Dosimetric advantages of robust optimization combined with flattening filter free in treating cancer of the left breast

Hongying Luo; Jianlin Lou; Wei Feng; Guoping Shan; Kainan Shao; Yiwei Yang; Jianliang Zhou; Shengye Wang

Dosimetric advantages of robust optimization combined with flattening filter free in treating cancer of the left breast

Am J Transl Res. 2022 Nov 15;14(11):7985-7993. eCollection 2022.

Authors

Hongying Luo¹, Jianlin Lou², Wei Feng³, Guoping Shan³, Kainan Shao³, Yiwei Yang³, Jianliang Zhou¹, Shengye Wang³

Affiliations

¹ University of South China, School of Nuclear Science and Technology Hengyang 421001, Hunan, China.
² Department of Head & Neck Surgery, The Cancer Hospital of The University of Chinese Academy of Sciences (Zhejiang Cancer Hospital), Institute of Basic Medicine and Cancer (IBMC), Chinese Academy of Sciences Hangzhou 310022, Zhejiang, China.
³ Department of Radiation Physics, The Cancer Hospital of The University of Chinese Academy of Sciences (Zhejiang Cancer Hospital), Institute of Basic Medicine and Cancer (IBMC), Chinese Academy of Sciences Hangzhou 310022, Zhejiang, China.

PMID: 36505297
PMCID: PMC9730055

Abstract

Objective: By comparing the target dose distribution with or without the robust optimization, the dosimetric advantages of robust optimization and flattening filter free (FFF) in radiation therapy for postmastectomy cancer of the left breast was explored when part of the chest wall target was moved out in case of respiratory motion.

Materials and methods: This is a retrospective study. The data of 21 postmastectomy patients with cancer of the left breast from 2019 to 2020 were retrospectively collected. The planned target volume (PTV) dose was prescribed 50 Gy/25 fractions and the treatment plans were designed using 6 MV FFF X ray and volumetric modulated arc therapy (VMAT) technology in RayStation treatment planning system (TPS), with and without robust optimization. The movement of the target area of the internal chest wall (0.50 cm) caused by respiratory movement was simulated by moving the isocenter of the beams.

Results: When the chest wall target moved outward, the PTV target area D₉₈, D₉₅, D₂, conformity index (CI) and homogeneity index (HI) with robust optimization were better than those without robust optimization. The coverage rate of Planned Target Volume-Chest (PTV-T) V₅₀ with robust optimization was significantly higher than that with no-robust optimization (P<0.001). Clinical target volume (CTV) V₅₀ coverage with robust optimization was 14.49% higher than that with no-robust optimization. In terms of organ-at-risk parameters, the average spinal cord dose of the plan with robust optimization was 13.19% lower than that of the plan with no-robust optimization, and the Lung-L V₅ of the plan with no-robust optimization was slightly (1.94%) lower than that of the plan with robust optimization. There was no significant difference in machine execution efficiency between the two groups (P>0.05).

Conclusions: Robust optimization could be adopted in the postoperative radiotherapy planning for cancer in the left breast, for it ensures that the target dose coverage and the dose limit of organ-at-risk still meet the clinical requirements under condition of chest wall displacement caused by respiratory movement.

Keywords: Robust optimization; dosimetric characteristics; flatten filter free mode; postoperative left breast cancer; volumetric modulated arc therapy.