Little is known about the repopulation, reoxygenation or number of clonogenic cells and how those factors contribute to the complex response to irradiation. 20,15Īdditionally, opposite to the dose response of healthy tissue which is similar in the group of patients irradiated to the same dose level, tumour reaction is much more complex and determined by many factors that influence the tumour response. underline the limited value of this method. Even though reduction methods are used to translate an inhomogeneous distribution into an equivalent dose delivered homogeneously to the whole volume, Kutcher et al. Available algorithms are based on parameters concerning a homogeneous dose distribution (effective volume) and estimated probabilities (TD 5/5 and TD 50/5). 18–20 Those methods are usually based on the dose-volume histogram representing the dose distribution inside irradiated volumes. 8 One of the most frequent mathematical models for NTCP calculations is the Lyman model and an alternative method with Kutcher-Burman reduction algorithm. Mathematical models for simulation of tumour control probability (TCP) and normal tissue complication probability (NTCP) are widely reported in the literature. Thus, will flexible and convenient tools for TCP and NTCP calculations benefit future treatment planning practice? We believe that TCP and NTCP maps calculated based on the spatial dose distribution assist plan evaluation and provide additional information about the spatial location of the “volume at risk” where low-local TCP or high-local NTCP may result in treatment failure or increased toxicity.Ĭomputer applications for translation of the spatial dose distribution into TCP and NTCP maps will help make the decision for the plan more successful and allow the use of different radiobiological parameters and mathematical models. Software for estimation of the results of radiotherapy is not widely accessible it is still considered as an insignificant tool in clinical practice and is not delivered with commercial treatment planning systems. However, there is no evidence that different dose distributions characterized by the same DVH parameters may lead to different clinical outcomes. 16Ĭalculations based on the dose-to-volume relation provide the same TCP and NTCP values when different spatial dose distributions result in the same dose-volume histogram (DVH). Treatment plan evaluation tools provided by commercial software for treatment planning are mostly based on the dose-to-volume relation, which reduces the spatial dose distribution to two-dimensional graphs 15 and neglects the biological effect of the delivered dose. 11–14 Alternative fractionation schedules are becoming more and more popular in modern radiotherapy, which explains the increased significance of evaluation of the biological response of tissue to radiotherapy. 9,10 It may lead to the conclusion that predicting radiotherapy outcomes have become demanding.įurther development in radiotherapy planning seems to be targeted at biologically based optimizations and biological evaluation of the radiotherapy plan. 8 Nevertheless, the response to irradiation is shown to be a diverse and complex process affected by many radiobiological factors and no longer can be characterized by a simple relationship between the prescribed dose and observed toxicity. Higher doses are proved to correlate with higher tumour control probability, while, simultaneously, escalating the dose in healthy tissue increases the risk of injury. The advent of the IMRT era has led to non-uniform organ irradiation significantly reducing the direct relation between the physical dose delivered to the treated volume and normal tissue reaction. 3–6 Further development of IMRT technique has led to image-guided treatment planning (IG IMRT) which additionally decreases the risk of geometric uncertainties caused by organ movements. In particular, the advantages of IMRT over conventional, conformal technique were noticeable in tumours in close proximity to critical structures or of irregular shape, when safe delivery of a high dose to the planning volume was challenging. 2 Dosimetric characteristics have significantly improved since intensity-modulated radiation therapy (IMRT) entered clinical practice. Therefore, for many years, the goal of radiotherapy development concerned constant improvement of the dose distribution conformity and normal tissue sparing in order to reduce treatment toxicity. For many years radiation therapy has been considered as a curative treatment in which the relatively high risk of complication was in balance with the tumour control probability.
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