Time‐resolved dosimetry using a pinpoint ionization chamber as quality assurance for IMRT and VMAT a)

Louwe, R.; Wendling, M.; Monshouwer, R.; Satherley, Thomas; Day, Rebecca A.; Greig, Lynne

doi:10.1118/1.4914395

Cited by 14 publications

(16 citation statements)

References 34 publications

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“…However for VMAT treatments in this study, the dose to skin could be regarded as exit dose because the majority of dose to the skin was delivered through medial beam angles. Using the methodology previously developed for time-resolved point dose QC to assess the TPS calculated dose per control point [48], it could be demonstrated that ∼80% of the dose delivered to 40 superficial HD-CTV points with D acc < 95% D presc was deposited at beam angles where the effective depth was larger than or equal to 4 mm. More detail on this analysis is provided in Supplementary Material G. In general, full scatter conditions can simply be achieved by immobilization devices such as radiation masks 'behind' the patient.…”

Section: Discussionmentioning

confidence: 99%

Dose accumulation to assess the validity of treatment plans with reduced margins in radiotherapy of head and neck cancer

Lowther

Marsh

Louwe

2020

Physics and Imaging in Radiation Oncology

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Background and purpose: Literature has reported reduced treatment toxicity in head-and-neck radiotherapy (HNRT) when reducing the planning target volume (PTV) margin from 5 to 3 mm but loco-regional control was not always preserved. This study used deformable image registration (DIR)-facilitated dose accumulation to assess clinical target volume (CTV) coverage in the presence of anatomical changes. Materials and methods: VMAT plans for 12 patients were optimized using 3 or 5 mm PTV and planning risk volume (PRV) margins. The planning computed tomography (pCT) scan was registered to each daily cone beam CT (CBCT) using DIR. The inverse registration was used to reconstruct and accumulate dose (D acc). CTV coverage was assessed using the dose-volume histogram (DVH) metric D acc 99% and by individual voxel analysis. Both approaches included an uncertainty estimate using the 95% level of confidence. Results: D acc 99% was less than 95% of the prescribed dose D presc for three cases including only one case where this was at the 95% level of confidence. However for many patients, the accumulated dose included a substantial volume of voxels receiving less than 95% D presc independent of margin expansion, which predominantly occurred in the subdermal region. Loss in target coverage was very patient specific but tightness of target volume coverage at planning was a common factor leading to underdosage. Conclusion: This study agrees with previous literature that PTV/PRV margin reduction did not significantly reduce CTV coverage during treatment, but also highlighted that tight coverage of target volumes at planning increases the risk of clinically unacceptable dose delivery. Patient-specific verification of dose delivery to assess the dose delivered to each voxel is recommended.

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Section: Discussionmentioning

confidence: 99%

Dose accumulation to assess the validity of treatment plans with reduced margins in radiotherapy of head and neck cancer

Lowther

Marsh

Louwe

2020

Physics and Imaging in Radiation Oncology

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“…ArcCHEK/MapCHECK, MatriXX with COMPASS, electronic portal imaging device, DAVID TM System, Dolphin®, Magic Plate, VANILLA, Delta4 Discover, and the double wedge-shaped ionization chamber IQM system (Casar et al, 2017;Fuangrod et al, 2016;Hoffman, Chung, Hess, Stern, & Benedict, 2017;Islam et al, 2009;Li et al, 2013;Louwe et al, 2015;Myers, Stathakis, Buckey, & Papanikolaou, 2013;Oinam, Singh, Sharma, & Goswami, 2009;Poppe et al, 2006;Björn, 2010;Sanatorium, Valley, & Kong, 2012;ScandiDos, 2016;Shimohigashi et al, 2012;Stelljes et al, 2015;Thoelking et al, 2016;Velthuis et al, 2014;Wendling et al, 2006;Wong et al, 2012;Woodruff et al, 2015). These QA systems have generally been accepted for VMAT quality assessment procedures.…”

Section: Octaviusmentioning

confidence: 99%

Sensitivity evaluation of two commercial quality assurance systems to organ-dose variations of patient-specific VMAT plans

Oderinde

Plessis

2019

Journal of Radiation Research and Applied Sciences

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The purpose of this study was to assess the dose variation sensitivity of two quality assurance (QA) devices (Integral quality monitoring (IQM®) and MatriXXEvolution systems) used for radiotherapy verification. Six volumetric-modulated arc therapy (VMAT) radiation plans were calculated, namely, three head-and-neck and three prostate cases. For sensitivity evaluation, the planning target volume (PTV) dose for each patient's plan was modified by 0.5%, 1.0%, 2.0%, and 3.0% of its original dose. The IQM and MatriXX detectors are sensitive to the dose errors considered. At 0.

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“…In advanced X‐ray radiotherapies, such as intensity modified radiotherapy (IMRT) and volumetric modulated arc therapy, several studies have been conducted to measure partial dose rather than an integrated dose to verify the dose at each control point (CP), which includes the gantry angle, the multileaf collimator aperture, and others. Because dose measurement is conducted over a period of seconds, this method is known as time‐resolved dosimetry (TRD) 3 . In the HIMAC system, the spots (not the CP) carry the most detailed information; therefore, the “spot” is a concept that is more closely related to the CP in IMRT.…”

Section: Introductionmentioning

confidence: 99%

“…Because dose measurement is conducted over a period of seconds, this method is known as time‐resolved dosimetry (TRD). 3 In the HIMAC system, the spots (not the CP) carry the most detailed information; therefore, the “spot” is a concept that is more closely related to the CP in IMRT. The spots are generated for all positions within a 3D field and, the number of spots is at least two digits larger than the number of CPs in X‐ray radiotherapy (Figure 1 ).…”

Section: Introductionmentioning

confidence: 99%

Time‐resolved dosimetry with pencil‐beam scanning for quality assurance/quality control in particle therapy

Han

Furukawa

Hara

et al. 2021

J Applied Clin Med Phys

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This study aimed to measure dose in a scanning carbon beam‐irradiation field with high sampling rate that is sufficient for identifying spots and verifying the characteristics of the scanning beam that cannot generally be derived from the dose. To identify the spot, which is the smallest control unit of beam information during irradiation, effecting measurements with a sampling time of 10 μs or shorter is necessary. The provided dose within a specific time is referred to as time‐resolved dose (TRD). We designed a circuit for time‐resolved dosimetry using a fast‐data acquisition unit (SL1000, Yokogawa Electric Co.), which can measure 100 000 samples per second. Moreover, we used converters to enable a connection between an ionization chamber (IC) and the SL1000. TRD was measured successfully using point irradiation and two‐dimensional irradiation patterns in a scanned carbon beam. Based on the moving time of the spot obtained from the position monitor, the dose delivered to the IC from each spot position (spot dose) was interpreted. The spot dose, displacement of the chamber from the beam's center axis, and beam size were derived using TRD and position monitor outputs, which were measured concurrent with TRD. Spot dose up to a radius of 8 mm area from the IC's center were observed. Using the spot‐dose equations and simulation, we show that the spot dose of each position varies depending on the beam size and displacement of the IC's center from the beam's center axis. We devise an interpretation method for the characteristics that may apply to quality assurance, such as the verification of the trend for the beam axis and isocenter to coincide, as well as beam‐size verification.

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Time‐resolved dosimetry using a pinpoint ionization chamber as quality assurance for IMRT and VMAT a)

Cited by 14 publications

References 34 publications

Dose accumulation to assess the validity of treatment plans with reduced margins in radiotherapy of head and neck cancer

Dose accumulation to assess the validity of treatment plans with reduced margins in radiotherapy of head and neck cancer

Sensitivity evaluation of two commercial quality assurance systems to organ-dose variations of patient-specific VMAT plans

Time‐resolved dosimetry with pencil‐beam scanning for quality assurance/quality control in particle therapy

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