Design and Testing of a Simulation Framework for Dosimetric Motion Studies Integrating an Anthropomorphic Computational Phantom into Four-dimensional Monte Carlo

Abstract

We have designed a simulation framework for motion studies in radiation therapy by integrating the anthropomorphic NCAT phantom into a 4D Monte Carlo dose calculation engine based on DPM. Representing an artifact-free environment, the system can be used to identify class solutions as a function of geometric and dosimetric parameters. A pilot dynamic conformal study for three lesions (~ 2.0 cm) in the right lung was performed (70 Gy prescription dose). Tumor motion changed as a function of tumor location, according to the anthropomorphic deformable motion model. Conformal plans were simulated with 0 to 2 cm margin for the aperture, with additional 0.5 cm for beam penumbra. The dosimetric effects of intensity modulated radiotherapy (IMRT) vs. conformal treatments were compared in a static case. Results show that the Monte Carlo simulation framework can model tumor tracking in deformable anatomy with high accuracy, providing absolute doses for IMRT and conformal radiation therapy. A target underdosage of up to 3.67 Gy (lower lung) was highlighted in the composite dose distribution mapped at exhale. Such effects depend on tumor location and treatment margin and are affected by lung deformation and ribcage motion. In summary, the complexity in the irradiation of moving targets has been reduced to a controlled simulation environment, where several treatment options can be accurately modeled and quantified The implemented tools will be utilized for extensive motion study in lung/liver irradiation.

Extension of the NCAT phantom for the investigation of intra-fraction respiratory motion in IMRT using 4D Monte Carlo

“…The general approach for the 4D Monte Carlo system used for this study has been outlined elsewhere (Riboldi et al 2008, Seco et al 2007, 2008). Briefly, 14 tissue subsets were used for the Monte Carlo dose calculations in accordance to the approach used by Vanderstraeten et al (2006).…”

“…DPM offers improved efficiency over EGSnrc in a patient geometry. Both codes were benchmarked against each other and showed agreement within 1% (Riboldi et al 2008). The low-energy electron and photon cutoff energies were set to 200 keV and 50 keV, respectively.…”

“…Previous efforts have focused on using the NCAT phantom in a Monte Carlo environment to investigate the effect of irradiating a gross target volume (GTV) via lesion tracking in a 3D conformal treatment (3DCRT). An IMRT plan was also developed for a static anatomy in this study (Riboldi et al 2008). Another closely related study used the VIP-Man phantom (Xu et al 2000) in a 4D IMRT study to investigate motion effects with a standard conformal treatment plan and 4D gated and image-guided IMRT treatments (Zhang et al 2008).…”

Synthetic 4DCT(MRI) lung phantom generation for 4D radiotherapy and image guidance investigations

“…32 In photon radiotherapy, phantoms have found applications in treatment planning studies 33 and simulations of gating and tracking. 15,[34][35][36] Arguably, however, the most sensitive radiation therapy modality to motion is pencil beam scanned (PBS) proton therapy. 37 Due to the sharp distal fall-off of the proton depth-dose curve and the sequential (in time) application of individually weighted and narrow proton "pencil beams" (each just a few millimeters in diameter), PBS proton therapy is especially sensitive to patient/tumor geometry changes and the interference with tumor motion.…”

“…Phantoms also provide the “ground truth” motion and can therefore be used for motion modeling 29–31 as well as for deformable image registration (DIR) performance validation 32 . In photon radiotherapy, phantoms have found applications in treatment planning studies 33 and simulations of gating and tracking 15,34–36 …”