Volume : 6, Issue : 5, May - 2017

Measurement of Radiation Dose at Abutment Region of Clinically Relevant Photon and Electron Field in External Beam Radiotherapy of Head and Neck Cancers

Vinod Pandey, Dr. Lalan Prasad, Mr. Silambarasan Nagloor Sivaji, Dr. Kc Pandey

Abstract :

<p>&nbsp;Purpose: The aim of this study was measurement of radiation dose at abutment region of clinically relevant photon and electron field in external beam radiotherapy of head and neck Cancers &nbsp; Methods and Materials: For 3 electron beam 6, 9, 12&nbsp; MeV&nbsp; with 6 MV asymmetric parallel opposed&nbsp; beam, 6 electron and&nbsp; photon beam plans and summed plans has been generated&nbsp; in eclipse TPS on a water phantom . Plans were delivered separately on RW3 solid water phantom having gafchromic EBT3 film strips placed at 0 to R80 +1 cm depth in the interval of 1 cm for 3 electron beam 6, 9, 12&nbsp; MeV . Profiles at the abutment regions were analyzed with Fimqa pro 3.0 film dosimetry software. &nbsp; Results: A hot spot of 32.8%, 36.4%and40.8% and a cold spot of -20%,-22.7% and -21.9%&nbsp;&nbsp; for 6MeV, 9MeV and 12 MeV beams with 6 MV photon beam has been found respectively .A set up error of &plusmn;2mm can vary the value of hot spot and cold spot significantly by &plusmn;15% to &plusmn;20% however, The location of hot spot was 0.14cm to 0.22cm toward the photon field adjacent to the junction line and location of cold spot was 0.18cm to 0.36cm towards electron field. Measured value are in good agreement with the calculated value of TPS with a average difference of 3 to 5% for high dose region and&nbsp; 30-40% variation for low dose region across the junction. &nbsp; Conclusion: abutment dose can be measured accurately with gafchormic EBT3 film along with filmqapro 3.0 dosimetry system with an uncertainty of 2-3%. The dose at abutment reason is very critical and needs to be evaluated properly and judiciously while treating patients. A 2mm gap between the field&rsquo;s edges can be adopted to reduce the hot spot at the abutment region.</p>