Skin Flash Versus Robust Optimization: What Is the Most Appropriate Approach for Accounting for Hypothetical Swelling In Treatment Planning?
Abstract
Purpose
To compare our clinical skin flash method, based on MLC openings on a fictitious swelling volume, with the robust optimization approach available in RayStation version 2023B.
Methods
Fifty-two patients were selected, each having two initial treatment plans (sarcoma treatment mainly) optimized with and without skin flash (inguinal, groin, flank, vulva, scrotum, knee, thigh, forearm and elbow). The flash technique consisted of creating a superficial volume on the body surface to simulate swelling. A minimum dose constraint with a weight of 0 was applied to this volume to force MLC leaf opening in the region. A 1 cm swelling was then simulated on the patients’ CT images in the most clinically relevant direction using the RayStation Simulate Organ Motion tool, generating new swelling CT images. On these datasets, treatment plans with and without flash were recalculated. In addition, a robust plan accounting for a 1 cm swelling uncertainty in a given direction was generated for each patient using the robust optimization tool. Plan evaluation focused on 100% and 95% prescription dose coverage of 100% of the PTV volume, as well as maximum dose.
Results
For 6 out of 52 patients, flash was beneficial when comparing plans on swelling CT images, with differences greater than 5% in PTV coverage. For these patients, the average maximum dose reached 130% for flash plans on swelling CT images, compared to 105.8% for flash plans on the original CT images. Robust plans demonstrated improved PTV coverage for all patients and better control of the maximum dose, which remained below 115%.
Conclusion
Robust optimization provides superior PTV coverage and improved maximum dose control when accounting for the potential occurrence of a 1 cm swelling during treatment planning. Determining the swelling direction remains challenging and often requires discussion with the physician to integrate clinical judgment.