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

Potential lethal damage repair in glioblastoma cells irradiated with ion beams of various types and levels of linear energy transfer

Glioblastoma (GBM), a Grade IV brain tumour, is a well-known radioresistant cancer. To investigate one of the causes of radioresistance, we studied the capacity for potential lethal damage repair (PLDR) of three altered strains of GBM: T98G, U87 and LN18, irradiated with various ions and various levels of linear energy transfer (LET). The GBM cells were exposed to 12C and 28Si ion beams with LETs of 55, 100 and 200 keV/μm, and with X-ray beams of 1.7 keV/μm. Mono-energetic 12C ions and 28Si ions were generated by the Heavy Ion Medical Accelerator at the National Institute of Radiological Science, Chiba, Japan. Clonogenic assays were used to determine cell inactivation. The ability of the cells to repair potential lethal damage was demonstrated by allowing one identical set of irradiated cells to repair for 24 h before subplating. The results show there is definite PLDR with X-rays, some evidence of PLDR at 55 keV/μm, and minimal PLDR at 100 keV/μm. There is no observable PLDR at 200 keV/μm. This is the first study, to the authors' knowledge, demonstrating the capability of GBM cells to repair potential lethal damage following charged ion irradiations. It is concluded that a GBM's PLDR is dependent on LET, dose and GBM strain; and the more radioresistant the cell strain, the greater the PLDR.

Report of a National Cancer Institute special panel: Characterization of the physical parameters of particle beams for biological research

PURPOSE

To define the physical parameters needed to characterize a particle beam in order to allow intercomparison of different experiments performed using different ions at the same facility and using the same ion at different facilities.

METHODS

At the request of the National Cancer Institute (NCI), a special panel was convened to review the current status of the field and to provide suggested metrics for reporting the physical parameters of particle beams to be used for biological research. A set of physical parameters and measurements that should be performed by facilities and understood and reported by researchers supported by NCI to perform pre-clinical radiobiology and medical physics of heavy ions were generated.

RESULTS

Standard measures such as radiation delivery technique, beam modifiers used, nominal energy, field size, physical dose and dose rate should all be reported. However, more advanced physical measurements, including detailed characterization of beam quality by microdosimetric spectrum and fragmentation spectra, should also be established and reported. Details regarding how such data should be incorporated into Monte Carlo simulations and the proper reporting of simulation details are also discussed.

CONCLUSIONS

In order to allow for a clear relation of physical parameters to biological effects, facilities and researchers should establish and report detailed physical characteristics of the irradiation beams utilized including both standard and advanced measures. Biological researchers are encouraged to actively engage facility staff and physicists in the design and conduct of experiments. Modeling individual experimental setups will allow for the reporting of the uncertainties in the measurement or calculation of physical parameters which should be routinely reported.

Technical Note: Reconstruction of physical and biological dose distributions of carbon-ion beam through deconvolution of longitudinal dosimeter responses

PURPOSE

This is a theoretical simulation study for proof of concept of radiochromic film dosimetry to measure physical and biological doses without plan-based quenching correction for patient-specific quality assurance of carbon-ion radiotherapy.

METHODS

We took a layer-stacking carbon-ion beam comprised of range-shifted beamlets. The dosimeter response was simulated according to an experimental quenching model. The beam model followed a treatment planning system. The beam was decomposed into finely arranged beamlets with weights estimated by deconvolution of longitudinal dosimeter responses. The distributions of physical and biological doses were reconstructed from the estimated weights and were compared with the plan. We also evaluated the sensitivity to measurement errors and to erratic delivery with an undelivered beamlet.

RESULTS

The reconstructed physical and biological doses accurately reproduced the simulated delivery with errors approximately corresponding to the measurement errors. The erratic beam delivery was easily detectable by comparison of biological dose distribution to the plan.

CONCLUSIONS

We have developed a method to measure physical and biological doses by longitudinal dosimetry of quenched response without using plan data. The method only involves a general optimization algorithm, a radiobiology model, and experimental beamlet data, and requires no extra corrections. Theoretically, this approach is applicable to various dosimeters and to proton and ion beams of any delivery method, regardless of quenching or biological effectiveness.

Single fraction carbon ion radiotherapy for colorectal cancer liver metastasis: A dose escalation study

Prognosis is usually grim for those with liver metastasis from colorectal cancer (CRC) who cannot receive resection. Radiation therapy can be an option for those unsuitable for resection, with carbon ion radiotherapy (CIRT) being more effective and less toxic than X-ray due to its physio-biological characteristics. The objective of this study is to identify the optimal dose of single fraction CIRT for colorectal cancer liver metastasis. Thirty-one patients with liver metastasis from CRC were enrolled in the present study. Twenty-nine patients received a single-fraction CIRT, escalating the dose from 36 Gy (RBE) in 5% to 10% increments until unacceptable incidence of dose-limiting toxicity was observed. Dose-limiting toxicity was defined as grade ≥3 acute toxicity attributed to radiotherapy. The prescribed doses were as follows: 36 Gy (RBE) (3 cases), 40 Gy (2 cases), 44 Gy (4 cases), 46 Gy (6 cases), 48 Gy (3 cases), 53 Gy (8 cases) and 58 Gy (3 cases). Dose-limiting toxicity was not observed, but late grade 3 liver toxicity due to biliary obstruction was observed in 2 patients at 53 Gy (RBE). Both cases had lesions close to the hepatic portal region, and, therefore, the dose was escalated to 58 Gy (RBE), limited to peripheral lesions. The 3-year actuarial overall survival rate of all 29 patients was 78%, and the median survival time was 65 months. Local control improved significantly at ≥53 Gy (RBE), with a 3-year actuarial local control rate of 82%, compared to 28% in lower doses. Treatment for CRC liver metastasis with single-fraction CIRT appeared to be safe up to 58 Gy (RBE) as long as the central hepatic portal region was avoided.

Radiobiological issues in prospective carbon ion therapy trials

Carbon ion radiotherapy (CIRT) is developing toward a versatile tool in radiotherapy; however, the increased relative biological effectiveness (RBE) of carbon ions in tumors and normal tissues with respect to photon irradiation has to be considered by mathematical models in treatment planning. As a consequence, dose prescription and definition of dose constraints are performed in terms of RBE weighted rather than absorbed dose. The RBE is a complex quantity, which depends on physical variables, such as dose and beam quality as well as on normal tissue- or tumor-specific factors. At present, three RBE models are employed in CIRT: (a) the mixed-beam model, (b) the Microdosimetric Kinetic Model (MKM), and (c) the local effect model. While the LEM is used in Europe, the other two models are employed in Japan, and unfortunately, the concepts of how the nominal RBE-weighted dose is determined and prescribed differ significantly between the European and Japanese centers complicating the comparison, transfer, and reproduction of clinical results. This has severe impact on the way treatments should be prescribed, recorded, and reported. This contribution reviews the concept of the clinical application of the different RBE models and the ongoing clinical CIRT trials in Japan and Europe. Limitations of the RBE models and the resulting radiobiological issues in clinical CIRT trials are discussed in the context of current clinical evidence and future challenges.

A retrospective multicenter study of carbon-ion radiotherapy for external auditory canal and middle ear carcinomas

Background

We conducted a retrospective multicenter study to assess the clinical outcomes of carbon‐ion radiotherapy (CIRT) for head and neck malignancies (Japan Carbon‐Ion Radiation Oncology Study Group [J‐CROS] study: 1402 HN). We aimed to evaluate the safety and efficacy of CIRT in patients with external auditory canal (EAC) and middle ear (ME) carcinomas.

Methods

Thirty‐one patients treated with CIRT at four Japanese institutions were analyzed. Fourteen patients (45.2%) had squamous cell carcinomas, 13 (41.9%) had adenoid cystic carcinomas, and four (12.9%) had other types. Nineteen (61.3%), six (19.4%), three (9.7%), and three (9.7%) patients had T4, T3, T2, and T1 disease, respectively. All patients had N0M0 status. The median radiation dose was 64 Gy (relative biological effectiveness) in 16 fractions. The median gross tumor volume was 33.3 mL.

Results

The median follow‐up period was 18.4 months (range, 5.1‐85.6). The 1‐ and 3‐year local control and overall survival rates were 75.0% and 55.0% and 79.3% and 58.7%, respectively. Regarding grade 3 or higher toxicities, three patients (9.7%) had grade 3 dermatitis, one (3.2%) had grade 3 mucositis, and two (6.5%) had grade 3 central nervous necrosis (ie, radiation‐induced brain necrosis). No grade 4 or worse reactions were observed.

Conclusion

CIRT was effective for EAC and ME carcinomas.

Sensitivity study of the microdosimetric kinetic model parameters for carbon ion radiotherapy

In carbon ion therapy treatment planning, the relative biological effectiveness (RBE) is accounted for by optimization of the RBE-weighted dose (biological dose). The RBE calculation methods currently applied clinically in carbon ion therapy are derived from the microdosimetric kinetic model (MKM) in Japan and the local effect model (LEM) in Europe. The input parameters of these models are based on fit to experimental data subjected to uncertainties. We therefore performed a sensitivity study of the MKM input parameters, i.e. the domain radius (r _d ), the nucleus radius (R _n ) and the parameters of the linear quadratic (LQ) model (α _x and β). The study was performed with the FLUKA Monte Carlo code, using spread out Bragg peak (SOBP) scenarios in water and a biological dose distribution in a clinical patient case. Comparisons were done between biological doses estimated applying the MKM with parameters based on HSG cells, and with HSG parameters varied separately by  ±{5, 25, 50}%. Comparisons were also done between parameter sets from different cell lines (HSG, V79, CHO and T1), as well as versions of the LEM. Of the parameters, r _d had the largest impact on the biological dose distribution, especially on the absolute dose values. Increasing this parameter by 25% decreased the biological dose level at the center of a 3 Gy(RBE) SOBP by 14%. Variations in R _n only influenced the biological dose distribution towards the particle range, and variations in α _x resulted in minor changes in the biological dose, with an increasing impact towards the particle range. β had the overall smallest influence on the SOBPs, but the impact could become more pronounced if alternative (LET dependent) implementations are used. The resulting percentage change in the SOBPs was generally less than the percentage change in the parameters. The patient case showed similar effects as with the SOBPs in water, and parameter variations had similar impact on the biological dose when using the clinical MKM and the general MKM. The clinical LEM calculated the highest biological doses to both tumor and surrounding healthy tissues, with a median target dose (D _50%) of 40.5 Gy(RBE), while the MKM with HSG and V79 parameters resulted in a D _50% of 34.2 and 36.9 Gy(RBE), respectively. In all, the observed change in biological dose distribution due to parameter variations demonstrates the importance of accurate input parameters when applying the MKM in treatment planning.

Carbon-ion radiotherapy for locally recurrent rectal cancer: Japan Carbon-ion Radiation Oncology Study Group (J-CROS) Study 1404 Rectum

PURPOSE

We investigated the efficacy and safety of carbon-ion radiotherapy (C-ion RT) for locally recurrent rectal cancer (LRRC).

PATIENTS AND METHODS

Data from patients with LRRC treated with C-ion RT from November 2003 to December 2014 at three institutions were retrospectively analyzed. The endpoints of this clinical trial were overall survival (OS), local control (LC), and acute/late toxicity.

RESULTS

A total of 224 patients' data were collected. The prescribed dose was 70.4 Gy (relative biological effectiveness [RBE]-weighted absorbed dose) or 73.6 Gy (RBE) in 16 fractions. The median follow-up period from the initiation of C-ion RT was 62 months (range 6-169 months). The OS rates were 73% (95% confidence interval [CI], 67%-79%) at 3 years and 51% (95%CI 44%-58%) at 5 years. The LC rates were 93% (95%CI 88%-96%) at 3 years, and 88% (95%CI 82%-93%) at 5 years. Grade 3 acute toxicity was observed in three patients: gastrointestinal toxicity (n = 1) and pelvic infection (n = 2). Grade 3 late toxicity was observed in 12 patients: skin reaction (n = 2), gastrointestinal toxicity (n = 2), neuropathy (n = 1), and pelvic infection (n = 7). There was no grade 4 or 5 acute or late toxicity.

CONCLUSIONS

This first multi-institutional analysis of C-ion RT for LRRC indicated relatively favorable outcomes with limited toxicities.

Concepts and terms for dose/volume parameters in carbon-ion radiotherapy: Conclusions of the ULICE taskforce

PURPOSE

The Union of Light Ion Centers in Europe (ULICE) program addressed the need for uniting scientific results for carbon-ion radiation therapy obtained by several institutions worldwide in different fields of excellence, and translating them into a real benefit to the community. Particularly, the concepts for dose/volume parameters developed in photon radiotherapy cannot be extrapolated to high linear energy transfer particles.

METHODS AND MATERIALS

The ULICE-WP2 taskforce included radiation oncologists involved in carbon-ion radiation therapy and International Commission on Radiation Units and Measurements, radiation biologists, expert physicists in the fields of carbon-ion radiation therapy, microdosimetry, biological modeling and image-guided radiotherapy. Consensual reports emerged from multiple discussions within both the restricted group and the wider ULICE community. Public deliverables were produced and disseminated to the European Commission.

RESULTS

Here we highlight the disparity in practices between treating centers, then address the main topics to finally elaborate specific recommendations. Although it appears relatively simple to add geometrical margins around the clinical target volume to obtain the planning target volume as performed in photon radiotherapy, this procedure is not appropriate for carbon-ion radiation therapy. Due to the variation of the radiation quality in depth, there is no generic relative biological effectiveness value for carbon-ions outside of an isolated point, for a given fractionation and specific experimental conditions. Absorbed dose and "equieffective dose" for specified conditions must always be reported.

CONCLUSIONS

This work contributed to the development of standard operating procedures for carbon-ion radiation therapy clinical trials. These procedures are now being applied, particularly in the first phase III international, multicenter trial (PHRC Étoile).

Phase I Study of Carbon Ion Radiotherapy and Image-Guided Brachytherapy for Locally Advanced Cervical Cancer

A phase I study was performed to determine the recommended dose of carbon ion radiotherapy and 3D image-guided brachytherapy for histologically confirmed stage II (≥4 cm), III, or IVA cervical cancer. Dose-limiting toxicities (treatment-related toxicities occurring within three months from the start of carbon ion radiotherapy) included Grade 3 non-hematological toxicity, Grade 4 hematological toxicity, or interruption of treatment for more than two weeks due to treatment-related toxicities. Carbon ion radiotherapy consisted of whole-pelvic irradiation with 36.0 Gy (relative biological effectiveness) in 12 fractions and local boost with 19.2 Gy in four fractions for the primary site, and for positive lymph nodes. Three sessions of three-dimensional (3D) image-guided brachytherapy were administered after completion of carbon ion radiotherapy. Weekly cisplatin at a dose of 40 mg/m² was given concurrently. At a dose level of one, a total rectosigmoid D2cc dose between 67.2 Gy and 71.3 Gy at a biological equivalent dose of 2 Gy per fraction from carbon ion radiotherapy and 3D image-guided brachytherapy was prescribed. Six patients were enrolled into this dose level. No patients developed the pre-defined dose-limiting toxicities. For late toxicities, however, one patient developed Grade 3 rectal hemorrhage requiring transfusion at 10 months after treatment. The median survival time was 50.0 months for the five surviving patients. No further dose escalation was performed, and we determined the dose of level one as the recommended rectosigmoid dose. Although our results are preliminary, the study regimen encourages further investigation (registration: UMIN000013340).

A single institutional experience of combined carbon-ion radiotherapy and chemotherapy for unresectable locally advanced pancreatic cancer

PURPOSE

The aim of this study was to evaluate the efficacy and safety of carbon-ion radiotherapy (C-ion RT) for unresectable locally advanced pancreatic cancer (LAPC).

METHODS AND MATERIALS

Patients with LAPC treated with definitive C-ion RT between April 2014 and July 2017 were analyzed retrospectively. The prescribed dose was 55.2 Gy (relative biological effectiveness [RBE] weighted absorbed dose) in 12 fractions. Overall survival (OS), local control (LC), progression free survival (PFS), and toxicity were evaluated.

RESULTS

Sixty-four patients were enrolled. All patients completed planned course of C-ion RT. The median follow-up time for survivors from the initiation of C-ion RT was 24.4 months (range, 5.1-46.1 months). Median survival time was 25.1 months. Two-year OS, LC, and PFS were 53% (95% confidence interval [CI], 39%-66%), 82% (95% CI, 66%-91%), and 23% (95% CI, 14%-36%), respectively. Four patients experienced acute grade 3 toxicities including 3 gastrointestinal (GI) toxicities. There was no grade 3 or more late toxicity.

CONCLUSIONS

The clinical results of C-ion RT for LAPC at our institution were comparable to those of a recent multi-institutional analysis.

Linear energy transfer (LET) spectra and survival fraction distribution based on the CR-39 plastic charged-particle detector in a spread-out Bragg peak irradiation by a 12C beam

Facilities for heavy ion therapies are steadily increasing in number worldwide. One of the advantages of heavy ions is their high relative biological effect (RBE). In a model used at NIRS (National Institute of Radiological Sciences), linear energy transfer (LET) spectra are required to estimate biological dose (physical dose  ×  RBE). The CR-39 plastic charged-particle detector (CR-39) is suitable for measurement of LET. For the present study, done at the Gunma University Heavy Ion Medical Center (GHMC), we measured LET spectra at 11 depths in spread-out Bragg peak (SOBP) irradiation by a ¹²C beam of 380 MeV/u. The lower threshold of the CR-39 to measure LET was about 5 keV µm^-1 due to poor sensitivity for low LET. Then we calculated biological dose and survival fraction distributions and compared them with treatment planning results at GHMC. We used Monte Carlo simulation (Geant4) to calculate LET spectra. The simulation results were in good agreement with the experimental spectra. Moreover, the biological dose and survival fraction distributions estimated from the CR-39 reproduced the treatment planning. The CR-39 is suitable for estimating biological dose in carbon ion therapy.

Postoperative re-irradiation using stereotactic body radiotherapy for metastatic epidural spinal cord compression

OBJECTIVE

This study aimed to clarify the outcomes of postoperative re-irradiation using stereotactic body radiotherapy (SBRT) for metastatic epidural spinal cord compression (MESCC) in the authors’ institution and to identify factors correlated with local control.

METHODS

Cases in which patients with previously irradiated MESCC underwent decompression surgery followed by spine SBRT as re-irradiation between April 2013 and May 2017 were retrospectively reviewed. The surgical procedures were mainly performed by the posterior approach and included decompression and fixation. The prescribed dose for spine SBRT was 24 Gy in 2 fractions. The primary outcome was local control, which was defined as elimination, shrinkage, or no change of the tumor on CT or MRI obtained approximately every 3 months after SBRT. In addition, various patient-, treatment-, and tumor-specific factors were evaluated to determine their predictive value for local control.

RESULTS

Twenty-eight cases were identified in the authors’ institutional databases as meeting the inclusion criteria. The histology of the primary disease was thyroid cancer in 7 cases, lung cancer in 6, renal cancer in 3, colorectal cancer in 3, and other cancers in 9. The most common previous radiation dose was 30 Gy in 10 fractions (15 cases). The mean interval since the most recent irradiation was 16 months (range 5–132 months). The median duration of follow-up after SBRT was 13 months (range 4–38 months). The 1-year local control rate was 70%. In the analysis of factors related to local control, Bilsky grade, number of vertebral levels in the treatment target, the interval between the latest radiotherapy and SBRT, recursive partitioning analysis (RPA), the prognostic index for spinal metastases (PRISM), and the revised Tokuhashi score were not significantly correlated with local control. The favorable group classified by the Rades prognostic score achieved a significantly higher 1-year local control rate than the unfavorable group (1-year local control rate: 100% vs 33%; p < 0.01). Radiation-induced myelopathy and vertebral compression fracture were observed in 1 and 3 patients, respectively. No other grade 3 or greater toxicities were encountered.

CONCLUSIONS

The results indicate that spine SBRT as postoperative re-irradiation was effective, and it was especially useful for patients classified as having a good survival prognosis according to the Rades score.

Dose constraints in the rectum and bladder following carbon-ion radiotherapy for uterus carcinoma: a retrospective pooled analysis

Background

Carbon-ion radiotherapy (C-ion RT) provides better dose distribution in cancer treatment compared to photons. Additionally, carbon-ion beams provide a higher biological effectiveness, and thus a higher tumor control probability. However, information regarding the dose constraints for organs at risk in C-ion RT is limited. This study aimed to determine the predictive factors for late morbidities in the rectum and bladder after carbon-ion C-ion RT for uterus carcinomas.

Methods

Between June 1995 and January 2010, 134 patients with uterus carcinomas were treated with C-ion RT with curative intent; prescription doses of 52.8–74.4 Gy (relative biological effectiveness) were delivered in 20–24 fractions. Of these patients, 132 who were followed up for > 6 months were analyzed. We separated the data in two subgroups, a 24 fractions group and a 20 fractions group. Late morbidities, proctitis, and cystitis were assessed according to the Radiation Therapy Oncology Group/European Organisation for Research and Treatment of Cancer criteria. The correlations of clinical and dosimetric parameters, V10–V60, D_5cc, D_2cc, and Dmax, with the incidence of ≥grade 1 morbidities were retrospectively analyzed.

Results

In the 24 fractions group, the 3-year actuarial occurrence rates of ≥grade 1 rectal and bladder morbidities were 64 and 9%, respectively. In addition, in the 20 fractions group, the 3-year actuarial occurrence rates of ≥grade 1 rectal and bladder morbidities were 32 and 19%, respectively. Regarding the dose–volume histogram data on the rectum, the D_5cc and D_2cc were significantly higher in patients with ≥grade 1 proctitis than in those without morbidity. In addition, the D_5cc for the bladder was significantly higher in patients with ≥grade 1 cystitis than in those without morbidity. Results of univariate analyses showed that D_2cc of the rectum was correlated with the development of ≥grade 1 late proctitis. Moreover, D_5cc of the bladder was correlated with the development of ≥grade 1 late cystitis.

Conclusions

The present study identified the dose–volume relationships in C-ion RT regarding the occurrence of late morbidities in the rectum and bladder. Assessment of the factors discussed herein would be beneficial in preventing late morbidities after C-ion RT for pelvic malignancies.

Trial registration

Retrospectively registered (NIRS: 16–040).

Electronic supplementary material

The online version of this article (10.1186/s13014-018-1061-7) contains supplementary material, which is available to authorized users.

Salvage Carbon Ion Radiation Therapy for Locally Recurrent or Radiation-Induced Second Primary Sarcoma of the Head and Neck

Purpose: Salvage radiation therapy (RT) is a potentially curative treatment option for head and neck sarcomas (HNS) that did not respond to previous treatment(s). We report the first clinical experience of carbon ion radiotherapy (CIRT) for salvage treatment of locally recurrent (LR) or RT-induced secondary HNS after surgery and/or radiotherapy.

Methods and Materials: A retrospective analysis of the ongoing prospective data registries from the Shanghai Proton and Heavy Ion Center was conducted. Patients with LR-HNS who underwent surgery and/or RT and those with RT-induced second primary HNS were included. Acute and late toxicities were evaluated using the Common Terminology Criteria for Adverse Events version 4.0 and the Radiation Therapy Oncology Group late radiation toxicity scoring system, respectively. The actuarial 12-month local progression-free and overall survival rates (LPFS and OS) were calculated using the Kaplan-Meier method.

Results: Between 10/2015 and 7/2017, 19 consecutive and non-selected patients with LR-HNS or RT-induced secondary HNS received definitive doses of CIRT delivered with pencil beam scanning technology for salvage. Six patients had locally recurrent soft-tissue sarcoma, and another 6 had chondrosarcoma. Among these 12 patients, 4 had received one prior course of RT. Seven additional patients had an RT-induced second primary soft tissue sarcoma (STS)/osteosarcoma after RT. The median time between the completion of initial treatment (either surgery only or surgery followed by adjuvant RT) and salvage CIRT was 30.6 months.

The median follow-up time was 13.1 (range 1.6-41.1) months. All patients except one (for re-irradiation) completed the planned CIRT for salvage. The median dose of salvage CIRT was 60 GyE. Three patients developed local progression, and another 3 developed distant metastasis after salvage CIRT. Deaths occurred (3 patients) only in patients with radiation-induced second primary sarcoma at the time of analysis. The actuarial 12-month LPFS, DMFS and OS rates were 74.6%, 82.6% and 86.5%, respectively.

Two patients irradiated for a second primary sarcoma had Grade 4 bleeding during CIRT, including one who experienced the rupture of an optic artery aneurysm unrelated to his disease or the salvage treatment. No patient had Grade 5 toxicity during treatment. Except for one patient who died of hemorrhage 3.5 months after the completion of CIRT, no moderate or severe late toxicities were observed.

Conclusions: With few observed acute and late toxicities, salvage CIRT can provide effective short-term tumor control. Further research, preferably in a prospective fashion, will be required to confirm the efficacy and safety of salvage CIRT in this patient population.

Multi-institutional Study of Carbon-ion Radiotherapy for Locally Advanced Pancreatic Cancer: Japan Carbon-ion Radiation Oncology Study Group (J-CROS) Study 1403 Pancreas

PURPOSE

The aim of this multi-institutional study was to evaluate the efficacy and safety of carbon-ion radiotherapy (C-ion RT) for locally advanced pancreatic cancer (LAPC).

METHODS AND MATERIALS

Patients with LAPC treated with C-ion RT from April 2012 to December 2014 at 3 institutions were retrospectively analyzed. Patients with pathologically-confirmed invasive ductal adenocarcinoma of the pancreas were eligible. The prescribed dose was 52.8 Gy (relative biological effectiveness weighted absorbed dose; RBE) or 55.2 Gy (RBE) in 12 fractions. Overall survival (OS), distant metastasis-free survival (DMFS), local recurrence (LR), and toxicity were evaluated.

RESULTS

In total, 72 patients were included in this study. Tumors in the head of the pancreas were seen in 30 patients (42%), while those in the body or tail of the pancreas were seen in 42 patients (58%). Fifty-six patients (78%) received concurrent chemotherapy. The OS rates were 73% (95% confidence interval [CI], 62%-84%) at 1 year, and 46% (95% CI, 31%-61%) at 2 years with a median OS of 21.5 months (95% CI, 11.8-31.2 months). The 1- and 2-year DMFS rates were 41% (95% CI, 29%-52%) and 28% (95% CI, 16%-40%), respectively. The 1- and 2-year cumulative incidences of LR were 16% (95% CI, 9%-26%) and 24% (95% CI, 14%-36%), respectively. Nineteen patients (26%) experienced acute grade 3 or 4 hematological toxicities. Two patients (3%) had grade 3 anorexia. Late gastrointestinal (GI) grade 3 toxicity was observed in 1 patient (1%). No patients developed late grade 4 or 5 toxicity.

CONCLUSIONS

The first multi-institutional analysis of C-ion RT for LAPC indicated relatively favorable outcomes with limited toxicities, especially for tumors not in close proximity to GI tract.

Carbon ion radiotherapy for inoperable pediatric osteosarcoma

Background

Unresectable pediatric osteosarcoma has poor outcomes with conventional treatments.

Results

Twenty-six patients aged 11–20 years (median 16) had inoperable osteosarcoma of the trunk (24 pelvic, 1 mediastinal and 1 paravertebral) without any other lesion at initial examination. There were 22 primary, 1 locally recurrent and 3 metastatic cases. Median CIRT dose was 70.4 Gy RBE (relative biological effectiveness) delivered in 16 fractions. Median follow-up was 32.7 months. Overall survival was 50.0% and 41.7% at 3 and 5 years, respectively. Ten patients survived for more than 5 years (range 5–20.7 years). Local control was 69.9% and 62.9% at 3 and 5 years, respectively and progression-free survival was 34.6% at 3 and 5 years. Only largest tumor diameter correlated with 5-year overall survival and local control. There were 4 grade 3-4 CIRT-related late toxicities, 1 case of bone fracture and no treatment-related mortalities. All patients (except 1) were able to ambulate after CIRT.

Conclusions

CIRT was safe and efficacious in the treatment of inoperable pediatric osteosarcoma with improved local control and overall survival compared to conventional treatments.

Methods

We retrospectively reviewed the records of pediatric and adolescent patients who received carbon ion radiotherapy (CIRT) for inoperable osteosarcoma between 1996 and 2014.

A retrospective multicenter study of carbon-ion radiotherapy for major salivary gland carcinomas: Subanalysis of J-CROS 1402 HN

A retrospective multicenter study was carried out to assess the clinical outcomes of carbon-ion radiotherapy for head and neck malignancies (Japan Carbon-Ion Radiation Oncology Study Group [J-CROS] study: 1402 HN). We evaluated the safety and efficacy of carbon-ion radiotherapy in patients with major salivary gland carcinoma. Sixty-nine patients treated with carbon-ion radiotherapy at four Japanese institutions were analyzed. Thirty-three patients (48%) had adenoid cystic carcinomas, 10 (14%) had mucoepidermoid carcinomas, and 26 (38%) had other disease types. Three patients (4%) had T1 disease, 8 (12%) had T2, 25 (36%) had T3, and 33 (48%) had T4. The median radiation dose was 64 Gy (relative biological effectiveness) in 16 fractions. The median gross tumor volume was 27 mL. The median follow-up period was 32.7 months. The 3-year local control rate and overall survival rate were 81% and 94%, respectively. Regarding acute toxicities, seven patients had grade 3 mucositis and seven had grade 3 dermatitis. Regarding late toxicities, one patient had grade 3 dysphagia and one had a grade 3 brain abscess. No grade 4 or worse late reactions were observed. In conclusion, definitive carbon-ion radiotherapy was effective with acceptable toxicity for major salivary gland carcinomas.

Carbon-ion radiotherapy for inoperable endometrial carcinoma

This is a pooled analysis to evaluate the toxicity and efficacy of carbon-ion radiotherapy (C-ion RT) for inoperable endometrial carcinoma. Eligible patients had previously untreated Stage I-III endometrial carcinoma without para-aortic lymph node metastasis. Total dose to the tumor was 62.4-74.4 Gy [relative biological effectiveness (RBE)] in 20 fractions, and the dose to the gastrointestinal tract was limited to <60 Gy (RBE). Intracavitary brachytherapy was not combined in the present study. Fourteen patients with endometrial carcinoma were analyzed. Ten of the 14 patients were judged medically inoperable, and the others refused surgery. The numbers of patients with Stage I, II and III disease were 1, 9 and 4, respectively. Tumor size was 3.8-13.8 cm in maximum diameter. Median follow-up periods for all patients and surviving patients were 50 months (range, 12-218 months) and 78 months (range, 23-218 months), respectively. Two of three patients receiving 62.4-64.8 Gy (RBE) had local recurrence whereas none of 11 patients receiving 68.0 Gy (RBE) or more had local recurrence. Three patients developed distant metastases and one of them also had local recurrence. The 5-year local control, progression-free survival, overall survival, and cause-specific survival rates were 86%, 64%, 68% and 73%, respectively. No patient developed Grade 3 or higher acute or late toxicity. The present study showed that C-ion RT alone could be a safe and curative treatment modality for inoperable endometrial carcinoma.

Feasibility of carbon-ion radiotherapy for re-irradiation of locoregionally recurrent, metastatic, or secondary lung tumors

Intrathoracic recurrence after carbon‐ion radiotherapy for primary or metastatic lung tumors remains a major cause of cancer‐related deaths. However, treatment options are limited. Herein, we report on the toxicity and efficacy of re‐irradiation with carbon‐ion radiotherapy for locoregionally recurrent, metastatic, or secondary lung tumors. Data of 95 patients with prior intrathoracic carbon‐ion radiotherapy who were treated with re‐irradiation with carbon‐ion radiotherapy at our institution between 2006 and 2016 were retrospectively analyzed. Seventy‐three patients (76.8%) had primary lung tumors and 22 patients (23.2%) had metastatic lung tumors. The median dose of initial carbon‐ion radiotherapy was 52.8 Gy (relative biological effectiveness) and the median dose of re‐irradiation was 66.0 Gy (relative biological effectiveness). None of the patients received concurrent chemotherapy. The median follow‐up period after re‐irradiation was 18 months. In terms of grade ≥3 toxicities, one patient experienced each of the following: grade 5 bronchopleural fistula, grade 4 radiation pneumonitis, grade 3 chest pain, and grade 3 radiation pneumonitis. The 2‐year local control and overall survival rates were 54.0% and 61.9%, respectively. In conclusion, re‐irradiation with carbon‐ion radiotherapy was associated with relatively low toxicity and moderate efficacy. Re‐irradiation with carbon‐ion radiotherapy might be an effective treatment option for patients with locoregionally recurrent, metastatic, or secondary lung tumors.

Evolution of Carbon Ion Radiotherapy at the National Institute of Radiological Sciences in Japan

Charged particles can achieve better dose distribution and higher biological effectiveness compared to photon radiotherapy. Carbon ions are considered an optimal candidate for cancer treatment using particles. The National Institute of Radiological Sciences (NIRS) in Chiba, Japan was the first radiotherapy hospital dedicated for carbon ion treatments in the world. Since its establishment in 1994, the NIRS has pioneered this therapy with more than 69 clinical trials so far, and hundreds of ancillary projects in physics and radiobiology. In this review, we will discuss the evolution of carbon ion radiotherapy at the NIRS and some of the current and future projects in the field.

Selection of carbon beam therapy: biophysical models of carbon beam therapy

Variation in the relative biological effectiveness (RBE) within the irradiation field of a carbon beam makes carbon-ion radiotherapy unique and advantageous in delivering the therapeutic dose to a deep-seated tumor, while sparing surrounding normal tissues. However, it is crucial to consider the RBE, not only in designing the dose distribution during treatment planning, but also in analyzing the clinical response retrospectively. At the National Institute of Radiological Sciences, the RBE model was established based on the response of human salivary gland cells. The response was originally handled with a linear-quadratic model, and later with a microdosimetric kinetic model. Retrospective analysis with a tumor-control probability model of non-small cell cancer treatment revealed a steep dose response in the tumor, and that the RBE of the tumor was adequately estimated using the model. A commonly used normal tissue complication probability model has not yet fully been accountable for the variable RBE of carbon ions; however, analysis of rectum injury after prostate cancer treatment suggested a highly serial-organ structure for the rectum, and a steep dose response similar to that observed for tumors.

Estimation of linear energy transfer distribution for broad-beam carbon-ion radiotherapy at the National Institute of Radiological Sciences, Japan

A treatment of carbon-ion radiotherapy (CIRT) is generally evaluated using the dose weighted by relative biological effectiveness (RBE) while ignoring the radiation quality varying in the patient. In this study, we have developed a method of estimating linear energy transfer (LET) from the RBE in an archived treatment plan to represent the radiation quality of the treatment. The LET in a beam database was associated with the RBE by two fitting functions per energy, one for the spread-out Bragg peak (SOBP) and the other for shallower depths, to be differentiated by RBE per energy per modulation. The estimated LET was generally consistent with the original calculation within a few keV/μm, except for the overkill region near the distal end of SOBP. The knowledge of experimental radiobiology can thereby be associated with CIRT treatments through LET, which will potentially contribute to deeper understanding of clinical radiobiology and further optimization of CIRT.

Metformin enhances the radiosensitivity of human liver cancer cells to γ-rays and carbon ion beams

The purpose of this study was to investigate the effect of metformin on the responses of hepatocellular carcinoma (HCC) cells to γ-rays (low-linear energy transfer (LET) radiation) and carbon-ion beams (high-LET radiation). HCC cells were pretreated with metformin and exposed to a single dose of γ-rays or carbon ion beams. Metformin treatment increased radiation-induced clonogenic cell death, DNA damage, and apoptosis. Carbon ion beams combined with metformin were more effective than carbon ion beams or γ-rays alone at inducing subG1 and decreasing G2/M arrest, reducing the expression of vimentin, enhancing phospho-AMPK expression, and suppressing phospho-mTOR and phospho-Akt. Thus, metformin effectively enhanced the therapeutic effect of radiation with a wide range of LET, in particular carbon ion beams and it may be useful for increasing the clinical efficacy of carbon ion beams.

Carbon-ion radiotherapy for locoregional recurrence after primary surgery for pancreatic cancer

The efficacy and safety of carbon ion radiotherapy (C-ion RT) for locoregional recurrence after surgery for pancreatic cancer were retrospectively evaluated. The results for 30 patients showed that C-ion RT was performed safely with relatively long overall survival, good local control, and minimal toxicity.

Induction of reproductive cell death in Caenorhabditis elegans across entire linear-energy-transfer range of carbon-ion irradiation

Heavy-ion radiation has attracted extensive attention as an effective cancer therapy because of the varying energy deposition along its track and its high cell-killing effect. Reproductive cell death (RCD), also known as clonogenic death, is an important mode of death of the cancer cells after radiotherapy. Although RCD induced by heavy-ion irradiation with various linear energy transfers has been demonstrated using clonogenic assay in vitro, little is known about the distribution of RCD across the range of heavy-ion irradiation at the level of whole organisms. In this study, a vulval tissue model of Caenorhabditis elegans was for the first time used to assess RCD in vivo induced by carbon-ion irradiation. A polymethyl methacrylate wedge was designed to provide a gradually varying thickness of shielding, so worms could be exposed to the entire range of carbon-ion irradiation. The carbon-ion irradiation led to a significant induction of RCD over the entire range in a dose-dependent manner. The biological peak did not correspond to the physical Bragg peak and moved forward, rather than spread forward, as radiation dose increased. The degree and shape of the range-distribution of RCD were also affected by the developmental stages of the worms. The gene mutations in DNA-damage checkpoints did not affect the responses of mutant worms positioned in biological peaks, compared to wild-type worms, but decreased radio-sensitivity in the entrance region. An increased induction of RCD was observed in the worms impaired in homologous recombination (HR), but not in non-homologous end jointing pathway, suggesting a crucial role of HR repair in vulval cells of C. elegans in dealing with the carbon-ion-induced DNA damage. These unique manifestations of RCD in vivo in response to carbon-ion irradiation might provide new clues for further investigating the biological effects of heavy-ion irradiation.

Efficacy and safety of carbon-ion radiotherapy for lacrimal gland carcinomas with extraorbital extension: a retrospective cohort study

Purpose

To evaluate the efficacy and safety of carbon-ion radiotherapy (CIRT) for patients with lacrimal gland carcinomas (LGCs) with extraorbital extension.

Results

The median follow-up period was 53.7 months. The 5-year local control and overall survival rates were 62% and 65%, respectively. Regarding late toxicities, 12 patients (36.4%) developed Grade 4 optic nerve disorders, including visual losses of the diseased side (N = 8; 66.7%), and 1 patient (3.0%) developed a Grade 3 optic nerve disorder. Three patients (9.0%) developed Grade 3 cataracts, 3 (9.0%) developed glaucoma, and 1 (3.0%) developed retinopathy. Two patients (6.1%) had Grade 4 central nervous system necrosis. No Grade 5 late toxicities were observed. The 5-year preservation rate of the ipsilateral eyeball was 86%.

Conclusion

Definitive CIRT is effective for LGCs with extraorbital extension with acceptable toxicity.

Methods

Thirty-three patients treated with CIRT at our institution were analyzed. Sixteen patients (48.5%) had adenoid cystic carcinoma, 8 (24.2%) had adenocarcinoma not otherwise specified, and 9 (27.3%) had other types of the disease. Thirty patients (90.9%) had T4c tumors. The prescribed doses were 57.6 Gy (relative biological effectiveness [RBE]) (N = 18; 54.5%) and 64.0 Gy (RBE) (N = 15; 45.5%) in 16 fractions.

Clinical outcomes of carbon ion radiotherapy with concurrent chemotherapy for locally advanced uterine cervical adenocarcinoma in a phase 1/2 clinical trial (Protocol 1001)

We conducted a phase 1/2 study to evaluate the efficacy and safety of carbon ion radiotherapy (C-ion RT) with concurrent chemotherapy for locally advanced uterine cervical adenocarcinoma. Thirty-three patients were enrolled between April 2010 and March 2014. Treatment consisted of C-ion RT with concurrent weekly cisplatin at a dose of 40 mg/m² . In the phase 1 component, the total dose was escalated from 68.0 Gy (relative biological effectiveness [RBE]) to 74.4 Gy (RBE) to determine the maximum tolerated dose of C-ion RT. In the phase 2 component, the efficacy and safety of C-ion RT with concurrent chemotherapy were evaluated using the dose determined in the phase 1 component. The median follow-up duration was 30 months. Two patients did not receive chemotherapy because of anemia or leukocytopenia immediately prior to commencing treatment; 31 patients were analyzed. None of the patients developed dose-limiting toxicities. The recommended dose (RD) was determined to be 74.4 Gy (RBE). In the phase 2 component, two patients developed Grade 3-4 toxicities in the gastrointestinal tract, due to repeated laser coagulation or peritonitis caused by appendicitis. In the patients treated with the RD, the 2-year local control, progression-free survival, and overall survival rates were 71%, 56%, and 88%, respectively. C-ion RT with concurrent weekly cisplatin was well tolerated in patients with locally advanced uterine cervical adenocarcinoma. Our findings support further investigations into the efficacy of this strategy.

Validation of the physical and RBE-weighted dose estimator based on PHITS coupled with a microdosimetric kinetic model for proton therapy

The microdosimetric kinetic model (MKM) is widely used for estimating relative biological effectiveness (RBE)-weighted doses for various radiotherapies because it can determine the surviving fraction of irradiated cells based on only the lineal energy distribution, and it is independent of the radiation type and ion species. However, the applicability of the method to proton therapy has not yet been investigated thoroughly. In this study, we validated the RBE-weighted dose calculated by the MKM in tandem with the Monte Carlo code PHITS for proton therapy by considering the complete simulation geometry of the clinical proton beam line. The physical dose, lineal energy distribution, and RBE-weighted dose for a 155 MeV mono-energetic and spread-out Bragg peak (SOBP) beam of 60 mm width were evaluated. In estimating the physical dose, the calculated depth dose distribution by irradiating the mono-energetic beam using PHITS was consistent with the data measured by a diode detector. A maximum difference of 3.1% in the depth distribution was observed for the SOBP beam. In the RBE-weighted dose validation, the calculated lineal energy distributions generally agreed well with the published measurement data. The calculated and measured RBE-weighted doses were in excellent agreement, except at the Bragg peak region of the mono-energetic beam, where the calculation overestimated the measured data by ~15%. This research has provided a computational microdosimetric approach based on a combination of PHITS and MKM for typical clinical proton beams. The developed RBE-estimator function has potential application in the treatment planning system for various radiotherapies.

Effective radiotherapeutic treatment intensification in patients with pancreatic cancer: higher doses alone, higher RBE or both?

Pancreatic cancer, especially in case of locally advanced stage has a poor prognosis. Radiotherapy in general can lead to tumor volume reduction, but further improvements, such as ion beam therapy have to be promoted in order to enable dose escalation, which in turn results in better local control rates and downsizing of the tumor itself. Ion beam therapy with its highly promising physical properties is also accompanied by distinct inter- and intrafractional challenges in case of robustness. First clinical results are promising, but further research in motion mitigation and biological treatment planning is necessary, in order to determine the best clinical rationales and conditions of ion beam therapy of pancreatic cancer. This review summarizes the current knowledge and studies on ion beam therapy of pancreatic cancer.

RBE and related modeling in carbon-ion therapy

Carbon ion therapy is a promising evolving modality in radiotherapy to treat tumors that are radioresistant against photon treatments. As carbon ions are more effective in normal and tumor tissue, the relative biological effectiveness (RBE) has to be calculated by bio-mathematical models and has to be considered in the dose prescription. This review (i) introduces the concept of the RBE and its most important determinants, (ii) describes the physical and biological causes of the increased RBE for carbon ions, (iii) summarizes available RBE measurements in vitro and in vivo, and (iv) describes the concepts of the clinically applied RBE models (mixed beam model, local effect model, and microdosimetric-kinetic model), and (v) the way they are introduced into clinical application as well as (vi) their status of experimental and clinical validation, and finally (vii) summarizes the current status of the use of the RBE concept in carbon ion therapy and points out clinically relevant conclusions as well as open questions. The RBE concept has proven to be a valuable concept for dose prescription in carbon ion radiotherapy, however, different centers use different RBE models and therefore care has to be taken when transferring results from one center to another. Experimental studies significantly improve the understanding of the dependencies and limitations of RBE models in clinical application. For the future, further studies investigating quantitatively the differential effects between normal tissues and tumors are needed accompanied by clinical studies on effectiveness and toxicity.

3D-structured illumination microscopy reveals clustered DNA double-strand break formation in widespread γH2AX foci after high LET heavy-ion particle radiation

DNA double-strand breaks (DSBs) induced by ionising radiation are considered the major cause of genotoxic mutations and cell death. While DSBs are dispersed throughout chromatin after X-rays or γ-irradiation, multiple types of DNA damage including DSBs, single-strand breaks and base damage can be generated within 1–2 helical DNA turns, defined as a complex DNA lesion, after high Linear Energy Transfer (LET) particle irradiation. In addition to the formation of complex DNA lesions, recent evidence suggests that multiple DSBs can be closely generated along the tracks of high LET particle irradiation. Herein, by using three dimensional (3D)-structured illumination microscopy, we identified the formation of 3D widespread γH2AX foci after high LET carbon-ion irradiation. The large γH2AX foci in G₂-phase cells encompassed multiple foci of replication protein A (RPA), a marker of DSBs undergoing resection during homologous recombination. Furthermore, we demonstrated by 3D analysis that the distance between two individual RPA foci within γH2AX foci was approximately 700 nm. Together, our findings suggest that high LET heavy-ion particles induce clustered DSB formation on a scale of approximately 1 μm³. These closely localised DSBs are considered to be a risk for the formation of chromosomal rearrangement after heavy-ion irradiation.

Predictive factors of acute skin reactions to carbon ion radiotherapy for the treatment of malignant bone and soft tissue tumors

Background

The skin is considered a critical organ at risk in carbon ion radiotherapy (CIRT) for locally advanced malignant bone and soft tissue tumors (MBSTs). The predictive factors for acute skin reactions after CIRT have not been investigated. The present study aimed to identify these factors and evaluate the correlation between the severity of acute skin reactions and skin dose parameters.

Methods

CIRT with total doses of 64.0–70.4 Gy (relative biological effectiveness [RBE]) was administered to 22 patients with MBSTs. The skin-tumor distance (STD), maximum skin total dose (Dmax), and area of the skin receiving a total dose of X Gy (RBE) were evaluated.

Results

All patients developed acute skin reactions after CIRT, including Grades 1 and 2 dermatitis in 15 (71%) and 6 (29%) patients, respectively. There was a significant difference in the STD between the two groups (P = 0.007), and the cut-off value of STD for predicting Grade 2 acute skin reactions was 11 mm. There was a significant difference in Dmax between the groups (P < 0.001), and the cut-off value of Dmax for predicting Grade 2 acute skin reactions was 52 Gy (RBE). Significant differences between the two groups were observed in terms of the area irradiated with 40 Gy (RBE) (S40), and the cut-off value of S40 for predicting Grade 2 acute skin reactions was 25 cm².

Conclusions

In acute skin reactions after CIRT for MBSTs, STD, Dmax, and S40 were found to be significant predictive factors for acute skin reactions.

Carbon ion radiotherapy for 80 years or older patients with hepatocellular carcinoma

BACKGROUND

To evaluate the safety and efficacy of carbon ion radiotherapy (C-ion RT) for 80 years or older patients with hepatocellular carcinoma (HCC).

METHODS

Eligibility criteria of this retrospective study were: 1) HCC confirmed by histology or typical hallmarks of HCC by imaging techniques of four-phase multidetector-row computed tomography or dynamic contrast-enhanced magnetic resonance imaging; 2) no intrahepatic metastasis or distant metastasis; 3) no findings suggesting direct infiltration of the gastrointestinal tract; 4) performance status ≤2 by Eastern Cooperative Oncology Group classification; and 5) Child-Pugh classification A or B. Patients received C-ion RT with 52.8 Gy (RBE) or 60.0 Gy (RBE) in four fractions for usual cases and 60.0 Gy (RBE) in 12 fractions for close-to-gastrointestinal tract cases. Toxicities were classified using the National Cancer Institute's Common Terminology Criteria for Adverse Events (Version 4.0).

RESULTS

Between March 2011 and November 2015, 31 patients were treated. The median follow-up period of all patients was 23.2 months (range: 8.4-55.3 months). Median age at the time of registration of C-ion RT was 83 years (range: 80-95 years). Child-Pugh grade A and B were 27 patients and 4 patients, respectively. The 2-year estimated overall survival, local control, and progression-free survival rates were 82.3%, 89.2%, and 51.3%, respectively. No patients had Grade 2 or higher acute toxicities (within 3 months after C-ion RT). One patient experienced progression in Child-Pugh classification from A to B within 3 months after C-ion RT. In late toxicities, Grade 3 encephalopathy was observed in 3 patients, and 2 improved with medication.

CONCLUSIONS

C-ion RT was effective with minimal toxicities for 80 years or older patients with hepatocellular carcinoma.

TRIAL REGISTRATION

UMIN000020571 : date of registration, 14 January 2016, retrospectively registered.

Cancer-specific mortality of high-risk prostate cancer after carbon-ion radiotherapy plus long-term androgen deprivation therapy

The treatment outcomes of patients with high‐risk localized prostate cancer (PC) after carbon‐ion radiotherapy (CIRT) combined with long‐term androgen deprivation therapy (LTADT) were analyzed, and compared with those of other treatment modalities, focusing on PC‐specific mortality (PCSM). A total of 1247 patients were enrolled in three phase II clinical trials of fixed‐dose CIRT between 2000 and 2013. Excluding patients with T4 disease, 608 patients with high‐risk or very‐high‐risk PC, according to the National Comprehensive Cancer Network classification system, who received CIRT with LTADT were evaluated. The median follow‐up time was 88.4 months, and the 5‐/10‐year PCSM rates were 1.5%/4.3%, respectively. T3b disease, Gleason score of 9–10 and percentage of positive biopsy cores >75% were associated with significantly higher PCSM on univariate and multivariate analyses. The 10‐year PCSM rates of patients having all three (n = 16), two (n = 74) or one of these risk factors (n = 217) were 27.1, 11.6 and 5.7%, respectively. Of the 301 patients with none of these factors, only 1 PCSM occurred over the 10‐year follow‐up (10‐year PCSM rate, 0.3%), and significant differences were observed among the four stratified groups (P <0.001). CIRT combined with LTADT yielded relatively favorable treatment outcomes in patients with high‐risk PC and very favorable results in patients without any of the three abovementioned factors for PCSM. Because a significant difference in PCSM among the high‐risk PC patient groups was observed, new categorization and treatment intensity adjustment may be required for high‐risk PC patients treated with CIRT.

Equivalency of the quality of sublethal lesions after photons and high-linear energy transfer ion beams

The quality of the sublethal damage (SLD) after irradiation with high-linear energy transfer (LET) ion beams was investigated with low-LET photons. Chinese hamster V79 cells and human squamous carcinoma SAS cells were first exposed to a priming dose of different ion beams at different LETs at the Heavy Ion Medical Accelerator in the Chiba facility. The cells were kept at room temperature and then exposed to a secondary test dose of X-rays. Based on the repair kinetics study, the surviving fraction of cells quickly increased with the repair time, and reached a plateau in 2-3 h, even when cells had received priming monoenergetic high-LET beams or spread-out Bragg peak beams as well as X-ray irradiation. The shapes of the cell survival curves from the secondary test X-rays, after repair of the damage caused by the high-LET irradiation, were similar to those obtained from cells exposed to primary X-rays only. Complete SLD repairs were observed, even when the LET of the primary ion beams was very high. These results suggest that the SLD caused by high-LET irradiation was repaired well, and likewise, the damage caused by the X-rays. In cells where the ion beam had made a direct hit in the core region in an ion track, lethal damage to the domain was produced, resulting in cell death. On the other hand, in domains that had received a glancing hit in the low-LET penumbra region, the SLD produced was completely repaired.

Margin estimation and disturbances of irradiation field in layer-stacking carbon-ion beams for respiratory moving targets

Carbon-ion therapy by layer-stacking irradiation for static targets has been practised in clinical treatments. In order to apply this technique to a moving target, disturbances of carbon-ion dose distributions due to respiratory motion have been studied based on the measurement using a respiratory motion phantom, and the margin estimation given by the square root of the summation Internal margin2+Setup margin2 has been assessed. We assessed the volume in which the variation in the ratio of the dose for a target moving due to respiration relative to the dose for a static target was within 5%. The margins were insufficient for use with layer-stacking irradiation of a moving target, and an additional margin was required. The lateral movement of a target converts to the range variation, as the thickness of the range compensator changes with the movement of the target. Although the additional margin changes according to the shape of the ridge filter, dose uniformity of 5% can be achieved for a spherical target 93 mm in diameter when the upward range variation is limited to 5 mm and the additional margin of 2.5 mm is applied in case of our ridge filter. Dose uniformity in a clinical target largely depends on the shape of the mini-peak as well as on the bolus shape. We have shown the relationship between range variation and dose uniformity. In actual therapy, the upper limit of target movement should be considered by assessing the bolus shape.

Carbon-ion radiotherapy for patients with advanced stage non-small-cell lung cancer at multicenters

Carbon-ion radiation therapy (CIRT) for advanced non-small-cell lung cancer (NSCLC) has not been well studied to date. This paper aimed to analyze a retrospective multicenter survey for detecting problems with the use of CIRT for Stage II and III NSCLC (7th UICC TNM Staging System). Inclusion was restricted to patients with Stage II and III NSCLC who received CIRT from November 2003 to December 2014. We gathered the data from three CIRT operating centers on July 2015. Patients with radiotherapy history, patients with cancers other than lung cancer, and those receiving palliative therapies were excluded. The patient characteristics, prescribed dose/fraction, survival rates, and adverse effects were analyzed. The total number of patients was 64 (male: 49, female: 15). Of these, 53 patients were medically inoperable. The median age was 76 years (range 46-91), and the median follow-up period was 18.5 months (range 3.2-121.5). The clinical staging consisted of 10 Stage IIA, 30 Stage IIB, 23 Stage IIIA and 1 Stage IIIB. The median prescribed dose was 72.0 Gy (RBE) (range 52.8-72.0) in 16 fractions (range 4-16). The 2-year overall survival, progression-free survival, and local control rates were 62.2% [confidence interval (CI): 47.5-76.9], 42.3% (CI: 28.8-55.8) and 81.8% (CI: 69.9-94.0), respectively. There were no higher than Grade 2 adverse effects observed. CIRT for inoperable Stage II and III NSCLC could be implemented without severe adverse effects, but the clinical staging (including lymph node status) was inhomogeneous. In addition, the prescribed dose and fractionation were not standardized. Further data accumulation and a multiple centers prospective trial for evaluating clinical stage-based results are required.

Dose-volume histogram analysis of brainstem necrosis in head and neck tumors treated using carbon-ion radiotherapy

BACKGROUND AND PURPOSE

We aimed to evaluate the relationship between brainstem necrosis and dose-volume histograms in patients with head and neck tumors after carbon-ion radiotherapy.

MATERIAL AND METHODS

We evaluated 85 patients with head and neck tumors who underwent carbon-ion radiotherapy and were followed-up for ≥12months. Brainstem necrosis was evaluated using the Common Terminology Criteria for Adverse Events (version 4.0).

RESULTS

The median follow-up was 24months, and four patients developed grade 1 brainstem necrosis, with 2-year and 3-year cumulative rates of 2.8% and 6.5%, respectively. Receiver operating characteristic curve analysis revealed the following significant cut-off values: a maximum brainstem dose of 48Gy (relative biological effectiveness [RBE]), D1cm³ of 27Gy (RBE), V40Gy (RBE) of 0.1cm³, V30Gy (RBE) of 0.7cm³, and V20Gy (RBE) of 1.4cm³. Multivariate analysis revealed that V30Gy (RBE) was most significantly associated with brainstem necrosis. The 2-year cumulative rates were 33% and 0% for V30Gy (RBE) of ≥0.7cm³ and <0.7cm³, respectively (p<0.001).

CONCLUSIONS

The present study indicated that the dose constraints might help minimize brainstem necrosis after carbon-ion radiotherapy.

Effect of low- and high-linear energy transfer radiation on in vitro and orthotopic in vivo models of osteosarcoma by activation of caspase-3 and -9

Osteosarcoma (OS) is a malignant tumor of the bone derived from primitive transformed cells of the mesenchymal origin. Local low-linear energy transfer (LET) radiotherapy has limited benefits on OS owing to its radioresistance. Thus, this study aimed to investigate the effects of high-LET radiation on human OS. Therefore, the human OS cell lines, U2O2 and KHOS/NP, were examined in vitro, or an orthotopic mouse xenograft model was studied in vivo after treatment with low-LET (gamma-ray) and high-LET (neutron) radiation. Notably, OS cells were significantly more sensitive to high-LET radiation in vitro and in the orthotopic xenograft tumor model. Specifically, neutron radiation treatment increased the relative percentage of apoptotic sub-G1 phase cells via caspase-3/9 activation; increased intracellular reactive oxygen species, autophagy, and DNA damage; and decreased invasion and migration. Similarly, the mean size of gamma-irradiated (8 Gy) orthotopic KHOS/NP OS was 195 mm³ at 6 weeks after gamma-irradiation (8 Gy), but it was only 150 mm³ in mice treated with high-LET neutron radiotherapy. Significantly, our results provide a rationale for the use of high-LET radiotherapy to treat patients with OS.

Prospective observational study of carbon-ion radiotherapy for non-squamous cell carcinoma of the head and neck

To evaluate the efficacy and safety of carbon-ion radiotherapy for non-squamous cell carcinoma of the head and neck, 35 patients were enrolled in this prospective study. The primary end-point was the 3-year local control rate, and the secondary end-points included the 3-year overall survival rate and adverse events. Acute and late adverse events were evaluated according to the Common Terminology Criteria for Adverse Events, version 4.0. The median follow-up time for all patients was 39 months. Thirty-two and three patients received 64.0 Gy (relative biological effectiveness) and 57.6 Gy (relative biological effectiveness) in 16 fractions, respectively. Adenoid cystic carcinoma was dominant (60%). Four patients had local recurrence and five patients died. The 3-year local control and overall survival rates were 93% and 88%, respectively. Acute grade 2-3 radiation mucositis (65%) and dermatitis (31%) was common, which improved immediately with conservative therapy. Late mucositis of grade 2, grade 3, and grade 4 were observed in 11, one, and no patients, respectively. There were no adverse events of grade 5. Carbon-ion radiotherapy achieved excellent local control and overall survival rates for non-squamous cell carcinoma. However, the late mucosal adverse events were not rare, and meticulous treatment planning is required. Trial registration no. UMIN000007886.

Evaluation of Risk Factors for Vertebral Compression Fracture after Carbon-Ion Radiotherapy for Primary Spinal and Paraspinal Sarcoma

Background and Purpose

Carbon-ion radiotherapy (C-ion RT) was effective therapy for inoperable spinal and paraspinal sarcomas. However, a significant adverse event following radiotherapies is vertebral compression fractures (VCFs). In this study, we investigated the incidence of and risk factors for post-C-ion RT VCFs in patients with spinal or paraspinal sarcomas.

Material and Methods

Thirty consecutive patients with spinal or paraspinal sarcomas treated with C-ion RT were retrospectively reviewed. Various clinical parameters and the Spinal Instability Neoplastic Score (SINS) were used to evaluate the risk factors for post-C-ion RT VCFs.

Results

The overall incidence of VCFs was 23% (median time: 7 months). Patients with VCFs showed a markedly higher SINS score (median value, 9 points) than those without VCF (5 points). The area under the receiver operating characteristic curve for the SINS score was 0.88, and the optimum SINS cut-off score was 8 points. The cumulative incidence of VCFs at 1 year was 9% for patients with a SINS score under 8 points, versus 80% for those with a SINS score of 8 points or higher (p < 0.0001).

Conclusions

In patients with a SINS score of 8 points or higher, referral to a spine surgeon for stabilization and multidisciplinary discussion is appropriate.

Long-term outcomes after carbon-ion radiotherapy for oral mucosal malignant melanoma

Oral mucosal malignant melanoma (OMM) is extremely rare and has a poor prognosis. Owing to its rarity, it has not yet been possible to establish an optimal treatment modality. The objective of this study was to evaluate the long-term efficacy of carbon-ion radiotherapy (C-ion RT) for OMM. Between 1997 and 2013, 19 patients with OMM were treated with C-ion RT alone. Patient ages ranged from 44 to 84 years (median, 69 years). Nine men and 10 women were included. OMMs were restaged in accordance with the seventh edition of the tumour/node/metastasis (TNM) Staging System of the International Union Against Cancer. Before treatment, 14 patients had T3 disease and 5 had T4a disease. Three patients were classified as having N1 disease. All patients were classified as having M0. The hard palate was the most frequently involved oral subsite. All patients were treated with 57.6 Gy (relative biological effectiveness) in 16 fractions. The median follow-up period was 61 months (range, 8-190 months). The 5-year local control, overall survival and progression-free survival rates were 89.5%, 57.4% and 51.6%, respectively. For local control and overall survival, T classification was found to be a significant prognostic factor. Grade 2 and 3 osteoradionecrosis was observed in three and four patients, respectively. The presence of teeth within the planning target volume was a significant risk factor for developing osteoradionecrosis. C-ion RT was an effective treatment option with acceptable toxicity for OMM.

Evaluation of a combination tumor treatment using thermo-triggered liposomal drug delivery and carbon ion irradiation

The combination of radiotherapy with chemotherapy is one of the most promising strategies for cancer treatment. Here, a novel combination strategy utilizing carbon ion irradiation as a high-linear energy transfer (LET) radiotherapy and a thermo-triggered nanodevice is proposed, and drug accumulation in the tumor and treatment effects are evaluated using magnetic resonance imaging relaxometry and immunohistology (Ki-67, n = 15). The thermo-triggered liposomal anticancer nanodevice was administered into colon-26 tumor-grafted mice, and drug accumulation and efficacy was compared for 6 groups (n = 32) that received or did not receive the radiotherapy and thermo trigger. In vivo quantitative R₁ maps visually demonstrated that the multimodal thermosensitive polymer-modified liposomes (MTPLs) can accumulate in the tumor tissue regardless of whether the region was irradiated by carbon ions or not. The tumor volume after combination treatment with carbon ion irradiation and MTPLs with thermo-triggering was significantly smaller than all the control groups at 8 days after treatment. The proposed strategy of combining high-LET irradiation and the nanodevice provides an effective approach for minimally invasive cancer treatment.

Intravenous dendritic cell administration enhances suppression of lung metastasis induced by carbon-ion irradiation

Carbon-ion radiotherapy (CIRT) is an advanced radiotherapy and has achieved good local control, even in tumors that are resistant to conventional photon beam radiotherapy (PBRT). However, distant metastasis control is an important issue. Recently, the combination of radiotherapy and immunotherapy has attracted the attention. In immunotherapy, dendritic cells (DCs) play a pivotal role in the anti-tumor immune system. However, the mechanisms underlying the combination therapy of DCs and radiotherapy have been unclear. In the present study, we evaluated anti-metastatic effects of this combination therapy, focused on the irradiation type and the route of DC administration, using a mouse model. C3H/He mice bearing NR-S1 cells were treated with CIRT or PBRT, using biologically equivalent doses. Subsequently, DCs were administered intratumorally (IT) or intravenously (IV). IV and IT DC administrations combined with CIRT to the local tumor, but not alone, significantly suppressed pulmonary metastasis, whereas the combination of DCs with PBRT suppressed metastasis at a relatively higher dose. Additionally, the anti-metastatic effect was greater in IV DC administration compared with in IT DC administration in both CIRT and PBRT. The expression levels of CD40 and IL-12 in DCs were significantly increased after co-culturing with CIRT-treated NR-S1 cells. In addition, IV administration of those co-cultured DCs significantly suppressed pulmonary metastasis. Furthermore, ecto-calreticulin levels from CIRT-treated NR-S1 cells significantly increased compared with those of a PBRT-treated tumor. Taken together, these results suggest that local CIRT combined with IV DCs augments an immunogenicity of the tumor cells by ecto-calreticulin expression and the maturation of DCs to stimulate anti-tumor immunity to decrease lung metastases.