Abstract:

Objective To compare the dosimetric differences and characteristics between carbon ion radiotherapy （CIRT） plans and photon radiotherapy plans [intensity-modulated radiation therapy （IMRT） and volumetric modulated arc therapy （VMAT）] in patients with thoracic esophageal cancer. Methods A total of 46 patients with thoracic esophageal cancer who received radiotherapy at Gansu Provincial Hospital and Anyang Tumor Hospital from March 2024 to February 2025 were enrolled，including 19 treated with IMRT and 27 with VMAT. The CT images of all patients were imported into the CIRT planning system CIPlan 2.0，and CIRT plans were generated based on the same patient data. Under the premise of meeting clinical requirements，the dosimetric parameters differences of the target volume and organs at risk were compared among the CIRT，IMRT，and VMAT plans. Results For target dose parameters，the D_2% values of the planning target volume （PTV） in the IMRT，VMAT，CIRT plans were （55.50±1.75），（55.38±1.75），（57.38±0.63） Gy，respectively； the D_98% values were 50.26 （50.04，50.88），49.65 （49.21，50.37），49.96 （49.26，50.62） Gy，respectively； the average dose （Avg） values were 52.79 （52.06，53.64），52.90 （52.32，53.35），53.30 （53.22，53.36） Gy，respectively； the conformity index （CI） values were 0.69 （0.65，0.75），0.75 （0.65，0.83），0.78 （0.74，0.82），respectively； and the homogeneity index （HI） values were 0.10±0.03，0.12±0.04，0.14±0.02，respectively，with statistically significant differences （F=32.93，P<0.001； H=9.39，P=0.009； H=9.90，P=0.007； H=10.94，P=0.004； F=15.03，P<0.001）. Compared with IMRT，VMAT showed a lower D_98% and a higher HI，CIRT showed higher D_2%，CI，and HI （all P<0.05）. Compared with VMAT，CIRT showed higher D_2%，Avg，CI，and HI （all P<0.05）. For organs at risk，the whole-lung V₅ values in the IMRT，VMAT，CIRT plans were （34.26±14.13）%，（37.47±11.35）%，（5.79±2.72）%，respectively； the V₁₀ values were （23.56±10.18）%，（26.26±8.52）%，（4.63±2.14）%，respectively； the V₁₅ values were （17.75±8.32）%，（18.36±6.57）%，（3.95±1.88）%，respectively； the V₂₀ values were （12.55±5.91）%，（12.14±4.86）%，（3.12±1.65）%，respectively； and the V₃₀ values were （4.34±1.89）%，（4.77±2.51）%，（1.80±1.01）%，respectively，with statistically significant differences （F=130.32，P<0.001； F=109.76，P<0.001； F=81.31，P<0.001； F=63.40，P<0.001； F=29.52，P<0.001）. Compared with IMRT and VMAT，CIRT showed lower V₅，V₁₀，V₁₅，V₂₀，V₃₀ values （all P<0.05）. The spinal cord D_max in the IMRT，VMAT，and CIRT plans were 33.13 （28.02，37.39），35.07 （31.90，38.73），7.13 （5.42，17.84） Gy，respectively. The heart V₃₀ values were 10.19 （0.00，20.31）%，10.47 （0.21，20.85）%，1.88 （0.00，4.77）%，respectively，and the heart V₄₀ values were 3.82 （0.00，7.85）%，2.53 （0.00，4.34）%，0.90 （0.00，2.15）%，respectively，with statistically significant differences （H=68.38，P<0.001； H=10.83，P=0.004； H=7.92，P=0.019）. Compared with IMRT and VMAT，CIRT showed lower spinal cord D_max，heart V₃₀，and heart V₄₀ （all P<0.05）. Conclusions For patients with thoracic esophageal cancer undergoing radiotherapy，CIRT has clear dosimetric advantages over IMRT and VMAT in protecting organs at risk. It can significantly reduce the doses to the lungs，heart，and spinal cord while maintaining adequate target dose coverage. IMRT shows better dose homogeneity within the target volume，whereas CIRT demonstrates superior target conformity.

Key words: Esophageal neoplasms, Radiotherapy, Radiotherapy dosage