Commissioning of carbon-ion radiotherapy for moving targets at the Osaka Heavy-Ion Therapy Center.

purposeHerein, we report the methods and results of the Hitachi carbon-ion therapy facility commissioning to determine the optimum values of the magnitude of movement and repaint number in respiratory-gated irradiation.

methodsA virtual-cylinder target was created using the treatment-planning system (VQA Plan), and measurements were performed to study the effects of respiratory movements using a two-dimensional ionization-chamber array detector and a phantom with movable wedge and stage. For simulations, we selected a 10 × 10 × 10 cm

resultsFrom the measurements, the gamma passing rates for which the criteria were 3%/3 mm exceeded 95% for displacements in the head-to-tail direction if the repaint number was greater than 3 and the magnitude of the residual motions was less than 5.0 mm. In simulations with the cubic irradiation pattern, the gamma passing rates (with criteria of 2%/2 mm) exceeded 95% when the magnitude of the residual motions was 3.0 mm and the repaint number was greater than 3. When the repaint number was set to 4 in the VQA with the actual liver cases, the flatness results for Case 2 was minimal. For ideal repainting, the flatness results for all ports fell within ∼3.0% even when the magnitude of the residual motions was 5.0 mm if the repaint number was 6. However, the flatness was less than 3.0% for almost all ports if the magnitude of the residual motions was less than 3.0 mm with a repaint number of 4 in case of both types of repaint methods.

conclusionsAt our facility, carbon-ion radiotherapy can be provided safely to a moving target with residual motions of 3.0 mm magnitude and with a repaint number of 4.