Dosimetric comparison of distal esophageal carcinoma plans for patients treated with small‐spot intensity‐modulated proton versus volumetric‐modulated arc therapies

摘要

Background Esophageal carcinoma is the eighth most common cancer in the world. Volumetric‐modulated arc therapy (VMAT) is widely used to treat distal esophageal carcinoma due to high conformality to the target and good sparing of organs at risk (OAR). It is not clear if small‐spot intensity‐modulated proton therapy (IMPT) demonstrates a dosimetric advantage over VMAT. In this study, we compared dosimetric performance of VMAT and small‐spot IMPT for distal esophageal carcinoma in terms of plan quality, plan robustness, and interplay effects. Methods 35 distal esophageal carcinoma patients were retrospectively reviewed; 19 patients received small‐spot IMPT and the remaining 16 of them received VMAT. Both plans were generated by delivering prescription doses to clinical target volumes (CTVs) on phase‐averaged 4D‐CT's. The dose‐volume‐histogram (DVH) band method was used to quantify plan robustness. Software was developed to evaluate interplay effects with randomized starting phases for each field per fraction. DVH indices were compared using Wilcoxon rank‐sum test. For fair comparison, all the treatment plans were normalized to have the same CTVsubhigh/sub Dsub95%/sub in the nominal scenario relative to the prescription dose. Results In the nominal scenario, small‐spot IMPT delivered statistically significantly lower liver Dsubmean/sub and Vsub30Gy[RBE]/sub, lung Dsubmean/sub, heart Dsubmean/sub compared with VMAT. CTVsubhigh/sub dose homogeneity and protection of other OARs were comparable between the two treatments. In terms of plan robustness, the IMPT and VMAT plans were comparable for kidney Vsub18Gy[RBE]/sub, liver Vsub30Gy[RBE]/sub, stomach Vsub45Gy[RBE]/sub, lung Dsubmean/sub, Vsub5Gy[RBE]/sub, and Vsub20Gy[RBE]/sub, cord Dsubmax/sub and , liver Dsubmean/sub, heart Vsub20Gy[RBE]/sub, and Vsub30Gy[RBE]/sub, but IMPT was significantly worse for CTVsubhigh/sub Dsub95%/sub, , and Dsub5%/sub‐Dsub95%/sub, CTVsublow/sub Dsub95%/sub, heart Dsubmean/sub, and Vsub40Gy[RBE]/sub, requiring careful and experienced adjustments during the planning process and robustness considerations. The small‐spot IMPT plans still met the standard clinical requirements after interplay effects were considered. Conclusions Small‐spot IMPT decreases doses to heart, liver, and total lung compared to VMAT as well as achieves clinically acceptable plan robustness. Our study supports the use of small‐spot IMPT for the treatment of distal esophageal carcinoma.