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The Accuracy of Out-Of-Field Dose Calculations of a Commercial Model Based Algorithm in Sliding Window Inaccuracy for Modern Technique of Patients with Prostate Cancer

Fahimeh Faghihi Moghadam

Introduction & Objective: The out-of-filed dose can be clinically important as it related to normal tissue irradiation as the aim of the radiation therapy is decrease Normal Tissue Complications (NTCP) while increasing Tumor Control Probability (TCP). Actually radiotherapy treatment planning systems are not commissioned for the outof- field dose calculations, although the estimation of dose distributions accuracy by TPSs beyond the borders of treatment fields receives less attention. Today’s using modern radiotherapy techniques such as IMRT because of many advantages is most common, while the increase time delivery and also higher number of Monitor Units (MU), results to increase dose outside the fields which can lead to increases potentially risk of secondary cancers after treatment. Based on documents, increase in collimator scatter and head leakage has been estimated to increase carcinogenic risk. Little work has been done to quantify this out-of-filed dose calculation Inaccuracy for Modern Technique (IMRT) and any type of TPSs. The objective of this study is evaluation of uncertainties of out-of-field dose calculation using model based dose calculation algorithm, Anisotropic Analytical Algorithm (AAA), through the comparison of phantom measurements. Method: In this study, experimental measurements were performed by Delta+4 phantoms for evaluation of IMRT technique. The calculations of the eclipse (AAA algorithm) treatment planning system in the dose values were compared with the measurement values by the Delta4+ phantom in 9 field sliding window IMRT technique for 10 patients with prostate cancer. The dose outside the field was calculated in absolute organ dose value and dose distribution as dose volume histogram values in all plans.