Clinical implications of the overshoot effect for treatment plan delivery and patient-specific quality assurance for step-and-shoot IMRT

Purpose: To evaluate the performance of Delta4DVH Anatomy in patient-specific intensity-modulated radiotherapy quality assurance. Materials and Methods: Dose comparisons were performed between Anatomy doses calculated with treatment plan dose measured modification and pencil beam algorithms, treatment planning system doses, film doses, and ion chamber measured doses in homogeneous and inhomogeneous geometries. The sensitivity of Anatomy doses to machine errors and output calibration errors was also investigated. Results: For a Volumetric Modulated Arc Therapy (VMAT) plan evaluated on the Delta4 geometry, the conventional gamma passing rate was 99.6%. For a water-equivalent slab geometry, good agreements were found between dose profiles in film, treatment planning system, and Anatomy treatment plan dose measured modification and pencil beam calculations. Gamma passing rate for Anatomy treatment plan dose measured modification and pencil beam doses versus treatment planning system doses was 100%. However, gamma passing rate dropped to 97.2% and 96% for treatment plan dose measured modification and pencil beam calculations in inhomogeneous head & neck phantom, respectively. For the 10 patients’ quality assurance plans, good agreements were found between ion chamber measured doses and the planned ones (deviation: 0.09% ± 1.17%). The averaged gamma passing rate for conventional and Anatomy treatment plan dose measured modification and pencil beam gamma analyses in Delta4 geometry was 99.6% ± 0.89%, 98.54% ± 1.60%, and 98.95% ± 1.27%, respectively, higher than averaged gamma passing rate of 97.75% ± 1.23% and 93.04% ± 2.69% for treatment plan dose measured modification and pencil beam in patients’ geometries, respectively. Anatomy treatment plan dose measured modification dose profiles agreed well with those in treatment planning system for both Delta4 and patients’ geometries, while pencil beam doses demonstrated substantial disagreement in patients’ geometries when compared to treatment planning system doses. Both treatment planning system doses are sensitive to multileaf collimator and monitor unit (MU) errors for high and medium dose metrics but not sensitive to the gantry and collimator rotation error smaller than 3°. Conclusions: The new Delta4DVH Anatomy with treatment plan dose measured modification algorithm is a useful tool for the anatomy-based patient-specific quality assurance. Cautions should be taken when using pencil beam algorithm due to its limitations in handling heterogeneity and in high-dose gradient regions.

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Patient-specific quality assurance measurements for VMAT treatments: Do we really catch errors?

Journal of Clinical Oncology ◽

10.1200/jco.2013.31.31_suppl.81 ◽

2013 ◽

Vol 31 (31_suppl) ◽

pp. 81-81 ◽

Cited By ~ 3

Author(s):

Wolfram Laub ◽

Charles R. Thomas

Keyword(s):

Quality Assurance ◽

Head And Neck ◽

Treatment Plan ◽

Patient Specific ◽

Imrt Qa ◽

Passing Rates ◽

Passing Rate ◽

Gamma Index ◽

Clinically Significant ◽

Alignment Errors

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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Design of a Reconfigurable Quality Assurance Phantom for Verifying the Spatial Accuracy of Radiosurgery Treatments for Multiple Brain Metastases

Journal of Medical Devices ◽

10.1115/1.4044402 ◽

2019 ◽

Vol 13 (4) ◽

Author(s):

Alban C. Cobi ◽

Luke Gray ◽

Elizabeth R. Mittmann ◽

Steven B. Link ◽

Nevan C. Hanumara ◽

...

Keyword(s):

Quality Assurance ◽

Brain Metastases ◽

Treatment Plan ◽

External Beam Radiotherapy ◽

Patient Specific ◽

Positional Error ◽

Active Volume ◽

Multiple Brain Metastases ◽

Measuring Machine ◽

Clinical Conditions

Abstract Radiation therapy frequently involves highly customized and complex treatments, employing sophisticated equipment, that require extensive patient-specific validation to verify the accuracy of the treatment plan as part of the clinical quality assurance (QA) process. This paper introduces a novel, reconfigurable QA phantom developed for the spatial validation of radiosurgery treatments of multiple brain metastases (MBM). This phantom works in conjunction with existing electronic portal imaging detector (EPID) technology to rapidly verify MBM treatment plans with submillimeter accuracy. The device provides a 12 × 12 × 12 cm3 active volume and multiple, independently configurable markers, in the form of 3 mm diameter radiopaque spheres, which serve as surrogates for brain lesions. The device is lightweight, portable, can be setup by a single operator, and is adaptable for use with external beam radiotherapy (EBRT) techniques and stereotactic linear accelerators (LINACs). This paper presents the device design and fabrication, along with initial testing and validation results both in the laboratory, using a coordinate measuring machine (CMM) and under simulated clinical conditions, using a radiosurgery treatment plan with 15 lesions. The device has been shown to place markers in space with a 0.45 mm root-mean-square error, which is satisfactory for initial clinical use. The device is undergoing further testing under simulated clinical conditions and improvements to reduce marker positional error.

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Analysis of EORTC-1219-DAHANCA-29 trial plans demonstrates the potential of knowledge-based planning to provide patient-specific treatment plan quality assurance

Radiotherapy and Oncology ◽

10.1016/j.radonc.2018.10.005 ◽

2019 ◽

Vol 130 ◽

pp. 75-81 ◽

Cited By ~ 4

Author(s):

Jim P. Tol ◽

Max Dahele ◽

Vincent Gregoire ◽

Jens Overgaard ◽

Ben J. Slotman ◽

...

Keyword(s):

Quality Assurance ◽

Treatment Plan ◽

Specific Treatment ◽

Patient Specific ◽

Plan Quality ◽

Knowledge Based ◽

Knowledge Based Planning

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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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