Dosimetry studies with TLDs for stereotactic radiation techniques for intraocular tumours

Ertl, Adolf; Zehetmayer, Martin; Schöggl, Andreas; Kindl, Peter; Hartl, Roman F E

doi:10.1088/0031-9155/42/11/009

Cited by 17 publications

(4 citation statements)

References 22 publications

(24 reference statements)

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“…Evaluation of the calibrated TLDs was carried out with a Harshaw 2000D TLD reader, revealing a deviation between ±1.5%. The accuracy of this process has been verified by previous investigations (Ertl et al 1996(Ertl et al , 1997.…”

Section: Measurements With Tld Crystalssupporting

confidence: 71%

Shuttle dose at the Vienna Leksell Gamma Knife

et al. 1998

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The aim of this study was to determine the shuttle dose for all collimator helmets (4, 8, 14 and 18 mm) of the Gamma Knife, model B, in Vienna, Austria. The additional dose accumulated during the transport of the patient in and out of the treatment position should be considered in the dose planning procedure of multicentre treatment regimens and in fractionated stereotactic Gamma Knife radiotherapy. The GafChromic film study was basically used to determine the shuttle dose of all four collimator helmets. In addition, measurements with an ionization chamber (18 and 14 mm collimator--and, for the 18 mm collimator helmet, TLD dosimetry--were performed in order to confirm the GafChromic film data. The shuttle dose ranged between 99.6 and 183.5 mGy, depending mainly on the size of the collimator and the irradiated isocentres at the half-life activity of Co-60 in a brand new Gamma unit. Our film-generated data were in good correlation with the dose levels obtained with the ionization chamber and the TLD dosimetry, showing a dose difference of less than 0.8%. Since it was possible to verify the shuttle dose even for the 4 and 8 mm collimator helmets, we consider it a non-negligible factor and would advocate the inclusion of the shuttle dose in radiosurgical dose planning.

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Section: Measurements With Tld Crystalssupporting

confidence: 71%

Shuttle dose at the Vienna Leksell Gamma Knife

et al. 1998

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“…In this work, cubic TLD-100 dosimeters and EBT3 films were used to measure the radiation dose [ 17 – 22 ], with the dose at each tumor location measured three times. Each cone-based linac and FFF-VMAT linac measurement was accompanied by alignment using the six degree-of-freedom image-guided cone-beam CT of the accelerator.…”

Section: Methodsmentioning

confidence: 99%

Dosimetric comparison of different treatment modalities for stereotactic radiotherapy

et al. 2017

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BackgroundThe modalities for performing stereotactic radiotherapy (SRT) on the brain include the cone-based linear accelerator (linac), the flattening filter-free (FFF) volumetric modulated arc therapy (VMAT) linac, and tomotherapy. In this study, the cone-based linac, FFF-VMAT linac, and tomotherapy modalities were evaluated by measuring the differences in doses delivered during brain SRT and experimentally assessing the accuracy of the output radiation doses through clinical measurements.MethodsWe employed a homemade acrylic dosimetry phantom representing the head, within which a thermoluminescent dosimeter (TLD) and radiochromic EBT3 film were installed. Using the conformity/gradient index (CGI) and Paddick methods, the quality of the doses delivered by the various SRT modalities was evaluated. The quality indicators included the uniformity, conformity, and gradient indices. TLDs and EBT3 films were used to experimentally assess the accuracy of the SRT dose output.ResultsThe dose homogeneity indices of all the treatment modalities were lower than 1.25. The cone-based linac had the best conformity for all tumors, regardless of the tumor location and size, followed by the FFF-VMAT linac; tomography was the worst-performing treatment modality in this regard. The cone-based linac had the best gradient, regardless of the tumor location and size, whereas the FFF-VMAT linac had a better gradient than tomotherapy for a large tumor diameter (28 mm). The TLD and EBT3 measurements of the dose at the center of tumors indicated that the average difference between the measurements and the calculated dose was generally less than 4%. When the 3% 3-mm gamma passing rate metric was used, the average passing rates of all three treatment modalities exceeded 98%.ConclusionsRegarding the dose, the cone-based linac had the best conformity and steepest dose gradient for tumors of different sizes and distances from the brainstem. The results of this study suggest that SRT should be performed using the cone-based linac on tumors that require treatment plans with a steep dose gradient, even as the tumor is slightly irregular, we should also consider using a high dose gradient of the cone base to treat and protect the normal tissue. If normal tissues require special protection exist at positions that are superior or inferior to the tumor, we can consider using tomotherapy or Cone base with couch at 0° for treatment.

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“…In a study of spatial dose cross-distribution in intraocular tumors, one study demonstrated that the computer-generated calculated dose was up to 30% less than the actual dose values measured in the anterior eye. 12 Despite the need to calculate a larger number of single beam extrapolations to determine the dose plan in prone compared with supine positions, there was no significant difference in calculated and measured doses at the isocenter or posterior component of the treated area for either position. This group theorized that the 24 preselected source-to-skull distances used in the GammaPlan treatment program may be the major factor in this discrepancy.…”

Section: Discussionmentioning

confidence: 87%