Abstract:

Objective To explore the dosimetric characteristics of proton radiotherapy plan and photon radiotherapy plan for esophageal cancer. Methods Four patients who were admitted to Shandong Cancer Hospital and Institute from January 2024 to April 2024 with esophageal cancer （cervical， middle thoracic and total esophageal tube， as well as the lymphatic drainage areas involved） and required radiotherapy were selected as the research subjects. Intensity modulated proton therapy （IMPT） and intensity modulated radiation therapy （IMRT） plans were designed respectively based on the clinical target volume and the dose constraints for organs at risk （OARs）. Dosimetric parameters， including conformity index （CI）， homogeneity index （HI）， gradient index （GI） for target coverage， as well as OARs dosimetric parameters were evaluated. The volume of additional dose deposition in the body was compared by assessing regions receiving 10%， 30%， and 50% of the prescription dose. Results For all four cases， IMPT plans yielded lower HI values （0.12， 0.10， 0.06， and 0.08） than IMRT plans （0.15， 0.13， 0.10， and 0.11）， and the GI values of IMPT plans （3.11， 3.21， 2.43， and 2.72） was lower than IMRT plans （4.52， 5.14， 3.09， and 3.92）. Moreover， the CI of the IMPT plans （0.59， 0.60， 0.77， and 0.72） was inferior to IMRT plans （0.81， 0.77， 0.91， and 0.85）. Compared with the IMRT plans， in the whole lung dose indicators of the IMPT plans for the 4 patients， V₅ decreased by 34.1%， 55.0%， 79.7% and 60.3%， respectively； V₂₀ decreased by 48.3%， 43.9%， 65.8% and 40.8%， respectively， and D_mean decreased by 43.4%， 57.2%， 76.2% and 45.4%， respectively. V₃₀ of the heart decreased by 36.2%， 45.3%， 40.1% and 52.4%， respectively， and D_mean of heart decreased by 96.6%， 57.9%， 58.5% and 55.3%， respectively. For the middle and lower thoracic target area， the liver was significantly protected in the IMPT plan （D_mean decreased by 76.0% compared with the IMRT plan）. In terms of the additional dose deposition in the patient's body， IMPT plans reduced the volumes receiving 10%， 30% and 50% of the prescription dose by 45.0%-61.4%， 41.2%- 61.8% and 34.8%-61.6%， respectively， compared with the IMRT plans. Conclusions By comparing the dosimetric parameters of IMPT and IMRT plans for 4 cases of esophageal cancer， the IMPT plans have advantages in reducing the doses to lung tissue， heart， and liver， and can also reduce additional dose deposition in the patient's body.

Key words: Esophageal neoplasms, Radiotherapy, Proton therapy, Radiotherapy dosage