PROFILE DOSE AND PDD ANALYSIS IN SMALL PHOTON FIELD WITH PTW PINPOINT CHAMBER 0.015cc
Description
Profile dose and PDD of a small field 6MV have been measured using a PTW PinPoint Chamber 0.015 cc detector. The aim of this study is to analyze the profile dose and PDD of small field using PTW PinPoint Chamber detector 0.015 cc. From the results of this study is expected optimal dose measurement accuracy can be achieved in clinical treatment. The analysis includes calculating the symmetry, penumbra value and PDD. Linear accelerator Electa Precise Treatment SystemTM and PTW PinPoint Chamber 0.015cc are the material used in this research. Profile Dose and PDD were measured with an SSD technique in 100 cm with a various of field sizes and depths. The results showed that the symmetry values for depth variations would decrease in ranges (0.55-6.27)% when the depth increase, and for field size variations will decrease in range (0.39-6.27)%. when the filed size increase. The result of the penumbra analysis shows that its value is more than 4 mm for all variations of depth and field size. PDD results showed that maximum dose for all fields size is achieved in maksimum depth (1.4 – 1.7) cm.
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There are modern radiation techniques such as 3D Conformal Radiation Therapy (3D CRT), Intensity Modulated Radiation Therapy (IMRT), and Volumetric Modulated Arc Therapy (VMAT). These techniques allow for a more optimal dose of radiation against the target tumor and low doses of healthy tissue. One way for dose optimization can be done using a small field during treatment, often known as segmentation, as used in IMRT and VMAT techniques. The use of this small field will ensure the received radiation dose is more accurate and precision on the cancer target. In IMRT techniques the use of a small field for cancer therapy is 50% more than the total number of segments used. The small field is a field of size < 4×4 cm2 [1-2]. External radiation safety verification may use results of commissioning test. External therapy commissioning test activities include dosimetry and geometry verification activities. Geometry verification activities are performed to ensure the correct position and form of a radiation field. While dosimetry verification includes measurement of the radiation beam of photons or electrons. The dosimetry of the photon profile dose in question includes the correction of the PDD, the output factor and the dose profile [3].