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Several studies have reported benefits derived from cancer treatment using various heavy-ion beams. Based on these reports, the National Institutes for Quantum and Radiological Science and Technology started developing intensity-modulated composite particle therapy (IMPACT) using He-, C-, O-, and Ne-ions. In ion beam therapy, nuclear interactions in the beamline devices or patient produce secondary neutrons. This study evaluated the characteristics of secondary neutrons in IMPACT. Neutron ambient dose equivalents were measured using WENDI-II. Measurements were performed under realistic case scenarios using He-, C-, O- and Ne-ion beams. Moreover, neutron ambient dose equivalents generated by He-, C-, O- and Ne-ion beams were compared with neutron ambient dose equivalents in proton therapy. No differences exist in the distance-dependence even when the primary ions are different. Neutrons generated by primary ion beams of high atomic numbers tend to emit forward. Moreover, in contrast with proton therapy, IMPACT can reduce neutron doses.

Background/Aim: The local control rate of chondrosarcomas treated with carbon-ion radiotherapy (CIRT) worsens as tumour size increases, possibly because of the intra-tumoural linear energy transfer (LET) distribution. This study aimed to evaluate the relationship between local recurrence and intra-tumoural LET distribution in chondrosarcomas treated with CIRT. Patients and Methods: Thirty patients treated with CIRT for grade 2 chondrosarcoma were included. Dose-averaged LET (LETd) distribution was calculated by the treatment planning system, and the relationship between LETd distribution in the planning tumour volume (PTV) and local control was evaluated. Results: The mean LETd value in PTV was similar between cases with and without recurrence. Recurrence was not observed in cases where the effective minimum LETd value exceeded 40 keV/μm. Conclusion: LETd distribution in PTV is associated with local control in chondrosarcomas and patients treated with ion beams of higher LETd may have an improved local control rate for unresectable chondrosarcomas.

Institutional imaging protocols for the verification of brachytherapy applicator placements were investigated in a survey study of domestic radiotherapy institutions. The survey form designed by a free on-line survey system was distributed via the mailing-list system of the Japanese Society for Radiation Oncology. Survey data of 75 institutions between August 2019 and October 2019 were collected. The imaging modalities used were dependent on resources available to the institutions. The displacement of a brachytherapy applicator results in significant dosimetric impact. It is essential to verify applicator placements using imaging modalities before treatment. Various imaging modalities used in institutions included a computed tomography (CT) scanner, an angiography X-ray system, a multi-purpose X-ray system and a radiotherapy simulator. The median total exposure time in overall treatment sessions was $\le$75s for gynecological and prostate cancers. Some institutions used fluoroscopy to monitor the brachytherapy source movement. Institutional countermeasures for reducing unwanted imaging dose included minimizing the image area, changing the imaging orientation, reducing the imaging frequency and optimizing the imaging conditions. It is worth noting that half of the institutions did not confirm imaging dose regularly. This study reported on the usage of imaging modalities for brachytherapy in Japan. More caution should be applied with interstitial brachytherapy with many catheters that can lead to potentially substantial increments in imaging doses for monitoring the actual brachytherapy source using fluoroscopy. It is necessary to share imaging techniques, standardize imaging protocols and quality assurance/quality control among institutions, and imaging dose guidelines for optimization of imaging doses delivered in radiotherapy should be developed.

In carbon-ion radiotherapy (CIRT), secondary neutrons are produced by nuclear interactions in the beamline devices or patient. Herein, the characteristics of secondary neutrons in CIRT with energy scanning (ES) were evaluated. Neutron ambient dose equivalents (H*(10)) were measured using WENDI-II. The neutron energy spectrum was calculated using the Monte Carlo simulation. Measurement and calculation were performed under realistic case scenarios using maximum beam energies (Emax) of 290, 350, and 400 MeV/u. Moreover, H*(10) in ES was compared with H*(10) in range-shifter scanning (RS) and hybrid scanning (HS). H*(10) in Emax = 290 MeV/u was 65% less than that in Emax = 400 MeV/u. At Emax = 350 MeV/u, H*(10) in ES at θ = 120 was 42% of that at θ = 60. The neutron dose in ES CIRT decreased to approximately 60% and 70% of that in RS and HS CIRT, respectively, at 50-cm distance from the beam axis.

Individual external doses for the first 4 months after the Fukushima accident have been estimated by the ‘Basic Survey’ of the Fukushima Health Management Survey. On the other hand, the UNSCEAR 2013 report presented the first-year effective dose due to external radiation for each municipality in nonevacuated areas of Fukushima Prefecture. In this study, the doses estimated by the Basic Survey were averaged for each of three age groups (infants, 0–5 y; children, 6–15 y; and adults, >16 y), in accordance with the categories adopted by the UNSCEAR report. The average dose ratios (infants/adults and children/adults) obtained from the Basic Survey were 1.08 and 1.06 for nonevacuated areas, respectively. These were smaller than the estimation by the UNSCEAR report (1.7 and 1.4, respectively). Three factors (body size factor, location factor and occupancy factor) were discussed and the location and occupancy factors were likely to be reasons for the difference.

Following the Fukushima Daiichi Nuclear Power Plant accident, a survey for estimating individual external doses for the first 4 months after the accident was started, and it remains ongoing. Since the authors’ previous paper, 44 605 new dose estimates have been made. The new dose estimates increase the number of dose estimates to 465 999 and are reported in this note. Since the previous paper, most of the recently collected responses have been gotten through public relations activities to encourage responses across the prefecture. Thus, recent respondents might be biased (‘selection bias’). Also, the dose estimates were based on self-administered responses about personal behaviour, which relied on memories of residents. In this respect, incorrect behaviour records possibly resulted as memories have faded over time (‘recall bias’). However, the effects of these biases on dose distribution on a whole-prefecture basis seemed to be small.

PURPOSE: To estimate out-of-field doses during carbon-ion radiotherapy (CIRT) for pediatric cerebellar ependymoma. METHODS: Given that the out-of-field dose of CIRT depends on beam parameters, we set them for treatment of typical pediatric cerebellar ependymoma based on a previous study. The out-of-field dose during CIRT for pediatric cerebellar ependymoma was then estimated using the Particle and Heavy-Ion Transport code System with Monte Carlo simulations and a computational phantom developed at the University of Florida. From the simulation results, out-of-field doses at dose equivalents of passive beam and active scanning beam CIRT were calculated and compared to the secondary neutron-equivalent dose of passive beam CIRT and proton therapy. RESULTS: The out-of-field dose equivalent decreases from 1.45 mSv/Gy (relative biological effectiveness - RBE) at the thyroid to 0.06 mSv/Gy (RBE) at the bladder, verifying decay as the distance from the treatment target increases. The out-of-field neutron-equivalent dose in organs per prescribed dose for passive beam CIRT is lower than that for passive beam proton therapy. Moreover, the out-of-field organ dose equivalent per prescribed dose for the active scanning beam CIRT is lower than that for the passive beam CIRT. CONCLUSIONS: Active scanning beam CIRT is promising for pediatric cerebellar ependymoma regarding out-of-field exposure, outperforming the comparison radiotherapy modalities.

日本医学物理学会が作成した、医学物理学の体型的教科書シリーズの一つ。

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.

Purpose: The QA team of the Japan carbon‐ion radiation oncology study group (J‐CROS) was organized in 2015 to enhance confidence in the accuracy of clinical dosimetry and ensure that the facility QA procedures are adequate. The team conducted onsite dosimetry audits in all the carbon‐ion radiation therapy centers in Japan. Materials and Methods: A special phantom was fabricated for the onsite dosimetry audit. Target volumes such as the GTV, CTV, and PTV were contoured to the obtained CT images, and two plans with different isocenter depths were created. The dose at the isocenter was measured by an ionization chamber, in the onsite audit and compared with the calculated dose. Results: For all the centers, the average of the percentage ratio between the measured and calculated doses (measured/calculated) was 0.5% (−2.7% to +2.6%) and the standard deviation, 1.7%. In all the centers, the beams were within the set tolerance level of 3%. Conclusions: The audit demonstrated that the dose at a single point in the water phantom was within tolerance, but it is a big step to say that all doses are correct. In addition, this external dosimetry audit encouraged centers to improve the quality of their dosimetry systems.

Radiochromic film is a very useful tool for 2D dosimetric measurements in radiotherapy because it is self-developing and has very high-spatial resolution. However, considerable care has to be taken in ion beam radiotherapy owing to the quenching effect of high-linear energy transfer (LET) radiation. In this study, the dose responses of GAFchromic EBT3 and EBT-XD films were experimentally investigated using the clinical carbon ion beam at the Heavy Ion Medical Accelerator in Chiba. Results showed that the relations between absorbed dose and net optical density could be expressed well using an equation proposed by Reinhardt (2015). The quenching effect was evaluated by determining their relative efficiencies for photon irradiation as a function of LET. A correction equation derived in this study allowed the absorbed dose to be determined in the small irradiation field used for carbon ion radiotherapy eye treatments. This study contributes to establishing an absolute dosimetry procedure for heavy ion beams using radiochromic film.

This is a feasibility study for radiochromic film (RCF) dosimetry to measure physical and biological doses for quality assurance of carbon-ion radiotherapy. We used a layer-stacking carbon-ion beam comprised of range-shifted beamlets from the Heavy Ion Medical Accelerator in Chiba (HIMAC) at the National Institute of Radiological Scienecs (NIRS). Using biophysical beam model in a treatment planning system with its measured RCF response, the layer-stacking beam was decomposed into finely arranged beamlets with weights estimated by deconvolution of longitudinal RCF responses. The distributions of physical and biological doses were reconstructed from the estimated weights and were compared with the plan. We have developed a method to measure physical and biological doses by longitudinal dosimetry of quenched response. 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., ESTRO Meets Asia 2019

Purpose: In radiotherapy, “dose” has been referred to the dose-to-water Dw. On the other hand, Monte Carlo (MC) simulation allows the material properties to be modeled using explicit material properties, and consequently provides the dose-to-medium Dm. Since the clinical experience has been based on Dw and dose description in practice is given by Dw, it is necessary to compute Dw when using MC simulation to calculate dose distribution for clinical usage or retrospective analysis. To compute Dw in MC simulation, we proposed a method to compute Dw in therapeutic carbon beam and verified the method using a heterogeneous layer phantom. Material and methods: We computed Dw based on Bragg-Gray theory. The energy deposited by a particle in water is approximately given by that in realistic materials multiplied by the stopping power ratio of water to the material. Thus, as a first-order approximation, Dw can be deduced by summing up the energy obtained by applying the factor, which differs in each particle and energy, to deposited energy by all the particles including primary and secondary particles. To verify the proposed method, we compared depth dose distribution of a 290 MeV/u carbon beam with 6 cm SOBP in a heterogeneous layer phantom. The material of heterogeneous layer was set as: (i) Lung and (ii) bone. Results: The difference of 80 %-dose depth d80 in the heterogeneous layer phantom between MC and TPS are within 1.5 mm and the difference of relative dose between TPS and Dw by MC were within ±1 % around the heterogeneous region. Conclusion: In this work, a method to compute Dw for Monte Carlo transport simulation in realistic materials has been proposed and the effectiveness has been verified., 第118回 日本医学物理学術大会

目的：炭素線治療はその線量分布と生物学的影響により、高い局所制御率を達成している。他方で、放射線治療後の生存日数が高くなるにつれ2次がんリスクが増大すること及び小児においては成人に比べて２次がんリスクが高くなることが知られている。２次がんリスクの評価においては、線量のみならず線質の評価も生物影響の観点から重要である。本研究は小児の頭蓋内炭素線治療における2次粒子の線質を評価するため、モンテカルロ計算を用いて線質係数の分布を算出することを目的とした。 方法：従来から放射線防護分野では線質の指標として放射線荷重係数が用いられてきたが、実験的な評価が不可能なこと及び防護量のため、当該指標は正確な２次がんの推定には不向きである。本研究においては線質を評価する指標としてLETの関数である線質係数を用いた。モンテカルロコードPHITS及びフロリダ大学が開発した5歳女児のボクセルファントムを用いてスキャニング法とパッシブ法の線質係数を算出した。線量当量は生体が受けた吸収線量の値に線質係数を乗じたものと定義されているため、線質係数の算出は線量当量の値を吸収線量の値で除して求めた。PHITSの計算においては、吸収線量はT-depositを用いて、線量当量はdedxfncオプションを有効にしたT-depositを用いて求めた。 結果：スキャニング法とパッシブ法ともに2次粒子の線質係数は照射野端からの距離とともに増加する傾向にあった。2次粒子の線質係数はパッシブ法がスキャニング法に比べてどの距離においても低い値を示した。 結論：炭素線治療時にで患者が受ける2次粒子の線質の分布を線質係数を用いて明らかにした。, 第118回日本医学物理学会学術大会参加・発表

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., 第118回日本医学物理学会学術大会

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., 58th Annual Conference of the Particle Therapy Co-Operative Group

1. 研究の目的とバックグラウンド 眼球脈絡膜悪性黒色腫の標準治療は手術、強膜縫着照射、粒子線治療の大きく3 つである。欧米ではすでに陽子線やヘリウム線照射で4000 例以の眼球脈絡膜悪性黒色腫に対する粒子線治療報告があり、その局所制御率は96%以上で5 年生存率は約60～85％という優れた成績が得られている。当施設においては、2001 年より眼球脈絡膜悪性黒色腫に対する重粒子線治療を5 回分割で施行しており、局所制御率93%、5 年生存率80%と良好な成績が得られている。一方で、緑内障の発生など、晩期の有害事象は改善の余地があると考えられる。 これを実現するためにエネルギースキャンと回転ガントリーを組み合わせることで、従来では叶わなかった、いかなる角度からも照射が可能となる。このことにより従来の治療では避けることのできなかった、角膜や毛様体への照射線量を下げ、有害事象を減らすことができると想定される。 平成29 年度の基礎的検討を踏まえ、本研究においてはG 室を使用した脈絡膜悪性黒色腫に対する重粒子線治療の安全性試験を行う。 2. 今年度の研究内容 臨床試験概要 試験デザイン 無対照非盲検症例集積研究（侵襲あり・介入研究） 評価指標 主要評価指標 正常組織の急性期反応 副次的評価指標 正常組織の遅発正反応 局所制御率 生存率 眼球温存率 対象者 選択基準 ・臨床的に診断された眼球の脈絡膜悪性黒色腫の患者。 ・腫瘍の計測が可能である。 ・Performance Status (ECOG)は0-2 である。 ・同意能力を有する患者。ただし、20 歳未満に関しては、十分な理解力、判断 力を有したうえで、文書での賛意を表することが可能であり、かつ代諾者の 同意が得られること。 除外基準 ・眼窩外病変の存在。 ・生存期間が6 か月に満たないと推定される。 ・照射部位に難治性感染症がある。 ・活動性の重複癌がある。 ・重篤な合併症を有する。 ・医学的、心理学的理由等により本研究の遂行が困難と判断される。 プロトコール治療方法 重粒子線治療1 回17Gy(RBE)で4 回、総線量68Gy(RBE)の照射を行う。最初の15例はSingle Field Uniform Dose で治療計画を行い、続く15例を Multi-Field Sequential Optimization 若しくはIntensity Modulated Particle Therapy と Single Field Uniform Dose で比較検討し、治療計画を行う。 研究対象者の研究参加予定期間 文書同意取得時から照射終了後36 か月までの期間。 3. 今年度の研究成果と解析結果 臨床試験実施準備 平成29 年度の検討を踏まえ、安全性試験が実施可能であると判断された。本試験の倫理審査は2018 年3 月5 日付で当機構研究倫理審査委員会において承認された。 臨床試験実施状況 2018 年4 月より登録を開始し、2019 年2 月20日現在で9 例の登録を行った。全例において、患者QA での誤差は許容範囲内であった。9 例中、5例は3 か月までの正常組織の急性期反応を評価済みであり、grade 2 以上の急性期反応は見られなかった。全例において局所再発、遠隔転移は認めていない。 患者QA 昨年度の成果を踏まえ、深部線量測定をBragg Peak chamber で、側方線量測定をPinpoint 電離箱および位置モニターで行った。結果、いずれの症例においても臨床上問題となる誤差は認められず、治療可能であることが確認された。, 平成30年度HIMAC共同利用研究成果発表会

Purpose: Most treatment planning system (TPS) used in carbon-ion radiotherapy (CIRT) facilities are implemented with pencil beam algorithm which cannot compute dose by secondary particle and neutron dose to whole body while these dose are thought to be the reasons of radiation-induced secondary cancer. In this work, we evaluated the CT conversion method and the accuracy of the beam modeling of a developing dedicated framework using Monte Carlo (MC) simulation code PHITS for retrospective analysis of CIRT. Materials and methods: For consistency to the TPS, the CT number to stopping power ratio table used in TPS and the standard tissues of reference adult phantoms published in ICRP-110 were used to converse CT number to density and material composition. To verify the conversion methods corresponding to the TPS, we calculated the depth dose distribution in ten different material by TPS and MC and compared the range. A 400 MeV/n carbon beam with an 8 cm SOBP was used for verifying the beam model in MC. Advanced Markus chamber and pin-point chamber were used for depth dose distribution and lateral dose distribution, respectively. In addition to dose distribution inside of field, the out-filed dose distribution was also compared in this work. Results: For all the range difference between TPS and MC are within 1 mm, while the dose difference are shown in some material with high CT number. The measured range agreed well with the range calculated by TPS and MC while significant dose difference in the fragmentation tail behind the Bragg peak was found when a relatively thick range shifter was implanted. Conclusion: In this work, the CT conversion method and the accuracy of the beam modeling of a developing dedicated framework for retrospective analysis of CIRT were evaluated., 第117回日本医学物理学会学術大会