Retrospective analysis of portal dosimetry pre-treatment quality assurance of prostate volumetric-modulated arc therapy (VMAT) plans

Maraghechi, B.; Davis, Jack L.; Badu, Shyam; Fleck, Andre; Darko, Johnson; Osei, Ernest

doi:10.1017/s1460396917000486

Cited by 6 publications

(10 citation statements)

References 27 publications

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“…[23][24][25] CI closer to 1 indicates conformal dose to the target volume while GI closer to 1 shows a faster dose fall off and better OAR sparing. 26…”

Section: Structures and Objective Parameters Used For Vmat And Imrt Plan Optimisationmentioning

confidence: 99%

An institutional review: dosimetry comparison between simultaneous integrated boost IMRT and VMAT for prostate cancer

et al. 2020

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Purpose: A comparative study was performed about the plan parameters and quality indices between volumetric arc therapy (VMAT) and intensity-modulated radiotherapy (IMRT) for the treatment of high-risk prostate cancer patients. The aim of this retrospective study was to compare the two methods of external beam radiotherapy IMRT and VMAT in terms of plan quality and efficacy. Material and method: Fifteen high-risk prostate patients were planned for radiotherapy using 6 MV photon. Three dose levels were contoured having Planning Tumour Volume 1 (PTV1 = 48 Gy), Planning Tumour Volume 2 (PTV2 = 57.6 Gy) and Planning Tumour Volume 3 (PTV3 = 60 Gy). Setup margins were given using the CHIP trial method. The prescribed PTV3 dose was 60 Gy in 20 fractions which is biologically equivalent to 74 Gy in 37 fractions using α/β = 3. In case of IMRT, seven fixed beam angles 30, 60, 105, 180, 255, 300 and 330 were used and the dose was optimised using the sliding window method. In case of rapid arc technique, one or two full arcs were used for dose optimisation while keeping all the dose constraints and other planning parameters same used in IMRT. The plan evaluation parameters and Organ at risks (OARs) doses were calculated using a dose volume histogram (DVH). Results: The average D2, D5, D95 and PTVmean for PTV3 were 61.22, 61.13, 58.12, 60.00 Gy and 62.41 62.24 59.53 61.12 Gy for IMRT and VMAT, respectively. The averages V60 for bladder and V30 for rectum were 22.81, 25 and 67, 65% for IMRT and VMAT, respectively. The average homogeneity index (HI), conformity index (CI) and gradient index (GI) were 1.04, 1.4833, 14.79 and 1.04, 1.704, 7.89 for IMRT and VMAT, respectively. Conclusion: VMAT takes less dose-delivery time and lesser number of monitoring units than IMRT, thus it compensates the intrafractional movements during dose delivery. The Dose GI in VMAT was much better than IMRT. This indicates sharper dose fall off near the normal tissue. No other major differences were observed in terms of plan evaluation parameters between IMRT and VMAT techniques. So, we conclude that VMAT technique is more efficient than IMRT in terms of plan quality and dose delivery.

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“…[23][24][25] CI closer to 1 indicates conformal dose to the target volume while GI closer to 1 shows a faster dose fall off and better OAR sparing. 26…”

Section: Structures and Objective Parameters Used For Vmat And Imrt Plan Optimisationmentioning

confidence: 99%

An institutional review: dosimetry comparison between simultaneous integrated boost IMRT and VMAT for prostate cancer

et al. 2020

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“…22,[30][31][32][33][34][35] In recent years, the use of the electronic portal imaging device (EPID) for pre-treatment patient-specific treatment plan verification has gained increased interest due to its simplicity. 22,23,[26][27][28][29][35][36][37][38][39] The Varian EPID has been shown to be capable of producing high-resolution measured dose digital images which can be compared with predicted portal dose images calculated by the Eclipse TM Treatment Planning System (TPS) based on the actual fluence distribution for every patient treatment plan fields. 22,23,[28][29][30]36,40,41 Various methods including the dose difference (DD), distance-to-agreement (DTA) and the gamma (γ) index have been used to compare the measured and predicted dose images.…”

Section: Introductionmentioning

confidence: 99%

“…22,23,[26][27][28][29][35][36][37][38][39] The Varian EPID has been shown to be capable of producing high-resolution measured dose digital images which can be compared with predicted portal dose images calculated by the Eclipse TM Treatment Planning System (TPS) based on the actual fluence distribution for every patient treatment plan fields. 22,23,[28][29][30]36,40,41 Various methods including the dose difference (DD), distance-to-agreement (DTA) and the gamma (γ) index have been used to compare the measured and predicted dose images. [22][23][24][26][27][28][29][30][35][36][37][38][39][42][43][44] The DD is the difference in dose at a specified point in each of the predicted and measured dose distributions, and it is reflected as a percentage of the maximum dose, whereas the DTA represents the nearest distance between two points of equal dose on the predicted and measured dose images when superimposed.…”

Section: Introductionmentioning

confidence: 99%

“…22,23,[28][29][30]36,40,41 Various methods including the dose difference (DD), distance-to-agreement (DTA) and the gamma (γ) index have been used to compare the measured and predicted dose images. [22][23][24][26][27][28][29][30][35][36][37][38][39][42][43][44] The DD is the difference in dose at a specified point in each of the predicted and measured dose distributions, and it is reflected as a percentage of the maximum dose, whereas the DTA represents the nearest distance between two points of equal dose on the predicted and measured dose images when superimposed. 22,23,30,42,43,45 According to Low et al 42 and Low & Dempsey, 43 the DD method is very sensitive in areas of high-dose gradient and a small spatial misalignment will cause a large DD between the measured and the calculated dose distributions, whereas the DTA method is sensitive in areas of low-dose gradient and a small DD in low-dose area could result in large DTA values.…”

Section: Introductionmentioning

confidence: 99%

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Retrospective analysis of portal dosimetry pre-treatment quality assurance of intracranial SRS/SRT VMAT treatment plans

2021

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Background: The complexity associated with the treatment planning and delivery of stereotactic radiosurgery (SRS) or stereotactic radiotherapy (SRT) volumetric modulated arc therapy (VMAT) plans which employs continuous dynamic modulation of dose rate, field aperture and gantry speed necessitates diligent pre-treatment patient-specific quality assurance (QA). Numerous techniques for pre-treatment VMAT treatment plans QA are currently available with the aid of several different devices including the electronic portal imager (EPID). Although several studies have provided recommendations for gamma criteria for VMAT pre-treatment QA, there are no specifics for SRS/SRT VMAT QA. Thus, we conducted a study to evaluate intracranial SRS/SRT VMAT QA to determine clinical action levels for gamma criteria based on the institutional estimated means and standard deviations. Materials and methods: We conducted a retrospective analysis of 118 EPID patient-specific pre-treatment QA dosimetric measurements of 47 brain SRS/SRT VMAT treatment plans using the integrated Varian solution (RapidArcTM planning, EPID and Portal dosimetry system) for planning, delivery and EPID QA analysis. We evaluated the maximum gamma (γmax), average gamma (γave) and percentage gamma passing rate (%GP) for different distance-to-agreement/dose difference (DTA/DD) criteria and low-dose thresholds. Results: The gamma index analysis shows that for patient-specific SRS/SRT VMAT QA with the portal dosimetry, the mean %GP is ≥98% for 2–3 mm/1–3% and Field+0%, +5% and +10% low-dose thresholds. When applying stricter spatial criteria of 1 mm, the mean %GP is >90% for DD of 2–3% and ≥88% for DD of 1%. The mean γmax ranges: 1·32 ± 1·33–2·63 ± 2·35 for 3 mm/1–3%, 1·57 ± 1·36–2·87 ± 2·29 for 2 mm/1–3% and 2·36 ± 1·83–3·58 ± 2·23 for 1 mm/1–3%. Similarly the mean γave ranges: 0·16 ± 0·06–0·19 ± 0·07 for 3 mm/1–3%, 0·21 ± 0·08–0·27 ± 0·10 for 2 mm/1–3% and 0·34 ± 0·14–0·49 ± 0·17 for 1 mm/1–3%. The mean γmax and mean γave increase with increased DTA and increased DD for all low-dose thresholds. Conclusions: The establishment of gamma criteria local action levels for SRS/SRT VMAT pre-treatment QA based on institutional resources is imperative as a useful tool for standardising the evaluation of EPID-based patient-specific SRS/SRT VMAT QA. Our data suggest that for intracranial SRS/SRT VMAT QA measured with the EPID, a stricter gamma criterion of 1 mm/2% or 1 mm/3% with ≥90% %GP could be used while still maintaining an in-control QA process with no extra burden on resources and time constraints.

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“…However, researches [10,19] described that daily MLC QA is essential. LINAC log file analysis is a good option to evaluate MLC movement accuracy in any VMAT session [1,4,16,[19][20][21][22]. However, these recommendations and Korean guideline [23] give general and comprehensive tolerance on MLC performance and said nothing of that for individual MLC leaf movement.…”

Section: Introductionmentioning

confidence: 99%

Mid-Term Performance of Clinical LINAC in Volumetric Modulated Arc Therapy

Rahman

Kim

2019

J Radiat Prot Res

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Background: The mid-term performance of clinical linear accelerator (LINAC) during volumetric modulated arc therapy (VMAT) treatment period is not performed in clinical practice and usually replaced with one-time plan quality assurance (QA). In this research we aim to monitor daily reproducibility of VMAT delivery from tracking individual leaf movement error and dosimetric error to evaluate the mid-term quality of the machine used. Materials and Methods: First, multileaf collimator (MLC) information was imported into MATLAB program to determine which of the MLC leaves in the leaf bank had the maximum RMS position error (maxRMS). We estimated where the maximum positional errors (maxPE) of the chosen leaf occur along its path length and tracked its daily variations over the entire treatment period. Secondly, picture information of dosimetric error from portal dosimetry was imported into MATLAB where representative high gamma index region (HGR) was determined as HGR with length of > 1 cm and their centers were daily tracked. Results and Discussion: The maxPEs in the brain and tongue cases were distributed broader than in other cases, but all data were found located within ± 0.5 mm. From first day to last day all of five cases show the similar visual pattern of HGRs and Centers of the longest HGRs remained within ± 1 mm of that in first day. These findings prove excellent mid-term performance of the LINAC used in VMAT treatments over a full course of treatment. Conclusion: Tracking the daily location changes of leaf movement and dosimetric error can be a good indicator of predicting the daily quality like stability and reproducibility of beam delivering in VMAT treatment.

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Retrospective analysis of portal dosimetry pre-treatment quality assurance of prostate volumetric-modulated arc therapy (VMAT) plans

Cited by 6 publications

References 27 publications

An institutional review: dosimetry comparison between simultaneous integrated boost IMRT and VMAT for prostate cancer

An institutional review: dosimetry comparison between simultaneous integrated boost IMRT and VMAT for prostate cancer

Retrospective analysis of portal dosimetry pre-treatment quality assurance of intracranial SRS/SRT VMAT treatment plans

Mid-Term Performance of Clinical LINAC in Volumetric Modulated Arc Therapy

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