Verification measurements and clinical evaluation of the iPlan RT Monte Carlo dose algorithm for 6 MV photon energy

Abstract

This study presents data for verification of the iPlan RT Monte Carlo (MC) dose algorithm (BrainLAB, Feldkirchen, Germany). MC calculations were compared with pencil beam (PB) calculations and verification measurements in phantoms with lung-equivalent material, air cavities or bone-equivalent material to mimic head and neck and thorax and in an Alderson anthropomorphic phantom. Dosimetric accuracy of MC for the micro-multileaf collimator (MLC) simulation was tested in a homogeneous phantom. All measurements were performed using an ionization chamber and Kodak EDR2 films with Novalis 6 MV photon beams. Dose distributions measured with film and calculated with MC in the homogeneous phantom are in excellent agreement for oval, C and squiggle-shaped fields and for a clinical IMRT plan. For a field with completely closed MLC, MC is much closer to the experimental result than the PB calculations. For fields larger than the dimensions of the inhomogeneities the MC calculations show excellent agreement (within 3%/1 mm) with the experimental data. MC calculations in the anthropomorphic phantom show good agreement with measurements for conformal beam plans and reasonable agreement for dynamic conformal arc and IMRT plans. For 6 head and neck and 15 lung patients a comparison of the MC plan with the PB plan was performed. Our results demonstrate that MC is able to accurately predict the dose in the presence of inhomogeneities typical for head and neck and thorax regions with reasonable calculation times (5-20 min). Lateral electron transport was well reproduced in MC calculations. We are planning to implement MC calculations for head and neck and lung cancer patients.

Dose calculation differences between Monte Carlo and pencil beam depend on the tumor locations and volumes for lung stereotactic body radiation therapy

“…The improvement in dose calculation accuracy by using the MC algorithm in the iPlan TPS over other algorithms has been demonstrated by several investigators. ( 16 – 18 ) Excellent agreements between MC calculations and measurements have been reported for both homogeneous and heterogeneous phantoms. These phantom studies have shown that, for small targets imbedded in low‐density environments, the MC calculated doses were significantly different from those calculated with the PB algorithm.…”

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.…”

Angular dependence correction of MatriXX and its application to composite dose verification

“…The optical density of RTQA2 was converted into an absolute dose measured with the ionization chamber. The dose distributions for $10\times 10{ \text{cm}}^2$, $15\times 15{ \text{cm}}^2$, and $20\times 20{ \text{cm}}^2$ fields, various simple plans, and IMRT plans were calculated using the Monte Carlo (MC) dose algorithm installed in the iPlan RT (Version 4.1.2, BrainLAB) 31 , 33 . MC calculations were performed via a full MLC geometry simulation with a spatial resolution of 2 mm and variance of 1%.…”