2236 - Automated Analysis of Log Files from Gated Delivery of Stereotactic Body Radiotherapy Using Motion Management in a 1.5 T MR-Linac: A Multi Institution Report

02:30pm - 04:00pm PT

Hall F

Screen: 20

POSTER

Presenter(s)

Ergys Subashi, PhD - MD Anderson Cancer Center, Houston, TX

E. D. Subashi¹, L. McCullum², G. Hutchinson³, S. Xing⁴, J. Yang¹, Y. Ding¹, P. Balter¹, J. Wang¹, I. Taranenko⁵, M. Hinojosa⁵, N. Tyagi⁴, and D. Hyer³; ¹Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, TX, ²UT MD Anderson Cancer Center UTHealth Houston Graduate School of Biomedical Sciences, Houston, TX, ³University of Iowa Hospitals and Clinics, Department of Radiation Oncology, Iowa City, IA, ⁴Department of Medical Physics, Memorial Sloan Kettering Cancer Center, New York, NY, ⁵Elekta Inc, Atlanta, GA

Purpose/Objective(s): The comprehensive motion management (CMM) upgrade in the 1.5 T MR-Linac enables gated treatments triggered by respiratory (RP) and non-respiratory (NRP) motion. We introduce a framework for automated analysis of machine log files and report preliminary results from the first three US institutions with a clinical implementation of CMM.

Materials/Methods: Delivery and CMM log files were used to extract and estimate the position of the target during measurements with cine MRI and while the treatment beam was on. Motion range was calculated as the 95^th percentile (p95) spread of the distribution of the target position. Beam-on motion was further separated into drift and respiratory motion by applying a low pass (LP) filter with a moving average window of 20 sec and a high pass (HP) filter with a frequency cutoff of 0.05 Hz. Spectral analysis was used to identify the dominant frequencies of the position vector. The duty cycle was separated based on CMM vs non-CMM events and estimated as the percent fraction of time during which each event did not hold treatment delivery. Eight patients/institution (4 RP + 4 NRP gated treatments) undergoing SBRT with five fractions or less were pooled for analysis. Institution-specific procedures were used for immobilization, simulation, treatment planning, gating strategy, and adaptation.

Results: A total of 50 and 38 fractions were analyzed for NRP and RP gated treatments. Median (IQR) delivery time was 12.7 (1.2) mins and 15.9 (4.2) mins, respectively. Table 1 summarizes the median (IQR) of beam-on motion range and the duty cycle from each event. For both gating strategies, median p95 along each cardinal axis was significantly different during monitoring and beam on. Additionally, there was a significant negative correlation between the range of measured motion and CMM duty cycle. Median (IQR) frequency of CMM beam-hold events due to low prediction accuracy or low tracking quality was 2.7 (18.5) % and 9.1 (37.8) %. The dominant frequencies estimated from power spectral analysis of the position vector were centered around respiratory motion and measurement noise.

Conclusion: An automated tool for CMM log file analysis complements current procedures for evaluating motion management strategy and extends longitudinal quality assurance measurements of gated treatments in the 1.5 T MR-Linac.

Abstract 2236 - Table SEQ Table \* ARABIC 1: Median (IQR) of motion range during beam-on and duty cycle for all SBRT treatments

	NRP			RP
	LR	AP	SI	LR	AP	SI
p95 [mm]	0.4 (0.6)	1.2 (0.9)	2.0 (1.3)	1.7 (1.6)	2.9 (1.9)	6.8 (2.7)
Prob (p95 < 3 mm) [%]	98	96	80
Prob (p95 < 10 mm) [%]				100	100	89
p95 LP [mm]	0.3 (0.4)	0.9 (0.8)	1.4 (0.8)	1.2 (1.1)	1.2 (0.8)	3.1 (2.2)
p95 HP [mm]	0.3 (0.3)	0.5 (0.4)	1.0 (0.6)	1.2 (1.0)	2.2 (1.5)	5.3 (2.2)
CMM Duty Cycle [%]	96.6 (2.2)			83.3 (14.2)
Non-CMM Duty Cycle [%]	56.2 (5.0)			61.1 (7.7)
Total Duty Cycle [%]	48.3 (7.5)			45.5 (10.1)