AUTHOR=Li Longhao , Yi Xin , Cui Haixia , Zhao Xuemei , Dang Jun , Jiang Qingfeng , Li Ying 

TITLE=Simultaneous Integrated Boost Intensity-Modulated Radiotherapy for Locally Advanced Drug-Resistant Gastrointestinal Stromal Tumors: A Feasibility Study

JOURNAL=Frontiers in Oncology

VOLUME=Volume 10 - 2020

YEAR=2020

URL=https://www.frontiersin.org/journals/oncology/articles/10.3389/fonc.2020.545892

DOI=10.3389/fonc.2020.545892

ISSN=2234-943X

ABSTRACT=Background: Locally advanced drug-resistant gastrointestinal stromal tumors (LADR-GISTs) has been an emerging clinical problem, with relatively few therapeutic schemes. While radiotherapy has not often been considered for GISTs, radiation therapy could be a valuable contributing modality. The aim of our study is to explore a safe and effective radiation regimen for LADR-GISTs.
Methods: 3 patients with LADR-GISTs were treated with simultaneous integrated boost intensity-modulated radiation therapy (SIB-IMRT) plans. In the SIB-IMRT plans, GTV was divided into GTV-outer, GTV-mid and GTV-center. And the prescribed dose of PGTV and GTV-outer both set to 50.4 Gy in 28 fractions. GTV-mid and GTV-center was simultaneously boosted to 60-62 Gy and 62-64 Gy respectively. For comparison purposes, conventional IMRT (Con-IMRT) plans with uniform dose distribution were generated in the same optimization objectives without a dose boost to GIV-mid and GTV-center. All these plans were optimized to deliver at least 95% of the prescription dose to PGTV. Isodose distribution, dose profiles, conformity indexes (CIs), monitor units (MUs), and dose volume histogram (DVH) was evaluated for each individual patient. After the three patients treated with SIB-IMRT plans, the relative changes in the tumor size and CT values were also tracked in CT examination.
Results: Compared with the Con-IMRT plans, there was a significant increase from D95 to D2 of the GTV in the SIB-IMRT plans. With steeper dose gradients in the dose profiles, the SIB-IMRT plans mainly accumulated higher dose to GTV-mid and GTV-center by delivering extra 93 MUs in average. However, there was no significant difference in CIs and OARs DVH. In the follow-up, the relative changes in tumor size and CT values of three patients were up to the Choi criteria and the three patients were all assessed as partial response.
Conclusions: The proposed SIB-IMRT technique may provide a new mean of achieving objective response and prolonging survival in selected GISTs patients.