2998 - Enhancing Multi-Lesion Lung SBRT Through Off-Axis Beam Optimization to Minimize Field Interplay

12:30pm - 01:45pm ET

Poster Hall - Exhibit Hall A

Screen: 27

POSTER

Presenter(s)

Reza Farjam, PhD - Johns Hopkins Radiation Oncology Bayview Medical Center, Baltimore, MD

M. Tajik-Mansoury, K. R. Voong, J. N. Lee, R. Kaur, and R. Farjam; Dept. of Radiation Oncology and Molecular Radiation Sciences, Johns Hopkins University School of Medicine, Baltimore, MD

Purpose/Objective(s):

Patients with oligometastatic lung cancer often require stereotactic body radiotherapy (SBRT) to multiple spatially distinct lesions, typically delivered using a multi-isocenter coplanar approach, which increases field overlap and normal tissue toxicity. While beam optimization can reduce field interplay, selection of optimal beam set for posterior lesions remain challenging due to gantry–couch collision constraints. To address these challenges, we developed an off-axis beam optimization framework designed to minimize field overlap and integral dose in multi-lesion coplanar lung SBRT. This approach enables safer, more efficient dose delivery with direct clinical relevance for multi-lesion coplanar treatment including posterior targets.

Materials/Methods:

Off-axis beam optimization enhances therapeutic gain by minimizing treatment depth from the beam’s-eye view while positioning the isocenter in the midsagittal plane to avoid collisions when necessary. Dosimetric differences, including plan conformity, target coverage, and doses to organs at risk (OARs), were compared across non-optimized, on-axis, and off-axis optimized beam sets using 25 posterior lung lesions. Plan efficiency was evaluated using isodose line volumes (IDLV_2.5–25 Gy), and reductions in field overlap were demonstrated in a complex multi-isocenter case.

Results: Optimized beamsets significantly reduced mean lung dose (252.1 ± 103.7 vs 236.5 ± 99.2 cGy, p < 1.3×10?8), lung V5 (445.1 ± 183.7 vs 385.0 ± 168.0 cc, p < 7.1×10?6), V10 (251.3 ± 123.9 vs 210.6 ± 107.4 cc, p < 8.1×10??), and V20 (104.7 ± 63.4 vs 98.2 ± 59.5 cc, p < 6×10?4), with improved sparing of other OARs and preserved target coverage and conformity. Off-axis optimization was dosimetrically equivalent to standard plans and eliminated gantry–couch collision risk. In a representative multi-lesion case, and decreased from 406.9 cc and 668.9 cc to 270.1 cc and 502.1 cc, respectively, with chest wall V30 reduced from 79.5 cc to 44.0 cc.

Conclusion:

Off-axis beam optimization improves multi-lesion coplanar lung SBRT by enabling optimal beam geometry, reducing integral dose, and minimizing normal tissue exposure, particularly in complex multi-isocenter cases where field overlap limits safety and efficiency.