Dataset of “Long-term beam stability assessment of the CATHL carbon ion pencil beam scanning system for clinical radiotherapy”

Carbon ion pencil beam scanning (PBS) therapy offers superior dose conformity and enhanced biological effectiveness for cancer treatment. While several international facilities have reported long-term beam stability data, no comprehensive assessment has been published for the domestically developed CATHL carbon ion therapy system deployed in China. In this study, we present a systematic evaluation of beam delivery performance over an eight-month period (August 2025 to March 2026) at the Zhejiang Cancer Hospital Heavy Ion Medical Center. The assessment encompasses dose output consistency from weekly quality assurance (QA) measurements across 12 beam configurations in two clinical treatment rooms, as well as daily spot position accuracy and beam spot size characterization from 69,382 individual spot measurements across four beam nozzles. Statistical process control (SPC) analysis of dose output revealed a mean deviation of $+0.15\% \pm 0.73\%$ from reference values, with 95.4\% of all measurements falling within the $\pm 3\%$ clinical tolerance. Spot position accuracy yielded a mean radial error of $0.53 \pm 0.31$~mm, with 95.6\% of spots within the 1~mm acceptance criterion. Beam spot sizes ($\sigma$) ranged from 1.3 to 4.4~mm, consistent with Coulomb scattering physics, and exhibited no systematic temporal drift. Additional beam quality metrics including spot symmetry (skewness $|mean| < 0.008$), 2D roundness ($3.66 \pm 3.92$\%), and amplitude uniformity (CV $< 5$\%) further confirmed robust beam delivery performance. These results demonstrate that the CATHL carbon ion PBS system achieves beam stability comparable to established international facilities, supporting its suitability for clinical radiotherapy applications.