Room: Exhibit Hall | Forum 4
Purpose: A technique for total skin electron therapy (TSET) with the patient lying on the floor (LOTF) at extended source to skin distance (SSD) is presented.
Methods: The LOTF TSET technique employs two parallel 40x40cmÂ² AP 6MeV electron beams separated by a gap. SSD was maximized by lowering a stretcher to its lowest position, and subtracting the anticipated patient separation. Beam quality at extended (175cm) SSD was measured using a parallel plate chamber at various depths in solid water. Output was measured using the same set-up, and verified with OSLDs. The beam profile was measured in air using Gafchromic film. The gap between the two parallel AP fields was calculated to maximize uniformity. Dose uniformity near the gap was measured using film wrapped around a cylindrical phantom. The same set-up was used to evaluate dose to lateral (oblique) surfaces.
Results: There was less than 1mm difference in beam quality parameters (dmax, R90, R50 and Rp) between LOTF TSET geometry (6MeV, 40x40cmÂ² field size, at 175cm SSD) and standard geometry (6MeV, 10x10cmÂ² field size, at 100cm SSD). Using LOTF TSET geometry, the dose rates at dmax and the surface were 0.286 and 0.215cGy/MU respectively. These results agreed within 2% of OSLD measurements.At 175cm SSD, the in-air dose profile FWHM was 78cm, while the light field width was 70cm. Dose at the light field edges was approximately 67% of the dose at central axis (CAX). A 9cm gap (at 175cm SSD) was determined to maximize uniformity across the match line. Phantom film measurements verified dose across the gap region to be within 8% of dose at CAX. Lateral surface dose enhancement greater than 8% was observed.
Conclusion: This technique yields acceptable uniformity and can be commissioned within an emergent timeframe to treat patients unable to stand.