Real-time magnetic resonance imaging guided accelerator in stereotactic body radiation therapy for non-small cell lung cancer

Abstract

Background: Stereotactic body radiotherapy (SBRT) is crucial for lung tumor treatment, but facing challenges like intra-fractional anatomical changes and organ risks. Magnetic resonance-guided online adaptive SBRT (MRg-SBRT) is an innovative technique promising safer delivery of ablative doses and protect organ at risk (OAR). This study aimed to investigate the feasibility of the whole process of MRg-SBRT for non-small cell lung cancer (NSCLC) patients.

Methods: Physical parameters of radiotherapy for 23 cases of NSCLC who underwent MRg-SBRT were retrospectively analyzed. This included patients' treatment course, planned target volume (PTV), target area coverage, and OAR recipient volume. The focus was on inter- and intra-fraction MR real-time monitoring to correct off-target. Local control and adverse event outcomes of patients' SBRT treatment were also retrospectively analyzed.

Results: All 23 patients completed treatment on time without any treatment interruptions or pauses due to the MR. Tumor movement was predominantly in the superior-inferior (SI) directions through Elekta Unity real-time online monitoring. The baseline plan was altered in four patients, and an adaptive plan was used to correct inter- and intra-fraction off-targeting in a timely manner. The prescribed dose coverage for PTV was 95.3%, with a median bilateral lung volume 20 (V20) GY of 6.3%, and a maximal dose to the spinal cord of 117.3 cGy. The response results showed that the disease control rate (DCR) was 100% with an objective response rate (ORR) of 82.6%. Follow-up results showed an acute grade one to two pneumonia incidence of 82.6% and grade three pneumonias in one patient.

Conclusions: MRg-SBRT can guide treatment plans for the clinical needs of SBRT for lung cancer patients, especially for old patients, proving the feasibility of SBRT for lung lesions with MRg-SBRT, and online real-time monitoring reduces intra- and inter-fraction off-targeting, and guarantees the treatment efficiency of patients without significantly increasing the incidence of serious adverse events.

Keywords: Magnetic resonance-guided radiotherapy (MR-guided radiotherapy); non-small cell lung cancer (NSCLC); stereotactic body radiotherapy (SBRT).

Figure 1

Real time MR before the first radiation therapy. The green line is the PTV. MR, magnetic resonance; PTV, planning volume target.

Figure 2

Progression free survival of all patients.