Dosimetric Evaluation of Shielding In Partial-Body Rotational Total Skin Electron Therapy
Abstract
Purpose
Total Skin Electron Therapy (TSET) treats cutaneous lymphomas and other superficial malignancies by delivering a uniform electron dose over the skin. Partial-body rotational TSET requires shielding of critical structures, but conventional bulky lead shields near the patient are cumbersome and limit flexibility. This study evaluates gantry-mounted and near-patient shielding to assess their dosimetric impact and clinical suitability.
Methods
Dosimetric analysis was performed using GafchromicTM EBT4 films calibrated for a 6 MeV electron beam. Two shielding configurations were compared: gantry-mounted and near-patient lead shields positioned 30 cm from the patient surface and 3 mm thick. Measurements were conducted on a Varian TrueBeam linear accelerator with a 40 × 40 cm2 field, collimator angle 45o, gantry 270o, and a customized scattering filter in the accessory slot. Films were exposed to 6000 MU at 1.1 cm depth in solid water. Longitudinal profiles were measured over 120 cm with 2 cm spacing and scanned 48 hours post-irradiation.
Results
Near-patient shielding maintained dose near the 2.0 Gy prescription (2.0–2.1 Gy) up to 70–80 cm, consistent with the unshielded case. A sharp dose reduction occurred at the shield, decreasing from approximately 1.9 Gy to below 0.5 Gy over 15–20 cm, with dose approaching zero beyond 105–110 cm. In contrast, gantry-mounted shielding produced a gradual, monotonic dose decrease, reaching approximately 1.2 Gy at 70–80 cm. The dose transition was broad, with no sharp inflection or well-defined shield edge.
Conclusion
While gantry-mounted shielding offers logistical advantages, its dosimetric limitations—including increased scatter and broad, poorly defined dose transitions—limit its clinical utility. In contrast, near-patient shielding delivers superior organ sparing, a predictable dose falloff, and a clinically controllable penumbra. Optimizing shield design and positioning may further simplify treatment and improve shielding reusability for partial-body TSET.