Monte Carlo simulations to replace film dosimetry in IMRT verification

Abstract

Patient-specific verification of intensity-modulated radiation therapy (IMRT) plans can be done by dosimetric measurements or by independent dose or monitor unit calculations. The aim of this study was the clinical evaluation of IMRT verification based on a fast Monte Carlo (MC) program with regard to possible benefits compared to commonly used film dosimetry.25 head-and-neck IMRT plans were recalculated by a pencil beam based treatment planning system (TPS) using an appropriate quality assurance (QA) phantom. All plans were verified both by film and diode dosimetry and compared to MC simulations. The irradiated films, the results of diode measurements and the computed dose distributions were evaluated, and the data were compared on the basis of gamma maps and dose-difference histograms.Average deviations in the high-dose region between diode measurements and point dose calculations performed with the TPS and MC program were 0.7 ± 2.7 % and Preprint submitted to Elsevier 11 February 20101.2 ± 3.1 %, respectively. For film measurements, the mean gamma values with 3 % dose difference and 3 mm distance-to-agreement were 0.74 ± 0.28 (TPS as reference) with dose deviations up to 10 %. Corresponding values were significantly reduced to 0.34 ± 0.09 for MC dose calculation. The total time needed for both verification procedures is comparable, however, by far less labor intensive in the case of MC simulations.The presented study showed that independent dose calculation verification of IMRT plans with a fast MC program has the potential to eclipse film dosimetry more and more in the near future. Thus, the linac-specific QA part will necessarily become more important. In combination with MC simulations and due to the simple set-up, point-dose measurements for dosimetric plausibility checks are recommended at least in the IMRT introduction phase.

Independent Monte-Carlo dose calculation for MLC based CyberKnife radiotherapy

“…Compared to measurements, software-based QA has been suggested as considerably less time consuming (Goetzfried et al 2011, Siochi et al 2013. Using independent calculation instead of measurements reduces effort for patient specific QA, as computations and analysis may be automated and do not require dedicated machine time (Blanck et al 2015, Bellec et al 2017.…”

“…IDC calculates dose independently from the TPS based on the treat-Independent Monte-Carlo dose calculation for MLC based CyberKnife radiotherapy ment plan to be delivered, ranging from point dose to full 3D dose calculation and dose reconstruction from measured fluence (Boggula et al 2011), depending on the software used. Monte Carlo (MC) techniques provide the most accurate dose calculation currently available and are consequently implemented more and more in treatment planning as computing power continues to grow (Goetzfried et al 2011). The construction of an IDC system fulfilling the requirements of stereotactic treatments poses substantial challenges (Bergman et al 2014).…”

Towards Effective and Efficient Patient-Specific Quality Assurance for Spot Scanning Proton Therapy

“…Independent dose calculations have been used as part of PSQA for IMRT with photons since the early days of IMRT [ 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 ]. These independent calculations provide additional confidence in dose calculations for all IMRT delivery techniques, including tomotherapy, and volumetric modulated arc therapy [ 38 ].…”

Secondary malignancy risk for patients with localized prostate cancer after intensity‐modulated radiotherapy with and without flattening filter

“…Some publications have demonstrated the applicability of this system for treatments of prostate cancer and other entities with IMRT and VMAT and also for FB and FFF. 12,[20][21][22][23][24][25][26][27][28] Limitations of the linear accelerator were considered setting the maximum of the variable gantry speed to a value of 6 degree per second and the minimum of the variable dose rate to a value of 20 MU per minute.…”