ABSTRACT
Deterministic method is a numerical calculation method based on photon-electron coupled transport with high computational accuracy and speed, which has been widely applied in photon radiotherapy dose calculation in recent years. However, this method has been introduced into radiotherapy for only a short period of time, which has been rarely studied in China, and systematic understanding of its characteristics is still lacking. In this article, the principles of deterministic method, current development state and clinical application were reviewed, aiming to provide reference for carrying out relevant research.
ABSTRACT
Objective:To compare the dosimetric difference between intensity-modulated photon radiaotherapy (IMRT) planning and intensity-modulated proton radiotherapy (IMPT) planning for glioma.Methods:The clinical data of 15 glioma patients who underwent IMRT in ion medical center of the First Affiliated Hospital of USTC from November 2020 to April 2022 were retrospectively analyzed. IMRT planning and IMPT planning were designed for the image of each patient in the therapy planning system. Main dosimetric parameters were compared including plan target volume (PTV), coverage index (CI), dose homogeneity index (HI), and maximal dose (D max) and mean dose (D mean) of organs at risk between both plans. Results:There were no significant differences between IMRT planning and IMPT planning in terms of D max and D mean of PTV1 and PTV2, CI and HI (all P > 0.05). Compared with IMRT planning, brainstem D mean [6.92 GyE (0.09 GyE, 12.58 GyE) vs. 24.41 GyE (2.59 GyE, 34.18 GyE)], left optic nerve D max [0.78 GyE (0.04 GyE, 25.18 GyE) vs. 20.42 GyE (6.38 GyE, 37.17 GyE)], left optic nerve D mean [0.10 GyE (0.01 GyE, 11.63 GyE) vs. 9.74 GyE (2.99 GyE, 20.87 GyE)], right optic nerve D mean [1.57 GyE (0.13 GyE, 14.90 GyE) vs. 14.08 GyE (2.66 GyE, 23.67 GyE)], left len D max [0 GyE (0 GyE, 2.91 GyE) vs. 4.84 GyE (1.42 GyE, 5.48 GyE)], left len D mean [0 GyE (0 GyE, 1.73 GyE) vs. 3.84 GyE (1.25 GyE, 4.30 GyE)], right len D max [0.25 GyE (0.04 GyE, 4.55 GyE) vs. 4.28 GyE (1.58 GyE, 5.84 GyE)], right len D mean [0.16 GyE (0.01 GyE, 1.95 GyE) vs. 3.73 GyE (1.04 GyE, 4.86 GyE)], pituitary D max [6.97 GyE (0.18 GyE, 39.70 GyE) vs. 36.60 GyE (2.74 GyE, 45.19 GyE)], pituitary D mean [1.36 GyE (0.06 GyE, 13.85 GyE) vs. 24.74 GyE (2.42 GyE, 32.80 GyE)], hippocampus D max [5.10 GyE (0.24 GyE, 26.52 GyE) vs. 35.83 GyE (5.03 GyE, 46.11 GyE)], hippocampus D mean [0.36 GyE (0.04 GyE, 25.65 GyE) vs. 18.79 GyE (2.37 GyE, 28.10 GyE)] in IMPT planning were lower, and the differences were statistically significant (all P < 0.05). There were no statistical differences in brainstem D max [51.98 GyE (0.66 GyE, 53.43 GyE) vs. 53.29 GyE (3.87 GyE, 53.48 GyE)], right optic nerve D max [9.60 GyE (0.01 GyE, 43.32 GyE) vs. 25.37 GyE (3.45 GyE, 41.25 GyE)] of both plans (all P > 0.05). Conclusion:In the radiotherapy for glioma, IMRT and IMPT can meet the dose demand in clinic. Furthermore, IMPT planning can protect organs at risk and reduce radiation dose in hippocampus, brainstem, optic nerve, lens and pituitary.
ABSTRACT
Objective To investigate the dosimetric advantages of proton and heavy ion radiotherapy ( particle radiotherapy) for liver cancer adjacent to gastrointestinal tract. Methods Ten patients with liver cancer adjacent to gastrointestinal tract receiving radiotherapy were recruited in this study. The prescription was first given with 50 Gy ( RBE )/25 fractions to planning target volume 1 ( PTV-1 ) using proton irradiation,and then administered with 15 Gy ( RBE)/5 fractions to PTV-2 using carbon-ion irradiation. A simultaneous integrated boost regime was established using the same variables and prescription. The organ at risk ( OAR) constraints were referred to RTOG 1201. All plans were performed for dose evaluation after qualifying the OAR constraints. Results The dose coverage of 95％ of the prescribed dose ( V95) for PTV-1 from the photon plan (97.15％±4. 27％),slightly better than (96.25±6. 69％) from the particle plan (P=0. 049).The V95 of PTV-2 from the particle plan was (94.6％±6. 22％),comparable to (95.12％±3. 49％) from the photon plan (P=0. 277).The integral dose of Body-PTV-1 delivered by the particle plan was merely 39. 9％ of that delivered by the photon plan. The mean liver-GTV dose from the particle plan was only 81. 8％ of that from the photon plan. The low-dose irradiation to the stomach and duodenum from the particle plan was significantly lower than that from the photon plan. Conclusions The dose to the liver-gross tumor volume ( GTV) is the main factor limiting the increase of total dose to the tumors. When the absolute GTV in the liver is relatively large,particle radiotherapy can maintain comparable dose coverage to the tumors as the photon radiotherapy whereas significantly reduce the dose to the liver-GTV.