RESUMEN
Objective To investigate the design and manufacture of 3D printed compensator in electron radiation therapy for Merkel cell carcinoma,and to verify the feasibility of this technique in electron radiation therapy.Methods Computed tomography was used to collect images of a human head phantom.The delineation of target volume of Merkel cell carcinoma was simulated in the planning system and a radiotherapy plan was formulated after adding the compensator.The compensator was printed out by a 3D printer and fixed on the head phantom.A second CT scan was performed to make a new treatment plan.For the two plans,several planes parallel to the beam were selected to calculate gamma passing rates.The actual dose distribution was measured using disposable films.The gamma passing rate was compared between the film system and the planning system.The conformity index (CI) and the heterogeneity index (HI) of target volume were compared between the plans using the printed compensator and the conventional compensator of the same thickness.Comparison between the two plans was made by paired t test.Results Using the dose distribution of the plan with simulated compensator,the gamma passing rate was 94.7±2.3％ in the plan with 3D printed compensator.Using the dose distribution measured by the film,the gamma passing rate was 96.6％ in the plan with 3D printed compensator.Compared with the conventional compensator,the 3D printed compensator achieved a significantly elevated CI (0.85 vs.0.69,P=0.004) and a slightly improved HI (1.30 vs.1.26,P=0.001).Conclusions The conformal dose distribution provided by 3D printed compensator for tumors at different depths meets the clinical need.