Analisis Dosis Serap Relatif Berkas Elektron dengan Variasi Ketebalan Blok Cerrobend pada Pesawat Linear Accelerator

During radiotherapy treatment, critical organs are shielded using cerrobend blocks. The objective of this study was to define the minimal thickness of cerrobend blocks so that the relative absorbed dose in target less than 5%. All measurements were performed using linac Siemens/Primus Mclass 5633. Phantom relative absorbed dose were measured for square field 10 x 10 cm2. The thickness of cerrobend blocks were 2, 4, 6, 8 and 10 mm. The measurements in water were performed using compact chamber fitted with acrylic build up caps.The minimal thickness of cerrobend blocks for 5, 10 and 14 MeV electron beams are 2, 4 and 6 mm, respectively. The relative absorbed dose for phantom's surface, maximum depth and x-ray tail using those blocks are 0.12%, 0.16%, 0.21%, 2.18%, 1.56%, 1.16%, 2.92%, 2.47% dan 1.70%.The relative absorbed dose decreases with the increasing of cerrobend block thickness and phantom depth. Therefore, if cerrobend blocks are used to protect critical organs, the thickness should be taken into account accurately