Testing of dynamic multileaf collimation

Chui, Chen‐Shou; Spirou, Spiridon V.; LoSasso, Thomas

doi:10.1118/1.597699

Cited by 153 publications

(135 citation statements)

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“…The authors compared these dose profiles with the profiles calculated using Eclipse TPS for the value of the DLG previously determined from ion chamber measurements in the sweeping gap configuration (13) . The actual value of the DLG used in the calculation is not explicitly stated, other than referred to by Chui et al (14) and a range of numbers published by Van Esch et al (13) …”

Section: Introductionmentioning

confidence: 99%

On using the dosimetric leaf gap to model the rounded leaf ends in VMAT/RapidArc plans

Szpala

Cao

Kohli

2014

J Applied Clin Med Phys

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Partial transmission through rounded leaf ends of Varian multileaf collimators (MLC) is accounted for with a parameter called the dosimetric leaf gap (DLG). Verification of the value of the DLG is needed when the dose delivery is accompanied by gantry rotation in VMAT plans. We compared the doses measured with GAFCHROMIC film and an ionization chamber to treatment planning system (TPS) calculations to identify the optimum values of the DLG in clinical plans of the whole brain with metastases transferred to a phantom. We noticed the absence of a single value of the DLG that properly models all VMAT plans in our cohort (the optimum DLG varied between 0.93±0.15 mm and 2.2±0.2 mm). The former value is considerably different from the optimum DLG in sliding window plans (about 2.0 mm) that approximate IMRT plans. We further found that a single‐value DLG model cannot accurately reproduce the measured dose profile even of a uniform static slit at a fixed gantry, which is the simplest MLC‐delimited field. The calculation overestimates the measurement in the proximal penumbra, while it underestimates in the distal penumbra. This prompted us to expand the DLG parameter from a plan‐specific number to a mathematical concept of the DLG being a function of the distance in the beam's eye view (BEV) between the dose point and the leaf ends. Such function compensates for the difference between the penumbras in a beam delimited with a rounded leaf MLC and delimited with solid jaws. Utilization of this concept allowed us generating a pair of step‐and‐shoot MLC plans for which we could qualitatively predict the value of the DLG providing best match to ionization chamber measurements. The plan for which the leafs stayed predominantly at positions requiring low values of the DLG (as seen in the profiles of 1D slits) yielded the combined DLG of 1.1±0.2 mm, while the plan with leafs staying at positions requiring larger values of the DLG yielded the DLG 2.4±0.2 mm. Considering the DLG to be a function of the distance (in BEV) between the dose point and the leaf ends allowed us to provide an explanation as to why conventional single‐number DLG is plan‐specific in VMAT plans.PACS numbers: 87.56.jf, 87.56.nk

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Section: Introductionmentioning

confidence: 99%

On using the dosimetric leaf gap to model the rounded leaf ends in VMAT/RapidArc plans

Szpala

Cao

Kohli

2014

J Applied Clin Med Phys

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“…Our experience with the Varian MLC and the experience from other centers (Memorial Sloane Kettering Cancer Center, New York, and Charite Hospital, Berlin) led us to decide to use dynamic delivery techniques for our first IMRT treatments. There are several excellent references discussing various individual aspects of IMRT which cover commissioning measurements, 1 , 2 planning techniques, 3 , 4 and treatment delivery quality assurance (QA) 5 8 Our intention in this paper is to provide a description of the procedures we undertook, from the commissioning of a commercially available inverse planning system (CadPlan/Helios, Varian Medical Systems, Palo Alto, CA), to routine treatment of prostate and pelvic nodes.…”

Section: Introductionmentioning

confidence: 99%

IMRT clinical implementation: Prostate and pelvic node irradiation using Helios and a 120‐leaf multileaf collimator

Clark

Mubata

Meehan

et al. 2002

J Applied Clin Med Phys

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Dynamic intensity modulated radiation therapy (IMRT) to treat prostate and pelvic nodes using the Varian 120‐leaf Millennium multileaf collimator (MLC) has been implemented in our clinic. This paper describes the procedures that have been undertaken to achieve this, including some of the commissioning aspects of Helios, verification of the dynamic dose delivery, and quality assurance (QA) of the dose delivered to the patient. Commissioning of Helios included measurements of transmission through the 120‐leaf MLC, which were found to be 1.7% for 6 mV and 1.8% for 10 MV. The rounded leaf edge effect, known as the dosimetric separation, was also determined using two independent methods. Values of 1.05 and 1.65 mm were obtained for 6 and 10 MV beams. Five test patients were planned for prostate and pelvic node irradiation to 70 and 50 Gy, respectively. Dose and fluence verification were carried out on specially designed phantoms and dose points in the prostate were measured to be within 2.0% (mean 0.9%, s.d. 0.6%) of the calculated dose and in the nodes within 3.0% (mean 1.6%, s.d. 1.1%). Following the results of this commissioning and implementation study, we have started to treat men with a target volume including the prostate and pelvic nodes using Helios optimized dynamic IMRT delivery in a dose escalation protocol.PACS number(s): 87.53.–j, 87.90.+y

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“…The PF test was first introduced by Chui et al (11). It was an intuitive test for the positioning of MLC.…”

Section: Discussionmentioning

confidence: 99%

Identical Quality Assurance for Volumetric Modulated Arc Therapy in Elekta and Varian Machines

Wang

Peng

et al. 2015

Technol Cancer Res Treat

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Volumetric modulated arc therapy (VMAT) has been adopted by many clinics for its higher delivery efficiency compared to conventional intensity modulated radiotherapy techniques.Currently, the quality assurance (QA) has remained a challenge in that no identical tests are available for accelerators from different vendors. This study is the first attempt to design identical QA tests for the VMAT technique for Varian and Elekta machines. Identical procedures testing MLC positions and movements, dose rate variations, and gantry positions and movement were created for both machines. These included picket fence (PF), dose rate vs. gantry speed (DRGS) and MLC speed vs. dose rate (MLCDR) tests. Deliverable plans for these tests were made with in-house software that was deliverable for linacs from two ven- dors (Elekta Synergy and Varian Trilogy). The electronic portal imaging device (EPID) wasused for these tests. An automated analysis method was established and software was created to quantitatively evaluate the result. The systematic gap position and width errors from PF tests were within 0.5 mm. We evaluated the detectability of this program for introduced errors down to 0.2 mm. Linear relationships existed between the introduced errors and measured errors. In the DRGS test, 99.8% and 100.0% of the intensity deviations from expected profiles were less than 3% for the Synergy and Trilogy, respectively. For the MLCDR, the intensity deviations from expected profiles less than 3% were 100.0% for Synergy and 98.1%for Trilogy. Identical test series were created and implemented for VMAT accelerators from two vendors. Test results were reported from both accelerators. Comparable results were obtained from both vendors, enabling uniform criteria to be established for VMAT quality assurance.Key words: EPID; QA; VMAT. IntroductionRoutine use of volumetric modulated arc therapy (VMAT) in the clinic is spreading rapidly. VMAT shows higher delivery efficiency with similar or better dosimetric benefits compared to traditional intensity modulated radiotherapy (IMRT) (1, 2).At present, two venders (Elekta and Varian) provide VMAT capabilities. The current VMAT quality assurance (QA) procedure for both venders' linacs was investigated by many groups. Ling et al. designed a series to test and commission the RapidArc system (Varian, Palo Alto, CA) (3). After that, automatic electronic portal imaging device (EPID) based test procedures and related tolerance levels were established

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Testing of dynamic multileaf collimation

Cited by 153 publications

References 0 publications

On using the dosimetric leaf gap to model the rounded leaf ends in VMAT/RapidArc plans

On using the dosimetric leaf gap to model the rounded leaf ends in VMAT/RapidArc plans

IMRT clinical implementation: Prostate and pelvic node irradiation using Helios and a 120‐leaf multileaf collimator

Identical Quality Assurance for Volumetric Modulated Arc Therapy in Elekta and Varian Machines

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