Investigation of optimal beam margins for stereotactic radiotherapy of lung-cancer using Monte Carlo dose calculations

Abstract

This work investigated the selection of beam margins in lung-cancer stereotactic body radiotherapy (SBRT) with 6 MV photon beams. Monte Carlo dose calculations were used to systematically and quantitatively study the dosimetric effects of beam margins for different lung densities (0.1, 0.15, 0.25, 0.35 and 0.5 g cm(-3)), planning target volumes (PTVs) (14.4, 22.1 and 55.3 cm3) and numbers of beam angles (three, six and seven) in lung-cancer SBRT in order to search for optimal beam margins for various clinical situations. First, a large number of treatment plans were generated in a commercial treatment planning system, and then recalculated using Monte Carlo simulations. All the plans were normalized to ensure that 95% of the PTV at least receives the prescription dose and compared quantitatively. Based on these plans, the relationships between the beam margin and quantities such as the lung toxicity (quantified by V20, the percentage volume of the two lungs receiving at least 20 Gy) and the maximum target (PTV) dose were established for different PTVs and lung densities. The impact of the number of beam angles on the relationship between V20 and the beam margin was assessed. Quantitative information about optimal beam margins for lung-cancer SBRT was obtained for clinical applications.

Evaluation of the cone beam CT for internal target volume localization in lung stereotactic radiotherapy in comparison with 4D MIP images

“…Even if this occurs, tumor motion amplitude on the order of 4 cm is very rare. Thus, even though our study was limited to the regular sinusoidal motion, the above finding may be applicable to most clinical situations, especially when a PTV margin over the ITV on the order of 5 mm or larger has been generally used, 28,37,38 which should account for uncertainty and a larger shift in the centroid ITV position resulting from an irregular breathing motion and larger motion amplitude. The implication of this finding is that center-to-center alignment for the ITVs shown in the two image modalities could be used when tumor motion amplitudes are at approximately 2 cm.…”

Evaluation of dosimetric misrepresentations from 3D conventional planning of liver SBRT using 4D deformable dose integration

“…Extending these results to other cases, one would expect even more pronounced effects in the case of very small fields, lung tumors, and high‐energy treatments 44 , 45 , 46 . It is worth noting that ${\text{HI}}_{3\mathrm{normalD}/4\mathrm{normalD}}$ of the PTV was well correlated to the motion–volume relationship (see Table 1); a greater ratio of motion to volume (i.e., smaller volume with larger motion) yields greater ${\text{HI}}_{3\mathrm{normalD}/4\mathrm{normalD}}$ than a larger volume with smaller motion.…”

Development and reproducibility evaluation of a Monte Carlo-based standard LINAC model for quality assurance of multi-institutional clinical trials

“…Many research studies have demonstrated that the MC method yields accurate calculations for dose distributions for clinical RT, particularly in heterogeneous tissues [13, 24–25]. …”