Monte Carlo characterization of target doses in stereotactic body radiation therapy (SBRT)

Abstract

To compare finite-size pencil beam/equivalent path-length (FSPB/EPL) and Monte Carlo (MC) SBRT dose computations for serial tomotherapy and to quantitatively assess dose differences between the dose calculation methods. Based on 72 SBRT plans for pulmonary targets, FSPB/EPL, considering the inhomogeneous lung environment, and MC calculations were performed to establish differences between FSPB/EPL predicted dose and MC derived doses. Compared with MC, FSPB/EPL consistently overestimated minimum doses to the clinical target volume and planning target volumes by an average of 18.1+/-7.15% (range 4 to 33.4%), and 21.9+/-10.4% (range 1.2 to 45.5%), respectively. The respective mean target dose differences were 15.5+/-7.4% (2.8-36.4%) and 19.2+/-7.6% (3.6-40.1%). Deviations from MC doses were lesion size and location dependent, with smaller lesions completely embedded into lung parenchyma being most susceptible. Larger lesion in contact with mediastinum and chest wall showed lesser differences. In comparison with MC dose calculation, FSPB/EPL overestimates doses delivered to pulmonary SBRT targets. The observed dose differences may have impact on local tumor control rates, and may deserve consideration when using fast, but less accurate dose calculation methods.

Comparison of Planned Dose Distributions Calculated by Monte Carlo and Ray-Trace Algorithms for the Treatment of Lung Tumors With CyberKnife: A Preliminary Study in 33 Patients

“…7, and a quantitative estimate of the differences can be achieved only after a complete analysis of each individual plan. These results are consistent with similar observations by Rassiah-Szegedi et al (29), who compared MC and pencil beam computations for SBRT of pulmonary targets using the Nomos serial tomotherapy system on a linac.…”

Comparison of pencil beam–based homogeneous vs inhomogeneous target dose planning for stereotactic body radiotherapy of peripheral lung tumors through Monte Carlo–based recalculation

“…9,11,[23][24][25][26] The presented results would serve as references for in-depth understanding of the PB-based dose distribution for lung SBRT, especially for the users of iPlan RT dose or BrainSCAN (predecessor version). 11,23 However, attention must be further paid to the differences among "correction-based" approaches, as the PB with radiologic path length ("1-dimensional (1D)" equivalent path length) generally overestimates the target dose compared with the PB convolution with the Batho power law ("3D" equivalent path length) implemented in Eclipse (Varian).…”

Stereotactic body radiation therapy for a new lung cancer arising after pneumonectomy: dosimetric evaluation and pulmonary toxicity

“…It should also be stressed that in our experience, the dose was prescribed using the equivalent path-length algorithm in 10 of 12 patients. Several studies [63][64][65] show that an equivalent pathlength (EPL)-based algorithm overestimates the dose delivered to pulmonary targets by 20% on average, compared with dose distributions calculated with more accurate algorithms (Monte Carlo or collapsed cone). This may explain why in the present study the actuarial local control probability at 2 years was only 65.5%.…”