Dosimetric verification and clinical evaluation of a new commercially available Monte Carlo-based dose algorithm for application in stereotactic body radiation therapy (SBRT) treatment planning

Abstract

Modern cancer treatment techniques, such as intensity-modulated radiation therapy (IMRT) and stereotactic body radiation therapy (SBRT), have greatly increased the demand for more accurate treatment planning (structure definition, dose calculation, etc) and dose delivery. The ability to use fast and accurate Monte Carlo (MC)-based dose calculations within a commercial treatment planning system (TPS) in the clinical setting is now becoming more of a reality. This study describes the dosimetric verification and initial clinical evaluation of a new commercial MC-based photon beam dose calculation algorithm, within the iPlan v.4.1 TPS (BrainLAB AG, Feldkirchen, Germany). Experimental verification of the MC photon beam model was performed with film and ionization chambers in water phantoms and in heterogeneous solid-water slabs containing bone and lung-equivalent materials for a 6 MV photon beam from a Novalis (BrainLAB) linear accelerator (linac) with a micro-multileaf collimator (m(3) MLC). The agreement between calculated and measured dose distributions in the water phantom verification tests was, on average, within 2%/1 mm (high dose/high gradient) and was within +/-4%/2 mm in the heterogeneous slab geometries. Example treatment plans in the lung show significant differences between the MC and one-dimensional pencil beam (PB) algorithms within iPlan, especially for small lesions in the lung, where electronic disequilibrium effects are emphasized. Other user-specific features in the iPlan system, such as options to select dose to water or dose to medium, and the mean variance level, have been investigated. Timing results for typical lung treatment plans show the total computation time (including that for processing and I/O) to be less than 10 min for 1-2% mean variance (running on a single PC with 8 Intel Xeon X5355 CPUs, 2.66 GHz). Overall, the iPlan MC algorithm is demonstrated to be an accurate and efficient dose algorithm, incorporating robust tools for MC-based SBRT treatment planning in the routine clinical setting.

Dose differences in intensity‐modulated radiotherapy plans calculated with pencil beam and Monte Carlo for lung SBRT

“…The method of tissue heterogeneity correction and the dose calculation algorithm are two important factors that affect the dose accuracy in lung SBRT. Several investigators have reported that the MC algorithm in the iPlan improved the dose calculation accuracy when compared to the PB algorithm 13 , 14 , 15 . In both homogeneous and heterogeneous phantoms, excellent agreements between the MC calculations and experimental measurements were reported in both high‐dose and high‐dose‐gradient regions.…”

Effect of the normalized prescription isodose line on the magnitude of Monte Carlo vs. pencil beam target dose differences for lung stereotactic body radiotherapy

“…For each plan, the chosen isodose line conformally covered the PTV. Therefore, after a total of 48 plans were created for the 12 patients using the iPlan PB algorithm, all plans were also recalculated using the iPlan MC algorithm (28) with the original MLC apertures and monitor units. The calculated dose differences between the PB and MC dose algorithms were then compared among the four plans prescribed to the varying isodose lines (60%–90%) for each patient.…”

Assessment of Monte Carlo algorithm for compliance with RTOG 0915 dosimetric criteria in peripheral lung cancer patients treated with stereotactic body radiotherapy

“…Therefore, we sought not to compare RTOG dosimetric compliance criteria on PTV coverage, understanding the fact that PB‐hete overpredicted the PTV coverage, underdosing the target volume that was consistent with aforementioned referenced literature 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 comparing the two algorithms.…”

“…There have been several studies reported in the literature on clinical validation of XVMC dose calculations in both homogenous and heterogeneous media utilizing the iPlan RT dose planning system 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 . In recent studies by Sethi and colleagues, (9) XVMC algorithm‐based calculation was scaled using ion chamber and EDR films in various depths in five different phantoms with four different density materials irradiated with 6 MV photons.…”