A Bayesian control chart based on the beta distribution for monitoring the two‐dimensional gamma index pass rate in the context of patient‐specific quality assurance

81 Background: Patient-specific quality assurance measurements are time consuming and Gamma pass/fail criteria are often picked based on typical criteria used for IMRT QA measurements in the past. The questions needs to be asked if with these criteria QA plans could still show clinically significant deviations from the treatment plan calculated and how we should be doing QA for treatment delivery of complex treatment plans. In our study DICOM files of clinical Rapidarc plans were modified with in-house developed software to mimic leaf alignment errors and gravitation shifts. The Octavius 2D-ARRAY (PTW-Freiburg) and the Delta4 device (Scandidos) were used to investigate the effect of the simulated errors on the passing rate of quality assurance results. The manipulated Rapidarc plans were recalculated on patient CT scans in Eclipse. Methods: Three different types of errors were simulated and applied to five prostate (two arcs), three 2-arc head and neck cases and three 3-arc head and neck cases. The MLC modifications were: (1) both MLC banks are opened by 0.25mm, 0.50mm and 1.00mm in opposing directions resulting in larger fields, (2) both MLC banks are closed by 0.10mm, 0.25mm and 0.50mm, (3) both MLC banks are shifted in the same direction for lateral gantry angles to simulate effects of gravitational forces onto the leaves by 1mm, 2mm and 3mm, (4) 25%, 50% 70% and 100% of all active leaves are shifted by 3mm as in (3). QA evaluations were performed according to a gamma-index criterion of 3mm and 3% as well as 2mm and 2%. Results: All unmodified plans and the majority of the plans with the smallest modification pass the gamma-index criterion of 2%/2mm with >90%. After that the passing rate drops below 90%. For the largest modifications passing rates were typically below 85%. The Delta4 is generally more sensitive and the passing rate for modified plans drops below 90% earlier and more drastically. With the standard criteria (3mm, 3%) even the largest modifications would satisfy a >90% passing rate. Conclusions: A stricter gamma-index (2mm, 2%) is necessary in order to detect MLC positional errors and a passing rate of >90% should be expected. Clinical pass/fail criteria need to be developed.

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Pretreatment patient-specific IMRT quality assurance: A correlation study between gamma index and patient clinical dose volume histogram

Medical Physics ◽

10.1118/1.4767763 ◽

2012 ◽

Vol 39 (12) ◽

pp. 7626-7634 ◽

Cited By ~ 119

Author(s):

M. Stasi ◽

S. Bresciani ◽

A. Miranti ◽

A. Maggio ◽

V. Sapino ◽

...

Keyword(s):

Quality Assurance ◽

Correlation Study ◽

Patient Specific ◽

Dose Volume Histogram ◽

Clinical Dose ◽

Dose Volume ◽

Gamma Index

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Evaluation of a two‐dimensional diode array for patient‐specific quality assurance of HyperArc

Journal of Applied Clinical Medical Physics ◽

10.1002/acm2.13438 ◽

2021 ◽

Author(s):

Richard A. Popple ◽

Rodney J. Sullivan ◽

Yuan Yuan ◽

Xingen Wu ◽

Elizabeth L. Covington

Keyword(s):

Quality Assurance ◽

Patient Specific ◽

Diode Array ◽

Two Dimensional

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Clinical experience using Delta 4 phantom for pretreatment patient-specific quality assurance in modern radiotherapy

Journal of Radiotherapy in Practice ◽

10.1017/s1460396918000572 ◽

2018 ◽

Vol 18 (02) ◽

pp. 210-214

Author(s):

R. P. Srivastava ◽

C. De Wagter

Keyword(s):

Quality Assurance ◽

Treatment Planning ◽

Volumetric Modulated Arc Therapy ◽

Planning System ◽

Treatment Planning System ◽

Patient Specific ◽

Dose Distributions ◽

Gamma Index ◽

Calculated Dose ◽

Treatment Plans

AbstractPurposeIn advanced radiotherapy techniques such as intensity-modulated radiation therapy (IMRT), the quality assurance (QA) process is essential. The aim of the study was to assure the treatment planning dose delivered during delivery of complex treatment plans. The QA standard is to perform patient-specific comparisons between planned doses and doses measured in a phantom.Materials and methodThe Delta 4 phantom (Scandidos, Uppsala, Sweden) has been used in this study. This device consists of diode matrices in two orthogonal planes inserted in a cylindrical acrylic phantom. Each diode is sampled per beam pulse so that the dose distribution can be evaluated on segment-by-segment, beam-by-beam, or as a composite plan from a single set of measurements. Ninety-five simple and complex radiotherapy treatment plans for different pathologies, planned using a treatment planning system (TPS) were delivered to the QA device. The planned and measured dose distributions were then compared and analysed. The gamma index was determined for different pathologies.ResultsThe evaluation was performed in terms of dose deviation, distance to agreement and gamma index passing rate. The measurements were in excellent agreement between with the calculated dose of the TPS and the QA device. Overall, good agreement was observed between measured and calculated doses in most cases with gamma values above 1 in >95% of measured points. Plan results for each test met the recommended dose goals.ConclusionThe delivery of IMRT and volumetric-modulated arc therapy (VMAT) plans was verified to correspond well with calculated dose distributions for different pathologies. We found the Delta 4 device is accurate and reproducible. Although Delta4 appears to be a straightforward device for measuring dose and allows measure in real-time dosimetry QA, it is a complex device and careful quality control is required before its use.

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Evaluation of patient specific quality assurance of gated field in field radiation therapy technique using two-dimensional detector array

Journal of Health Sciences ◽

10.17532/jhsci.2020.886 ◽

2020 ◽

Author(s):

Dražan Jaroš ◽

Goran Kolarević ◽

Aleksandar Kostovski ◽

Milovan Savanović ◽

Dejan Ćazić ◽

...

Keyword(s):

Breast Cancer ◽

Quality Assurance ◽

Radiation Therapy ◽

Treatment Plan ◽

Detector Array ◽

Patient Specific ◽

Two Dimensional ◽

Palo Alto ◽

Medical Systems ◽

Rpm System

Introduction: Gated tangential field-in-field (FIF) technique is used to lower the dose to organs at risk for breast cancer radiotherapy (RT). In this study, the authors investigated the accuracy of the delivered treatment plan with and without gating using a two-dimensional detector array for patient-specific verification purposes.Methods: In this study, a 6MV beams were used for the merged FIF RT (forward Intensity Modulated Radiation Therapy). The respiration signals for gated FIF delivery were obtained from the one-dimensional moving phantom using the real-time position management (RPM) system (Varian Medical Systems, Palo Alto, CA). RPM system used for four-dimensional computed tomography scanner light-speed, GE is based on an infrared camera to detect motion of external 6-point marker. The beams were delivered using a Clinac iX (Varian Medical Systems, Palo Alto, CA) with the multileaf collimator Millennium 120. The MapCheck2 (SunNuclear, Florida) was used for the evaluation of treatment plans. MapCheck2 was validated through a comparison with measurements from a farmer-type ion chamber. Gated beams were delivered using a maximum dose rate with varying duty cycles and analyzed the MapCheck2 data to evaluate treatment plan delivery accuracy.Results: Results of the gamma passing rate for relative and absolute dose differences for all ungated and gated beams were between 95.1% and 100%.Conclusion: Gated FIF technique can deliver an accurate dose to a detector during gated breast cancer RT. There is no significance between gated and ungated patient-specific quality assurance (PSQA); one can use ungated PSQA for verification of treatment plan delivery

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Portal Dosimetry as a patient specific Quality Assurance tool for Volumetric Arc Radiotherapy

International Journal of Medical Research and Review ◽

10.17511/ijmrr.2021.i01.04 ◽

2021 ◽

Vol 9 (1) ◽

pp. 29-33

Author(s):

Vikram Rathore ◽

◽

Mr. V.K Mishra ◽

Dr. V Choudhary ◽

Mr. G.S. Gautam ◽

...

Keyword(s):

Quality Assurance ◽

Patient Specific ◽

Advanced Technique ◽

Mean Values ◽

Treatment Patient ◽

Portal Dosimetry ◽

Gamma Index ◽

Patient Specific Qa ◽

The Mean ◽

Pre Treatment

Introduction: Volumetric Arc Radiotherapy (VMAT) is an advanced technique. Calculations of VMATplans are not so accurate even with State-of-Art dose calculation algorithms due to their complexity.Hence pre-treatment patient specific Quality Assurance (QA) of each VMAT plan is required. In thepresent study Electronic Portal Imaging Device (EPID) based portal dosimetry system was used forpre-treatment patient specific QA. Material and Methods: A total of 50 patients were chosen inthis study. Verification plans of each patient were calculated for portal dosimetry then executed onthe EPID system to measure the spatial distribution of radiation dose. Calculated and measured dosedistribution were compared to evaluate Gamma Index (GI) passing criteria of Dose Difference (DD)of 3% and Distance–to-Agreement (DTA) of 3mm, Area Gamma (γ% ≤1) >95%, Average Gamma(gAve) <0.5% and Maximum Gamma (gMax) <3.5%. Results: The mean values of Area Gamma (γ%≤1) were observed to be varied from 99.14±0.23% to 99.87±0.18%. The Mean Values of AverageGamma (gAve) are found to vary from 0.19±0.05% to 0.15±0.04% and the mean values ofMaximum Gamma (gMax) found to be varied from 1.94±0.37% to 1.59±0.41%. All the plans werepassed the gamma index criteria with very good agreement. Thus the use of Portal Dosimetry forpre-treatment patient QA is found to be a very useful, quick, precise, efficient and effective pre-treatment patient specific QA tool for VMAT treatment. Conclusion: Portal Dosimetry can be utilizedfor routine use for patient specific quality assurance for Volumetric Arc Radiotherapy treatment.

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