An integrated system for measuring 3D dose distributions of carbon-ion pencil beams in regular QA practice

The accurate measurement of three-dimensional (3D) dose distribution of carbon-ion pencil beams in water is crucial for regular quality assurance (QA) practice. Although ionization chambers scanned in a water tank is conventionally used for this purpose, these measuring methods are time-consuming and labor-intensive. In addition, the beam of Heavy Ion Medical Machine (HIMM) changes continuously in each extracted duration, these methods cannot obtain the accurate 3D dose distribution. To solve these problems, an integrated system (PBDOSE) is conceived and established, which employs multi-strip ionization chambers (MSICs) to measure 2D lateral profile dose distributions. The lateral profile dose distribution in the context of various depths is measured by a mobile MSIC and normalized by the measurement of a reference MSIC to reduce the effect of beam instability. On this basis, a 3D dose distribution is created by stacking those profiles in depth direction. By conducting a single depth scan within 3 min at HIMM, information such as the 3D dose distribution, lateral contour images, the Bragg curve, beam spot size, beam position, incident direction, and energy of the beam can be obtained. The Bragg curve acquired from PBDOSE with statistical uncertainties of 1.5% was almost identical to those measured by a commercial water phantom. Besides that, the lateral profiles revealed a remarkable agreement with Gafchromic EBT3 film measurements within differences less than 0.1 mm. PBDOSE shows great prospects in the accurate and efficient measurement of 3D dose distribution for carbon-ion therapy, and the clinical application of this system will improve the efficiency of regular QA procedures to a great extent. •A new method for rapid measurement of 3D dose distribution of carbon-ion pencil beams is developed.•Two MSICs are used for synchronous measurement to reduce the impact of beam instability on the measurements.•PBDOSE usually takes less than 3 min to perform a single depth scan in clinical practice at HIMM.•In addition to obtaining the 3D dose distribution, PBDOSE can also measure some parameters of the incident beam.•The clinical application of PBDOSE will improve the work efficiency of medical physicists in the QA practice.