| Shrnutí: | The success of external beam radiotherapy is mainly depended on how to commission and safety precaution is maintained before beam is
heated to infected cells. CC13, an intermediate size ionization chamber is frequently used for the commissioning process of dose
calculation for both standard and non-standard sizes field. The measurements of PDDs (Percentage of Depth Dose) were performed using
TG-51 at the North East Cancer Hospital, Bangladesh using Varian Clinac IX-5982 with 6 MV & 15 MV photon beam energies for a set of
9 field sizes (4 × 4, 6 × 6, 8 × 8, 10 × 10, 15 × 15, 20 × 20, 25 × 25, 30 × 30 and 40 × 40 cm2
), keeping the same conditions such as
pressure, temperature, incremental step, direction, geometry, chamber voltage, and polarity. The PDD for 6 & 15 MV photon beams were
obtained with the above mentioned field sizes and at SSD 100 cm. The obtained PDD results showed that maximum dose depth (dmax) for
above all mentioned field sizes were varied within 11.8 to 15.8 mm and 21.9 to 29.9 mm respectively for 6 and 15 MV photon energies. In
modern clinical radiotherapy PDD is the most essential parameters for the commissioning of medical linear accelerator. Our measured
values for depth dose (dmax) and PDD applying TG-51 protocol at 10 cm depth (d10) for both 6 MV and 15 MV photon energies are found
within the international refereed limits.
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