Recommendations on the practice of calibration, dosimetry, and quality assurance for gamma stereotactic radiosurgery: Report of AAPM Task Group 178

Petti, Paula L.; Rivard, Mark J.; Alvarez, P.; Bednarz, Greg; Bourland, J. Daniel; DeWerd, Larry A.; Drzymala, Robert E.; Johansson, Jonas; Kunugi, Keith A.; Ma, Lijun; Meltsner, Sheridan; Neyman, Gennady; Seuntjens, Jan; Shiu, Almon S.; Goetsch, Steven J.

doi:10.1002/mp.14831

Cited by 24 publications

(57 citation statements)

References 91 publications

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“…For instance, in the case of the Gamma Knife PPS, an on‐site diode tool (termed the focus precision tool) is used to verify the constancy of the PPS/RFP position at the center point of the stereotactic coordinate space on a monthly (although some sites run this test as frequently as daily) basis. This test reports output at a resolution of 0.1 mm, and has pass/fail tolerance of 0.4 mm (vector magnitude) 29 . Changes in system performance below this resolution may not be detected using this tool.…”

Section: Discussionmentioning

confidence: 99%

“…For equipment more specific to radiosurgery, reports such as AAPM TG‐75, 26 TG 148, 27 and TG 135 28 codify recommendations for frame‐based radiosurgery, helical tomotherapy, and robotic radiosurgery, respectively. Of particular significance, AAPM TG‐178 was recently published detailing recommendations for Gamma Knife QA 29 . These task groups include recommendations for specific QA tests and associated tolerance levels.…”

Section: Discussionmentioning

confidence: 99%

“…Of particular significance, AAPM TG-178 was recently published detailing recommendations for Gamma Knife QA. 29 These task groups include recommendations for specific QA tests and associated tolerance levels. However, the reasoning behind the specific tolerance levels is often not included in the reports, nor are the reports referenced against specific vendor criteria.…”

Section: Discussionmentioning

confidence: 99%

“…This test reports output at a resolution of 0.1 mm, and has pass/fail tolerance of 0.4 mm (vector magnitude). 29 Changes in system performance below this resolution may not be detected using this tool.…”

Section: Discussionmentioning

confidence: 99%

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8+ Year Performance of the Gamma Knife Perfexion/Icon Patient Positioning System and Possibilities for Preemptive Fault Detection Using Statistical Process Control

et al. 2021

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Background: The large fractional doses, steep dose gradients, and small targets found in intracranial radiosurgery require extremely low beam delivery uncertainty. In the case of Gamma Knife radiosurgery (GKRS), this includes minimizing patient positioning system (PPS) positioning uncertainty. Existing QA techniques are recipe based, and feature point in time pass/fail tolerances. However, modern treatment machines, including the Gamma Knife Perfexion/Icon systems, record extensive internal data in treatment logs. These data can be analyzed through statistical process control (SPC) methods which are designed to detect changes in process behavior. The purpose of this study was to characterize the long-term (8+ year) performance of a Perfexion/Icon unit and use SPC methods to determine if performance changes could be detected at levels lower than existing QA and internal manufacturer performance tolerances. Methods: In-house software was developed to parse Perfexion/Icon log-files and store relevant information on shot delivery in a relational database. A last-in, first-out (LIFO) queuing algorithm was created to heuristically match messages associated with a given delivered shot. Filtering criteria were developed to filter QA and uncompleted shots. The resulting matched shots were extracted. Achieved versus planned PPS position was determined for each PPS motor as well as for the vector magnitude difference in PPS position. Exponentially weighted moving average (EWMA) control charts were plotted to determine when process behavior changed over time. Results: 53833 shots were delivered over an 8+ year span in the study. The mean vector magnitude PPS difference was 32.7 µm, with 97.5% of all shots within 70.1 µm. Several changes in PPS positioning behavior were observed over time, corresponding with control system faults on several occasions requiring PPS recalibration. EWMA control charts clearly demonstrate that these faults could be identified and possibly predicted as many as 3 years before there were faults beyond control system tolerance. Conclusion:The PPS of Gamma Knife Perfexion/Icon systems has extremely low positioning uncertainties. EWMA control chart method can be utilized to track PPS performance over time and can potentially detect changes in performance that may indicate a component requiring maintenance. This would allow planned service visits to mitigate problems and prevent unplanned downtime.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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8+ Year Performance of the Gamma Knife Perfexion/Icon Patient Positioning System and Possibilities for Preemptive Fault Detection Using Statistical Process Control

et al. 2021

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“…10 Detailed information on SRS/SRT dedicated systems can be found in various references. 6,7,11 Table 1 summarizes the smallest collimator settings available on such radiotherapy delivery systems.…”

Section: Introductionmentioning

confidence: 99%

Report of AAPM Task Group 155: Megavoltage photon beam dosimetry in small fields and non‐equilibrium conditions

et al. 2021

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Abbreviations: %dd(10) x , The photon component of the percent depth dose at 10 cm depth in water for a 10 cm 2 × 10 cm 2 field; L∕ w air , Restricted mass collision stopping power ratio of water to air; en ∕ , Spectrum-averaged mass energy-absorption coefficient; AAPM, American Association of Physicists in Medicine; CPE, Charged Particle Equilibrium; DLG, Dosimetric leaf gap; D f msr w,Q msr , Absorbed dose to water at the reference depth z ref in water in the absence of the detector in a field specified by f msr and beam quality Q msr .; f clin , Clinical (clin) non-reference radiation field; f msr , Machine-specific reference (msr) field; f ref , Reference field (ref) specified in dosimetry protocols for which the calibration coefficient of an ionization chamber in terms of absorbed dose to water is provided by a standards laboratory; FWHM, Full-width at half-maximum; GUM, Guide to the expression of Uncertainty in Measurements.; IAEA, International Atomic Energy Agency; ICRU, International Commission on Radiation Units and Measurements; IMRT, Intensity-modulated radiation therapy; k Q,Q 0 , The beam-quality correction factor, which corrects for the differences between the response of an ionization chamber in the reference beam of quality Q o used for calibrating the chamber and the beam of quality Q (defined as k Q . in TG-51 4 ); k f ref Q,Q 0 , Correction factor that accounts for the differences between the response of a detector in field f ref in a beam of quality Q and reference beam quality Q 0 as defined in TRS-483. 1 and Palmans et al 2 ; k fclin,fmsr Qclin,Q msr , The detector-specific correction factor that accounts for the difference between the responses of the detector in fields f clin in a beam of quality Q clin and in fields f msr in beam of quality Q msr as defined by Alfonso et al. 3 ; LCPE, Lateral charged particle equilibrium; M fmsr Qmsr , Detector reading in field f msr and beam quality Q msr corrected for influence of changes in pressure and temperature, incomplete charge collection, polarity effect and electrometer correction factor (TRS-483 1 ); MU, Monitor unit; N D,w,Q 0 , This is N D,w in TG-51, 4 and defined as the calibration coefficient in terms of absorbed dose to water for an ionization chamber at a reference beam of quality,Q 0 and field size f ref ; N f ref D,w,Q 0

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Replacing gamma knife beam‐profiles on film with point‐detector scans

Rudek

Bernstein

Osterman

et al. 2022

J Applied Clin Med Phys

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Purpose Detector arrays and profile‐scans have widely replaced film‐measurements for quality assurance (QA) on linear accelerators. Film is still used for relative output factor (ROF) measurements, positioning, and dose‐profile verification for annual Leksell Gamma Knife (LGK) QA. This study shows that small‐field active detector measurements can be performed in the easily accessed clinical mode and that they are an effective replacement to time‐consuming and exacting film measurements. Methods Beam profiles and positioning scans for 4‐mm, 8‐mm, and 16‐mm‐collimated fields were collected along the x‐, y‐, and z‐axes. The Exradin W2‐scintillator and the PTW microdiamond‐detector were placed in custom inserts centered in the Elekta solid‐water phantom for these scans. GafChromic EBT3‐film was irradiated with single uniformly collimated exposures as the clinical‐standard reference, using the same solid‐water phantom for profile tests and the Elekta film holder for radiation focal point (RFP)/patient‐positioning system (PPS) coincidence. All experimental data were compared to the tissue‐maximum‐ratio‐based (TMR10) dose calculation. Results The detector‐measured beam profiles and film‐based profiles showed excellent agreement with TMR10‐predicted full‐width, half‐maximum (FWHM) values. Absolute differences between the measured FWHM and FWHM from the treatment‐planning system were on average 0.13 mm, 0.08 mm, and 0.04 mm for film, microdiamond, and scintillator, respectively. The coincidence between the RFP and the PPS was measured to be ≤0.5 mm with microdiamond, ≤0.41 mm with the W2‐1 × 1 scintillator, and ≤0.22 mm using the film‐technique. Conclusions Small‐volume field detectors, used in conjunction with a clinically available phantom, an electrometer with data‐logging, and treatment plans created in clinical mode offer an efficient and viable alternative for film‐based profile tests. Position verification can be accurately performed when CBCT‐imaging is available to correct for residual detector‐position uncertainty. Scans are easily set up within the treatment‐planning‐system and, when coupled with an automated analysis, can provide accurate measurements within minutes.

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Recommendations on the practice of calibration, dosimetry, and quality assurance for gamma stereotactic radiosurgery: Report of AAPM Task Group 178

Cited by 24 publications

References 91 publications

8+ Year Performance of the Gamma Knife Perfexion/Icon Patient Positioning System and Possibilities for Preemptive Fault Detection Using Statistical Process Control

8+ Year Performance of the Gamma Knife Perfexion/Icon Patient Positioning System and Possibilities for Preemptive Fault Detection Using Statistical Process Control

Report of AAPM Task Group 155: Megavoltage photon beam dosimetry in small fields and non‐equilibrium conditions

Replacing gamma knife beam‐profiles on film with point‐detector scans

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