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Abstract Background For a given prescribed dose of radiotherapy, with the successive generations of dose calculation algorithms, more monitor units (MUs) are generally needed. This is due to the implementation of successive improvements in dose calculation: better heterogeneity correction and more accurate estimation of secondary electron transport contribution. More recently, there is the possibility to report the dose-to-medium, physically more accurate compared to the dose-to-water as the reference one. This last point is a recent concern and the main focus of this study. Methods In this paper, we propose steps for a general analysis procedure to estimate the dosimetric alterations, and the potential clinical changes, between a reference algorithm and a new one. This includes dosimetric parameters, gamma index, radiobiology indices based on equivalent uniform dose concept and statistics with bootstrap simulation. Finally, we provide a general recommendation on the clinical use of new algorithms regarding the dose prescription or dose limits to the organs at risks. Results The dosimetrical and radiobiological data showed a significant effect, which might exceed 5–10%, of the calculation method on the dose the distribution and clinical outcomes for lung cancer patients. Wilcoxon signed rank paired comparisons indicated that the delivered dose in MUs was significantly increased (> 2%) using more advanced dose calculation methods as compared to the reference one. Conclusion This paper illustrates and explains the use of dosimetrical, radiobiologcal and statistical tests for dosimetric comparisons in radiotherapy. The change of dose calculation algorithm may induce a dosimetric shift, which has to be evaluated by the physicists and the oncologists. This includes the impact on tumor control and on the risk of toxicity based on normal tissue dose constraints. In fact, the alteration in dose distribution makes it hard to keep exactly the same tumor control probability along with the same normal tissue complication probability.

Commercial TPSs typically model the tongue-and-groove (TG) by extending the projections of the leaf sides by a certain constant width. However, this model may produce discrepancies of as much as 7%–10% in the calculated average doses, especially for the High Definition multi-leaf collimator (MLC) (Hernandez et al 2017 Phys. Med. Biol. 62 6688–707). The purpose of the present study is to introduce and validate a new method for modelling the TG that uses a non constant TG width. We provide the theoretical background and a detailed methodology to determine the optimal shape of this TG width from measurements and we fit an empirical function to the TG width that depended on two parameters and . Parameter represents the TG width and introduces a curvature correction in the width near the leaf tip end. The new TG model was implemented in MATLAB and when the curvature correction was zero () it caused the same discrepancies as the constant width model used by the Eclipse TPS. On the other hand, when the experimentally determined was used the new model's calculations were in close agreement with measurements, with all differences in average doses 1%. Additionally, film dosimetry was used to successfully validate the potential of the new TG model to recreate the fine spatial details associated to TG effects. We also showed that the parameters , depend solely on the MLC design by evaluating three different linear accelerators for each MLC model considered, namely Varian's High Definition and Millennium120 MLCs. In conclusion, a new method was presented that greatly improves the TG modelling. The present method can be easily implemented in commercial TPSs and has the potential to further increase their accuracy, especially for MLCs with rounded leaf ends. [ABSTRACT FROM AUTHOR]