Personalised motion management for Stereotactic Ablative Radiation Therapy to the Lung

Background/Purpose

SABR is a mainstay treatment option for stage 1 lung cancer. Our service has offered lung SABR treatment for 10 years. Standardly, these patients are treated in free breathing, with breathing motion accounted for in treatment planning, via Internal Target Volume concept. For targets in lower lobes though, significant breathing motion could lead to larger target volumes and increased dose to surrounding healthy tissue. An alternative motion management approach is deep inspiration breath-hold (DIBH). In 2023, the service initiated a pilot study on Lung SABR in DIBH and undertook a retrospective audit assessing the reliability of target position in repeated breath-hold.

Method

The audit assessed the residual inter-breath-hold target repositioning variability for the first eight patients by analysing intra-fractional imaging (IFI) CBCT taken during treatment delivery in repeated breath-hold. From this data, the patient with the most variability was analysed further. Each of the four fractions were re-created in the treatment planning system, applying the residual positioning error from the respective IFI CBCT and a sum plan of these four plans was created to compare dose statistics to the original plan.

Results

This patient's overall largest errors were 0.76cm in longitudinal, 0.31cm lateral and 0.26cm vertical directions, all still within the planning target volume. The patient's setup was discussed within a multidisciplinary team. A plan review was performed by applying the daily residual errors to a "plan per fraction" and then summed to a final "treated plan" - all dose statistics were comparable to the original plan.

Conclusion

Lessons were learned from this complex patient and hence implemented. The re-calculation of this patient's plan with target position "as treated daily" provided reassurance that the Lung SABR in DIBH technique is a valuable alternative to SABR in free breathing.