Room: Exhibit Hall | Forum 9
Purpose: To minimize undesired dose to a patient at out-of-field region by using Superflab boluses.
Methods: To evaluate the dosimetric effect on the skin, various thickness of Superflab boluses were placed at in-field or out-of-field region and on the incident-side or exit-side of the radiation beam. Thermoluminescent dosimeters (TLD) packets (approximately 1x1x0.1 cmÂ²) were placed on the phantom surface to compare doses with and without bolus on top. 6 and 10 MV photons of static and IMRT beams were delivered. To evaluate dose reductions at shallow depth, ion chamber (IC) measurements were performed at various distances from beam axis, at various depths and under various thicknesses of bolus using static and IMRT beams. To evaluate for a clinical case, we used VMAT, 4-field IMRT and Tomotherapy on an anthropomorphic phantom. TLDs measurements were performed on the surface on the contralateral breast with and without a1-cm Superflab bolus placed on top.
Results: It is found that surface dose was reduced only when the point of interest is out of the beam and on the incident side of the beam. Doses increased at the other points due to an increased build-up or back scattering effect. The bolus effect was more significant at closer distances from the beam, and was effective up to 3.0 cm for all conditions and became negligible at 4.0 cm depth. With the bolus on the contralateral breast, the skin dose reductions were showed ~60% and ~20% for 4-field IMRT and VMAT plans respectively, while there was no dose reduction for Tomotherapy.
Conclusion: A Superflab bolus can be used to reduce surface and shallow depth doses during external beam radiotherapy when it is placed out of the beam and on the incident side of the beam, and can potentially reduce patientsâ€™ risk of developing radiation-induced side effects.
Radiation Therapy, Surface Dose, TLDs
TH- External beam- photons: out of field dosimetry/risk analysis