The MLC tongue-and-groove effect on IMRT dose distributions

Abstract

We have investigated the tongue-and-groove effect on the IMRT dose distributions for a Varian MLC. We have compared the dose distributions calculated using the intensity maps with and without the tongue-and-groove effect. Our results showed that, for one intensity-modulated treatment field, the maximum tongue-and-groove effect could be up to 10% of the maximum dose in the dose distributions. For an IMRT treatment with multiple gantry angles (> or = 5), the difference between the dose distributions with and without the tongue-and-groove effect was hardly visible, less than 1.6% for the two typical clinical cases studied. After considering the patient setup errors, the dose distributions were smoothed with reduced and insignificant differences between plans with and without the tongue-and-groove effect. Therefore, for a multiple-field IMRT plan (> or = 5), the tongue-and-groove effect on the IMRT dose distributions will be generally clinically insignificant due to the smearing effect of individual fields. The tongue-and-groove effect on an IMRT plan with small number of fields (< 5) will vary depending on the number of fields in a plan (coplanar or non-coplanar), the MLC leaf sequences and the patient setup uncertainty, and may be significant (> 5% of maximum dose) in some cases, especially when the patient setup uncertainty is small (< or = 2 mm).

Stereotactic IMRT for prostate cancer: Dosimetric impact of multileaf collimator leaf width in the treatment of prostate cancer with IMRT

“…The characteristics of the Siemens MLC and the Radionics mMLC, such as leaf leakage, scatter, and tongue‐and‐groove effect, are not directly modeled in the inverse treatment planning. However, the MLC tongue‐and‐groove effect on IMRT dose distributions is known to be small (22) or clinically negligible for the composite plan (23) . The effect of leaf‐end is modeled by using the leaf offset, which accounts for the poor penumbra of the curved leaf ends.…”

Determining the optimal dosimetric leaf gap setting for rounded leaf‐end multileaf collimator systems by simple test fields

“…Individual patient quality assurance (QA) is required for MLC‐involved intensity‐modulated plans (i.e., intensity‐modulated radiation therapy (IMRT) and volumetric‐modulated arc therapy (VMAT)) to verify agreement between the planned and delivered doses, which is critical for patient care (1) . Over two decades, MLC properties, their uncertainties, and their potential clinical effects have been extensively investigated 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 . With recently developed narrow leaf MLC systems and their applications in hypofractionated treatment, it is necessary to more accurately determine the properties and associated uncertainties.…”

“…Monte Carlo simulation for small fields can be accurate, but very slow. Furthermore, the T&G effects can significantly change the dose distribution, especially when the dose distribution is verified field‐by‐field, as done in individual IMRT QA (5) . Compared to the fields formed by jaws or cones, the fields formed by MLCs have specific penumbras.…”

Monte Carlo modeling and simulations of the High Definition (HD120) micro MLC and validation against measurements for a 6 MV beam

“…Furthermore, the leaves have complex geometries and can even move during beam delivery (dynamic MLC). Modeling the details of the MLC using MC methods is considered of primordial importance to fully account for the loss of electronic equilibrium and for the effects of the MLC tongue and groove, 6 leaf transmission, leaf side and end transmissions, and abutting leaf leakage, which have a significant impact on the penumbra and ultimately on patient dose calculations. 7 BEAMNRC (Ref.…”