Quality Control And Dosimetry Of A Wooden Couch Top For Megavoltage External Beam Radiotherapy.

ABSTRACT 

The purpose of this study was to determine an appropriate locally fabricated wood sample that could be used to replace the wire mesh incorporated at the treatment area of EBRT couch top to circumvent dose discrepancies associated with the sagging effect of the wire mesh as a result of prolonged use. Linear attenuation coefficient and transmission factor were determined at three stipulated field sizes (5cm x 5cm, 10cm x 10cm,15cm x 15cm) and two treatment depths of 0.5cm and 5cm for five (5) wood species with each consisting of six (6) square slabs of 2.5cm thickness each. It was observed that for a particular depth, linear attenuation coefficient generally decreases as the field size increases whilst transmission factor was vice-versa. Triplochiton scleroxylon had the lowest average linear attenuation coefficient across the three field size as 0.0248cm-1  at a depth of 0.5cm This was followed by Terminalia superba of 0.0312cm-1 and that of Albizia zygia , Entandrophragma candollei and Nesogogordonia papaverifera were 0.0353cm-1 , 0.0410cm-1 and 0.0563cm-1 respectively at the same depth. The percentage deviation in the order as arranged above were 3.6%, 3.8%, 4.5%, 2.4% and 3.9% respectively. There was the same trend (decrease µ as Fs increases) at a depth of 5cm. However, transmission factor for all the wood species increases with increased in field size with Terminalia superba recording a highest average TF as 0.981 and 0.952 followed by Triplochiton scleroxylon as 0.979 and 0.947 at a depth of 0.5cm and 5cm respectively. Triplochiton scleroxylon of about 2cm thickness could serve as a more affordable material to be used to replace the wire mesh.