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

Abstract

Background

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

Method

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 (IDLV_25 Gy), IDLV_20 Gy, IDLV_15 Gy, IDLV_10 Gy, and IDLV_5 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.

Results

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 IDLV_25 Gy, IDLV_20 Gy, IDLV_15 Gy, IDLV_10 Gy, and IDLV_5 Gy, respectively.

Conclusion

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.