GTV-based prescription in SBRT for lung lesions using advanced dose calculation algorithms
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METHODOLOGY
Open Access
GTV-based prescription in SBRT for lung lesions using advanced dose calculation algorithms Thomas Lacornerie1*, Albert Lisbona2, Xavier Mirabel3, Eric Lartigau3 and Nick Reynaert1
Abstract Background: The aim of current study was to investigate the way dose is prescribed to lung lesions during SBRT using advanced dose calculation algorithms that take into account electron transport (type B algorithms). As type A algorithms do not take into account secondary electron transport, they overestimate the dose to lung lesions. Type B algorithms are more accurate but still no consensus is reached regarding dose prescription. The positive clinical results obtained using type A algorithms should be used as a starting point. Methods: In current work a dose-calculation experiment is performed, presenting different prescription methods. Three cases with three different sizes of peripheral lung lesions were planned using three different treatment platforms. For each individual case 60 Gy to the PTV was prescribed using a type A algorithm and the dose distribution was recalculated using a type B algorithm in order to evaluate the impact of the secondary electron transport. Secondly, for each case a type B algorithm was used to prescribe 48 Gy to the PTV, and the resulting doses to the GTV were analyzed. Finally, prescriptions based on specific GTV dose volumes were evaluated. Results: When using a type A algorithm to prescribe the same dose to the PTV, the differences regarding median GTV doses among platforms and cases were always less than 10% of the prescription dose. The prescription to the PTV based on type B algorithms, leads to a more important variability of the median GTV dose among cases and among platforms, (respectively 24%, and 28%). However, when 54 Gy was prescribed as median GTV dose, using a type B algorithm, the variability observed was minimal. Conclusion: Normalizing the prescription dose to the median GTV dose for lung lesions avoids variability among different cases and treatment platforms of SBRT when type B algorithms are used to calculate the dose. The combination of using a type A algorithm to optimize a homogeneous dose in the PTV and using a type B algorithm to prescribe the median GTV dose provides a very robust method for treating lung lesions.
Background The differences between radiotherapy dose calculation algorithms that take into account the electron transport phenomenon inside non-homogeneous environments (category 3&4 or type B) and those that do not (category 1&2 or type A) are well known [1]. The clinical implications of Monte-Carlo dose calculation algorithms [2,3] have been described, as well. However, the differences between type A and type B algorithms for small fields – with a penumbra region that occupies most of the field area – depend on many factors, such as lung density, beam sizes, and the position and size of the target. It is still not clearly understood how to adapt the protocols * Correspondence: [email protected] 1 Service de Physique Médica
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