engleski

Dosimetric verification of advanced radiotherapy techniques – Patient specific dosimetry

The main goal of radiotherapy is to increse dose to target volume while minimizing it to the sorrounding healthy tissue. Implementation of advanced radiation therapy techniques in clinical practice makes this goal achivable, but also makes radiotherapy chain much more complex. Regarding this potential for errors increases. Keeping this in mind, the patient specific quality assurance (QA) programme is required prior to treatment to assure correct treatment outcome. Two-dimensional (2D) dosimetric treatment verifications were performed for patients planned with advanced radiotherapy treatments and treated with Siemens Oncor Expression equipped with 160 multileaf collimator. The dosimetric treatment verification consisted of with 2D detector IBA Matrixx. It is consisted of 1020 ionization chambers arranged in matrix dimension 32×32 with 0, 7619 cm resolution. Due to limited resolution additional measurement with Gafchromic EBT3 radiochromic film measurement were performed. Using dedicated software measured distributions are compared with distributions calculated by treatment planning system. The comparison between planed and observed dose distribution was performed using the gamma method. It takes into consideration the dose difference and the spatial displacement between analyzed points to provide a gama-index as a result of comparison. The agreement between the calculated and the measured dose distributions with different detectors was evaluated with the gamma parameter calculated (3 mm and 3%). Good agreement was found between measured and calculated dose distributions for treating different anatomies so we can conclude that both methods are convenient for patient specific dosimetry. For regular patient QA IBA Matrixx is more easier to handle, but in some occasions for complex treatment plans it`s necessary to perform patient QA with films, in spite of the fact that radiochromic films are delicate to handle with.

radiotherapy ; patient specific dosimetry

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