Effect of Material and Wall Thickness Buildup Caps on the Head Scatter Factor Measurements in Irregular Fields Shielded by Cerrobend

Ali Jomehzadeh, Daryoush Shahbazi-Gahrouei, Vahid Jahanbakhsh

DOI: 10.4103/jmss.JMSS_10_17

Abstract


Background: The head scatter factor (Sc) is important to measurements radiation beam and beam
modeling of treatment planning systems used for advanced radiation therapy techniques. This study
aimed to investigate the design of a miniphantom to measurement variations in collimator Sc in the
presence of shielding blocks for shaping the beam using different field sizes. Materials and Methods:
Copper, Brass, and Perspex buildup caps were designed and fabricated locally as material with three
different thicknesses for buildup caps (miniphantoms). Measurements were performed on an Elekta
Compact medical linear accelerator (6 MV) in Shafa Kerman Hospital, Iran. The Farmer-type ion
chamber FG65-P (Scanditronix, Wellhofer) was used for all measurements. To measure the Sc,
miniphantom was positioned in a stand vertical to the beam central axis. Results: The data indicate
that the S
c measurements using different buildup cap materials and thicknesses in 5 × 10, 7.5 × 7.5, and
two 10 × 10 cm Cerrobend shield blocks ranged 0.98 to 1.00, 1.04 to 1.05, and 1.04 to 1.06, respectively.
Also, it was observed that by increasing the block shield area from 50 cm2 to both 56.25 and 100 cm2, the
S
c increased in all situations. Conclusion: Results showed that using Brass compared to Perspex and
Copper has less uncertainty due to its simple preparation and cutting which is useful to measurement of
variations in collimator S
c and shaping the photon beam.

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