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Commissioning and Clinical Implementation of Varian Surface Applicators
S66
Abstracts / Brachytherapy 14 (2015) S11eS106
For the clinical plan having an irregularly-shaped CTV, the CTV was 1.83 cm3 and PTV was 46.29 cm3. The same prescriptive goal of 90 Gy to PTV100 5 90% was used. The DHI values for the three clinical plans were 0.80, 0.82, and 0.77, which compared favorably to the 0.73 mean value by Das et al (2004) for HDR 192Ir interstitial breast brachytherapy. The mean observed PTV200 value for the three plan variations (i.e., 6.2%, range 5.9%-6.6%) was about four times lower than that observed by Pignol et al. (2006). However, the results of this single, irregularly shaped CTV should not be generalized to all CTV shapes, sizes, and clinical geometries. Conclusions: There is potential for interstitial LDR 103Pd PBSI using the CivaString to provide a better DHI and less skin dose.
PHSOR12 Presentation Time: 10:57 AM Commissioning and Clinical Implementation of Varian Surface Applicators Ileana Iftimia, PhD, Mike Talmadge, MS, Per Halvorsen, MS. Radiation Oncology, Lahey Clinic, Burlington, MA, USA. Purpose: To validate the dosimetric performance of Varian surface applicators with the source vertically positioned as well as to develop procedures for clinical implementation. Materials and Methods: Varian surface applicators with the source vertically positioned are circular or ovoid in shape, ranging in diameter from 10 to 45 mm. The variety of applicator sizes that are available make them clinically advantageous, though the orthogonal source orientation and the steepness of the resulting dose gradient in the region of prescription depth (3-4 mm) presents multiple challenges. In the absence of published guidelines, the following tests were designed for commissioning: 1) Verification of functional integrity and physical dimensions by visual inspection and measurement; 2) Dosimetric measurements to validate data provided by Varian (based on ionization chamber measurements performed in plastic phantoms during the 1990’s) as well as obtained using the Brachyvision Treatment Planning System equipped with the Acuros BV GBBS algorithm for heterogeneity corrected dose calculation. a) Absolute Dose Measurements Two sets of measurements were performed with the source positioned at -10 mm and -15 mm from the center of the first nominal dwell position. Corrections were applied to account for the electrometer, temperature and pressure, polarity effects, as well as recombination. A solid water phantom was scanned and the Acuros algorithm was used to compute the dose at 5 mm depth and at surface for all applicators, using a resolution of 0.05 cm and assuming medium is water. The measurement results were then compared to the vendor’s data and the Acuros calculated dose. i) Measurements were taken at 5 mm depth in a solid water phantom using a Markus chamber in a 2.5-cm polystyrene slab with a 5-cm solid water slab for backscatter, using a calibration factor for 60Co in water. A previously determined phantom factor was then used to convert the results into dose to water. ii) Measurements at the applicator surface were performed in air using an Exradin A20 ion chamber and a Standard Imaging jig designed for such measurements. The calibration factor for 192Ir was obtained through interpolation between the factors for 137Cs and a 250 kV beam. The corrected reading was converted to dose using the AAPM TG 61 formalism. b) Relative Dose Measurements Measurements using GafChromic film were taken at a depth of 4 mm in solid water with the source positioned at -15 mm from the center of the first nominal dwell position. Dwell times were selected to deliver a dose at depth of 1- 2 Gy. The exposed films were scanned and from the digital dataset profiles were generated for comparison with those predicted by the Acuros algorithm. Results: 1) All applicators were found to be functional with physical dimensions within 1 mm of specifications.
2) Dosimetric Measurements (excluding the 10 mm applicator): ai) Measurements taken in solid water at a depth of 5 mm were within 15% of the vendor’s data when using a source at -10 mm position and within 10% when using a source at -15 mm position. These measured data were also within 5% and 4% of the Acuros predictions, respectively. aii) Measurements taken at the surface of each applicator were found to be within 8% of the vendor’s data when using a source at -10 mm position and within 6% when using a source at -15 mm position. These measured data were also within 16% and 5% of the Acuros predictions, respectively. It should also be noted that the vendor’s dataset and the Acuros data at surface were within 15% agreement when using a source at -10 mm position and within 5.5% agreement when using a source at -15 mm position. Measurements taken using the 10 mm applicator showed poor agreement with both the vendor’s data as well as the Acuros calculations. b) The full widths of the measured dose profiles were within 2 mm of those predicted by Acuros at the 90% dose level. Based on the dosimetric results, a quality assurance program and procedures for clinical implementation were developed. Conclusions: Treatment planning will be performed using a single dwell position located at -15 mm from the center of the first nominal dwell position. 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. As a conservative approach, the applicator selection will be based on the 90% dose level width at 4 mm depth from Acuros plans.
PHSOR16 Presentation Time: 11:01 AM An Experimental Modal Investigation of the Dosimetry Parameters for Self-Expandable Esophageal Stent Loaded With I-125 Seeds Lei Lin, PhD, MD, Junjie Wang, PhD, MD, Ruijie Yang, PhD, Yuliang Jiang, MD, Weijuan Jiang, MD, Shukun Jiang, MD, Ziyi Liu, MD, Min Wang, MD. Department of Radiation Oncology, Peking University 3rd Hospital, Beijing, China. Purpose: With the widespread adoption of self-expandable esophageal stent loaded with 125I seeds, a number of parameters of the irradiation stent dosimetry were needed to identify. The aim of this study was to investigate potential dosimetry distribution for self-expandable esophageal stent loaded with 125I seeds and to propose standard dosimetry parameters. Materials and Methods: Six models of stents (Nanjing Micro-Tech Co Ltd, Nanjing, China) which were 8.0cm length2.0cm diameter with 1.5cm spacing of the seed center (A), 8.0cm length2.0cm diameter with 1.0cm spacing of the seed center (B), 8.0cm length1.3cm diameter with 1.0cm spacing of the seed center (C), 8.0cm length2.4cm diameter with 1.0cm spacing of the seed center (D), 12.0cm length2.0cm diameter with 1.0cm spacing of the seed center (E), and 16.0cm length2.0cm diameter with 1.0cm spacing of the seed center (F), were studied. The treatment planning system (TPS) used to calculate the dose delivery at specific points. The points were defined at polar angles of 0-90 in 10 increments and at radial distances from outer surface of the stent were 0.5, 0.75, 1, 1.25, 1.5, 2, 2.5, 3, 3.5, 4, 5, and 7cm. A cross section of the detector was arranged. The thermoluminescence detector (TLD) used for this study was LiF:Mg,Cu,P (GR 200A). The detectors were defined at polar angles of 0-90 in 10 increments and at radial distances from outer surface of the stent were 0.5, 0.75, 1, 1.25, 1.5, 2, 2.5, 3, 3.5, 4, 5, and 7cm. A cross section of the detector was arranged. The readout system was a TL Reader (Thermo, USA). The heating cycle consisted of preheat, readout, anneal and cool segments. The Monte Carlo (MC) were used for the dosimetry simulations around the irradiation stent. The range for photon and electron transport extends from 1 KeV to 100 MeV. The irradiation stents have been simulated in the centre of a spherical phantom of water with 20 cm radius, large enough to consider all the scattering effects of the surrounding medium. The detectors were
Abstracts / Brachytherapy 14 (2015) S11eS106
For the clinical plan having an irregularly-shaped CTV, the CTV was 1.83 cm3 and PTV was 46.29 cm3. The same prescriptive goal of 90 Gy to PTV100 5 90% was used. The DHI values for the three clinical plans were 0.80, 0.82, and 0.77, which compared favorably to the 0.73 mean value by Das et al (2004) for HDR 192Ir interstitial breast brachytherapy. The mean observed PTV200 value for the three plan variations (i.e., 6.2%, range 5.9%-6.6%) was about four times lower than that observed by Pignol et al. (2006). However, the results of this single, irregularly shaped CTV should not be generalized to all CTV shapes, sizes, and clinical geometries. Conclusions: There is potential for interstitial LDR 103Pd PBSI using the CivaString to provide a better DHI and less skin dose.
PHSOR12 Presentation Time: 10:57 AM Commissioning and Clinical Implementation of Varian Surface Applicators Ileana Iftimia, PhD, Mike Talmadge, MS, Per Halvorsen, MS. Radiation Oncology, Lahey Clinic, Burlington, MA, USA. Purpose: To validate the dosimetric performance of Varian surface applicators with the source vertically positioned as well as to develop procedures for clinical implementation. Materials and Methods: Varian surface applicators with the source vertically positioned are circular or ovoid in shape, ranging in diameter from 10 to 45 mm. The variety of applicator sizes that are available make them clinically advantageous, though the orthogonal source orientation and the steepness of the resulting dose gradient in the region of prescription depth (3-4 mm) presents multiple challenges. In the absence of published guidelines, the following tests were designed for commissioning: 1) Verification of functional integrity and physical dimensions by visual inspection and measurement; 2) Dosimetric measurements to validate data provided by Varian (based on ionization chamber measurements performed in plastic phantoms during the 1990’s) as well as obtained using the Brachyvision Treatment Planning System equipped with the Acuros BV GBBS algorithm for heterogeneity corrected dose calculation. a) Absolute Dose Measurements Two sets of measurements were performed with the source positioned at -10 mm and -15 mm from the center of the first nominal dwell position. Corrections were applied to account for the electrometer, temperature and pressure, polarity effects, as well as recombination. A solid water phantom was scanned and the Acuros algorithm was used to compute the dose at 5 mm depth and at surface for all applicators, using a resolution of 0.05 cm and assuming medium is water. The measurement results were then compared to the vendor’s data and the Acuros calculated dose. i) Measurements were taken at 5 mm depth in a solid water phantom using a Markus chamber in a 2.5-cm polystyrene slab with a 5-cm solid water slab for backscatter, using a calibration factor for 60Co in water. A previously determined phantom factor was then used to convert the results into dose to water. ii) Measurements at the applicator surface were performed in air using an Exradin A20 ion chamber and a Standard Imaging jig designed for such measurements. The calibration factor for 192Ir was obtained through interpolation between the factors for 137Cs and a 250 kV beam. The corrected reading was converted to dose using the AAPM TG 61 formalism. b) Relative Dose Measurements Measurements using GafChromic film were taken at a depth of 4 mm in solid water with the source positioned at -15 mm from the center of the first nominal dwell position. Dwell times were selected to deliver a dose at depth of 1- 2 Gy. The exposed films were scanned and from the digital dataset profiles were generated for comparison with those predicted by the Acuros algorithm. Results: 1) All applicators were found to be functional with physical dimensions within 1 mm of specifications.
2) Dosimetric Measurements (excluding the 10 mm applicator): ai) Measurements taken in solid water at a depth of 5 mm were within 15% of the vendor’s data when using a source at -10 mm position and within 10% when using a source at -15 mm position. These measured data were also within 5% and 4% of the Acuros predictions, respectively. aii) Measurements taken at the surface of each applicator were found to be within 8% of the vendor’s data when using a source at -10 mm position and within 6% when using a source at -15 mm position. These measured data were also within 16% and 5% of the Acuros predictions, respectively. It should also be noted that the vendor’s dataset and the Acuros data at surface were within 15% agreement when using a source at -10 mm position and within 5.5% agreement when using a source at -15 mm position. Measurements taken using the 10 mm applicator showed poor agreement with both the vendor’s data as well as the Acuros calculations. b) The full widths of the measured dose profiles were within 2 mm of those predicted by Acuros at the 90% dose level. Based on the dosimetric results, a quality assurance program and procedures for clinical implementation were developed. Conclusions: Treatment planning will be performed using a single dwell position located at -15 mm from the center of the first nominal dwell position. 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. As a conservative approach, the applicator selection will be based on the 90% dose level width at 4 mm depth from Acuros plans.
PHSOR16 Presentation Time: 11:01 AM An Experimental Modal Investigation of the Dosimetry Parameters for Self-Expandable Esophageal Stent Loaded With I-125 Seeds Lei Lin, PhD, MD, Junjie Wang, PhD, MD, Ruijie Yang, PhD, Yuliang Jiang, MD, Weijuan Jiang, MD, Shukun Jiang, MD, Ziyi Liu, MD, Min Wang, MD. Department of Radiation Oncology, Peking University 3rd Hospital, Beijing, China. Purpose: With the widespread adoption of self-expandable esophageal stent loaded with 125I seeds, a number of parameters of the irradiation stent dosimetry were needed to identify. The aim of this study was to investigate potential dosimetry distribution for self-expandable esophageal stent loaded with 125I seeds and to propose standard dosimetry parameters. Materials and Methods: Six models of stents (Nanjing Micro-Tech Co Ltd, Nanjing, China) which were 8.0cm length2.0cm diameter with 1.5cm spacing of the seed center (A), 8.0cm length2.0cm diameter with 1.0cm spacing of the seed center (B), 8.0cm length1.3cm diameter with 1.0cm spacing of the seed center (C), 8.0cm length2.4cm diameter with 1.0cm spacing of the seed center (D), 12.0cm length2.0cm diameter with 1.0cm spacing of the seed center (E), and 16.0cm length2.0cm diameter with 1.0cm spacing of the seed center (F), were studied. The treatment planning system (TPS) used to calculate the dose delivery at specific points. The points were defined at polar angles of 0-90 in 10 increments and at radial distances from outer surface of the stent were 0.5, 0.75, 1, 1.25, 1.5, 2, 2.5, 3, 3.5, 4, 5, and 7cm. A cross section of the detector was arranged. The thermoluminescence detector (TLD) used for this study was LiF:Mg,Cu,P (GR 200A). The detectors were defined at polar angles of 0-90 in 10 increments and at radial distances from outer surface of the stent were 0.5, 0.75, 1, 1.25, 1.5, 2, 2.5, 3, 3.5, 4, 5, and 7cm. A cross section of the detector was arranged. The readout system was a TL Reader (Thermo, USA). The heating cycle consisted of preheat, readout, anneal and cool segments. The Monte Carlo (MC) were used for the dosimetry simulations around the irradiation stent. The range for photon and electron transport extends from 1 KeV to 100 MeV. The irradiation stents have been simulated in the centre of a spherical phantom of water with 20 cm radius, large enough to consider all the scattering effects of the surrounding medium. The detectors were