PROFILE DOSE ANALYSIS OF HALF BLOCKED TECHNIQUE ON LINEAR ACCELERATOR (LINAC)

Abstract

Linear Accelerator (LINAC) is done radiotherapy planning before radiation to provide the correct evaluation dose. Half blocked technique is a technique which is using two asymmetry fields with one isocentre. This technique is mostly used because it can produce precision dose distribution. Remember that almost all of cancercous is irregular, so it needs precision field limitation in efficient time. To see the obtained dose distribution so profile analysis is needed to conduct. Measurement is conducted to relative dose on profile dose by using photon energy of 6 MV in maximum depth that is 1.5 cm in water phantom with 100 cm SSD, by giving the various field spaces (10 x 10 cm2, 15 x 15 cm2 and 20 x 20 cm2). The treatment against the detector is towards crossline and inline.The measurement result is obtained the flatness, symmetry, and penumbra value less than 2%, the overlapp dose value is 102,88% to 105,23%, and the highest value in differences is 5,12% for all of the various fields and detector treatment either towards crossline or inline. This obtained value is still in tolerance limit according to ICRU Report 50, 1993 that is optimal between 95% and 107%. Keywords: Linear Accelerator (LINAC), photon beam, half blocked technique, profile dose, flatness, symmetry, penumbra