Dose Rate Effect on Cell Survival in BNCT.

The output constancy of the accelerator used for boron neutron capture therapy (BNCT) is essential to ensuring anti-tumor efficacy and safety. BNCT as currently practiced requires a wide variety of beam quality assessments to ensure that RBE dose errors are maintained within 5%. However, the necessity of maintaining a constant beam dose rate has not been fully discussed. We therefore clarified the effect of different physical dose rates of the accelerator BNCT on biological effects. SAS and A172 cells exposed to 10B-boronophenylalanine were irradiated using a neutron beam (normal operating current, 100 µA) at the Aomori Quantum Science Center. Thermal neutron flux was attenuated to 50.0 ± 0.96% under 50 µA irradiation compared to that under 100 µA irradiation. Cells were given physical doses of 1.67 and 3.36 Gy at 30 and 60 mC, respectively, and survival was significantly increased after 50 µA irradiation for both cell types (p = 0.0052 for SAS; p = 0.046 for A172, for 60 mC). Differences in accelerator BNCT beam dose rates have non-negligible effects on biological effects. Dose rate fluctuations and differences should not be easily permitted to obtain consistent biological effects.

Clinical results of proton beam therapy for hepatocellular carcinoma over 5 cm.

AIM: This study aimed to evaluate the safety and efficacy of proton beam therapy for large hepatocellular carcinoma (HCC). METHODS: Twenty-four patients with a HCC larger than 5.0 cm were treated with proton beam therapy at our institution between 2008 and 2015. RESULTS: The clinical stage was I in 2 patients, II in 9 patients, and IIIB in 13 patients. Ten of the 24 patients were not surgical candidates because of advanced HCC or old age. Median tumor size was 90 mm (range, 50-180 mm). Median total dose delivered was 72.6 Gray-equivalents (GyE) in 22 fractions (range, 60.8-85.8 GyE). Median follow-up period was 17.5 months (range, 3-70 months). Local control rate at 2 years was 87.0%. The 2-year overall survival rate was 52.4%. The predominant tumor progression pattern was new hepatic tumor development outside the irradiated field. No acute or late treatment-related toxicity of grade 3 or higher, other than dermatitis, was observed. CONCLUSIONS: These results show that proton beam therapy offers an effective and safe method for treating patients with large HCC. Proton beam therapy represents a promising method for treatment of large-volume HCC.

High Dose Hypofractionated Proton Beam Therapy is a Safe and Feasible Treatment for Central Lung Cancer.

BACKGROUND: There have been few reports about high total dose hypofractionated proton beam therapy for central lung cancer. The aim of this study was to examine retrospectively the safety and efficacy of high total dose hypofractionated proton beam therapy for central lung cancer. PATIENTS AND METHODS: Patients treated by proton beam therapy for central lung cancer located less than 2 cm from the trachea, mainstem bronchus, or lobe bronchus were included in this study. All patients received 80 Gy of relative biological dose effectiveness (RBE) in 25 fractions with proton beam therapy over 5 weeks between January 2009 and February 2015. The toxicities were evaluated using the Radiation Therapy Oncology Group and European Organization for Research and Treatment of Cancer criteria. RESULTS: Twenty patients, including 14 clinically inoperable patients (70%), received proton beam therapy for central lung cancer. The median patient age was 75 years (range: 63-90 years), the median follow up time was 27.5 months (range: 12-72 months), and the median tumor diameter was 39.5 mm (range: 24-81 mm). All patients were followed for at least 20 months or until death. The 2-year overall survival rate was 73.8% (100% in operable patients, and 62.5% in inoperable patients), and the 2-year local control rate was 78.5%. There was no Grade 3 or higher toxicities, including bronchial stricture, obstruction, and fistula. CONCLUSIONS: The present study suggests that a high total dose hypofractionated proton beam therapy for central lung cancer was safe and feasible.

Review of the sources and behaviors of plutonium isotopes in the atmosphere and ocean.

Plutonium, as well as fission products such as 137Cs, had been released into the earth environment in 1945 after the first atmospheric nuclear explosion of plutonium bomb in the desert of New Mexico (USA, July 16) and later over Nagasaki (August 9), followed then by many other explosions. Thus, plutonium cycling in the atmosphere and ocean has become a major public concern as a result of the radiological and chemical toxicity of plutonium. However, plutonium isotopes and 137Cs are important transient tracers of biogeochemical and physical processes in the environment, respectively. In this review, we show that both physical and chemical approaches are needed to comprehensively understand the behaviors of plutonium in the atmosphere and ocean. In the atmosphere, plutonium and 137Cs attach with aerosols; thus, plutonium moves according to physical and chemical processes in connection with aerosols; however, since plutonium is a chemically reactive element, its behavior in an aqueous environment is more complicated, because biogeochemical regulatory factors, in addition to geophysical regulatory factors, must be considered. Meanwhile, 137Cs is chemically inert in aqueous environments. Therefore, the biogeochemical characteristics of plutonium can be elucidated through a comparison with those of 137Cs, which show conservative properties and moves according to physical processes. Finally, we suggest that monitoring of both plutonium and 137Cs can help elucidate geophysical and biogeochemical changes from climate changes.

Clinical Results and Prognostic Factors in Boron Neutron Capture Therapy for Recurrent Squamous Cell Carcinoma of the Head and Neck Under the Japan National Health Insurance System: A Retrospective Study of the Initial 47 Patients.

PURPOSE: Recurrent head and neck cancer presents a therapeutic challenge because of cumulative toxicity from initial radiation therapy, limiting reirradiation options. Boron neutron capture therapy (BNCT) offers a promising alternative, selectively delivering a radical dose to tumors while sparing adjacent normal tissue. This study investigates the initial clinical outcomes and prognostic factors associated with BNCT for recurrent squamous cell carcinoma of the head and neck. METHODS AND MATERIALS: This retrospective analysis investigated the initial 47 patients treated with BNCT between May 2020 and February 2021 in Japan. All patients had received radiation therapy with a median dose of 70 Gy (range, 44-176) before BNCT. Median tumor size was 11 cm3 (range, 1-117 cm3), with 23% of tumors larger than 30 cm3, and 87% of patients had prior systemic therapy. The most common prescribed dose to the pharyngeal mucosa was 15 Gy-Eq (36%), followed by 18 Gy-Eq (34%). The minimum dose given to tumor was 27.4 Gy-Eq (range, 13.3-45.2). In 23 patients, 18F-fluoro-borono-phenylalanine positron emission tomography was performed within 1 week before BNCT, and the tumor-to-blood 10B ratio was 3.5 (range, 2.0-8.7). RESULTS: Efficacy analysis revealed a 51% complete response rate and a 74% overall response rate. Disease-free survival rates at 1 and 2 years were 34.6% and 26.6%, respectively. Overall survival rates at 1 and 2 years were 86.1% and 66.5%, respectively. Multivariate analysis revealed that, among the patient characteristics, whether the lesion was mucosal had a significant effect on achieving complete response. CONCLUSIONS: This study provided valuable insights into the early integration of BNCT into routine clinical practice, highlighting its efficacy and safety. Technical improvements are needed to ensure precise dose administration. Ongoing prospective studies, such as the phase II REBIVAL study, will further elucidate the role of BNCT in recurrent head and neck cancer.

Effects on local atmospheric environment of volcanic ash from Sakurajima volcano, inferred from atmospheric deposition of Potassium-40 at Kagoshima City, Japan.

In this study, we statistically demonstrated that an anomalous high of 40K fallout in the atmospheric fallout in Kagoshima City is caused by heavy ashfall associated with eruptions of Sakurajima volcano. Sakurajima is one of the most active volcanoes in Japan, and its repeated explosive eruptions cause large amounts of ash to fall on Kagoshima City. The fallout of crust-derived natural radionuclides, 40K, 212Pb, and 214Bi, from the atmosphere in Kagoshima City showed a significant correlation with the number of eruptions of Sakurajima volcano and the amount of ashfall in Kagoshima City. In contrast, no significant correlation was found between 40K and 7Be fallout. The 40K fallout indicates that almost all of the atmospheric fallout in Kagoshima City is composed of volcanic ash particles. The contribution from mineral and sea salt particles other than volcanic ash is minimal. The mass balance of the observed 40K fallout, ashfall, and atmospheric fallout yield indicates that there is a significant amount of volcanic ash deposition that is not accounted for as ashfall. In most cases, the ash deposition observed as ashfall is only 30-70 wt% of the total deposition collected as atmospheric fallout samples, and the remaining portion is fine-grained and behaves as suspended volcanic ash particles, which significantly impact the atmospheric environment.

Efficacy and safety of boron neutron capture therapy for Hypopharyngeal/Laryngeal cancer patients with previous head and neck irradiation in Japan.

BACKGROUND AND PURPOSE: Patients with hypopharyngeal cancer (HPC)/laryngeal cancer (LCA) with a history of head and neck irradiation are often difficult to treat with conventional radiotherapy. This study aimed to clarify the efficacy and safety of boron neutron capture therapy (BNCT) for HPC/LCA. MATERIALS AND METHODS: In this retrospective study, HPC/LCA with local lesions were analyzed, including both recurrent cases after treatment and second primary cases. The primary endpoints were tumor response and incidence of adverse events (AEs) after BNCT. The secondary endpoints were local control (LC), progression-free survival (PFS), and overall survival (OS). Evaluation of tumor response was terminated when any additional treatment was administered, and only survival data were collected. RESULTS: The analysis included 25 and 11 cases of HPC and LCA, respectively. All had a history of head and neck irradiation, and median dose of prior radiotherapy was 70 Gy. The complete response (CR) rate was 72%, overall response rate was 84%, and the 1-year LC and PFS were 63.1% and 53.7%, respectively. The median survival time was 15.5 months, and the 2-year OS was 79.8%. Of the 27 patients with CR, 11 cases recurred at a median of 6.0 months. The acute G3 AEs were oral mucositis (6%), pharyngeal mucositis (3%), and soft tissue infection (3%). Acutely, there were no G4-5 AEs, except hyperamylasemia, and in the late phase, there were no G3 or higher AEs. CONCLUSION: BNCT can be achieve good tumor response while preserving the larynx without severe AEs.

Chemical implication of the partition coefficient of 137Cs between the suspended and dissolved phases in natural water.

After the Fukushima Daiichi nuclear power plant accident, the terrestrial environment became severely contaminated with radiocesium. Consequently, the river and lake water in the Fukushima area exhibited high radiocesium levels, which declined subsequently. The partition coefficient of 137Cs between the suspended sediment (SS) and dissolved phases, Kd, was introduced to better understand the dynamic behavior of 137Cs in different systems. However, the Kd values in river water, ranging from 2 × 104 to 7 × 106 L kg-1, showed large spatiotemporal variability. Therefore, the factors controlling the 137Cs partition coefficient in natural water systems should be identified. Herein, we introduce a chemical model to explain the variability in 137Cs Kd in natural water systems. The chemical model includes the complexation of Cs+ with mineral and organic binding sites in SS, metal exchange reactions, and the presence of colloidal species. The application of the chemical model to natural water systems revealed that Cs+ is strongly associated with binding sites in SS, and a major chemical interaction between 137Cs and the binding sites in SS is the isotope exchange reaction between stable Cs and 137Cs, rather than metal exchange reactions with other metal ions such as potassium ions. To explain the effect of the SS concentration on Kd, the presence of colloidal 137Cs passing through a filter is significant as the dominant dissolved species of 137Cs in river water. These results suggest that a better understanding of stable Cs dissolved in natural water is important for discerning the geochemical and ecological behaviors of 137Cs in natural water.

Safety of Boron Neutron Capture Therapy with Borofalan(10B) and Its Efficacy on Recurrent Head and Neck Cancer: Real-World Outcomes from Nationwide Post-Marketing Surveillance.

BACKGROUND: This study was conducted to evaluate the real-world safety and efficacy of boron neutron capture therapy (BNCT) with borofalan(10B) in Japanese patients with locally advanced or locally recurrent head and neck cancer (LA/LR-HNC). METHODS: This prospective, multicenter observational study was initiated in Japan in May 2020 and enrolled all patients who received borofalan(10B) as directed by regulatory authorities. Patient enrollment continued until at least 150 patients were enrolled, and adverse events attributable to drugs, treatment devices, and BNCT were evaluated. The patients with LA/LR-HNC were systematically evaluated to determine efficacy. RESULTS: The 162 patients enrolled included 144 patients with squamous cell carcinoma of the head and neck (SCCHN), 17 patients with non-SCCHN (NSCCHN), and one patient with glioblastoma. Treatment-related adverse events (TRAEs) were hyperamylasemia (84.0%), stomatitis (51.2%), sialoadenitis (50.6%), and alopecia (49.4%) as acute TRAEs, and dysphagia (4.5%), thirst (2.6%), and skin disorder (1.9%) as more common late TRAEs. In patients with LA/LR-HNC, the overall response rate (ORR) was 72.3%, with a complete response (CR) in 63 (46.0%) of 137 patients with SCCHN. Among 17 NSCCHN patients, the ORR was 64.7%, with eight cases (47.1%) of CR. One- and two-year OS rates in patients with recurrent SCCHN were 78.8% and 60.7%, respectively. CONCLUSIONS: This post-marketing surveillance confirmed the safety and efficacy of BNCT with borofalan(10B) in patients with LA/LR-HNC in a real-world setting.

Temporal changes of 137Cs concentrations in the Far Eastern Seas: partitioning of 137Cs between overlying waters and sediments.

Deep-ocean sediments, similarly to seawater, are important reservoirs of 137Cs, an anthropogenic radionuclide with a relatively long half-live found in the Earth system. To better understand the geochemical behaviour of 137Cs in the ocean, we examined the temporal changes of 137Cs activity concentrations in the overlying waters and in sediments from the Far Eastern Seas (Sea of Japan, SOJ, and Okhotsk Sea, OS) during the period of 1998-2021. The 137Cs activity levels showed exponential changes during the observed period. The decay-corrected change rates of 137Cs in deep waters of SOJ exhibited a slow increase, while 137Cs levels in seawater and sediment in OS decreased gradually. This reflects a topographical difference, as SOJ is a semi-closed sea, whereas OS receives continuously inflow of subarctic waters. It was confirmed that 137Cs released after the Fukushima Dai-ichi Nuclear Power Plant accident was rapidly transported into the deep waters of the SOJ. To elucidate the transfer processes of 137Cs from seawater to sediment, we discussed the temporal changes of the partition coefficients (Kd) of 137Cs between the overlying water and the surface sediment. In shallow areas (< 1500 m water depth), Kd values were almost constant within the sampling periods, although the temporal changes in the Kd values occurred in deeper waters (> 2500 m depth). The Kd values increased with increasing depth, which may reflect a pressure effect as a possible mechanism. These findings suggest that chemical processes may be important factors controlling the transport of 137Cs between seawater and sediment, although more complicated phenomena occurred in deep waters and sediments of the SOJ (> 3000 m depth).

Initiatives Toward Clinical Boron Neutron Capture Therapy in Japan.

Boron neutron capture therapy (BNCT) has been performed at nuclear research reactors for many years. The development of accelerators for BNCT resulted in a paradigm shift from research to real clinical applications. In Japan, BNCT was approved as a clinical therapy covered by the National Health Insurance in 2020. In this article, the status of BNCT in Japan is briefly introduced.

Characterization and clinical utility of different collimator shapes in accelerator-based BNCT systems for head and neck cancer.

NeuCure® is the only accelerator-based boron neutron capture therapy (BNCT) system in the world with pharmaceutical approval. Until now, only flat collimators (FCs) on the patient side have been installed. However, in some cases of head and neck cancer patients, positioning the patient close enough to the collimator when using FCs was difficult. Thus, there are concerns about the prolongation of the irradiation time and overdose to normal tissues. To address these issues, a collimator with a convex-extended section on the patient side (extended collimators [ECs]) was developed, and its pharmaceutical approval was obtained in February 2022. This study evaluated the physical characterization and usefulness of each collimator using a simple geometry water phantom model and human model. In the water phantom model, the thermal neutron fluxes at 2 cm depth on the central axis were 5.13 × 108, 6.79 × 108, 1.02 × 109, and 1.17 × 109n/cm2/s for FC(120), FC(150), EC50(120), and EC100(120), respectively, when the distance from the irradiation aperture was kept constant at 18 cm. With ECs, the relative off-axis thermal neutron flux decreased steeply. In the hypopharyngeal cancer human model, the tumor dose changes were within <2%, but the maximum oral mucosa doses were 7.79, 8.51, 6.76, and 4.57 Gy-Eq, respectively. The irradiation times were 54.3, 41.3, 29.2, and 24.8 min, respectively. In cases where positioning the patient close to the collimator is difficult, the use of ECs may reduce the dose to normal tissues and shorten the irradiation time.

Radiostrontium in the western North Pacific: characteristics, behavior, and the Fukushima impact.

The impact of the Fukushima-derived radiostrontium ((90)Sr and (89)Sr) on the western North Pacific Ocean has not been well established, although (90)Sr concentrations recorded in surface seawater offshore of the damaged Fukushima Dai-ichi nuclear power plant were in some areas comparable to or even higher than (as those in December 2011 with 400 kBq m(-3)(90)Sr) the (137)Cs levels. The total amount of (90)Sr released to the marine environment in the form of highly radioactive wastewater could reach about 1 PBq. Long-term series (1960-2010) of (90)Sr concentration measurements in subtropical surface waters of the western North Pacific indicated that its concentration has been decreasing gradually with a half-life of 14 y. The pre-Fukushima (90)Sr levels in surface waters, including coastal waters near Fukushima, were estimated to be 1 Bq m(-3). To better assess the impact of about 4-5 orders of magnitude increased radiostrontium levels on the marine environment, more detail measurements in seawater and biota of the western North Pacific are required.

Temporal variability of plutonium in surface waters of the Sea of Japan.

Long-term temporal variations of plutonium in Sea of Japan (SOJ) surface waters have been examined with the aim to better understand its behavior during several decades. The first observation is that 239,240Pu activity concentrations in surface waters of the SOJ during 1977-2019 were 6.5 ± 4.7 mBq m-3 in average, and 5.1 mBq m-3 as the median, whereas 137Cs and 90Sr activity concentrations decreased with time, except of the perturbation due to the 2011 Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident. Another observation is that sporadic high 239,240Pu activity concentrations occurred in the east Japan Basin, ranging from 1 to 39 mBq m-3. The spatial distribution of 239,240Pu activity concentrations in surface waters revealed that high 239,240Pu levels (>20 mBq m-3) occurred in 1994 in the northern SOJ, which was considered to be due to winter convection. To elucidate factors controlling the temporal variability of surface 239,240Pu levels in the SOJ, a relationship between surface 239,240Pu activity concentrations and vertical diffusion coefficients was examined. The results revealed that this relationship could be classified into two groups: one group did not show a change with increasing diffusion coefficient, while the other group showed a positive correlation. The vertical 239,240Pu distribution in SOJ waters suggests that the high surface 239,240Pu levels occurred due to the upwelling of cyclonic eddy. The rapid recycling of deeper plutonium occurred in the SOJ due to deep winter convection and upwelling associated with cyclonic eddy. The plutonium levels in the SOJ have been found to be sensitive to climate changes. Warming of the SOJ may cause a reduction of winter convection and eddy activity as a result of increasing sea surface temperature. This leads to a decline of recirculation of plutonium and other bioavailable elements from Japan Sea Proper Water (JSPW) to surface water layers. Plutonium would be, therefore, an important indicator of biogeochemical processes in the marine environment, helping to assess climate change impacts on marine ecological systems.

Ten years of investigations of Fukushima radionuclides in the environment: A review on process studies in environmental compartments.

In March 2011, severe nuclear accident happened at the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) after the gigantic earthquake and following huge tsunami wave. A lot of investigations to assess environmental and radiological impacts of released radionuclides have been conducted by domestic and international organizations. Environmental radioactivity research related to the FDNPP accident has spread widely over different scientific fields due to specific features of the accident, and specifically its impact on the marine environment. The present paper summarizes major lessons learned from the environmental investigations of the FDNPP accident. Environmental radioactivity studies have typical interdisciplinary character; especially physics and chemistry are fundamental as a base of process studies in the environment. In this sight, we review chemical aspects regarding FDNPP-derived radiocesium transfer within and between compartments (atmosphere, ocean and land). We also discuss future trends in investigations of behavior of anthropogenic radionuclides in the environment, important not only for a better understanding of impacts of the FDNPP accident on the environment, but also for improving our general knowledge of the total environment in the Anthropocene era and its protection for the future.

RGD Peptide-Conjugated Dodecaborate with the Ga-DOTA Complex: A Preliminary Study for the Development of Theranostic Agents for Boron Neutron Capture Therapy and Its Companion Diagnostics.

A boron neutron capture therapy (BNCT) system, using boron-10-introduced agents coupled with companion diagnostics, is anticipated as a promising cancer theranostic. Thus, this study aimed to synthesize and evaluate a probe closo-dodecaborate-(Ga-DOTA)-c(RGDfK) (16) [Ga = gallium, DOTA =1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid, and c(RGDfK) = cyclo(arginine-glycine-aspartate-d-phenylalanine-lysine] containing closo-dodecaborate ([B12H12]2-) as a boron cluster, a [67Ga]Ga-DOTA derivative for nuclear medicine imaging, and an RGD peptide for tumor targeting. Moreover, we prepared a radioiodinated probe [125I]17 in which I-125 is introduced into a closo-dodecaborate moiety of 16. [67Ga]16 and [125I]17 showed high stability and high uptake in cancer cells in vitro. Biodistribution experiments in tumor-bearing mice revealed similar biodistribution patterns between [67Ga]16 and [125I]17, such as a high uptake in the tumor and a low uptake in other non-target tissues. Meanwhile, [125I]17 exhibited higher accumulation in most tissues, including the tumor, than [67Ga]16, probably because of higher albumin binding. The higher the [125I]17 accumulation in the tumor, the more desirable it is for BNCT, with the possibility that the iodo-closo-dodecaborate site may work as an albumin binder.

Profile analysis of adverse events after boron neutron capture therapy for head and neck cancer: a sub-analysis of the JHN002 study.

The purpose of this study was to outline the course and profile of adverse events specific to boron neutron capture therapy (BNCT) for head and neck cancer. This was a sub-analysis of the phase II JHN002 trial. Patients received 400 mg/kg borofalan(10B), followed by neutron irradiation. The course of adverse events after BNCT was documented in the JHN002 Look Up study. Patients were grouped into face/front (FF), face/lateral (FL) and neck (N) beam groups according to the point of skin incidence of the epithermal neutron beam axis, and the profile of adverse events dependent on beam incidence position was examined. The courses of adverse events in eight recurrent squamous cell carcinoma (R-SCC) and 13 recurrent or locally advanced non-SCC cases were analyzed. Median interval to complete recovery was 23 days (interquartile range (IQR), 14-48 days) for oral mucositis, 40 days (IQR, 24-56 days) for dermatitis, 58 days (IQR, 53-80 days) for dysgeusia and 156 days (IQR, 82-163 days) for alopecia. In the FF beam group, parotitis (P = 0.007) was less frequent, while oral mucositis (P = 0.032), fatigue (P = 0.002), conjunctivitis (P = 0.001), epistaxis (P = 0.001) and abdominal discomfort (P = 0.029) tended to be more frequent than in the FL and N beam groups. Courses and irradiation site-specific profiles of adverse events in BNCT for head and neck cancer were identified. This profile may be useful for considering interventions to prevent exacerbation of treatment-related adverse events on BNCT.

Dosimetric effect of set-up error in accelerator-based boron neutron capture therapy for head and neck cancer.

The dosimetric effect of set-up error in boron neutron capture therapy (BNCT) for head and neck cancer remains unclear. In this study, we analyzed the tendency of dose error by treatment location when simulating the set-up error of patients. We also determined the tolerance level of the set-up error in BNCT for head and neck cancer. As a method, the distal direction was shifted with an interval of 2.5 mm, from 0.0 mm to +20.0 mm and compared with the dose at the reference position. Similarly, the horizontal direction and vertical direction were shifted, with an interval of 5.0 mm, from -20.0 mm to +20.0 mm. In addition, cases with 3.0 mm and 5.0 mm simultaneous shifts in all directions were analyzed as the worst-case scenario. The dose metrics of the minimum dose of the tumor and the maximum dose of the mucosa were evaluated. From unidirectional set-up error analysis, in most cases, the set-up errors with dose errors within ±5% were Δdistal < +2.5 mm, Δhorizontal < ±5.0 mm and Δvertical < ±5.0 mm. In the simulation of 3.0 mm shifts in all directions, the errors in the minimum tumor dose and maximum mucosal dose were -3.6% ±1.4% (range, -5.4% to -0.6%) and 2% ±1.4% (range, 0.4% to 4.5%), respectively. From these results, if the set-up error was within ±3.0 mm in each direction, the dose errors of the tumor and mucosa could be suppressed within approximately ±5%, which is suggested as a tolerance level.

Determining a methodology of dosimetric quality assurance for commercially available accelerator-based boron neutron capture therapy system.

The irradiation field of boron neutron capture therapy (BNCT) consists of multiple dose components including thermal, epithermal and fast neutron, and gamma. The objective of this work was to establish a methodology of dosimetric quality assurance (QA), using the most standard and reliable measurement methods, and to determine tolerance level for each QA measurement for a commercially available accelerator-based BNCT system. In order to establish a system of dosimetric QA suitable for BNCT, the following steps were taken. First, standard measurement points based on tissue-administered doses in BNCT for brain tumors were defined, and clinical tolerances of dosimetric QA measurements were derived from the contribution to total tissue relative biological effectiveness factor-weighted dose for each dose component. Next, a QA program was proposed based on TG-142 and TG-198, and confirmed that it could be assessed whether constancy of each dose component was assured within the limits of tolerances or not by measurements of the proposed QA program. Finally, the validity of the BNCT QA program as an evaluation system was confirmed in a demonstration experiment for long-term measurement over 1 year. These results offer an easy, reliable QA method that is clinically applicable with dosimetric validity for the mixed irradiation field of accelerator-based BNCT.

Dosimetric effects of the ipsilateral shoulder position variations in the sitting-positioned boron neutron capture therapy for lower neck tumor.

We aimed to evaluate dosimetric effects of ipsilateral shoulder position variations (ISPVs) in sitting-positioned boron neutron capture therapy (BNCT) for lower neck tumor. The ISPVs were simulated using deformed shoulder images that can simulate arbitrary shape. The dose-volume parameters for the tumor in the rotated shoulder plans considerably varied compared with that for the mucosa. Even in a small number of cases, these differences were clearly observed among patients. The ISPVs in lower neck BNCT have great dosimetric effects.