Comparison between the ideal reference dose level and the actual reference dose level from clinical 3D radiotherapy treatment plans |
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Authors: | Antonella Bufacchi Giorgio Arcangeli Tiziana Malatesta Riccardo Fragomeni Luisa Begnozzi |
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Institution: | a AFaR U.O.C. Medical Physics, S. Giovanni Calibita Fatebenefratelli Hospital, Rome, Italy b Radiotherapy, Pio XI Clinic and S.C. Radiotherapy, Regina Elena National Cancer Institute, Rome, Italy c AFaR U.O.C. Radiotherapy, S. Giovanni Calibita Fatebenefratelli Hospital, Rome, Italy |
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Abstract: | PurposeRetrospective study of 3D clinical treatment plans based on radiobiological considerations in the choice of the reference dose level from tumor dose-volume histograms.Methods and materialsWhen a radiation oncologist evaluates the 3D dose distribution calculated by a treatment planning system, a decision must be made on the percentage dose level at which the prescribed dose should be delivered. Much effort is dedicated to deliver a dose as uniform as possible to the tumor volume. However due to the presence of critical organs, the result may be a rather inhomogeneous dose distribution throughout the tumor volume. In this study we use a formulation of tumor control probability (TCP) based on the linear quadratic model and on a parameter, the F factor. The F factor allows one to write TCP, from the heterogeneous dose distribution (TCP{(εj,Dj)}), as a function of TCP under condition of homogeneous irradiation of tumor volume (V) with dose D (TCP(V,D)). We used the expression of the F factor to calculate the “ideal” percentage dose level (iDLr) to be used as reference level for the prescribed dose D delivery, so as to render TCP{(εj,Dj)} equal to TCP(V,D).The 3D dose distributions of 53 clinical treatment plans were re-evaluated to derive the iDLr and to compare it with the one (DtpL) to which the dose was actually administered.ResultsFor the majority of prostate treatments, we observed a low overdosing following the choice of a DtpL lower than the iDLr. While for the breast and head-and-neck treatments, the method showed that in many cases we underdosed choosing a DtpL greater than the iDLr. The maximum difference between the iDLr and the DtpL was −3.24% for one of the head-and-neck treatments.ConclusionsUsing the TCP model, the probability of tumor control is compromised following an incorrect choice of DtpL; so we conclude that the application of the F factor is an effective tool and clinical aid to derive the optimal reference dose level from the dose-volume histogram (DVH) of each treatment plan. |
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Keywords: | Reference dose level 3D treatment planning Dose-volume histograms Tumor control probability Normal tissue complication probability |
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