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

Abstract

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 CTVhigh D95% in the nominal scenario relative to the prescription dose. Results In the nominal scenario, small‐spot IMPT delivered statistically significantly lower liver Dmean and V30Gy[RBE], lung Dmean, heart Dmean compared with VMAT. CTVhigh 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 V18Gy[RBE], liver V30Gy[RBE], stomach V45Gy[RBE], lung Dmean, V5Gy[RBE], and V20Gy[RBE], cord Dmax and D0.03boldcboldm3, liver Dmean, heart V20Gy[RBE], and V30Gy[RBE], but IMPT was significantly worse for CTVhigh D95%, D2boldcboldm3, and D5%‐D95%, CTVlow D95%, heart Dmean, and V40Gy[RBE], 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.

Volumetric modulated arc therapy versus intensity-modulated proton therapy in neoadjuvant irradiation of locally advanced oesophageal cancer

“…The use of proton beam therapy (PBT) in the radiooncological treatment of oesophagal carcinomas is the result of efforts to reduce the known toxicities further. Previously published dosimetric comparisons of PBT and IMRT indicate a considerable reduction of radiation exposure of organs at risk, especially regarding heart and lungs [23][24][25]. Welsh [26], in a dosimetric study, investigated the role of intensity-modulated proton therapy (IMPT) for advanced distal oesophagal tumors and showed a considerable reduction of the dose to the organs at risk compared to IMRT.…”

“…Likewise, Shiraishi [27] demonstrated a significant decrease in radiation exposure to the whole heart and to the cardiac structures comparing PBT vs IMRT. Liu [25] compared at planning level the potential of VMAT versus IMPT for distal oesophagal cancer patients. The study concluded that protons resulted in dosimetrically preferable plans compared to VMAT.…”

Beam angle comparison for distal esophageal carcinoma patients treated with intensity‐modulated proton therapy

“…58 Liu et al carried out a comparative study between small-spot IMPT and volumetric-modulated arc therapy (VMAT), and found that small-spot IMPT significantly improved sparing of heart, liver, and lungs with clinically acceptable plan robustness. 34 Most recently, Lin et al reported the result of a phase IIB trial that for locally advanced esophageal cancer, proton beam therapy (PBT) reduced the risk and severity of adverse events (AEs) while maintaining similar progression-free survival (PFS) when compared with IMRT. 59 Specifically for IMPT, different configurations may lead to different outcomes, such as spot sizing and spacing.…”

Assessing the Need for Adjusted Organ-at-Risk Planning Goals for Patients Undergoing Adjuvant Radiation Therapy for Locally Advanced Breast Cancer with Proton Radiation

“…There now exists a significant body of in silico and in vivo literature describing the potential to decrease integral RT dose exposure to normal tissues when PBT is used across several body sites. [33][34][35][36][37][38][39][40][41] For breast cancer specifically, small series have described significantly reduced cardiac and pulmonary exposures when RT is delivered with photons compared with protons, with particular emphasis on cardiac structures. [20][21][22]42 However, clinicians and national clinical trial protocols 43 continue to base RT planning goals (and, by extrapolation, plan quality) on historical photon constraints.…”