Skin And Build Up Region Dose Measurement With Ball Phantom By Using Gaf Chromic EBT2Film And TLD In Radiation Therapy

The dose in the build-up region comprises a primary component fromphotons that originate in the x-ray target, head scattered photons, phantomscattered photons and electrons, and contamination electrons from the treatmenthead and volume of air between the treatment head and patient. The magnitudeand importance of each of these components will vary with depth and, with theexception of the primary component, with field size and beam incidence angles.The purpose of this study was to measure the dose of build up region inball phantom to imitate the dose in patients surface when receiving treatment.Elekta Precise medical linear ccelerator was adopted to deliver radiation dosein this experiment. GAF chromic EBT2film were used for the dosemeasurement. The films must be cutted into little pieces in3cm diametercompassed in a plastic water proof bag to be embedded into liquid forabsolutely dose measurement. The conversion of raw scanner-signal and dosewould be calibrated. This was achieved by placing3cm x3cm pieces of filmsat the thickness of5cm solid water phantom of field size10cm x10cm,Source Axis Distance (SAD)100cm, and were irradiated to dose ranges of5,10,15,20,40,60,80,100,120,150and200cGy. Epson XL10000scanner andassociated software was employed for imaging the films. TLD was used only inball phantom superficial dose check because TLD was unable to be insertedinto phantom like film. A complicate calibration procedure both of TLD andfilm were done prior to do the dose verification and check. After film wasirradiated by the same treatment planning design perform in ball phantom. Thefilms optical density signal was read and converted to dose distribuation byadopting the H-D calibration curve. TLD glowing curve was read from the TLD Raxion UL-320TLD reader and converted the dose by using the wellcalibrated TLD signal-dose calibration curve.The more gantry incidence angle, the more build up region doseperformed. The film and TLD results showed good coincidence in superficialregion while the results of superficial build up region showed poor coincidencewith planning.