficient of variance < 2%) in biological effectiveness among them. The RBE values of protons relative to Linac X-rays ranged from 1.0 to 1.11 at the middle of a 6-cm SOBP (spread-out Bragg peak) and from 0.96 to 1.01 at the entrance plateau. The coefficient of variance for protons ranged between 4.0 and 5.1%. The biological comparison of carbon ions showed fairly good agreement in that the difference in biological effectiveness between NIRS/HIMAC and GSI/SIS was 1% for three positions within the 6-cm SOBP. The coefficient of variance was < 1.7, < 0.6 and < 1.6% for proximal, middle and distal SOBP, respectively. We conclude that the inter-institutional variation of biological effectiveness is smaller for carbon ions than protons, and that beam-spreading methods of carbon ions do not critically influence gut crypt survival.

Irradiation System for HIMAC

Clinical trials of carbon radiotherapy started at HIMAC in 1994 using three treatment rooms and four beam ports, two horizontal and two vertical. The broad beam method was adopted to make a three-dimensionally uniform field at an isocenter. A spot beam extracted from an accelerator was laterally spread out by using a pair of wobbler magnets and a scatterer. A bar ridge filter modulated the beam energy to obtain the spread out Bragg peak (SOBP). The SOBP was designed to be flat in terms of the biological dose based on the consideration that the field consisted of various beams with different LET. Finally, the field of 20 cm in diameter with +/- 2.5% uniformity was formed at the isocenter. The width of the maximum SOBP was 15 cm. When treating the lung or liver, organs that move due to breathing, the beam was irradiated only during the expiration period in a respiration-gated irradiation method. This reduced the treatment margin of the moving target. In order to prevent normal tissues adjacent to the target volume from irradiation by an unwanted dose, a layer-stacking method was developed. In this method, thin SOBP layers which have different ranges were piled up step by step from the distal end to the entrance of the target volume. At the same time, a multi-leaf collimator was used to change the aperture shape to match the shape of each layer to the cross-sectional shape of the target. This method has been applied to rather large volume cancers including bone and soft-tissue cancers. Only a few serious problems in the irradiation systems have been encountered since the beginning of the clinical trials. Overall the systems have been working stably and reliably.

Dose contributions from large-angle scattered particles in therapeutic carbon beams

In carbon therapy, doses at center of spread-out Bragg peaks depend on field size. For a small field of 5 x 5 cm2, the central dose reduces to 96% of the central dose for the open field in case of 400 MeV/n carbon beam. Assuming the broad beam injected to the water phantom is made up of many pencil beams, the transverse dose distribution can be reconstructed by summing the dose distribution of the pencil beams. We estimated dose profiles of this pencil beam through measurements of dose distributions of broad uniform beams blocked half of the irradiation fields. The dose at a distance of a few cm from the edge of the irradiation field reaches up to a few percent of the central dose. From radiation quality measurements of this penumbra, the large-angle scattered particles were found to be secondary fragments which have lower LET than primary carbon beams. Carbon ions break up in beam modifying devices or in water phantom through nuclear interaction with target nuclei. The angular distributions of these fragmented nuclei are much broader than those of primary carbon particles. The transverse dose distribution of the pencil beam can be approximated by a function of the three-Gaussian form. For a simplest case of mono-energetic beam, contributions of the Gaussian components which have large mean deviations become larger as the depth in the water phantom increases.

Carbon-ion radiotherapy for locally advanced or unfavorably located choroidal melanoma: a Phase I/II dose-escalation study

PURPOSE

To evaluate the applicability of carbon ion beams for the treatment of choroidal melanoma with regard to normal tissue morbidity and local tumor control.

METHODS AND MATERIALS

Between January 2001 and February 2006, 59 patients with locally advanced or unfavorably located choroidal melanoma were enrolled in a Phase I/II clinical trial of carbon-ion radiotherapy at the National Institute of Radiologic Sciences. The primary endpoint of this study was normal tissue morbidity, and secondary endpoints were local tumor control and patient survival. Of the 59 subjects enrolled, 57 were followed >6 months and analyzed.

RESULTS

Twenty-three patients (40%) developed neovascular glaucoma, and three underwent enucleation for eye pain due to elevated intraocular pressure. Incidence of neovascular glaucoma was dependent on tumor size and site. Five patients had died at analysis, three of distant metastasis and two of concurrent disease. All but one patient, who developed marginal recurrence, were controlled locally. Six patients developed distant metastasis, five in the liver and one in the lung. Three-year overall survival, disease-free survival, and local control rates were 88.2%, 84.8%, and 97.4%, respectively. No apparent dose-response relationship was observed in either tumor control or normal tissue morbidity at the dose range applied.

CONCLUSION

Carbon-ion radiotherapy can be applied to choroidal melanoma with an acceptable morbidity and sufficient antitumor effect, even with tumors of unfavorable size or site.