KEY POINTS
- This retrospective planning study included 25 posterior lung lesions treated with stereotactic body radiotherapy: 23 prescribed 50 Gy in 5 fractions and 2 prescribed 48 Gy in 4 fractions.
- Original clinical plans were compared with on-axis and off-axis optimized plans. Off-axis optimization shifted the isocenter toward the midsagittal plane, permitting shorter beam paths while reducing gantry–couch collision risk.
- Beam optimization reduced average lesion depth by 28.4% ± 14.4%. Compared with original plans, off-axis plans maintained planning target volume coverage while reducing mean lung dose from 2.50 to 2.36 Gy and lung V5, V10, and V20 from 445.1 to 385.0 cm³, 251.3 to 212.0 cm³, and 104.7 to 98.2 cm³, respectively.
- Off-axis and on-axis optimization produced broadly comparable dose–volume metrics. Off-axis planning also reduced spinal cord, chest-wall, skin, pericardial, airway, and esophageal doses relative to the original plans.
- In a representative multi-isocenter case, optimization reduced the 25 Gy isodose volume from 406.9 to 270.1 cm³, mean lung dose from 3.2 to 2.8 Gy, and chest-wall V30 from 79.5 to 44.0 cm³.
CLINICAL TAKEAWAY
Off-axis beam optimization may help preserve optimal beam paths for posterior lung lesions when collision constraints limit conventional geometry, particularly in multi-isocenter treatments. However, this was a retrospective planning analysis without systematic phantom or patient-specific delivery validation and without clinical toxicity outcomes, making it technically relevant rather than practice-changing.