Challenging issues in treatment planning for scanned carbon-ion (C-ion) therapy are (i) accurate calculation of dose distribution, including the contribution of large angle-scattered fragments, (ii) reduction in the memory space required to store the dose kernel of individual pencil beams and (iii) shortening of computation time for dose optimization and calculation. To calculate the dose contribution from fragments, we modeled the transverse dose profile of the scanned C-ion beam with the superposition of three Gaussian distributions. The development of pencil beams belonging to the first Gaussian component was calculated analytically based on the Fermi-Eyges theory, while those belonging to the second and third components were transported empirically using the measured beam widths in a water phantom. To reduce the memory space for the kernels, we stored doses only in the regions of interest considered in the dose optimization. For the final dose calculation within the patient's whole body, we applied a pencil beam redefinition algorithm. With these techniques, the triple Gaussian beam model can be applied not only to final dose calculation but also to dose optimization in treatment planning for scanned C-ion therapy. To verify the model, we made treatment plans for a homogeneous water phantom and a heterogeneous head phantom. The planned doses agreed with the measurements within ±2% of the target dose in both phantoms, except for the doses at the periphery of the target with a high dose gradient. To estimate the memory space and computation time reduction with these techniques, we made a treatment plan for a bone sarcoma case with a target volume of 1.94 l. The memory space for the kernel and the computation time for final dose calculation were reduced to 1/22 and 1/100 of those without the techniques, respectively. Computation with the triple Gaussian beam model using the proposed techniques is rapid, accurate and applicable to dose optimization and calculation in treatment planning for scanned C-ion therapy.

A set of RGD output correction factors was determined for field size changes and wedge insertions. The results obtained from recent postal dose audits were analyzed, and the mean differences between the measured and stated doses were within 0.5% for every field size and wedge angle. The SDs of the distribution were within the estimated uncertainty, except for one condition that was not reliable because of poor statistics.

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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 (LET d ) distribution was calculated by the treatment planning system, and the relationship between LET d distribution in the planning tumour volume (PTV) and local control was evaluated. Results: The mean LET d value in PTV was similar between cases with and without recurrence. Recurrence was not observed in cases where the effective minimum LET d value exceeded 40 keV/μm. Conclusion: LET d distribution in PTV is associated with local control in chondrosarcomas and patients treated with ion beams of higher LET d may have an improved local control rate for unresectable chondrosarcomas.

Background and purpose: Several studies have focused on increasing the linear energy transfer (LET) within tumours to achieve higher biological effects in carbon-ion radiotherapy (C-ion RT). However, it remains unclear whether LET affects late complications. We assessed whether physical dose and LET distribution can be specific factors for late rectal complications in C-ion RT. Materials and methods: Overall, 134 patients with uterine carcinomas were registered and retrospectively analysed. Of 134 patients, 132 who were followed up for >6 months were enrolled. The correlations between the relative biological effectiveness (RBE)-weighted dose based on the Kanai model (the ostensible ''clinical dose"), dose-averaged LET (LETd), or physical dose and rectal complications were evaluated. Rectal complications were graded according to the Radiation Therapy Oncology Group/European Organization for Research and Treatment of Cancer criteria. Results: Nine patients developed grade 3 or 4 late rectal complications. Linear regression analysis found that D 2cc in clinical dose was the sole risk factor for !grade 3 late rectal complications (p = 0.012). The receiver operating characteristic analysis found that D 2cc of 60.2 Gy (RBE) was a suitable cut-off value for predicting !grade 3 late rectal complications. Among 35 patients whose rectal D 2cc was !60.2 Gy (RBE), no correlations were found between severe rectal toxicities and LETd alone or physical dose per se. Conclusion: We demonstrated that severe rectal toxicities were related to the rectal D 2cc of the clinical dose in C-ion RT. However, no correlations were found between severe rectal toxicities and LETd alone or physical dose per se.

This study reports the commissioning methodology and results of a respiratory gating system [AZ – 733 V/733 VI (Anzai Medical Co., Japan)] using a pressure sensor in carbon‐ion scanning radiotherapy. Commissioning includes choosing a location and method for pressure sensor installation, delay time measurement of the system, and the final flow test. Additionally, we proposed a methodology for the determination of a threshold level of generating an on/off gate for the beam to the respiratory waveform, which is important for clinical application. Regarding the location and method for installation of the pressure sensor, the actual person's abdomen, back of the body position, and supine/prone positioning were checked. By comparing the motion between the pressure sensor output and the reference LED sensor motion, the chest rear surface was shown to be unsuitable for the sensor installation, due to noise in the signal caused by the cardiac beat. Regarding delay time measurement of the system, measurements were performed for the following four steps: (a). Actual motion to wave signal generation; (b). Wave signal to gate signal generation; (c). Gate signal to beam on/off signal generation; (d). Beam on/off signal to the beam irradiation. The total delay time measured was 46 ms (beam on)/33 ms (beam off); these were within the prescribed tolerance time (<100 ms). Regarding the final flow test, an end‐to‐end test was performed with a patient verification system using an actual carbon‐ion beam; the respiratory gating irradiation was successfully performed, in accordance with the intended timing. Finally, regarding the method for determining the threshold level of the gate generation of the respiration waveform, the target motion obtained from 4D‐CT was assumed to be correlated with the waveform obtained from the pressure sensor; it was used to determine the threshold value in amplitude direction.

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BackgroundCarbon-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.MethodsBetween 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, D5cc, D2cc, and Dmax, with the incidence of ≥grade 1 morbidities were retrospectively analyzed.ResultsIn 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 D5cc and D2cc were significantly higher in patients with ≥grade 1 proctitis than in those without morbidity. In addition, the D5cc for the bladder was significantly higher in patients with ≥grade 1 cystitis than in those without morbidity. Results of univariate analyses showed that D2cc of the rectum was correlated with the development of ≥grade 1 late proctitis. Moreover, D5cc of the bladder was correlated with the development of ≥grade 1 late cystitis.ConclusionsThe 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 registrationRetrospectively registered (NIRS: 16–040).Electronic supplementary materialThe online version of this article (10.1186/s13014-018-1061-7) contains supplementary material, which is available to authorized users.