# Quantitative beam optimization for radiotherapy of peripheral lung lesions: A pilot study in stereotactic body radiotherapy

## TL;DR

This study introduces a new method for optimizing radiation beam angles in lung cancer treatment, which reduces radiation spread and improves treatment precision.

## Contribution

A novel beam optimization approach for SBRT is introduced, using therapeutic gain and lesion depth to improve treatment plans.

## Key findings

- The new beam optimization reduced treatment depth by an average of 20.03% across 25 cases.
- Plan size reductions were statistically significant for multiple isodose lines (IDLV25 to IDLV5).
- Lesion depth and plan size were inversely proportional, suggesting a robust metric for beam-set selection.

## Abstract

To quantify beam optimization for stereotactic body radiotherapy (SBRT) of peripheral lung lesions.

The new beam optimization approach was based on maximizing the therapeutic gain (TG) of the beam set by minimizing the average physical depth of the lesion with respect to the beam's eye view (BEV). The new approach was evaluated by replanning the 25 SBRT lesions retrospectively to assess if a better plan is achievable in all aspects. Difference in 25 Gy isodose line volume (IDLV25 Gy), IDLV20 Gy, IDLV15 Gy, IDLV10 Gy, and IDLV5 Gy between the two plan cohorts were calculated as a measure of plan size and fitted in a linear regression model against the changes in the lesion depth with respect to the BEV to assess the relationship between the changes in the treatment depth and that of the plan size.

Beam optimization achieved a better plan in all cases by lowering the depth of treatment with an average of % 20.03 ± 12.30 (3.66%–45.78%). As the depth of treatment decreases, the size of the plan also decreases. We observed a reduction of % 4.64 ± 4.55 (0.02%–21.58%, p < 3.8 × 10−5), %5.16 ± 5.54 (0.03%‐24.68%, p < 0.005), %6.46 ± 6.95 (−1.35%‐29.05%, p < 0.009), %12.83 ± 9.06 (0.89%–37.65%, p < 0.0001), and %14.01 ± 9.87 (1.43%–41.84%, p < 4.5 × 10−6) in IDLV25 Gy, IDLV20 Gy, IDLV15 Gy, IDLV10 Gy, and IDLV5 Gy, respectively.

Physical depth of the lesion with respect to the BEV is inversely proportional to the TG of a beam‐set and can be used as a robust and standard metric to select an appropriate beam‐set for SBRT of the peripheral lung lesions. Further evaluation warrants the utility of such concept in routine clinical use.