Dosimetric discrepancies caused by differing MLC parameters for dynamic IMRT

Wasbø, Ellen; Valen, Harald

doi:10.1088/0031-9155/53/2/008

Cited by 15 publications

(20 citation statements)

References 9 publications

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“…This result is consistent with the previous study 15) and the increase in the TF and DLG according to the field size is likely caused by the increase in collimator scatter.…”

Section: Discussionsupporting

confidence: 93%

“…MV photon beams, the results are similar to those reported by Wasbø et al 15) The increase in the TF and DLG as a function of depth is likely caused by the larger phantom scatter. As shown in Fig.…”

Section: Discussionsupporting

confidence: 89%

“…[7][8][9] They have investigated the impact of the DLG on the dose distribution and calculation by using the Millennium 120 MLC (Varian Medical Systems, Palo, Alto, CA, USA) under only one fixed depth. [10][11][12][13][14][15] It was shown that the DLG value was different from the value measured at…”

Section: Introductionmentioning

confidence: 82%

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Clinical Implications of High Definition Multileaf Collimator (HDMLC) Dosimetric Leaf Gap (DLG) Variations

Chang

Kwak

et al. 2016

Prog Med Phys

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This study is to evaluate the dosimetric impact of dosimetric leaf gap (DLG) and transmission factor (TF) at different measurement depths and field sizes for high definition multileaf collimator (HD MLC). Consequently, its clinical implication on dose calculation of treatment planning system was also investigated for pancreas stereotactic body radiation therapy (SBRT). The TF and DLG were measured at various depths (5, 8, 10, 12, and 15 cm) and field sizes (6×6, 8×8, and 10×10 cm 2 ) for various energies (6 MV, 6 MV FFF, 10 MV, 10 MV flattening filter free [FFF], and 15 MV). Fifteen pancreatic SBRT cases were enrolled in the study. For each case, the dose distribution was recomputed using a reconfigured beam model of which TF and DLG was the closest to the patient geometry, and then compared to the original plan using the results of dose-volume histograms (DVH). For 10 MV FFF photon beam, its maximum difference between 2 cm and 15 cm was within 0.9% and it is increased by 0.05% from 6×6 cm 2 to 10×10 cm 2 for depth of 15 cm. For 10 MV FFF photon beam, the difference in DLG between the depth of 5 cm and 15 cm is within 0.005 cm for all field sizes and its maximum difference between field size of 6×6 cm 2 and 10×10 cm 2 is 0.0025 cm at depth of 8 cm. TF and DLG values were dependent on the depth and field size. However, the dosimetric difference between the original and recomputed doses were found to be within an acceptable range (＜0.5%). In conclusion, current beam modeling using single TF and DLG values is enough for accurate dose calculation.

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“…This result is consistent with the previous study 15) and the increase in the TF and DLG according to the field size is likely caused by the increase in collimator scatter.…”

Section: Discussionsupporting

confidence: 93%

Section: Discussionsupporting

confidence: 89%

See 1 more Smart Citation

Clinical Implications of High Definition Multileaf Collimator (HDMLC) Dosimetric Leaf Gap (DLG) Variations

Chang

Kwak

et al. 2016

Prog Med Phys

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“…Other energy‐relevant parameters would include the dosimetric leaf gap parameters and leaf transmission factors. Using the same methodology described by Wasbo and Valen, (13) the measured leaf gap parameters of the TrueBeam HD120 MLC were 0.732 mm and 0.669 mm for 6XFF and 6XFFF, respectively, while they were 0.832 mm and 0.798 mm for 10XFF and 10XFFF, respectively. The leaf transmission factors of the TrueBeam HD120 MLC were measured as 0.012 and 0.010 for 6XFF and 6XFFF, respectively, and 0.014 and 0.012 for 10XFF and 10XFFF, respectively.…”

Section: Discussionmentioning

confidence: 99%

Practical approach for pretreatment verification of IMRT with flattening filter‐free (FFF) beams using Varian portal dosimetry

Min

Choi

Kwak

et al. 2014

J Applied Clin Med Phys

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Patient‐specific pretreatment verification of intensity‐modulated radiation therapy (IMRT) or volumetric‐modulated arc therapy (VMAT) is strongly recommended for all patients in order to detect any potential errors in treatment planning process and machine deliverability, and is thus performed routinely in many clinics. Portal dosimetry is an effective method for this purpose because of its prompt setup, easy data acquisition, and high spatial resolution. However, portal dosimetry cannot be applied to IMRT or VMAT with flattening filter‐free (FFF) beams because of the high dose‐rate saturation effect of the electronic portal imaging device (EPID). In our current report, we suggest a practical QA method of expanding the conventional portal dosimetry to FFF beams with a QA plan generated by the following three steps: 1) replace the FFF beams with flattening filtered (FF) beams of the same nominal energy; 2) reduce the dose rate to avoid the saturation effect of the EPID detector; and 3) adjust the total MU to match the gantry and MLC leaf motions. Two RapidArc plans with 6 and 10 MV FFF beams were selected, and QA plans were created by the aforementioned steps and delivered. The trajectory log files of TrueBeam obtained during the treatment and during the delivery of QA plan were analyzed and compared. The maximum discrepancies in the expected trajectories between the treatment and QA plans were within 0.002 MU for the MU, 0.06° for the motion of gantry rotation, and 0.006 mm for the positions of the MLC leaves, indicating much higher levels of accuracy compared to the mechanical specifications of the machine. For further validation of the method, direct comparisons of the delivered QA FF beam to the treatment FFF beam were performed using film dosimetry and show that gamma passing rates under 2%/2 mm criteria are 99.0%–100% for the all four arc beams. This method can be used on RapidArc plans with FFF beams without any additional procedure or modifications on the conventional portal dosimetry of IMRT and is, therefore, a practical option for routine clinical use.PACS numbers: 87.53.Kn, 87.55.T‐, 87.56.bd, 87.59.‐e

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“…The dosimetric leaf separation or dosimetric leaf gap can be determined by the integral dose method using sweeping gaps of various widths (47)(48)(49). A tolerance of 0.1 mm is advised.…”

Section: Dosimetric Leaf Separation (For Sw Only)mentioning

confidence: 99%

NCS Report 22: Code of practice for the quality assurance and control for intensity modulated radiotherapy

Wal¹,

Wiersma²,

Ausma³

et al. 2013

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Dosimetric discrepancies caused by differing MLC parameters for dynamic IMRT

Cited by 15 publications

References 9 publications

Clinical Implications of High Definition Multileaf Collimator (HDMLC) Dosimetric Leaf Gap (DLG) Variations

Clinical Implications of High Definition Multileaf Collimator (HDMLC) Dosimetric Leaf Gap (DLG) Variations

Practical approach for pretreatment verification of IMRT with flattening filter‐free (FFF) beams using Varian portal dosimetry

NCS Report 22: Code of practice for the quality assurance and control for intensity modulated radiotherapy

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