Experimental validation of recommended msr-correction factors for the calibration of Leksell Gamma Knife® Icontm unit following IAEA TRS-483

Mirzakhanian, Lalageh; Sarfehnia, Arman; Seuntjens, Jan

doi:10.1088/1361-6560/ab6953

Cited by 5 publications

(12 citation statements)

References 18 publications

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“…For the ABS phantom, the dose‐rates were also on average 1.6% greater when using the parallel detector orientation as opposed to the perpendicular orientation. The results presented by Mirzakhanian et al 17 agree with this study, in that applying the correction factors by Mirzakhanian et al 14 accounted for the differences between the SW phantom and ABS phantom.…”

Section: Discussionsupporting

confidence: 87%

“…Mirzakhanian et al 17 recently investigated TRS‐483 using the correction factors by Mirzakhanian et al 14 and compared it to TG‐21 and TG‐51. Three phantoms and three ICs were used, and included the ABS and SW phantoms and a 31010 IC.…”

Section: Discussionmentioning

confidence: 99%

“…[13][14][15] Despite a surge of interest in small-field correction factors for the LGK Icon, few attempts have been made to verify them experimentally. 16,17 During commissioning of an LGK Icon at Karolinska University Hospital, Stockholm, Sweden, in September 2018, dose-rates were determined using an acrylonitrile butadiene styrene (ABS) phantom, and a Certified Medical Grade Solid Water ® (SW) phantom. A discrepancy in determined dose-rates between using the two phantom models was seen (M. Fager, personal communication, 25 April 2019).…”

Section: Introductionmentioning

confidence: 99%

“…Since the publication of TRS‐483, at least three additional sets of

k_{Q_{msr}, Q_{0}}^{f_{msr}, f_{ref}}

values have been published, all of which exhibit slight differences in methodology and results 13–15 . Despite a surge of interest in small‐field correction factors for the LGK Icon, few attempts have been made to verify them experimentally 16,17 . During commissioning of an LGK Icon at Karolinska University Hospital, Stockholm, Sweden, in September 2018, dose‐rates were determined using an acrylonitrile butadiene styrene (ABS) phantom, and a Certified Medical Grade Solid Water® (SW) phantom.…”

Section: Introductionmentioning

confidence: 99%

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Experimental investigation of TRS‐483 reference dosimetry correction factors for Leksell Gamma Knife® Icon™ beams

2020

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Purpose: Radiosurgery using the Leksell Gamma Knife ® (LGK) Icon ™ is an established technique used for treating intracranial lesions. The largest beam field size the LGK Icon can produce is a 16 mm diameter sphere. Despite this, reference dosimetry on the LGK Icon is typically performed using ionization chambers calibrated in 10 × 10 cm 2 fields. Furthermore, plastic phantoms are widely used instead of liquid water phantoms. In an effort to resolve these issues, the International Atomic Energy Agency (IAEA) in collaboration with American Association of Physicists in medicine (AAPM) recently published Technical Report Series No. 483 (TRS-483) as a Code of Practice for small-field dosimetry. TRS-483 includes small-field correction factors, k f msr ,f ref Q msr ,Q 0 , intended to account for the differences between setups when using small-field modalities such as the LGK Icon, and conventional setups. Since the publication of TRS-483, at least three new sets of values of k f msr ,f ref Q msr ,Q 0 for the LGK Icon have been published. The purpose of this study was to experimentally investigate the published values of k f msr ,f ref Q msr ,Q 0 for commonly used phantom and ionization chamber (IC) models for the LGK Icon. Methods: Dose-rates from two LGK units were determined using acrylonitrile butadiene styrene (ABS) and Certified Medical Grade Solid Water ® (SW) phantoms, and PTW 31010 and PTW 31016 ICs. Correction factors were applied, and the resulting dose-rates compared. Relative validity of the correction factors was investigated by taking the ratios of dose-rate correction factor products. Additionally, dose-rates from the individual sectors were determined in order to calculate the beam attenuation caused by the ABS phantom adapter. Results and Conclusions: It was seen that the dose-rate is underestimated by at least 1% when using the ABS phantom, which was attributed to fluence perturbation caused by the IC and phantom adapter. Published correction factors k f msr ,f ref Q msr ,Q 0 account for these effects to varying degree and should be used. The SW phantom is unlikely to underestimate the dose-rate by more than 1%, and applying k f msr ,f ref Q msr ,Q 0 could not be shown to be necessary. Out of the two phantom models, the ABS phantom is not recommended for use in LGK reference dosimetry. The use of newly published values of k f msr ,f ref Q msr ,Q 0 should be considered.

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Section: Discussionsupporting

confidence: 87%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

“…Since the publication of TRS‐483, at least three additional sets of

k_{Q_{msr}, Q_{0}}^{f_{msr}, f_{ref}}

Section: Introductionmentioning

confidence: 99%

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Experimental investigation of TRS‐483 reference dosimetry correction factors for Leksell Gamma Knife® Icon™ beams

2020

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“…According to Mirzakhanian et al [15], the detector orientation is different for the solid water phantom and the ABS phantom. Updating these values by including the results of more recent published studies is mandatory [14][15][16][17][18]. Once the absolute value of the absorbed dose rate is correctly measured for an MSR field, the field output factors should be determined.…”

Section: Small-field Dosimetrymentioning

confidence: 99%

Stereotactic Radiosurgery

Chung

Lee

2020

Progress in Medical Physics

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Stereotactic radiosurgery is one of the most sophisticated forms of modern advanced radiation therapy. Unlike conventional fractionated radiotherapy, stereotactic radiosurgery uses a high dose of radiation with steep gradient precisely delivered to target lesions. Lars Leksell presented the principle of radiosurgery in 1951. Gamma Knife ® (GK) is the first radiosurgery device used in clinics, and the first patient was treated in the winter of 1967. The first GK unit had 179 cobalt 60 sources distributed on a hemispherical surface. A patient could move only in a single direction. Treatment planning was performed manually and took more than a day. The latest model, Gamma Knife ® Icon TM , shares the same principle but has many new dazzling characteristics. In this article, first, a brief history of radiosurgery was described. Then, the physical properties of modern radiosurgery machines and physicists' endeavors to assure the quality of radiosurgery were described. Intrinsic characteristics of modern radiosurgery devices such as small fields, steep dose distribution producing sharp penumbra, and multi-directionality of the beam were reviewed together with the techniques to assess the accuracy of these devices. The reference conditions and principles of GK dosimetry given in the most recent international standard protocol, International Atomic Energy Agency TRS 483, were shortly reviewed, and several points needing careful revisions were highlighted. Understanding the principles and physics of radiosurgery will be helpful for modern medical physicists.

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Feasibility of isodose‐shaped scintillation detectors for the measurement of gamma knife output factors

et al. 2022

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Purpose Scintillation detectors were 3D printed based on a gamma knife (GK) dose distribution to calculate the volume averaging effect. The collimator output factors were measured using isodose‐shaped scintillators (ISSs) and compared with those of a micro‐diamond detector and previous reports. Methods An absorbed dose distribution in a spherical dosimetry phantom with a radius of 8 cm was obtained from GK treatment planning software (Leksell GammaPlan [LGP], Elekta AB, Stockholm, Sweden). Two types of ISSs were fabricated to fit the 97.2% (ISS‐1) and 95.6% (ISS‐2) isodose surfaces. The volume averaging correction factors were obtained by dividing the absorbed dose to water in the central voxel (CV) by that in the ISS. The correction effect due to the difference between the ISS and water was calculated by Monte Carlo simulations. Ten ISS detectors, five of each type, were used to measure the output factors of the 4‐ and 8‐mm collimators of a GK Icon to assess system consistency. The output factors of seven GKs were measured using two ISS detectors, one of each type, and a PTW T60019 (PTW, Freiburg, Germany) micro‐diamond detector. Results The detector output ratios (DORs) measured using the five ISSs of each type were consistent, with standard uncertainties less than 0.2%. In the 4‐mm field, the volume averaging correction factor ratios were 1.018 and 1.026, and the output factors after all corrections were 0.827 (0.006) and 0.825 (0.006) for ISS‐1 and ISS‐2, respectively. In the 8‐mm field, the volume averaging correction factor ratios were 1.000 for both ISS types, and the output factors were 0.898 (0.003) and 0.900 (0.003) for ISS‐1 and ISS‐2, respectively. The ISS detectors could measure the output factors of a GK with uncertainties comparable to that of the PTW 60019 detector. The output factors of all detectors decreased with the dose rate. Conclusion The volume averaging effect of an ISS developed in‐house could be calculated using known dose distributions. The collimator output factors of the GK Perfexion/Icon models measured using ISS detectors were consistent with those of a commercial synthetic micro‐diamond detector and recent studies.

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Experimental validation of recommended msr-correction factors for the calibration of Leksell Gamma Knife^® Icon^tm unit following IAEA TRS-483

Cited by 5 publications

References 18 publications

Experimental investigation of TRS‐483 reference dosimetry correction factors for Leksell Gamma Knife® Icon™ beams

Experimental investigation of TRS‐483 reference dosimetry correction factors for Leksell Gamma Knife® Icon™ beams

Stereotactic Radiosurgery

Feasibility of isodose‐shaped scintillation detectors for the measurement of gamma knife output factors

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