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

Adenovirus-mediated FIR demonstrated TP53-independent cell-killing effect and enhanced antitumor activity of carbon-ion beams

Combination therapy of carbon-ion beam with the far upstream element-binding protein (FBP)-interacting repressor, FIR, which interferes with DNA damage repair proteins, was proposed as an approach for esophageal cancer treatment with low side effects regardless of TP53 status. In vivo therapeutic antitumor efficacy of replication-defective adenovirus (E1 and E3 deleted adenovirus serotype 5) encoding human FIR cDNA (Ad-FIR) was demonstrated in the tumor xenograft model of human esophageal squamous cancer cells, TE-2. Bleomycin (BLM) is an anticancer agent that introduces DNA breaks. The authors reported that Ad-FIR involved in the BLM-induced DNA damage repair response and thus applicable for other DNA damaging agents. To examine the effect of Ad-FIR on DNA damage repair, BLM, X-ray and carbon-ion irradiation were used as DNA damaging agents. The biological effects of high linear energy transfer (LET) radiotherapy used with carbon-ion irradiation are more expansive than low-LET conventional radiotherapy, such as X-rays or γ rays. High LET radiotherapy is suitable for the local control of tumors because of its high relative biological effectiveness. Ad-FIR enhanced BLM-induced DNA damage indicated by γH2AX in vitro. BLM treatment increased endogenous nuclear FIR expression in TE-2 cells, and P27Kip1 expression was suppressed by TP53 siRNA and BLM treatment. Further, Ad-FIRΔexon2, a dominant-negative form of FIR that lacks exon2 transcriptional repression domain, decreased Ku86 expression. The combination of Ad-FIR and BLM in TP53 siRNA increased DNA damage. Additionally, Ad-FIR showed synergistic cell toxicity with X-ray in vitro and significantly increased the antitumor efficacy of carbon-ion irradiation in the xenograft mouse model of TE-2 cells (P=0.03, Mann-Whitney's U-test) and was synergistic with the sensitization enhancement ratio (SER) value of 1.15. Therefore, Ad-FIR increased the cell-killing activity of the carbon-ion beam that avoids late-phase severe adverse effects independently of the TP53 status in vitro. Our findings indicated the feasibility of the combination of Ad-FIR with DNA damaging agents for future esophageal cancer treatment.

Clinical trial of prophylactic extended-field carbon-ion radiotherapy for locally advanced uterine cervical cancer (protocol 0508)

To evaluate the efficacy and the toxicity of prophylactic extended-field carbon-ion radiotherapy (C-ion RT, Protocol 0508) for locally advanced squamous cell carcinoma of the uterine cervix in phase I / II clinical trial. Between May 2006 and January 2012, 26 patients of Protocol 0508 were treated with C-ion RT. The numbers of patients with stage IIB, IIIB, and IVA disease were 13, 11, and 2, respectively. Twenty patients had pelvic lymph node metastases. Median tumor size was 6.1 cm (range, 4.0–10.0 cm). The treatment consisted of extended-field irradiation of 39.0 gray equivalents (GyE) in 13 fractions, and additional 15.0 GyE in 5 fractions was given to the gross tumor volume (GTV) and surrounding tissues. With regard to local boost, 18.0 GyE in 2 fractions was given to GTV only. Total dose to the cervical tumor was 72.0 GyE over 20 fractions. The median follow-up period was 37 months. Twenty-one patients had grade 1 or 2 acute gastrointestinal toxicity, but all patients completed the treatment on schedule. There were no grade 3 or higher late complications, with 8 patients having grade 1 or 2 toxicities, 1 had grade 2 gastrointestinal toxicity and 2 had grade 2 genitourinary toxicity. Four patients (15.4%) developed local recurrence, and 8 patients (30.8%) had distant metastases. The 2-year local control rate, progression-free survival rate and overall survival rate were 83.6%, 61.5% and 73.1%, respectively. There were no severe acute or late complications in this trial. Prophylactic extended-field C-ion RT for locally advanced squamous cell carcinoma of the uterine cervix was a safe treatment. Although the number of patients in this study was small, the results support further investigations to confirm the therapeutic efficacy and to avoid or reduce toxicity.

TRIAL REGISTRATION

UMIN-CTR UMIN000016169.

Difference in distant failure site between locally advanced squamous cell carcinoma and adenocarcinoma of the uterine cervix after C-ion RT

We investigated the first site of distant failure after carbon ion radiotherapy (C-ion RT) for locally advanced cervical cancer in three clinical trials. A total of 91 cases were enrolled in the three trials (Protocol 9702, 9704 and 9902). Histologically, 36 cases had squamous cell carcinoma (SqCC) and 55 cases had adenocarcinoma (AC), including 13 with adenosquamous cell carcinoma. The number of cases with Stage IIB, IIIB and IVA disease was 21, 59 and 11, respectively. Of the 91 cases, 42 had positive pelvic lymph nodes (PLNs). The median tumor size was 6.0 cm (range, 3.0–12.0 cm). The median follow-up duration for all cases was 40 months (range, 7–181 months). A total of 40 cases developed distant failure as the first site of failure: 13 of 36 (36.1%) SqCC cases had distant failure, with 9 of them with para-aortic lymph node (PALN) failure; 27 of 55 (44.0%) AC cases had distant failure, and 23 of them had distant failure excluding PALN metastasis. Distant failure rates of SqCC cases who had positive and negative PLNs before C-ion RT were 61.1% and 11.1%, respectively (P = 0.0045). Those of AC cases were 54.2% and 45.2%, respectively (P = 0.507). In conclusion, there were high rates of distant failure after C-ion RT in AC cases regardless of PLN status, and there were high rates of distant failure after C-ion RT, especially PALN failure, in SqCC cases with positive PLNs.

Heavy-ion-induced sucrose radicals investigated using EPR and UV spectroscopy

The potential use of a sucrose dosimeter for estimating both linear energy transfer (LET) and the absorbed dose of heavy ion and X-ray radiation was investigated. The stable free radicals were produced when sucrose was irradiated with heavy ions, such as helium, carbon, silicon and neon ions, and when the X-ray radiation was similar to the obtained electron paramagnetic resonance (EPR) spectra, which were ∼7 mT wide and composed of several hyperfine structures. In addition, the total spin concentration resulting from heavy-ion irradiation increased linearly as the absorbed dose increased, and decreased logarithmically as the LET increased. These empirical relations imply that the LET at a certain dose can be determined from the spin concentration. For sucrose and alanine, both cross-sections following C-ion irradiation with a 50 Gy dose were ∼1.3 × 10(-12) [μm(2)], taking into account the molecular size of the samples. The values of these cross-sections imply that multiple ionizing particles were involved in the production of stable radicals. Furthermore, UV absorbance at 267 nm of an aqueous solution of irradiated sucrose was found to linearly increase with increasing absorbed dose. Therefore, the EPR and UV results suggest that sucrose can be a useful dosimeter for heavy-ion irradiation.

Confinement effects of ion tracks in ultrathin polymer films

We show direct experimental evidence that radiation effects produced by single MeV heavy ions on a polymer surface are weakened when the length of the ion track in the material is confined into layers of a few tens of nanometers. Deviation from the bulk (thick film) behavior of ion-induced craters starts at a critical thickness as large as ∼40  nm, due to suppression of long-range additive effects of excited atoms along the track. Good agreement was found between the experimental results, molecular dynamic simulations, and an analytical model.

The major DNA repair pathway after both proton and carbon-ion radiation is NHEJ, but the HR pathway is more relevant in carbon ions

The purpose of this study was to identify the roles of non-homologous end-joining (NHEJ) or homologous recombination (HR) pathways in repairing DNA double-strand breaks (DSBs) induced by exposure to high-energy protons and carbon ions (C ions) versus gamma rays in Chinese hamster cells. Two Chinese hamster cell lines, ovary AA8 and lung fibroblast V79, as well as various mutant sublines lacking DNA-PKcs (V3), X-ray repair cross-complementing protein-4 [XRCC4 (XR1), XRCC3 (irs1SF) and XRCC2 (irs1)] were exposed to gamma rays ((137)Cs), protons (200 MeV; 2.2 keV/μm) and C ions (290 MeV; 50 keV/μm). V3 and XR1 cells lack the NHEJ pathway, whereas irs1 and irs1SF cells lack the HR pathway. After each exposure, survival was measured using a clonogenic survival assay, in situ DSB induction was evaluated by immunocytochemical analysis of histone H2AX phosphorylation at serine 139 (γ-H2AX foci) and chromosome aberrations were examined using solid staining. The findings from this study showed that clonogenic survival clearly depended on the NHEJ and HR pathway statuses, and that the DNA-PKcs(-/-) cells (V3) were the most sensitive to all radiation types. While protons and γ rays yielded almost the same biological effects, C-ion exposure greatly enhanced the sensitivity of wild-type and HR-deficient cells. However, no significant enhancement of sensitivity in cell killing was seen after C-ion irradiation of NHEJ deficient cells. Decreases in the number of γ-H2AX foci after irradiation occurred more slowly in the NHEJ deficient cells. In particular, V3 cells had the highest number of residual γ-H2AX foci at 24 h after C-ion irradiation. Chromosomal aberrations were significantly higher in both the NHEJ- and HR-deficient cell lines than in wild-type cell lines in response to all radiation types. Protons and gamma rays induced the same aberration levels in each cell line, whereas C ions introduced higher but not significantly different aberration levels. Our results suggest that the NHEJ pathway plays an important role in repairing DSBs induced by both clinical proton and C-ion beams. Furthermore, in C ions the HR pathway appears to be involved in the repair of DSBs to a greater extent compared to gamma rays and protons.

Preclinical evaluation of bioabsorbable polyglycolic acid spacer for particle therapy

PURPOSE

To evaluate the efficacy and safety of a polyglycolic acid (PGA) spacer through physical and animal experiments.

METHODS AND MATERIALS

The spacer was produced with surgical suture material made of PGA, forming a 3-dimensional nonwoven fabric. For evaluation or physical experiments, 150-MeV proton or 320-MeV carbon-ion beams were used to generate 60-mm width of spread-out Bragg peak. For animal experiments, the abdomens of C57BL/6 mice, with or without the inserted PGA spacers, were irradiated with 20 Gy of carbon-ion beam (290 MeV) using the spread-out Bragg peak. Body weight changes over time were scored, and radiation damage to the intestine was investigated using hematoxylin and eosin stain. Blood samples were also evaluated 24 days after the irradiation. Long-term thickness retention and safety were evaluated using crab-eating macaques.

RESULTS

No chemical or structural changes after 100 Gy of proton or carbon-ion irradiation were observed in the PGA spacer. Water equivalency of the PGA spacer was equal to the water thickness under wet condition. During 24 days' observation after 20 Gy of carbon-ion irradiation, the body weights of mice with the PGA spacer were relatively unchanged, whereas significant weight loss was observed in those mice without the PGA spacer (P<.05). In mice with the PGA spacer, villus and crypt structure were preserved after irradiation. No inflammatory reactions or liver or renal dysfunctions due to placement of the PGA spacer were observed. In the abdomen of crab-eating macaques, thickness of the PGA spacer was maintained 8 weeks after placement.

CONCLUSIONS

The absorbable PGA spacer had water-equivalent, bio-compatible, and thickness-retaining properties. Although further evaluation is warranted in a clinical setting, the PGA spacer may be effective to stop proton or carbon-ion beams and to separate normal tissues from the radiation field.

Influence of nuclear interactions in polyethylene range compensators for carbon-ion radiotherapy

PURPOSE

A recent study revealed that polyethylene (PE) would cause extra carbon-ion attenuation per range shift by 0.45%/cm due to compositional differences in nuclear interactions. The present study aims to assess the influence of PE range compensators on tumor dose in carbon-ion radiotherapy.

METHODS

Carbon-ion radiation was modeled to be composed of primary carbon ions and secondary particles, for each of which the dose and the relative biological effectiveness (RBE) were estimated at a tumor depth in the middle of spread-out Bragg peak. Assuming exponential behavior for attenuation and yield of these components with depth, the PE effect on dose was calculated for clinical carbon-ion beams and was partly tested by experiment. The two-component model was integrated into a treatment-planning system and the PE effect was estimated in two clinical cases.

RESULTS

The attenuation per range shift by PE was 0.1%-0.3%/cm in dose and 0.2%-0.4%/cm in RBE-weighted dose, depending on energy and range-modulation width. This translates into reduction of RBE-weighted dose by up to 3% in extreme cases. In the treatment-planning study, however, the effect on RBE-weighted dose to tumor was typically within 1% reduction.

CONCLUSIONS

The extra attenuation of primary carbon ions in PE was partly compensated by increased secondary particles for tumor dose. In practical situations, the PE range compensators would normally cause only marginal errors as compared to intrinsic uncertainties in treatment planning, patient setup, beam delivery, and clinical response.

Review of carbon ion radiotherapy for skull base tumors (especially chordomas)

AIM

To review the clinical feasibility of carbon ion radiotherapy (C-ion RT) for skull base tumors, especially for chordomas which are often seen in the skull base area.

BACKGROUND

Skull base tumors treated by C-ion RT consist of primary chordomas and chondrosarcomas, and enormously extended head and neck cancer with a histology of adenoid cystic carcinomas, adenocarcinomas and malignant melanomas. These tumors are located on anatomically complex sites where they are close to important normal tissues and therefore demand better physical dose distribution to avoid unnecessary doses for surrounding normal tissues. These tumors are also known as radio-resistant tumors for low linear energy transfer (LET) radiotherapy and show favorable results after treatment by high LET carbon ion radiotherapy.

MATERIALS AND METHODS

Biological reports of C-ions for the chordoma cell line, clinical results of C-ion RT for skull base tumors, dose comparative studies between two representative facilities and tumor control probability (TCP) of chordomas by C-ion RT were reviewed.

RESULTS

C-ion RT for skull base tumors, especially for chordomas, shows favorable results of tumor control and acceptable complications. The C-ion dose of 57.36 gray equivalent (GyE)/16 fractions/4 weeks will deliver 90% of local control for chordomas. The limiting doses for surrounding normal tissues are clearly revealed. The dose difference between institutes was assumed within 10%.

CONCLUSIONS

C-ion RT is recommended for skull base tumors because of high LET characteristics and clinical results.

A prospective nonrandomized phase I/II study of carbon ion radiotherapy in a favorable subset of locally advanced non-small cell lung cancer (NSCLC)

BACKGROUND

Although concurrent chemoradiotherapy (CCRT) has become the standard approach for unresectable locally advanced non-small cell lung cancer (LA-NSCLC), most patients are not candidates for this treatment because of comorbidities. We evaluated the safety and efficacy of carbon ion radiotherapy (CIRT) in LA-NSCLC patients.

METHODS

Patients with stage IIA to IIIA (UICC 7th edition) LA-NSCLC were enrolled in a sequential phase I/II trial. For a phase I dose escalation study, the total prescribed dose was increased by 4 Gray equivalents (GyE) in 2 steps, from 68 to 72 GyE and then to 76 GyE, using 16 fractions over 4 weeks. After determining the recommended dose, the phase II trial was started in an expanded cohort.

RESULTS

Of the 36 patients treated in phase I, 2 grade 3 adverse events (radiation pneumonitis and tracheoesophageal fistula) were observed in the 76 GyE group. Accordingly, for phase II, the next consecutive 26 patients were treated with 72 GyE, with no grade 3 to 5 toxicities resulting. A total of 62 eligible patients were recruited. The majority of patients (49 of 62) were N0 or N1 patients, and the rest (13 of 62) were single-station N2 patients. The median follow-up period was 25.2 months. The 2-year local control rate (LCR) and overall survival (OS) for the entire cohort were 93.1% and 51.9%, respectively. In particular, patients with cT3-4N0 had an excellent prognosis; the 2-year OS and LCR were 69.3% and 100%, respectively.

CONCLUSIONS

Short-course CIRT monotherapy shows promise as an effective nonsurgical treatment for inoperable LA-NSCLC.

Low-dose total-body carbon-ion irradiations induce early transcriptional alteration without late Alzheimer's disease-like pathogenesis and memory impairment in mice

The cause and risk factors of Alzheimer's disease (AD) are largely unknown. Studies on possible radiation-induced AD-like pathogenesis and behavioral consequences are important because humans are exposed to ionizing radiation (IR) from various sources. It was reported that total-body irradiations (TBI) at 10 cGy of low linear energy transfer (LET) X-rays to mice triggered acute transcriptional alterations in genes associated with cognitive dysfunctions. However, it was unknown whether low doses of IR could induce AD-like changes late after exposure. We reported previously that 10 cGy X-rays induced early transcriptional response of several AD-related genes in hippocampi without late AD-like pathogenesis and memory impairment in mice. Here, further studies on two low doses (5 or 10 cGy) of high LET carbonion irradiations are reported. On expression of 84 AD-related genes in hippocampi, at 4 hr after TBI, 5 cGy induced a significant upregulation of three genes (Abca1, Casp3, and Chat) and 10 cGy led to a marked upregulation of one gene (Chat) and a downregulation of three genes (Apoe, Ctsd, and Il1α), and, at 1 year after TBI, one gene (Il1α) was significantly downregulated in 10 cGy-irradiated animals. Changes in spatial learning ability and memory and induction of AD-like pathogenesis were not detected by in vivo brain imaging for amyloid-β peptide accumulation and by immunohistochemical staining of amyloid precursor protein, amyloid-β protein, tau, and phosphorylated tau protein. These findings indicate that low doses of carbon-ion irradiations did not cause behavioral impairment or AD-like pathological change in mice.

ICRP Publication 127: Radiological Protection in Ion Beam Radiotherapy

The goal of external-beam radiotherapy is to provide precise dose localisation in the treatment volume of the target with minimal damage to the surrounding normal tissue. Ion beams, such as protons and carbon ions, provide excellent dose distributions due primarily to their finite range, allowing a significant reduction of undesired exposure of normal tissue. Careful treatment planning is required for the given type and localisation of the tumour to be treated in order to maximise treatment efficiency and minimise the dose to normal tissue. Radiation exposure in out-of-field volumes arises from secondary neutrons and photons, particle fragments, and photons from activated materials. These unavoidable doses should be considered from the standpoint of radiological protection of the patient. Radiological protection of medical staff at ion beam radiotherapy facilities requires special attention. Appropriate management and control are required for the therapeutic equipment and the air in the treatment room that can be activated by the particle beam and its secondaries. Radiological protection and safety management should always conform with regulatory requirements. The current regulations for occupational exposures in photon radiotherapy are applicable to ion beam radiotherapy with protons or carbon ions. However, ion beam radiotherapy requires a more complex treatment system than conventional radiotherapy, and appropriate training of staff and suitable quality assurance programmes are recommended to avoid possible accidental exposure of patients, to minimise unnecessary doses to normal tissue, and to minimise radiation exposure of staff.

Carbon-ion scanning lung treatment planning with respiratory-gated phase-controlled rescanning: simulation study using 4-dimensional CT data

Background

To moving lung tumors, we applied a respiratory-gated strategy to carbon-ion pencil beam scanning with multiple phase-controlled rescanning (PCR). In this simulation study, we quantitatively evaluated dose distributions based on 4-dimensional CT (4DCT) treatment planning.

Methods

Volumetric 4DCTs were acquired for 14 patients with lung tumors. Gross tumor volume, clinical target volume (CTV) and organs at risk (OARs) were delineated. Field-specific target volumes (FTVs) were calculated, and 48Gy(RBE) in a single fraction was prescribed to the FTVs delivered from four beam angles. The dose assessment metrics were quantified by changing the number of PCR and the results for the ungated and gated scenarios were then compared.

Results

For the ungated strategy, the mean dose delivered to 95% of the volume of the CTV (CTV-D95) was in average 45.3 ± 0.9 Gy(RBE) even with a single rescanning (1 × PCR). Using 4 × PCR or more achieved adequate target coverage (CTV-D95 = 46.6 ± 0.3 Gy(RBE) for ungated 4 × PCR) and excellent dose homogeneity (homogeneity index =1.0 ± 0.2% for ungated 4 × PCR). Applying respiratory gating, percentage of lung receiving at least 20 Gy(RBE) (lung-V20) and heart maximal dose, averaged over all patients, significantly decreased by 12% (p < 0.05) and 13% (p < 0.05), respectively.

Conclusions

Four or more PCR during PBS-CIRT improved dose conformation to moving lung tumors without gating. The use of a respiratory-gated strategy in combination with PCR reduced excessive doses to OARs.

Direct evaluation of radiobiological parameters from clinical data in the case of ion beam therapy: an alternative approach to the relative biological effectiveness

The relative biological effectiveness (RBE) concept is commonly used in treatment planning for ion beam therapy. Whether models based on in vitro/in vivo RBE data can be used to predict human response to treatments is an open issue. In this work an alternative method, based on an effective radiobiological parameterization directly derived from clinical data, is presented. The method has been applied to the analysis of prostate cancer trials with protons and carbon ions.Prostate cancer trials with proton and carbon ion beams reporting 5 year-local control (LC5) and grade 2 (G2) or higher genitourinary toxicity rates (TOX) were selected from literature to test the method. Treatment simulations were performed on a representative subset of patients to produce dose and linear energy transfer distribution, which were used as explicative physical variables for the radiobiological modelling. Two models were taken into consideration: the microdosimetric kinetic model (MKM) and a linear model (LM). The radiobiological parameters of the LM and MKM were obtained by coupling them with the tumor control probability and normal tissue complication probability models to fit the LC5 and TOX data through likelihood maximization. The model ranking was based on the Akaike information criterion.Results showed large confidence intervals due to the limited variety of available treatment schedules. RBE values, such as RBE = 1.1 for protons in the treated volume, were derived as a by-product of the method, showing a consistency with current approaches. Carbon ion RBE values were also derived, showing lower values than those assumed for the original treatment planning in the target region, whereas higher values were found in the bladder. Most importantly, this work shows the possibility to infer the radiobiological parametrization for proton and carbon ion treatment directly from clinical data.

Tumor induction in mice after local irradiation with single doses of either carbon-ion beams or gamma rays

PURPOSE

To determine the dose-dependent relative biological effectiveness (RBE) for tumor prevalence in mice receiving single localized doses to their right leg of either carbon ions (15, 45 or 75 keV/μm) or 137Cs gamma rays.

METHODS AND MATERIALS

A total of 1647 female C3H mice were irradiated to their hind legs with a localized dose of either reference gamma rays or 15, 45 or 75 keV/μm carbon-ion beams. Irradiated mice were evaluated for tumors twice a month during their three-year life span, and the dimensions of any tumors found were measured with a caliper. The tumor induction frequency was calculated by Kaplan-Meier analysis.

RESULTS

The incidence of tumors from 50 Gy of 45 keV/μm carbon ions was marginally higher than those from 50 Gy of gamma rays. However, 60 Gy of 15 keV/μm carbon ions induced significantly fewer tumors than did gamma rays. RBE values of 0.87 + 0.12, 1.29 + 0.08 or 2.06 + 0.39 for lifetime tumorigenesis were calculated for 15, 45 or 75 keV/μm carbon-ion beams, respectively. Fibrosarcoma predominated, with no Linear Energy Transfer (LET)-dependent differences in the tumor histology. Experiments measuring the late effect of leg skin shrinkage suggested that the carcinogenic damage of 15 keV/μm carbon ions would be less than that of gamma rays.

CONCLUSIONS

We conclude that patients receiving radiation doses to their normal tissues would face less risk of secondary tumor induction by carbon ions of intermediate LET values compared to equivalent doses of photons.

Influence of the nucleus area distribution on the survival fraction after charged particles broad beam irradiation

It is well known that broad beam irradiation with heavy ions leads to variation in the number of hit(s) received by each cell as the distribution of particles follows the Poisson statistics. Although the nucleus area will determine the number of hit(s) received for a given dose, variation amongst its irradiated cell population is generally not considered. In this work, we investigate the effect of the nucleus area's distribution on the survival fraction. More specifically, this work aims to explain the deviation, or tail, which might be observed in the survival fraction at high irradiation doses. For this purpose, the nucleus area distribution was added to the beam Poisson statistics and the Linear-Quadratic model in order to fit the experimental data. As shown in this study, nucleus size variation, and the associated Poisson statistics, can lead to an upward survival trend after broad beam irradiation. The influence of the distribution parameters (mean area and standard deviation) was studied using a normal distribution, along with the Linear-Quadratic model parameters (α and β). Finally, the model proposed here was successfully tested to the survival fraction of LN18 cells irradiated with a 85 keV µm(- 1) carbon ion broad beam for which the distribution in the area of the nucleus had been determined.

Relative biological effectiveness of therapeutic proton beams for HSG cells at Japanese proton therapy facilities

We investigated the relative biological effectiveness (RBE) of therapeutic proton beams at six proton facilities in Japan with respect to cell lethality of HSG cells. The RBE of treatments could be determined from experimental data. For this purpose, we used a cell survival assay to compare the cell-killing efficiency of proton beams. Among the five linear accelerator (LINAC) X-ray machines at 4 or 6 MeV that were used as reference beams, there was only a small variation (coefficient of variation CV = 3.1% at D10) in biological effectiveness. The averaged value of D10 for the proton beams at the middle position of the spread-out Bragg peak (SOBP) was 4.98. These values showed good agreement, with a CV of 4.3% among the facilities. Thus, the average RBE10 (RBE at the D10 level) at the middle position of the SOBP beam for six facilities in Japan was 1.05 with a CV of 2.8%.

Phase I/II trial of definitive carbon ion radiotherapy for prostate cancer: evaluation of shortening of treatment period to 3 weeks

BACKGROUND

The purpose of this study was to evaluate the feasibility of a new shortened 3-week treatment schedule of carbon ion radiotherapy (CIRT) for prostate cancer.

METHODS

Beginning in May 2010, patients with T1b-T3bN0M0, histologically proven prostate adenocarcinoma were enrolled in the phase II trial of CIRT. Patients received 51.6 GyE in 12 fractions over 3 weeks (protocol 1002). The primary end point was defined as the incidence of late adverse events that were evaluated based on the Common Terminology Criteria for Adverse Events version 4.0. Biochemical failure was determined using the Phoenix definition (nadir +2.0 ng ml(-1)).

RESULTS

Forty-six patients were enrolled, and all patients were included in the analysis. The number of low-, intermediate-, and high-risk patients was 12 (26%), 9 (20%), and 25 (54%), respectively. The median follow-up period of surviving patients was 32.3 months. Two patients had intercurrent death without recurrence, and the remaining 44 patients were alive at the time of this analysis. In the analysis of late toxicities, grade 1 (G1) rectal haemorrhage was observed in 3 (7%) patients. The incidence of G1 haematuria was observed in 6 (13%) patients, and G1 urinary frequency was observed in 17 (37%) patients. No ⩾G2 late toxicities were observed. In the analysis of acute toxicities, 2 (4%) patients showed G2 urinary frequency, and no other G2 acute toxicities were observed.

CONCLUSIONS

The new shortened CIRT schedule over 3 weeks was considered as feasible. The analysis of long-term outcome is warranted.

Effects of the dose-volume relationship on and risk factors for maxillary osteoradionecrosis after carbon ion radiotherapy

Background

Osteoradionecrosis (ORN) is a critical complication after carbon ion (C-ion) or photon radiotherapy (RT) for head and neck tumors. However, the risk factors for ORN after C-ion RT remain unclear. Therefore, the present study aimed to investigate the effects of the dose-volume relationship on and risk factors for ORN development after C-ion RT. We, however, focused on the maxillary bone because most tumors treated with C-ion RT were primarily located in the sinonasal cavity.

Methods

The patients enrolled in this study received more than 10% of the prescribed total dose of 57.6 Gy equivalent (GyE) in 16 fractions to their maxilla. All patients were followed up for more than 2 years after C-ion RT. Those with tumor invasion to the maxilla before C-ion RT or local recurrence after the treatment were excluded from the study to accurately evaluate the effects of irradiation on the bone. Sixty-three patients were finally selected. The severity of ORN was assessed according to the Common Terminology Criteria for Adverse Events version 4.0. The correlation between clinical and dosimetric parameters and ORN incidence was retrospectively analyzed.

Results

The median follow-up period was 79 months. Of the 63 enrolled patients, 26 developed ORN of grade ≥1. Multivariate analysis revealed that the maxilla volume receiving more than 50 GyE (V50) and the presence of teeth within the planning target volume were significant risk factors for ORN. Dose-volume histogram analysis revealed that V10 to V50 parameters were significantly higher in patients with ORN than in those without ORN.

Conclusions

V50 and the presence of teeth within the planning target volume were independent risk factors for the development of ORN after C-ion RT using a 16-fraction protocol.

First experience of carbon-ion radiotherapy for early breast cancer

Breast cancer is increasingly being detected at earlier stages, and partial breast irradiation for patients with low-risk-group tumor has come to be applied in the US and Europe as an alternative to whole-breast irradiation. Based on those experiences, some institutes have tried using particle beams for partial breast irradiation for postoperative or radical intent for early breast cancer, but technical difficulties have hindered its progress. The National Institute of Radiological Sciences has been preparing for carbon-ion radiotherapy (C-ion RT) with radical intent for stage I breast cancer since 2011, and we carried out the first treatment in April 2013. In this case report, we explain our first experience of C-ion RT as a treatment procedure for breast tumor and present the radiation techniques and preliminary treatment results as a reference for other institutes trying to perform the same kind of treatment.

Clinical outcomes of carbon ion radiotherapy for locally advanced adenocarcinoma of the uterine cervix in phase 1/2 clinical trial (protocol 9704)

BACKGROUND

This study sought to evaluate the toxicity and efficacy of carbon ion radiotherapy (C-ion RT) for locally advanced adenocarcinoma of the uterine cervix in a phase 1/2 clinical trial.

METHODS

The treatment consisted of whole-pelvic irradiation of 36.0 gray equivalents (GyE) in 12 fractions and local boost with dose escalation from 26.4 to 38.4 GyE in 8 fractions. The dose escalation was performed with careful observation of acute normal tissue responses. Total dose to the cervical tumor was 62.4 to 74.4 GyE in 20 fractions.

RESULTS

Between April 1998 and February 2010, 58 patients were treated with C-ion RT in this clinical trial. The number of patients with stage IIB, IIIB, and IVA disease were 20, 35, and 3, respectively. Median tumor size was 5.5 cm (range, 3.0-11.8 cm). Twenty-seven patients had pelvic lymph node metastases. The median follow-up period was 38 months. All patients completed the treatment schedule. Grade 2 or higher late toxicity was found in 8 patients: 5 with bladder and 2 with small intestine grade 2 toxicities, and 1 patient had grade 4 rectal complication, which was surgically salvaged. The 5-year local control rate, local control rate including salvage surgery, and overall survival rate in all cases were 54.5%, 68.2%, and 38.1%, respectively.

CONCLUSIONS

Dose escalation of C-ion RT for adenocarcinoma of the uterine cervix was accomplished without severe toxicities except in 1 case. Although the number of patients in this study was small, the results support continued investigation and analysis to confirm therapeutic efficacy.

Clinical trial of carbon ion radiotherapy for gynecological melanoma

Carbon ion radiotherapy (C-ion RT) is an advanced modality for treating malignant melanoma. After we treated our first case of gynecological melanoma using C-ion RT in November 2004, we decided to conduct a clinical trial to evaluate its usefulness for the treatment of gynecological melanoma. The eligibility criteria for enrollment in this study were histologically proven malignant melanoma of the gynecological regions with lymph node metastasis remaining in the inguinal and pelvic regions. The small pelvic space, including the GTV and the metastatic lymph node, was irradiated with up to a total dose of 36 GyE followed by a GTV boost of up to a total dose of 57.6 GyE or 64 GyE in 16 fractions. A series of 23 patients were treated between November 2004 and October 2012. Patient age ranged from 51-80 with a median of 71. Of the tumor sites, 14 were located in the vagina, 6 in the vulva, and 3 in the cervix uteri. Of the 23 patients, 22 were irradiated with up to a total dose of 57.6 GyE, and 1 patient was irradiated with up to a total dose of 64 GyE. Chemotherapy and interferon-β were also used to treat 11 of the patients. Acute and late toxicities of Grade 3 or higher were observed in 1 patient treated with concurrent interferon-β. The median follow-up time was 17 months (range, 6-53 months). There was recurrence in 14 patients, and the 3-year local control and overall survival rates were 49.9% and 53.0%, respectively. C-ion RT may become a non-invasive treatment option for gynecological melanoma.

Risk factors for brain injury after carbon ion radiotherapy for skull base tumors

BACKGROUND AND PURPOSE

This study aimed to determine the risk factors for radiation-induced brain injury (RIBI) after carbon ion radiotherapy (CIRT) for treating skull base tumors.

MATERIALS AND METHODS

Between April 1997 and January 2009, CIRT at a total dose of 48.0-60.8Gy equivalent (GyE) was administered in 16 fractions to 47 patients with skull base tumors. Of these patients, 39 who were followed up with magnetic resonance imaging (MRI) for more than 24months were analyzed. RIBI was assessed according to the MRI findings based on the Late Effects of Normal Tissue-Subjective, Objective, Management, Analytic criteria; clinical symptoms were assessed according to the Radiation Therapy Oncology Group/European Organisation for Research and Treatment of Cancer tables. The correlations of clinical and dosimetric parameters with incidence of ⩾grade 2 RIBI were retrospectively analyzed.

RESULTS

The median follow-up period was 67months. The 5-year actuarial likelihoods of ⩾grade 2 RIBI and ⩾grade 2 clinical symptoms were 24.5% and 7.0%, respectively. Multivariate analysis demonstrated that the brain volume receiving more than 50GyE (V50) was a significant risk factor for the development of ⩾grade 2 RIBI (p=0.004).

CONCLUSION

V50 was a significant risk factor for ⩾grade 2 RIBI after CIRT using a 16-fraction regimen.

Comparison of the repair of potentially lethal damage after low- and high-LET radiation exposure, assessed from the kinetics and fidelity of chromosome rejoining in normal human fibroblasts

Potentially lethal damage (PLD) and its repair (PLDR) were studied in confluent human fibroblasts by analyzing the kinetics of chromosome break rejoining after X-ray or heavy-ion exposures. Cells were either held in the non-cycling G0 phase of the cell cycle for 12 h, or forced to proliferate immediately after irradiation. Fusion premature chromosome condensation (PCC) was combined with fluorescence in situ hybridization (FISH) to study chromosomal aberrations in interphase. The culture condition had no impact on the rejoining kinetics of PCC breaks during the 12 h after X-ray or heavy-ion irradiation. However, 12 h after X-ray and silicon irradiation, cycling cells had more chromosome exchanges than non-cycling cells. After 6 Gy X-rays, the yield of exchanges in cycling cells was 2.8 times higher than that in non-cycling cells, and after 2 Gy of 55 keV/μm silicon ions the yield of exchanges in cycling cells was twice that of non-cycling cells. In contrast, after exposure to 2 Gy 200-keV/μm or 440-keV/μm iron ions the yield of exchanges was similar in non-cycling and cycling cells. Since the majority of repair in G0/G1 occurs via the non-homologous end joining process (NHEJ), increased PLDR in X-ray and silicon-ion irradiated cells may result from improved cell cycle-specific rejoining fidelity through the NHEJ pathway, which is not the case in high-LET iron-ion irradiated cells.

Dose-escalation study of carbon ion radiotherapy for locally advanced squamous cell carcinoma of the uterine cervix (9902)

OBJECTIVE

The authors performed phase I/II clinical trial to evaluate the toxicity and efficacy of carbon ion radiotherapy (C-ion RT) for locally advanced squamous cell carcinoma of the uterine cervix.

METHODS

Between April 2000 and January 2006, 22 patients for Protocol 9902 were treated with C-ion RT. The number of patients with stage IIB, IIIB, and IVA diseases was 1, 18, and 3, respectively. All patients had bulky tumors measuring 4.0-12.0 cm (median 6.2 cm). The whole pelvic dose was fixed at 39.0 GyE for 13 fractions, and additional 15.0 GyE for 5 fractions was given to the gross tumor volume (GTV) and surrounding tissues. With regard to local boost, a dose-escalation study was planned for 2 fractions to GTV. Total dose to the cervical tumor was 64.0-72.0 GyE for 20 fractions.

RESULTS

All patients completed the scheduled therapy and no patient developed Grade 2 or higher acute toxicity. There was no Grade 3 or higher late complications at each dose. The 5-year overall survival rate and local control rate were 50.0% and 68.2%, respectively. Seven out of the 16 patients who received 64.0-68.0 GyE developed local recurrences, but all patients who received 72.0 GyE maintained local control.

CONCLUSIONS

There were no severe acute or late complications in this trial. C-ion RT has the potential to improve the treatment for locally advanced bulky cervical cancer by applying a total dose of 72.0 GyE, with the results lending incentive to further investigations to confirm the therapeutic efficacy.

Chromatin compaction protects genomic DNA from radiation damage

Genomic DNA is organized three-dimensionally in the nucleus, and is thought to form compact chromatin domains. Although chromatin compaction is known to be essential for mitosis, whether it confers other advantages, particularly in interphase cells, remains unknown. Here, we report that chromatin compaction protects genomic DNA from radiation damage. Using a newly developed solid-phase system, we found that the frequency of double-strand breaks (DSBs) in compact chromatin after ionizing irradiation was 5–50-fold lower than in decondensed chromatin. Since radical scavengers inhibited DSB induction in decondensed chromatin, condensed chromatin had a lower level of reactive radical generation after ionizing irradiation. We also found that chromatin compaction protects DNA from attack by chemical agents. Our findings suggest that genomic DNA compaction plays an important role in maintaining genomic integrity.

Modeling the biological response of normal human cells, including repair processes, to fractionated carbon beam irradiation

To understand the biological response of normal cells to fractionated carbon beam irradiation, the effects of potentially lethal damage repair (PLDR) and sublethal damage repair (SLDR) were both taken into account in a linear-quadratic (LQ) model. The model was verified by the results of a fractionated cell survival experiment with normal human fibroblast cells. Cells were irradiated with 200-kV X-rays and monoenergetic carbon ion beams (290 MeV/u) at two irradiation depths, corresponding to linear energy transfers (LETs) of approximately 13 keV/μm and 75 keV/μm, respectively, at the Heavy Ion Medical Accelerator in Chiba of the National Institute of Radiological Sciences. When we only took into account the repair factor of PLDR, γ, which was derived from the delayed assay, the cell survival response to fractionated carbon ion irradiation was not fully explained in some cases. When both the effects of SLDR and PLDR were taken into account in the LQ model, the cell survival response was well reproduced. The model analysis suggested that PLDR occurs in any type of radiation. The γ factors ranged from 0.36-0.93. In addition, SLD was perfectly repaired during the fraction interval for the lower LET irradiations but remained at about 30% for the high-LET irradiation.

Participation of gap junction communication in potentially lethal damage repair and DNA damage in human fibroblasts exposed to low- or high-LET radiation

Existing research has not fully explained how different types of ionizing radiation (IR) modulate the responses of cell populations or tissues. In our previous work, we showed that gap junction intercellular communication (GJIC) mediates the propagation of stressful effects among irradiated cells exposed to high linear energy transfer (LET) radiations, in which almost every cells is traversed by an IR track. In the present study, we conducted an in-depth study of the role of GJIC in modulating the repair of potentially lethal damage (PLDR) and micronuclei formation in cells exposed to low- or high-LET IR. Confluent human fibroblasts were exposed in the presence or absence of a gap junction inhibitor to 200kV X rays (LET∼1.7keV/μm), carbon ions (LET∼76keV/μm), silicon ions (LET∼113keV/μm) or iron ions (LET∼400keV/μm) that resulted in isosurvival levels. The fibroblasts were incubated for various times at 37°C. As expected, high-LET IR were more effective than were low-LET X rays at killing cells and damaging DNA shortly after irradiation. However, when cells were held in a confluent state for several hours, PLDR associated with a reduction in DNA damage, occurred only in cells exposed to X rays. Interestingly, inhibition of GJIC eliminated the enhancement of toxic effects, which resulted in an increase of cell survival and reduction in the level of micronucleus formation in cells exposed to high, but not in those exposed to low-LET IR. The experiment shows that gap-junction communication plays an important role in the propagation of stressful effects among irradiated cells exposed to high-LET IR while GJIC has only a minimal effect on PLDR and DNA damage following low-LET irradiation. Together, our results show that PLDR and induction of DNA damage clearly depend on gap-junction communication and radiation quality.

A model of radiation-induced cell killing: insights into mechanisms and applications for hadron therapy

A mechanism-based, two-parameter biophysical model of cell killing was developed with the aim of elucidating the mechanisms underlying radiation-induced cell death and predicting cell killing by different radiation types, including protons and carbon ions at energies and doses of interest for cancer therapy. The model assumed that certain chromosome aberrations (dicentrics, rings and large deletions, called "lethal aberrations") lead to clonogenic inactivation, and that aberrations derive from μm-scale misrejoining of chromatin fragments, which in turn are produced by "dirty" double-strand breaks called "cluster lesions" (CLs). The average numbers of CLs per Gy per cell were left as a semi-free parameter and the threshold distance for chromatin-fragment rejoining was defined the second parameter. The model was "translated" into Monte Carlo code and provided simulated survival curves, which were compared with survival data on V79 cells exposed to protons, carbon ions and X rays. The agreement was good between simulations and survival data and supported the assumptions of the model at least for doses up to a few Gy. Dicentrics, rings and large deletions were found to be lethal not only for AG1522 cells exposed to X rays, as already reported by others, but also for V79 cells exposed to protons and carbon ions of different energies. Furthermore, the derived CL yields suggest that the critical DNA lesions leading to clonogenic inactivation are more complex than "clean" DSBs. After initial validation, the model was applied to characterize the particle and LET dependence of proton and carbon cell killing. Consistent with the proton data, the predicted fraction of inactivated cells after 2 Gy protons was 40-50% below 7.7 keV/μm, increased by a factor ∼1.6 between 7.7-30.5 keV/μm, and decreased by a factor ∼1.1 between 30.5-34.6 keV/μm. These LET values correspond to proton energies below a few MeV, which are always present in the distal region of hadron therapy spread-out Bragg peaks (SOBP). Consistent with the carbon data, the predicted fraction of inactivated cells after 2 Gy carbon was 40-50% between 13.7-32.4 keV/μm, it increased by a factor ∼1.7 between 32.4-153.5 keV/μm, and decreased by a factor ∼1.1 between 153.5-339.1 keV/μm. Finally, we applied the model to predict cell death at different depths along a carbon SOBP used for preclinical experiments at HIMAC in Chiba, Japan. The predicted fraction of inactivated cells was found to be roughly constant (less than 10%) along the SOBP, suggesting that this approach may be applied to predict cell killing of therapeutic carbon beams and that, more generally, dicentrics, rings and deletions at the first mitosis may be regarded as a biological dose for these beams. This study advanced our understanding of the mechanisms of radiation-induced cell death and characterized the particle and LET dependence of proton and carbon cell killing along a carbon SOBP. The model does not use RBE values, which can be a source of uncertainty. More generally, this model is a mechanism-based tool that in minutes can predict cell inactivation by protons or carbon ions of a given energy and dose, based on an experimental photon curve and in principle, a single (experimental) survival point for the considered ion type and energy.

Visualisation of γH2AX foci caused by heavy ion particle traversal; distinction between core track versus non-track damage

Heavy particle irradiation produces complex DNA double strand breaks (DSBs) which can arise from primary ionisation events within the particle trajectory. Additionally, secondary electrons, termed delta-electrons, which have a range of distributions can create low linear energy transfer (LET) damage within but also distant from the track. DNA damage by delta-electrons distant from the track has not previously been carefully characterised. Using imaging with deconvolution, we show that at 8 hours after exposure to Fe (∼200 keV/µm) ions, γH2AX foci forming at DSBs within the particle track are large and encompass multiple smaller and closely localised foci, which we designate as clustered γH2AX foci. These foci are repaired with slow kinetics by DNA non-homologous end-joining (NHEJ) in G1 phase with the magnitude of complexity diminishing with time. These clustered foci (containing 10 or more individual foci) represent a signature of DSBs caused by high LET heavy particle radiation. We also identified simple γH2AX foci distant from the track, which resemble those arising after X-ray exposure, which we attribute to low LET delta-electron induced DSBs. They are rapidly repaired by NHEJ. Clustered γH2AX foci induced by heavy particle radiation cause prolonged checkpoint arrest compared to simple γH2AX foci following X-irradiation. However, mitotic entry was observed when ∼10 clustered foci remain. Thus, cells can progress into mitosis with multiple clusters of DSBs following the traversal of a heavy particle.

Experimental verification of dose calculation using the simplified Monte Carlo method with an improved initial beam model for a beam-wobbling system

A beam delivery system using a single-radius-beam-wobbling method has been used to form a conformal irradiation field for proton radiotherapy in Japan. A proton beam broadened by the beam-wobbling system provides a non-Gaussian distribution of projection angle different in two mutually orthogonal planes with a common beam central axis, at a certain position. However, the conventional initial beam model for dose calculations has been using an approximation of symmetric Gaussian angular distribution with the same variance in both planes (called here a Gaussian model with symmetric variance (GMSV)), instead of the accurate one. We have developed a more accurate initial beam model defined as a non-Gaussian model with asymmetric variance (NonGMAV), and applied it to dose calculations using the simplified Monte Carlo (SMC) method. The initial beam model takes into account the different distances of two beam-wobbling magnets from the iso-center and also the different amplitudes of kick angle given by each magnet. We have confirmed that the calculation using the SMC with NonGMAV reproduced the measured dose distribution formed in air by a mono-energetic proton beam passing through a square aperture collimator better than with the GMSV and with a Gaussian model with asymmetric variance (GMAV) in which different variances of angular distributions are used in the two mutually orthogonal planes. Measured dose distributions in a homogeneous phantom formed by a modulated proton beam passing through a range shifter and an L-shaped range compensator, were consistent with calculations using the SMC with GMAV and NonGMAV, but in disagreement with calculations using the SMC with GMSV. Measured lateral penumbrae in a lateral direction were reproduced better by calculations using the SMC with NonGMAV than by those with GMAV, when an aperture collimator with a smaller opening was used. We found that such a difference can be attributed to the non-Gaussian angular distribution of the initial beam at a lateral position for the beam-wobbling system. Calculations using the SMC with NonGMAV are effective to reproduce dose distributions formed by a beam-wobbling system more accurately than that with GMSV or that with GMAV.

Calculation method using Clarkson integration for the physical dose at the center of the spread-out Bragg peak in carbon-ion radiotherapy

PURPOSE

In broad-beam carbon-ion radiotherapy performed using the heavy-ion medical accelerator in Chiba, the number of monitor units is determined by measuring the physical dose at the center of the spread-out Bragg peak (SOBP) for the treatment beam. The total measurement time increases as the number of treatment beams increases, which hinders the treatment of an increased number of patients. Hence, Kusano et al. [Jpn. J. Med. Phys. 23(Suppl. 2), 65-68 (2003)] proposed a method to calculate the physical dose at the center of the SOBP for a treatment beam. Based on a recent study, the authors here propose a more accurate calculation method.

METHODS

The authors measured the physical dose at the center of the SOBP while varying the circular field size and range-shifter thickness. The authors obtained the physical dose at the center of the SOBP for an irregularly shaped beam using Clarkson integration based on these measurements.

RESULTS

The difference between the calculated and measured physical doses at the center of the SOBP varied with a change in the central angle of the sector segment. The differences between the calculated and measured physical doses at the center of the SOBP were within ± 1% for all irregularly shaped beams that were used to validate the calculation method.

CONCLUSIONS

The accuracy of the proposed method depends on both the number of angular intervals used for Clarkson integration and the fineness of the basic data used for calculations: sampling numbers for the field size and thickness of the range shifter. If those parameters are properly chosen, the authors can obtain a calculated monitor unit number with high accuracy sufficient for clinical applications.