Feasibility study: Use of an optical scanning system to obtain 3D body surface images suitable for total skin electron therapy treatment dosimetry.

backgroundTotal skin electron therapy (TSET, also known as TSE, TSI, TSEI or TSEBT) provides an effective treatment for extensive superficial lesions such as mycosis fungoides, although the standing setups and large distances used for treatment mean that comprehensive three-dimensional (3D) dose calculations are rarely achievable clinically. PURPOSE: This study investigated the use of photogrammetry and Monte Carlo simulations as a proposed method to verify TSET treatment dose.

methodsTrueBeam 6 MeV electron beam phase-space (PHSP) data supplied by Varian Medical Systems was validated for use in TSET treatment calculations via comparisons with existing TSET commissioning data. The PHSP data was then used to perform Monte Carlo simulations of TSET treatments delivered to a humanoid phantom and eight healthy participants who were all imaged standing in a Vectra WB360 photogrammetry system. Monte Carlo simulation results were visualized for qualitative analysis using in-house developed Python code, using the matplotlib module and 3D Slicer. The simulation calculations were compared against and past in vivo dose measurements to evaluate the performance of the Monte Carlo simulations in the context of clinical experience of TSET treatment delivery.

resultsThe near-instantaneous acquisition of photogrammetry images made the Vectra WB360 system appealing for potential patient imaging. Monte Carlo simulations generally took less than 2 h per beam and produced 3DDOSE files that ranged in size up to 1.75 GB before being reduced by 99% when summed and exported. Validation calculations generally agreed with measurements in water phantoms and the humanoid phantom, and the participant calculations resulted in a mean B factor of 2.8 ± 0.1 as well as useful illustrations of surface dose homogeneity that showed agreement between participant doses and published in vivo results, in terms of hot and cold spots.

conclusionsMonte Carlo simulations using the 3D surface imaging data were found to be useful in evaluating surface dose homogeneity and verifying the locations of hot and cold spots, potentially allowing shielding and boost interventions to be pre-planned. Ideally, 3D patient images derived from photogrammetry (or other surface scans) would be imported into a commercial treatment planning system and used in a more conventional treatment planning and delivery workflow.