Output Factor Considerations Of 12 and 16 Mev Electron Beams At Non - Standard Extended Target To Surface Distance in Blocked Beam Technique
Abstract
Objective: The electron output determination of non-standard technique, especially for extended target to surface distance (TSD) in blocked beam technique is a complicated procedure. This study was performed to prove whether the effective TSDequmated ono of standard cone can be properly used in an inverse square law formula in TSD effective method for its cutout output factor determination.
Materials and methods: The relative output factors (ROFs) of electron output measurements at depth of maximum of 12 and 16 MeV from a Varian Clinac 2100C linear accelerator with standard 10 x 10 cm" cone and its 21 cutouts were measured by a cylindrical ionization chamber farmer type 0.6 cc and PTW electrom- eter in solid water phantom at four source to target distances of 100, 105, 110 and 115 cm. The output factors measured at each cutout and TSD were then compared to to the output factor values that were calculated by effective TSD method of the same cutout with effective TSD own cutout and effective TSD
Results: For output factor consideration, it was found that the magnitude of difference by using TSD of its cutout varied within 1196 for all extended distances and cutouts in both energies. Using of standard cone to calculate the ROF, the magnitude of difference of the two energies increased as the small cutouts and longer TSDs were introduced. The error was up to 7.23% and 8.33% for circular cutout 3 cm in diameter at TSD 115 cm of 12 MeV and 16 MeV, respectively.
Conclusion: The effective TSDeft,natand one of standard cone can be used to determine the relative output factor in effective TSD method. It shows a very good agreement for all cutouts if a side of cutout shields is larger than electron practical range / 2 and extended TSD is shorter than 110 cm. of its Deft standand coce of standard cone. TSD elf standand come
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