Determination of MLC model parameters for Monaco using commercial diode arrays

Abstract

Multileaf collimators (MLCs) need to be characterized accurately in treatment planning systems to facilitate accurate intensity‐modulated radiation therapy (IMRT) and volumetric‐modulated arc therapy (VMAT). The aim of this study was to examine the use of MapCHECK 2 and ArcCHECK diode arrays for optimizing MLC parameters in Monaco X‐ray voxel Monte Carlo (XVMC) dose calculation algorithm. A series of radiation test beams designed to evaluate MLC model parameters were delivered to MapCHECK 2, ArcCHECK, and EBT3 Gafchromic film for comparison. Initial comparison of the calculated and ArcCHECK‐measured dose distributions revealed it was unclear how to change the MLC parameters to gain agreement. This ambiguity arose due to an insufficient sampling of the test field dose distributions and unexpected discrepancies in the open parts of some test fields. Consequently, the XVMC MLC parameters were optimized based on MapCHECK 2 measurements. Gafchromic EBT3 film was used to verify the accuracy of MapCHECK 2 measured dose distributions. It was found that adjustment of the MLC parameters from their default values resulted in improved global gamma analysis pass rates for MapCHECK 2 measurements versus calculated dose. The lowest pass rate of any MLC‐modulated test beam improved from 68.5% to 93.5% with 3% and 2 mm gamma criteria. Given the close agreement of the optimized model to both MapCHECK 2 and film, the optimized model was used as a benchmark to highlight the relatively large discrepancies in some of the test field dose distributions found with ArcCHECK. Comparison between the optimized model‐calculated dose and ArcCHECK‐measured dose resulted in global gamma pass rates which ranged from 70.0%–97.9% for gamma criteria of 3% and 2 mm. The simple square fields yielded high pass rates. The lower gamma pass rates were attributed to the ArcCHECK overestimating the dose in‐field for the rectangular test fields whose long axis was parallel to the long axis of the ArcCHECK. Considering ArcCHECK measurement issues and the lower gamma pass rates for the MLC‐modulated test beams, it was concluded that MapCHECK 2 was a more suitable detector than ArcCHECK for the optimization process.PACS number(s): 87.55.Qr

Monte Carlo and analytic modeling of an Elekta Infinity linac with Agility MLC: Investigating the significance of accurate model parameters for small radiation fields

“…Besides less complexity, another advantage of using VSMs is fas- The relationship between appropriate modeling of the MLC leaf parameters and accurate dose calculations in treatment planning systems has been investigated by several research groups. [25][26][27] Bedford et al 25 verified the performance of the Agility MLC model implemented in the beam model of the Pinnacle 3 (Philips Radiation Oncology System, Fitchburg, WI, USA) for calculations and delivery of VMAT plans. Kinsella et al 26 and Synder et al 27 used specifically designed measurements to fine tune model parameters (e.g., leaf transmission, groove width, interleaf leakage) of the Agility MLC model implemented in the Monaco treatment planning system.…”

Adjustment of multi-leaf collimator parameters in 4-MV and 6-MV IMRT: A study of veterinary clinical cases

“…To adjust the MLC parameters in the human medicine, diodes, such as MapCHECK 2, Gafchromic EBT3 film, and ionization chambers were used in the study ( Grofsmid et al ., 2010 ; Kinsella et al ., 2016 ; Roche et al ., 2018 ). Dosimetric validation of a commercial AAPM TG-106 proposes the use of films, portal images, or diodes as measurement devices to determine MLC parameters ( Das et al ., 2008 ).…”

Análisis dosimétrico y verificación de tratamientos VMAT en aceleradores gemelos

“…En primer lugar, fueron verificados 8 campos predefinidos en el acelerador: 3ABUT, 7SEC, FOURL, DMLC, HIMRT y HDMLC ¶ ; 17 10 × 10 cm 2 ; 20 × 20 cm 2 . Y en segundo lugar, fueron medidos 43 tratamientos completos de pacientes: 6 SBRT (Stereotactic Body Radiotherapy), 9 próstatas, 10 ORL (lesiones tumorales derivadas de otorrinolaringología), 9 pulmones, 5 cérvix, 1 columna, 1 hígado, 1 inguinal y 1 radiocirugía.…”