Dosimetric characterization and output verification for conical brachytherapy surface applicators. Part II. High dose rate <sup>192</sup>Ir sources

Fulkerson, Regina K.; Micka, J; DeWerd, Larry A.

doi:10.1118/1.4862506

Cited by 21 publications

(37 citation statements)

References 20 publications

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“…Typical prescription depth with these applicators is between 3 mm and 4 mm. Clini-cal implementation and dosimetry of skin applicators have been reported elsewhere in the literature [2][3][4][5][6][7][8][9][10].…”

Section: Purposementioning

confidence: 99%

Dosimetric Characteristics of a New Unit for Electronic Skin Brachytherapy

et al. 2014

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Purpose: Brachytherapy with radioactive high dose rate (HDR) 192 Ir source is applied to small skin cancer lesions, using surface applicators, i.e. Leipzig or Valencia type. New developments in the field of radiotherapy for skin cancer include electronic brachytherapy. This technique involves the placement of an HDR X-ray source close to the skin, therefore combining the benefits of brachytherapy with the reduced shielding requirements and targeted energy of low energy X-rays. Recently, the Esteya ® Electronic Brachytherapy System (Esteya EBS, Elekta AB-Nucletron, Stockholm, Sweden) has been developed specifically for HDR brachytherapy treatment of surface lesions. The system provides radionuclide free HDR brachytherapy by means of a small 69.5 kV X-ray source. The purpose of this study is to obtain the dosimetric characterization required for clinical implementation, providing the detailed methodology to perform the commissioning.Material and methods: Flatness, symmetry and penumbra, percentage of depth dose (PDD), kV stability, HVL, output, spectrum, linearity, and leakage have been evaluated for a set of applicators (from 10 mm to 30 mm in diameter).Results: Flatness and symmetry resulted better than 5% with around 1 mm of penumbra. The depth dose gradient is about 7%/mm. A kV value of 68.4 ± 1.0 kV (k = 1) was obtained, in good agreement with manufacturer data (69.5 kV). HVL was 1.85 mm Al. Dose rate for a typical 6 Gy to 7 Gy prescription resulted about 3.3 Gy/min and the leakage value was < 100 µGy/min. Conclusions:The new Esteya ® Electronic Brachytherapy System presents excellent flatness and penumbra as with the Valencia applicator case, combined with an improved PDD, allowing treatment of lesions of up to a depth of 5 mm in combination with reduced treatment duration. The Esteya unit allows HDR brachytherapy superficial treatment within a minimally shielded environment due its low energy.

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Section: Purposementioning

confidence: 99%

Dosimetric Characteristics of a New Unit for Electronic Skin Brachytherapy

et al. 2014

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“…Corrections were also made to account for the electrometer, temperature, and pressure. The corrected reading was converted to dose (as if the applicator were in contact with a water phantom) following the methodology described in the AAPM Task Group 61 report: (9)

D_{w, z = 0} = M_{r a w} \times P_{p o l} \times P_{i o n} \times P_{e l} \times P_{T, P} \times N_{k} \times B_{w} \times P_{s t e m, a i r} \times {[{(\frac{μ_{e n}}{ρ})}_{a i r}^{w}]}_{f r e e a i r} \times P O M,

where

P O M false(p o italicint o f m e a s u r e m e n t false) = {(\frac{S S D + d}{S S D})}^{2} .

Here SSD is 14.7 mm and 19.7 mm for a single source located at

- 10 mm

and

- 15 mm

from the center of the first nominal dwell position, respectively, and d is 3.4 mm [1.6 mm ion chamber cap thickness (10) and 1.8 mm shift for the point of measurement relative to the ion chamber tip (11) ]. The plastic inset thickness is 1.7 mm (included in the SSD).…”

Section: Methodsmentioning

confidence: 99%

“…The Exradin A20 ion chamber was designed by Standard Imaging for measurements with the HDR

^{192} Ir

surface applicators and recommended by Varian. Similar setup for surface applicators dose measurements was previously used by other groups 10 , 11 for either source vertically or horizontally positioned relative to the skin surface. Future work will be performed using a very thin‐walled, well‐guarded parallel plate detector.…”

Section: Methodsmentioning

confidence: 99%

Varian HDR surface applicators — commissioning and clinical implementation

Iftimia

McKee

Halvorsen

2016

J Applied Clin Med Phys

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The purpose of this study was to validate the dosimetric performance of Varian surface applicators with the source vertically positioned and develop procedures for clinical implementation. The Varian surface applicators with the source vertically positioned provide a wide range of apertures making them clinically advantageous, though the steep dose gradient in the region of 3‐4 mm prescription depth presents multiple challenges. The following commissioning tests were performed: 1) verification of functional integrity and physical dimensions; and 2) dosimetric measurements to validate data provided by Varian as well as data obtained using the Acuros algorithm for heterogeneity corrected dose calculation. A solid water (SW) phantom was scanned and the Acuros algorithm was used to compute the dose at 5 mm depth and at surface for all applicators. Two sets of reference dose measurements were performed, with the source positioned at (i) −10 mm and (ii) −15 mm from the center of the first nominal dwell position. Measurements were taken at 5 mm depth in a SW phantom and in air at the applicator surface. The results were then compared to the vendor's data and to the Acuros calculated dose. Relative dose measurements using Gafchromic films were taken at a depth of 4 mm in SW. Percent depth ionization (PDI) measurements using ion chamber were performed in SW. The profiles generated from film measurements and the PDI plots were compared with those computed using the Acuros algorithm and vendor's data, when available. Preliminary leakage tests were performed using optically stimulated luminescence dosimeters (OSLDs) and the results were compared with Acuros predictions. All applicators were found to be functional with physical dimensions within 1 mm of specifications. For scenario (ii) measurements taken in SW at 5 mm depth and in air at the surface of each applicator were within 10% and 4% agreement with vendor's data, respectively. Compared with Acuros predictions, these measurements were within 6% and 5%, respectively. Measurements taken for scenario (i) showed reduced agreement with both the vendor's data as well as the Acuros calculations, especially when using the 10 mm applicator. The full widths of the measured dose profiles were within 2 mm of those predicted by Acuros at the 90% dose level. The PDI plots and measured leakage dose were in good agreement with vendor's data and Acuros predictions. Based on the dosimetric results, a quality assurance program and procedures for clinical implementation were developed. Treatment planning will be performed using scenario (ii). The 10 mm applicator will not be released for clinical use. A prescription depth of 4 mm is recommended, to ensure full coverage at 3 mm and a minimum dose of 90% of prescribed dose at 4 mm depth.PACS number(s): 87.55 Qr, 87.56 Da, 87.90 +y

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“…Published data and manufacturer instructions refer to “in-phantom” measurements [12,13], wherein treatment time calculations are typically done using a lookup table of depth-dose profiles along the applicator central axis, and assume the applicator is face down, replicating phantom measurements.…”

Section: Introductionmentioning

confidence: 99%

Impact of source position on high-dose-rate skin surface applicator dosimetry

et al. 2016

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Purpose Skin surface dosimetric discrepancies between measured and treatment planning system (TPS) predicted values were traced to source position sag inside the applicator and to source transit time. We quantified their dosimetric impact and propose corrections for clinical use. Material and methods We measured the dose profiles from the Varian Leipzig-style HDR skin applicator, using EBT3 film, photon diode, and optically stimulated luminescence dosimeter for three different GammaMedplus™ HDR afterloaders. The measured dose profiles at several depths were compared with BrachyVision Acuros™ calculated profiles. To assess the impact of the source sag, two different applicator orientations were considered. The dose contribution during source transit was assessed by comparing diode measurements using a HDR timer and an electrometer timer. Results Depth doses measured using the three dosimeters were in good agreement, but were consistently higher than the Acuros dose calculations. Measurements with the applicator face up were significantly (exceeding 10%) lower than those in the face down position, due to source sag inside the applicator. Based on the inverse square law, the effective source sag was evaluated to be about 0.5 mm from the planned position. The additional dose during source transit was evaluated to be about 2.8% for 30 seconds of treatment with a 40700 U (10 Ci) source. Conclusion With a very short source-to-surface distance, the small source sag inside the applicator has a significant dosimetric impact. This effect is unaccounted for in the vendor’s treatment planning template, and should be considered before the clinical use of the applicator. Further investigation of other applicators with large source lumen diameter may be warranted.

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Dosimetric characterization and output verification for conical brachytherapy surface applicators. Part II. High dose rate ¹⁹²Ir sources

Abstract: The novel output verification methods described in this work will reduce uncertainties in dose delivery for treatments with these kinds of surface applicators, ultimately improving patient care.

Cited by 21 publications

References 20 publications

Dosimetric Characteristics of a New Unit for Electronic Skin Brachytherapy

Dosimetric Characteristics of a New Unit for Electronic Skin Brachytherapy

Varian HDR surface applicators — commissioning and clinical implementation

Impact of source position on high-dose-rate skin surface applicator dosimetry

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Dosimetric characterization and output verification for conical brachytherapy surface applicators. Part II. High dose rate 192Ir sources

Abstract: The novel output verification methods described in this work will reduce uncertainties in dose delivery for treatments with these kinds of surface applicators, ultimately improving patient care.

Cited by 21 publications

References 20 publications

Dosimetric Characteristics of a New Unit for Electronic Skin Brachytherapy

Dosimetric Characteristics of a New Unit for Electronic Skin Brachytherapy

Varian HDR surface applicators — commissioning and clinical implementation

Impact of source position on high-dose-rate skin surface applicator dosimetry

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Product

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Dosimetric characterization and output verification for conical brachytherapy surface applicators. Part II. High dose rate ¹⁹²Ir sources