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Research Paper | Radiotherapy | India | Volume 13 Issue 12, December 2024 | Rating: 4.9 / 10
Effect of Different SSDS and Oblique Beam Incidences on Surface Dose Measurements
Satish M. Pelagade, Tushar Agrawal, Suchitra Laishram, Ankita Parikh
Abstract: Introduction: The purpose of this study was to measure the surface dose and its effect for different source to surface distances (SSD) and oblique beam incidences for 6 MV, 10 MV and 15 MV photon beams using parallel plate chamber. Material and Methods: All measurements were conducted in a water equivalent Polymethyl Methacrylate (PMMA) slab phantom under machine-specific reference conditions. Markus type parallel plate ionization chamber with fixed separation between collecting electrodes was used to measure the surface dose. The Markus type parallel plate chamber over-responds on the surface which was corrected by the Gerbi?s formula. Results: It was found that as the SSD increases surface dose is decreases and vice versa, also this effect is significant for higher energies. The surface dose increases from the normal incidence with increasing angle of beam incidence which is due to additional forward scattered electrons from the phantom reaching to the point of measurement. The surface dose increases to twice its value near 60? oblique angle compared to 0? angle of incidence. Conclusion: The surface dose is clearly decreases with increase in energy. There is a large difference for surface dose between 6 and 10 MV photon beam but small difference between 10 and 15 MV photon beam. This knowledge of surface dose can be used to prevent and manage potential of acute skin reaction and late skin toxicity from treatments with radiotherapy.
Keywords: surface dose, parallel plate chamber, megavoltage photon beam
Edition: Volume 13 Issue 12, December 2024,
Pages: 1757 - 1761