ABSTRACT
This study was performed to evaluate surface doses and the effect of air gaps under bolus on surface dose during external beam radiotherapy for photon beam energies of 6 MV and 15 MV. Surface doses were measured by using calibrated GafChromic EBT3 films and the Roos chamber for various bolus-to-surface distances (including no bolus and bolus placed directly on the RW3 phantom surface) and various field sizes. Dose verification was also done for beam energies of 6 MV and 15 MV on the RANDO phantom by measuring doses at dmax using a diode. The introduction of the bolus increased the surface dose for all field sizes and beam energies. For 5×5 cm2 the surface dose increased by 61% and 72% with the introduction of the bolus for 6 MV and 15 MV respectively using the Roos chamber. For both 6 MV and 15 MV, surface doses increased significantly with the introduction of the bolus. Also, due to more skin sparing in 15 MV than 6 MV, surface doses recorded for the 6 MV photons were generally of higher value than those for the 15 MV photons especially for field sizes that were smaller. As the bolus-to-surface distance increased, the doses recorded at the surface decreased. This decrease however was seen for the small field sizes (5×5 cm2 and 10×10 cm2 ). For field sizes that were larger (15×15 cm2 and 20×20 cm2 ) the change in dose to the surface as a result of change in air gap was negligible. For 5×5 cm2 , dose to the surface decreased by 21% and 33% with a 5 cm air gap for 6 MV and 15 MV respectively compared to 20×20 cm2 field, where the change was negligible with only a 2% and 1% increase in surface dose recorded for both 6 MV and 15 MV respectively when the ion chamber was used. The field size of 5×5 cm2 showed the most variation of surface dose with changing air iv gaps showing that change in skin dose as a result of air gaps is only significant for small field sizes.
NII, L (2021). Evaluation of Surface Doses And Effect of Air Gaps Under Bolus During External Photon Beam Radiotherapy. Afribary. Retrieved from https://afribary.com/works/evaluation-of-surface-doses-and-effect-of-air-gaps-under-bolus-during-external-photon-beam-radiotherapy
NII, LAMPTEY "Evaluation of Surface Doses And Effect of Air Gaps Under Bolus During External Photon Beam Radiotherapy" Afribary. Afribary, 07 Apr. 2021, https://afribary.com/works/evaluation-of-surface-doses-and-effect-of-air-gaps-under-bolus-during-external-photon-beam-radiotherapy. Accessed 25 Nov. 2024.
NII, LAMPTEY . "Evaluation of Surface Doses And Effect of Air Gaps Under Bolus During External Photon Beam Radiotherapy". Afribary, Afribary, 07 Apr. 2021. Web. 25 Nov. 2024. < https://afribary.com/works/evaluation-of-surface-doses-and-effect-of-air-gaps-under-bolus-during-external-photon-beam-radiotherapy >.
NII, LAMPTEY . "Evaluation of Surface Doses And Effect of Air Gaps Under Bolus During External Photon Beam Radiotherapy" Afribary (2021). Accessed November 25, 2024. https://afribary.com/works/evaluation-of-surface-doses-and-effect-of-air-gaps-under-bolus-during-external-photon-beam-radiotherapy