Technical Implementation and Commissioning of an Ergonomic "Lying-on-Couch" Total Skin Electron Irradiation Technique
Abstract
Purpose
Total Skin Electron Irradiation (TSEI) is traditionally delivered with the patient standing at an extended source-to-surface distance, a position often intolerable for frail or compromised patients. While floor-based recumbent alternatives exist, they necessitate cumbersome setups and present significant ergonomic challenges for therapists. We developed and commissioned a "lying-on-couch" TSEI technique to improve patient comfort, streamline clinical workflow, and enhance reproducibility for non-ambulatory patients.
Methods
The technique utilizes 9 MeV high-dose-rate electron beams. A custom flattening filter composed of tungsten, PLA, and PMMA was fabricated to improve field uniformity. A custom rotational couch top was designed to facilitate transitions between Head-First Supine and Feet-First Supine orientations. With the couch rotated to 90° and the vertical position lowered to -57 cm, 8 pairs of AP/PA beams were delivered using lateral shifts of ±24.5 cm and longitudinal shifts of ±22 cm and ±80 cm. The direction of the longitudinal shifts (+/−) was achieved through rotation of the customized couch top. Longitudinal dose profiles were optimized by deriving field weights from ion chamber measurements. End-to-end validation was performed using OSLD dosimetry on a Rando phantom.
Results
Ion chamber profiles demonstrated a FWHM of 70 cm at 135 cm SSD. Lateral shifts of ±24.5 cm achieved dose uniformity within ±10% over a 74 cm width. Longitudinal uniformity within ±10% was achieved over 190 cm using a relative weighting factor of 0.64 for the inner beams (±22 cm) compared to the outer beams (±80 cm). End-to-end OSLD measurements on the Rando phantom confirmed a homogeneous skin dose distribution, ranging from 93.7% to 110.1% of prescription.
Conclusion
This couch-based TSEI technique achieves dose uniformity comparable to conventional standing techniques while significantly improving patient comfort and minimizing therapist ergonomic strain. It represents a robust clinical solution for patients unable to maintain the standing position for standard TSEI.