Abstract: ObjectiveTo compare target dosimetric distribution and normal tissue radiation between different static intensitymodulated radiation therapy (IMRT) plans and volumetric modulated arc therapy (VMAT), and to identify the best IMRT plan for lymphoma patients needed mediastinal radiation. MethodsA total of 11 patients with lymphoma who received first course radiotherapy in the mediastinal region after chemotherapy in Cancer Hospital & Shenzhen Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College from March 2017 to January 2019 were included in the study. There were 8 males and 3 females, 2 patients were in Ann Arbor stage ⅠⅡ, and 9 cases in ⅢⅣ stage. There were 6 patients with Hodgkin lymphoma (HL) and 5 patients with nonHodgkin lymphoma (NHL). Patients with HL and NHL were given prescript doses of 36 Gy and 50 Gy, respectively. Three plans were designed for each patient: static 5FIMRT, 7FIMRT and VMAT plan. The target dosimetric distribution, normal tissue radiation dose, and efficiency of each plan were evaluated. ResultsThe mean conformity index (CI) and homogeneity index (HI) values of plan target volume (PTV) in 5FIMRT, 7FIMRT, VMAT plan were 0.64±0.06, 0.67±0.05, 0.76±0.04 (F=17.045, P＜0.001) and 1.07±0.01, 1.07±0.01, 1.09±0.01 (F=9.258, P=0.001), respectively. VMAT showed significantly better CI than two static IMRT plans (both P<0.001), but worse HI (both P<0.001). The lungs low dose irradiation volume (V5) and high dose irradiation volume (V30) in 5FIMRT, 7FIMRT, VMAT plan were (43.98±7.77)%, (42.71±4.98)%, (55.92±8.16)% (F=8.281, P=0.001) and (8.19±2.97)%, (8.25±2.87)%, (7.53±3.16)% (F=0.140, P=0.870), respectively. The volume of low dose irradiation in lungs of VMAT plan was significantly higher than 5FIMRT and 7FIMRT plans (both P＜0.001), while high dose volume was no significant difference. The left and right breast low dose irradiation volume (V4) in 5FIMRT, 7FIMRT and VMAT plan were (24.29±8.14)%, (23.87±7.70)%, (80.17±22.92)% (F=14.505, P=0.005) and (22.12±13.28)%, (21.13±13.01)%, (81.77±20.76)% (F=13.938, P=0.006), respectively. VMAT showed significantly higher breast low dose irradiation volume than static IMRT plan (both P＜0.05). The number of monitor units and treatment time in 5FIMRT, 7FIMRT, VMAT plan were (1 622±281) MU, (1 729±286) MU, (411±75) MU (F=105.277, P<0.001) and (6.79±0.93) min, (7.42±0.95) min, (4.98±0.00) min (F=29.545, P＜0.001), respectively. VMAT showed significantly less monitor units than static IMRT (both P<0.001) and shorter treatment time (both P<0.001). ConclusionFor lymphoma patients who have the indication of mediastinal radiotherapy, VMAT is highly efficient and has no definite dose advantage, the static 5FIMRT or 7FIMRT plan has good conformal and uniform target area, and some organs at risk exposure is even lower.

Key words: Lymphoma, Radiotherapy planning, computer-assisted, Radiotherapy plan comparison