An Investigation of Non-Coplanar Volumetric Modulated Radiation Therapy for Locally Advanced Unresectable Pancreatic Cancer Using a Trajectory Optimization Method.

Gong Wang,Hongqing Zhuang,Hao Wang,Ruijie Yang

doi:10.3389/fonc.2021.717634

Abstract

PurposeThis study was conducted in order to develop a trajectory optimization algorithm for non-coplanar volumetric modulated arc therapy (VMAT) and investigate the potential of organs at risk (OARs) sparing in locally advanced pancreatic cancer patients using non-coplanar VMAT.Methods and MaterialsFirstly, a cost map that represents the ray–OAR voxel intersections at each source position was generated using a ray-tracing algorithm. A graph search algorithm was then used to determine the least-cost path from the cost map. Lastly, full arcs or partial arcs were selected based on the least-cost path to generate the non-coplanar VMAT (ncVMAT) trajectories. Clinical coplanar VMAT (coVMAT) plans for 11 patients diagnosed with locally advanced unresectable pancreatic cancer (LAPC) receiving 45 to 70 Gy in 25 fractions were replanned using non-coplanar VMAT trajectories. Both coplanar and non-coplanar plans were normalized to cover 95% of the PTV45 Gy volume with a prescription dose of 45 Gy. The conformity index (CI), homogeneity index (HI), PTV coverage, and dose to the OARs were compared between coVMAT and ncVMAT plans.ResultsWith ncVMAT, the mean coverage of PTV50 Gy, PTV54 Gy, PTV60 Gy, and PTV70 Gy increased significantly. The mean conformity index of PTV45 Gy, PTV54 Gy, and PTV70 Gy was also improved in the ncVMAT plans. Compared with coVMAT plans, the ncVMAT plans resulted in significantly lower doses to the spinal cord, bilateral kidneys, stomach, and duodenum. The maximum dose to the spinal cord decreased by 6.11%. The mean dose to the left and right kidneys decreased by an average of 5.52% and 11.71%, respectively. The D max, D mean, and D 15% of the stomach were reduced by an average of 7.45%, 15.82%, and 16.79%, separately. The D 15% and D mean of the duodenum decreased 6.38% and 5.64%, respectively.ConclusionA trajectory optimization algorithm was developed for non-coplanar VMAT. Compared with conventional coplanar VMAT, non-coplanar VMAT resulted in improved coverage and conformity to the targets. The sparing of OARs was significantly improved in non-coplanar VMAT compared with coVMAT plans for locally advanced pancreatic cancer.

Highlights

According to the American Cancer Society, pancreatic cancer was the seventh leading cause of cancer-related death worldwide for both genders in 2018 [1]
We present an implementation of non-coplanar VMAT technique which utilized cost map generation and trajectory optimization algorithm for OAR dose sparing in locally advanced pancreatic cancer (LAPC) patients
This study investigates the organ at risk sparing in locally advanced pancreatic cancer patients using the non-coplanar VMAT technique

Summary

Introduction

According to the American Cancer Society, pancreatic cancer was the seventh leading cause of cancer-related death worldwide for both genders in 2018 [1]. Conventionally fractionated radiotherapy which delivers 40 to 60 Gy in 1.8–2.0 Gy per fraction showed minimal to no local tumor control benefit for patients with locally advanced pancreatic cancer (LAPC) [4]. A study that investigated the outcomes of patients treated with SBRT using the National Cancer Data Base (NCDB) showed that the median overall survival (OS) (13.9 vs 11.6 months) and the 2-year OS rate (21.7% vs 16.5%) were significantly higher with SBRT versus conventionally fractionated radiation therapy [5]. The reason why SBRT resulted in a better survival rate is that SBRT allows to deliver a higher biological effective dose (BED) to patients and higher BED is associated with better local control. The sparing of radiosensitive gastrointestinal organs such as the stomach, small intestines, colon, and duodenum near the pancreas becomes the main difficulty of dose escalation in LAPC patients [4]

Methods

Results

Conclusion