Implications of a high-definition multileaf collimator (HD-MLC) on treatment planning techniques for stereotactic body radiation therapy (SBRT): a planning study

PurposeAdvanced radiotherapy delivery systems designed for high‐dose, high‐precision treatments often come equipped with high‐definition multi‐leaf collimators (HD‐MLC) aimed at more finely shaping radiation dose to the target. In this work, we study the effect of a high definition MLC on spine stereotactic body radiation therapy (SBRT) treatment plan quality and plan deliverability.Methods and MaterialsSeventeen spine SBRT cases were planned with VMAT using a standard definition MLC (M120), HD‐MLC, and HD‐MLC with an added objective to reduce monitor units (MU). M120 plans were converted into plans deliverable on an HD‐MLC using in‐house software. Plan quality and plan deliverability as measured by portal dosimetry were compared among the three types of plans.ResultsOnly minor differences were noted in plan quality between the M120 and HD‐MLC plans. Plans generated with the HD‐MLC tended to have better spinal cord sparing (3% reduction in maximum cord dose). HD‐MLC plans on average had 12% more MU and 55% greater modulation complexity as defined by an in‐house metric. HD‐MLC plans also had significantly degraded deliverability. Of the VMAT arcs measured, 94% had lower gamma passing metrics when using the HD‐MLC.ConclusionModest improvements in plan quality were noted when switching from M120 to HD‐MLC at the expense of significantly less accurate deliverability in some cases.

Section: Discussionmentioning

confidence: 99%

The impact of a high‐definition multileaf collimator for spine SBRT

Younge

Kuchta

Mikell

et al. 2017

“…One of the important studies to assess the impact of MLC on dose distribution was performed by Bortfeld et al (4) They showed that theoretically calculated optimum leaf width for 6 MV photon beam was in the range of

1.5 - 2.0 mm

. The dosimetric benefit of thin leaf MLCs has been investigated for small target using IMRT technique 5 , 6 , 7 , 8 , 9 , 10 . Tanyi et al (10) analyzed the impact of two MLC systems for linear accelerator‐based intracranial SRS using three‐dimensional conformal radiotherapy (3D CRT), IMRT, and DCRT.…”

Section: Discussionmentioning

confidence: 99%

“…The dosimetric benefit of thin leaf MLCs has been investigated for small target using IMRT technique 5 , 6 , 7 , 8 , 9 , 10 . Tanyi et al (10) analyzed the impact of two MLC systems for linear accelerator‐based intracranial SRS using three‐dimensional conformal radiotherapy (3D CRT), IMRT, and DCRT. They found a small dosimetric advantage of 2.5 mm leaf width MLC system over 5 mm MLC system in terms of dose conformation, normal tissue exposure, and a rapid dose falloff.…”

Section: Discussionmentioning

confidence: 99%

“…Dhabaan et al (9) compared the 3 mm leaf width BrainLAB micro‐MLC with the 5 mm leaf width Varian Millennium 120 MLC, using the dynamic conformal arc radiotherapy (DCRT) technique and reported that the micro‐MLC had comparatively better conformity and greater normal tissue sparing. Tanyi et al (10) compared 2.5 mm 120 leaf Varian high‐definition MLC (HDMLC) with the widely used 5 mm 120 leaf millennium MLC (MMLC) using intensity‐modulated radiotherapy (IMRT) and dynamic conformal arc techniques. They reported that the HDMLC has a dosimetric advantage over the MMLC.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Is 5 mm MMLC suitable for VMAT‐based lung SBRT? A dosimetric comparison with 2.5 mm HDMLC using RTOG‐0813 treatment planning criteria for both conventional and high‐dose flattening filter‐free photon beams

Subramanian

Subramani

Swamy

et al. 2015

The aim of this study is to assess the suitability of 5 mm millennium multileaf collimator (MMLC) for volumetric‐modulated arc therapy (VMAT)‐based lung stereotactic body radiotherapy (SBRT). Thirty lung SBRT patient treatment plans along with their planning target volumes (ranging from 2.01 cc to 150.11 cc) were transferred to an inhomogeneous lung phantom and retrospectively planned using VMAT technique, along with the high definition multileaf collimator (HDMLC) and MMLC systems. The plans were evaluated using Radiation Therapy Oncology Group (RTOG‐0813) treatment planning criteria for target coverage, normal tissue sparing, and treatment efficiency for both the MMLC and HDMLC systems using flat and flattening filter‐free (FFF) photon beams. Irrespective of the target volumes, both the MLC systems were able to satisfy the RTOG‐0813 treatment planning criteria without having any major deviation. Dose conformity was marginally better with HDMLC. The average conformity index (CI) value was found to be 1.069±0.034 and 1.075±0.0380 for HDMLC and MMLC plans, respectively. For the 6 MV FFF beams, the plan was slightly more conformal, with the average CI values of 1.063±0.029 and 1.073±0.033 for the HDMLC and MMLC plans, respectively. The high dose spillage was the maximum for 2 cc volume set (3% for HDMLC and 3.1% for MMLC). In the case of low dose spillage, both the MLCs were within the protocol of no deviation, except for the 2 cc volume set. The results from this study revealed that VMAT‐based lung SBRT using 5 mm MMLC satisfies the RTOG‐0813 treatment planning criteria for the studied target size and shapes.PACS numbers: 87.53.Ly, 87.53D, 87.56.jk

“…These advancements can include flattening filter‐free (FFF) technology 1 , 2 to achieve high dose rates, image‐guidance capabilities (including MV, 3 , 4 kV, (5) and CBCT (6) imaging), high‐definition MLC widths for enhanced beam shaping, 7 , 8 abilities for real‐time tumor tracking, (9) motion management, 10 , 11 and a patient positioning system 12 , 13 to enable submillimeter precision in target localization.…”

Section: Introductionmentioning

confidence: 99%

Generation and verification of QFix kVue Calypso‐compatible couch top model for a dedicated stereotactic linear accelerator with FFF beams

Gardner

Gulam

Song

et al. 2015

This study details the generation, verification, and implementation of a treatment planning system (TPS) couch top model for patient support system used in conjunction with a dedicated stereotactic linear accelerator. Couch top model was created within the TPS using CT simulation images of the kVue Calpyso‐compatible couchtop (with rails). Verification measurements were compared to TPS dose prediction for different energies (6 MV FFF and 10 MV FFF) and rail configurations (rails in and rails out) using: 1) central axis point‐dose measurements with pinpoint chamber in water‐equivalent phantom at 42 gantry angles for various field sizes (2×2 cm2,4×4 cm2,10×10 cm2); and 2) Gafchromic EBT3 film parallel to beam in acrylic slab to assess changes in surface and percent depth doses in PA geometry. To assess sensitivity of delivered dose to variations in patient lateral position, measurements at central axis using the pinpoint chamber geometry were taken at lateral couch displacements of 2, 5, and 10 mm for 6 MV FFF. The maximum percent difference for point‐dose measurements was 3.24% (6 MV FFF) and 2.30% (10 MV FFF). The average percent difference for point‐dose measurements was less than 1.10% for all beam energies and rail geometries. The maximum percent difference between calculated and measured dose can be as large as 13.0% if no couch model is used for dose calculation. The presence of the couch structures also impacts surface dose and PDD, which was evaluated with Gafchromic film measurements. The upstream shift in the depth of dose maximum (dmax) was found to be 10.5 mm for 6 MV FFF and 5.5 mm for 10 MV FFF for ‘Rails In’ configuration. Transmission of the treatment beam through the couch results in an increase in surface dose (absolute percentage) of approximately 50% for both photon energies (6 MV FFF and 10 MV FFF). The largest sensitivity to lateral shifts occurred at the lateral boundary of the rail structures. The mean magnitude (standard deviation) of the deviation between shifted and centered measurements over all field sizes tested was 0.61% (0.61%) for 2 mm shifts, 0.46% (0.67%) for 5 mm shifts, and 0.86% (1.46%) for 10 mm shifts.PACS numbers: 87.56.‐v, 87.56.Da, 87.56.Fc