1. Department of Radiotherapy, Navy 971 Hospital of Chinese People’s Liberation Army, Qingdao Shandong 266000, China丨
2. Department of Radiotherapy, The Sixth Medical Center of PLA General Hospital, Beijing 100048, China
Abstract：Objective To explore the dosimetric differencees of gamma knife, intensity modulated radiation therapy (IMRT) and
volumetric modulated arc therapy (VMAT) planning in patients with lung tumor treated by hypofractionated radiotherapy. And to
analyze the advantages and disadvantages of three stereotactic therapies in the treatment of lung cancer. Methods A total of 20
patients with lung metastases who received radiotherapy in Navy 971 Hospital from 2018 to 2020 were selected. Using the planning
system, 20 patients were treated with gamma knife, IMRT and VMAT. The dose, volume and other related parameters of the target
and the organs at risk were analyzed by dose volume histogram, and statistical analysis was performed to compare the dosimetric
differences between the three treatment plans. Results The levels of V5, V10, V15, V20, V25, V30 in the affected lung and whole lung,
gamma knife is lower than those in IMRT and VMAT (P<0.05). IMRT was lower than V10 and V15 of VMAT (P<0.05). However,
V25 and V30 were slightly higher than VMAT, there was no significant statistical difference (P>0.05). The average dose of Dmean in the
affected lung of the three treatments was basically the same (P>0.05). There was no significant difference in the average dose Dmean
of whole lung between gamma knife and IMRT (P=0.106), but gamma knife was slightly lower than VMAT (P=0.025). Treated
with gamma knife, the V20, V30, V40 of heart, overall were better than accelerator-based IMRT and VMAT, except that V40 had little
difference compared with VMAT (P=0.086), other differences were statistically significant (P<0.05). The average cardiac dose of
gamma knife Dmean was lower than that of IMRT (P=0.007), but there was no significant difference among other groups (P>0.05).
The maximum dose of spinal cord treated with gamma knife was lower than that of IMRT (P<0.05), but there was no significant
difference between IMRT and VMAT (P=0.411). The esophageal Dmean of gamma knife, IMRT and VMAT increased sequentially(P<0.05). The maximum dose of Dmax gamma knife was significantly lower than that of VMAT (P=0.029). But there were no
significant differences between gamma knife and IMRT or between IMRT and VMAT (P>0.05). The conformity index of IMRT
was better than that of gamma knife and VMAT (P<0.05), but there was no significant difference between gamma knife and VMAT
(P=0.866). The homogeneity index of gamma knife was significantly higher than that of IMRT and VMAT (P<0.05), the VMAT
was slightly higher than that of IMRT (P=0.008). The Dmax and Dmean of the target area treated with gamma knife were significantly
higher than those of IMRT and VMAT (P<0.05), and the VMAT was slightly higher than that of IMRT (P<0.05). Conclusion The
dose distribution in the target area of gamma knife is the most uneven, and the conformity index is slightly worse, but it can better
protect the surrounding normal lung tissue and other organs at risk, especially suitable for smaller intralobar tumors. IMRT used in
stereotactic body radiation therapy (SBRT) reduces the range of low-dose radiation in the lung compared with VMAT, but the range
of high-dose radiation is slightly larger. VMAT should be used with caution in the application of SBRT in intralobar tumors.
