Journal Article

Impact of interplay effects on spot scanning proton therapy with motion mitigation techniques for lung cancer: SFUD versus robustly optimized IMPT plans utilizing a four-dimensional dynamic dose simulation tool

Yagihashi, Takayuki, Nagata, Hironori, Minagawa, Yumiko, Shiraishi, Sachika, Inoue, Tatsuya, Nitta, Kazunori, Matsumoto, Kazuki, Chang, Weishan, Tokuuye, Koichi, Omura, Motoko, Shirata, Ryosuke, Yamano, Akihiro, Yamanaka, Masashi, Shimo, Takahiro

2024

Overview

Background The interaction between breathing motion and scanning beams causes interplay effects in spot-scanning proton therapy for lung cancer, resulting in compromised treatment quality. This study investigated the effects and clinical robustness of two types of spot-scanning proton therapy with motion-mitigation techniques for locally advanced non-small cell lung cancer (NSCLC) using a new simulation tool (4DCT-based dose reconstruction). Methods Three-field single-field uniform dose (SFUD) and robustly optimized intensity-modulated proton therapy (IMPT) plans combined with gating and re-scanning techniques were created using a VQA treatment planning system for 15 patients with locally advanced NSCLC (70 GyRBE/35 fractions). In addition, gating windows of three or five phases around the end-of-expiration phase and two internal gross tumor volumes (iGTVs) were created, and a re-scanning number of four was used. First, the static dose (SD) was calculated using the end-of-expiration computed tomography (CT) images. The four-dimensional dynamic dose (4DDD) was then calculated using the SD plans, 4D-CT images, and the deformable image registration technique on end-of-expiration CT. The target coverage (V 98%, V 100% ), homogeneity index (HI), and conformation number (CN) for the iGTVs and organ-at-risk (OAR) doses were calculated for the SD and 4DDD groups and statistically compared between the SD, 4DDD, SFUD, and IMPT treatment plans using paired t-test. Results In the 3- and 5-phase SFUD, statistically significant differences between the SD and 4DDD groups were observed for V 100% , HI, and CN. In addition, statistically significant differences were observed for V 98% , V 100% , and HI in phases 3 and 5 of IMPT. The mean V 98% and V 100% in both 3-phase plans were within clinical limits (> 95%) when interplay effects were considered; however, V 100% decreased to 89.3% and 94.0% for the 5-phase SFUD and IMPT, respectively. Regarding the significant differences in the deterioration rates of the dose volume histogram (DVH) indices, the 3-phase SFUD plans had lower V 98% and CN values and higher V 100% values than the IMPT plans. In the 5-phase plans, SFUD had higher deterioration rates for V 100% and HI than IMPT. Conclusions Interplay effects minimally impacted target coverage and OAR doses in SFUD and robustly optimized IMPT with 3-phase gating and re-scanning for locally advanced NSCLC. However, target coverage significantly declined with an increased gating window. Robustly optimized IMPT showed superior resilience to interplay effects, ensuring better target coverage, prescription dose adherence, and homogeneity than SFUD. Trial registration : None.

• Publisher: BioMed Central,BioMed Central Ltd,BMC
• Subject: 4DDD / Aged / Analysis / Biomedical and Life Sciences / Biomedicine / Cancer / Cancer Research / Carcinoma, Non-Small-Cell Lung - radiotherapy / Care and treatment / Chemotherapy / CT imaging / Diagnosis / Female / Four-Dimensional Computed Tomography - methods / Health aspects / Humans / Imaging / IMPT / Interplay effects / Lung cancer / Lung cancer, Non-small cell / Lung Neoplasms - radiotherapy / Male / Methods / Middle Aged / Motion / Oncology / Organs at Risk - radiation effects / Patient outcomes / Proton therapy / Proton Therapy - methods / Radiology / Radiotherapy / Radiotherapy Dosage / Radiotherapy Planning, Computer-Assisted - methods / Radiotherapy, Intensity-Modulated - methods / Respiration / Robust optimization