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Objective: We assessed the impact of changes in patient position on carbon-ion scanning beam distribution during treatment for prostate cancer. Methods: 68 patients were selected. Carbon-ion scanning dose was calculated. Two different planning target volumes (PTVs) were defined: PTV1 was the clinical target volume plus a set-up margin for the anterior/lateral sides and posterior side, while PTV2 was the same as PTV1 minus the posterior side. Total prescribed doses of 34.4 Gy [relative biological effectiveness (RBE)] and 17.2 Gy (RBE) were given to PTV1 and PTV2, respectively. To estimate the influence of geometric variations on dose distribution, the dose was recalculated on the rigidly shifted single planning CT based on two dimensional-three dimensional rigid registration of the orthogonal radiographs before and after treatment for the fraction of maximum positional changes. Results: Intrafractional patient positional change values averaged over all patients throughout the treatment course were less than the target registration error = 2.00 mm and angular error = 1.27°. However, these maximum positional errors did not occur in all 12 treatment fractions. Even though large positional changes occurred during irradiation in all treatment fractions, lowest dose encompassing 95% of the target (D95)-PTV1 was >98% of the prescribed dose. Conclusion: Intrafractional patient positional changes occurred during treatment beam irradiation and degraded carbon-ion beam dose distribution. Our evaluation did not consider non-rigid deformations, however, dose distribution was still within clinically acceptable levels. Advances in knowledge: Inter- and intrafractional changes did not affect carbon-ion beam prostate treatment accuracy. [ABSTRACT FROM AUTHOR]

At the Heavy Ion Medical Accelerator in Chiba (HIMAC), more than 8000 patients have been successfully treated by carbon ion beams since 1994. The successful results of treatments have led us to construct a new treatment facility equipped with a 3-D pencil beam scanning irradiation system. For the implementation of this irradiation technique, we developed a fast scanning magnet and its power supply, which are required to have field ramp rate of more than 250 T/s. The scanning magnets set at the entrance of the irradiation system are two dipole magnets to scan the beam in both horizontal and vertical directions and used to form the irradiation field to be tumor shape. Before the installation, performance test including both static and dynamic field measurement was carried out. Severe delay of the field and temperature rise were not observed as expected. Measured field ramp rate reached up to 300 T/s. After the installation, we verified the accuracy and stability of the scanned ion beam through the commissioning with the beam. As a successful result of the commissioning, treatment using the new scanning system was started in 2011. [ABSTRACT FROM PUBLISHER]

Objective: To evaluate the impact of variation in respiratory cycle between treatment planning and irradiation for pencil beam scanning and phase-controlled rescanning (PCR) on the resulting dose distribution, we conducted a simulation study based on four-dimensional CT (4DCT) data for lung cancer patients. Methods: 4DCT data were acquired for seven patients with lung tumours. Treatment planning was designed to ensure the delivery of 95% of the prescribed dose to the clinical target volume in respective phases of the 4DCT by taking account of intrafractional beam range variations. Carbon ion pencil beam scanning dose distributions were calculated for various respiratory cycles that differed from the reference respiration (=4.4s) but which stayed regular during irradiation. The number of rescannings was changed to 1, 4 or 8 times. PCR was correlated with the gating window in treatment planning to calculate the beam weighting map. Results: 8xPCR improved dose conformation to the target for all irradiation respiratory cycles. Minimum dose (Dmin) and lowest dose encompassing 95% of the target (D95) values with 4XPCR were decreased from 94.1% and 98.1% to 88.4% and 93.5% with an altered irradiation respiratory cycle of 2.4s. However, these values were improved with 8xPCR to over 94.9% for Dmin and 98.6% for D95 for respective irradiation respiratory cycles. Conclusion: Pencil beam scanning treatment with eight or more PCRs consistently improved dose conformation for moving lung targets even when different respiratory cycles were used for treatment planning and irradiation. Advances in knowledge: Scanning treatment with eight or more rescannings consistently improved dose homogeneity to a moving target even though respiratory cycles varied during treatment. [ABSTRACT FROM AUTHOR]

Abstract: A project to construct a new treatment facility as an extension of the existing HIMAC facility has been initiated for the further development of carbon-ion therapy. In the new facility, one of the treatment rooms will be equipped with an iso-centric gantry system employing a 3D pencil beam scanning irradiation method. In order to realize a compact design, the final 90° bending magnet is divided into two bending magnets of 60° and 30°. The scanning magnets are set between these two bending magnets, although the aperture of the 30° magnet increases. Finally, we achieved 350 tons of total weight for 400MeV/u carbon beams with a 150mm square field. [Copyright &y& Elsevier]

Abstract: For the effective utilization of the favorable properties of heavy-ion beams in cancer treatment, it is important to evaluate the range of incident ions and the deposited dose distribution in a patient''s body. For this purpose, the utilization of positron emitters induced in therapeutic irradiation is, at present, the only feasible method for in situ and non-invasive monitoring of heavy-ion therapy. In this study, we performed irradiation experiments with three species of ions to a water target, and the annihilation gamma-ray distributions were obtained with a positron camera. We applied the maximum likelihood estimation (MLE) method for the detected distributions to derive the range of incident ions and the deposited dose distribution in the target. As a result, the ranges were determined with a difference between the MLE range R MLE and the experimental range R exp less than 1.1mm. The good agreement between the estimated dose distribution with the MLE method and the measured one implies that a deposited dose distribution in a target could be estimated from a detected annihilation gamma-ray distribution. [Copyright &y& Elsevier]

Abstract: We proposed to apply the MLE method for determining the range of heavy ions and demonstrated the effectiveness of this method by experiments with 12C beams. We performed irradiation experiments with stable 12C ions of mono-energetic 290MeV/u to a water, a polyethylene and a PMMA target. The theoretical ranges for 12C ions of 290MeV/u in these targets are 160.5, 157.9 and 139.8mm, respectively. The annihilation events from positron emitters generated by 12C ions were detected with a positron camera for 500s just after the irradiation. To evaluate the range of 12C ions, the MLE method was applied to the annihilation gamma ray distribution. The derived ranges for the three targets were 160.6, 158.9 and 140.4mm, respectively. Therefore, we can conclude that the range of 12C ions was determined within an accuracy of 1.0mm for all targets. [Copyright &y& Elsevier]

Abstract: For spot-scanning irradiation, we have developed a new control system in the experiments involving secondary beams of short half-lives. Fast beam switching and spot-by-spot dose monitoring were incorporated into this system. The control system can interface with various instruments, perform sequencing of measurements, control the motion of instruments and data acquisition. Synchronized communications with the period of beam spills in the LAN are introduced in the system to avoid the conflicts among computer communications. As an example of measurement, the results of dose distribution in 3D spot-scanning irradiation are presented. [Copyright &y& Elsevier]