Evaluation of IMRT Patient Specific Quality Assurance with Ion Chambers of Different Active Volumes
Objectives: IMRT is a novel technique in radiotherapy. Our aim is to compare the point dosimetry in treatment planning system and on actual phantom with different volume chambers in IMRT QA.
Methods/Statistical Analysis: 18 patient plans of IMRT with different lesions were selected for this work. Ionization chambers with 0.6 cc , 0.13 cc and IMRT slab phantom were used. Both the chambers were calibrated in national standard laboratory. Treatment machine calibration was verified before doing this dosimetry. Electrometer stability is also verified for the good results. QA plans were exported to linear accelerator after the TPS measurements. All the results were compared.
Findings: The maximum variation observed between the chambers in measured data is 3.51 % where as in TPS this is 2.2 % only which is within acceptable limit. Also, it is observed that, 0.13 cc chamber showed less deviation in few cases where dose gradient is more in the plan. With the advancements in the equipment and technology, varieties of ionization chambers with different sensitive volumes are currently available in the market. Also, intensity modulated radiotherapy practice has been increasing constantly due to its proved results. It is very important for a physicist to select a suitable chamber for doing patient specific QA. Hence, this type of study will help for practicing physicists/dosimetrists.
Application/Improvements: This study can be extended with more number of sensitive volume chambers from different vendors.
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