Room: Exhibit Hall
Purpose: For Mycosis Fungoides treatment, certain regions of the skin that do not get the prescribed dose require an electron boost. Since the lowest electron beam energy is typically 6 MeV, there is a need to degrade the electron beam to treat to a shallower depth and increase the surface dose. The objective of this study was to investigate use of acrylic plates to degrade the electron beam so that it could improve superficial coverage for the boost fields while not penetrating too far deep beneath the skin.
Methods: To quantify influence of acrylic templates in the path of a 9MeV beam, water tank measurements were made with no acrylic, 1 (0.6cm), 2 (1.2cm), and 3 (1.8cm) slabs of templates. Measurements were acquired for 9 MeV electron beam using a field size of 25x25cm2 at SSDs of 100cm, 105cm and 110cm. Both PDDs and profiles at dmax (inline and crossline) where obtained as well as output factors.
Results: Shifts in the depth of maximum dose towards the water surface were noted with increase in thickness of acrylic. For example at an SSD of105cm, dmax shifted from 2.01cm to 0.47cm with 1.8cm of acrylic plate in the path. Similarly, the R50 and Rp values were shown to decrease with increasing acrylic thickness, regardless of the SSD. As for the beam profiles, the symmetry was shown to remain similar to the field with no acrylic in the path. However, the beam penumbra increases with increasing acrylic thickness in the beam path.
Conclusion: Using the acrylic plates, it is possible to degrade the electron beam. This helps modulate the depth of penetration of the electron beam, while optimizing surface dose. However, caution must be taken to ensure lateral coverage.