2867
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Conclusions: Because of the shorter radioactive decay half-life of the 131Cs seeds, post-implant dosimetry for 131Cs implants should be performed within 10 2 days. Additional external beam irradiation of multiple 2-Gy fractions may be needed to completely compensate edema-induced dose deficits depending on edema magnitudes. Author Disclosure: Z. Chen, None; J. Deng, None; K. Roberts, None; R. Nath, None. 2867 Comparison of 131Cs, 103Pd and 125I Isotopes in Preplanning for Permanent Prostate Brachytherapy F. Trichter, E. Furhang, D. Shasha, R. D. Ennis St. Luke’s-Roosevelt Hospital Center, Continuum Health Partners, New York, NY Purpose/Objective(s): A new radioactive isotope, 131Cs (IsoRay Medical Inc., Richland, WA), has recently been introduced for permanent interstitial brachytherapy treatment of prostate cancer. The nuclear characteristics of 131Cs are: average decay energy, 29 keV; half-life, 9.7 days. The nuclear characteristics of the commonly used isotopes 103Pd and 125I are, respectively: average decay energy, 20.7 keV and 28.4 keV; half life, 17 days and 59.4 days. This study evaluates implant preplanning using the 131Cs isotope and compares it to implant preplanning using 103Pd and 125I. Materials/Methods: A treatment planning study for 12 patients, who had undergone permanent prostate implant, is presented. The patients were planned using the Variseed (Varian Medical Systems, Palo Alto, CA) treatment planning system using Dose-Optimized placement. Treatment plans utilizing 131Cs, 103Pd and 125I seeds were generated using the ultrasound images acquired during the actual implant. The images included contours of the PTV and urethra. The urethra was visualized by instilling aerated gel before ultrasound image acquisition. Dose prescription was 135Gy for the treatment with103Pd seeds - activity 2.5U, 144Gy for the study with 125I - activity 0.51U and 115Gy in the study with 131Cs. Treatment plans using 131Cs were generated for two source activities: 2.0U and 2.2U (the vendor recommended and maximum activities). Results: There was a significant difference in the number of seeds needed to achieve the treatment objectives using different isotopes. The average number of seeds for implants was 10% less using 131Cs-2U, 20% less using 131Cs-2.2U, and 15% less using 125I than for implants using 103Pd, with higher differences for larger glands. The difference in the number of needles between each type of isotope was insignificant for all patients. Equivalent PTV coverage resulted in lower V200 and V150 and higher urethra V150 and V125 for higher energy seeds. The average V200 was 42.1% for 103Pd, 30.1% for 125I, and 26% for 131Cs. The average V150 was 74.6% for 103Pd, 67.5% for 125I, and 61% for 131Cs. The PTV D100 was 30% higher for 131Cs and 21% higher for 125I seeds. The average urethra V150 was 6.6% for 103Pd, 19.4% for 125I, 8.7% for 131Cs 2U seeds, and 11.5% for 131Cs 2.2U seeds. Conclusions: The choice of isotope for prostate brachytherapy depends on many variables and treatment philosophy. Preplanning using 131Cs results in more homogeneous dose distribution in the PTV, but higher urethra doses. Author Disclosure: F. Trichter, None; E. Furhang, None; D. Shasha, None; R.D. Ennis, None. 2868 Novel Recommendations for Dosimetry of Elongated Low Energy Photon Emitter Brachytherapy Sources S. A. Dini, S. B. Awan, K. Dou, R. Mokhberiosgouei, A. S. Meigooni University of Kentucky, Lexington, KY Purpose/Objective(s): Recently, elongated RadioCoilTM 103Pd (RCPD) sources have been introduced to eliminate short comings associated with seed type sources such as seed migration and embolization1. For clinical application of this source, the dosimetric characteristic of this source model needs to be evaluated using the AAPM TG-43U1 protocol. This protocol is mainly based on experiences with seed type sources where the variation of the 2D anisotropy function between the two subsequent radii is minimal. However, for an elongated brachytherapy source, where a significant portion of the treatment volume may fall within the active length of source, this assumption may not be valid. In this project the applicability of TG-43U1 protocol for determination of dosimetric characteristics around elongated RCPD brachytherapy sources been investigated. Materials/Methods: The new RCPD source design is available in 1.0 to 6.0cm integral lengths with 0.8cm outer diameter. Dosimetric characteristics of the new sources were determined following TG-43U1 recommendations in Solid Water™ material using TLD dosimetry and MCNP5 Monte Carlo simulation techniques and in liquid water using Monte Carlo simulation technique. F(r,) of RCPD were determined for angles 0o to 90o Radial dose function, g(r) was measured at radial distances ranging from 0.5cm to 7.0cm and calculated from 0.2cm to 7.0cm. Results: Dose rate constant of the RCPD source was found to reduce by increasing active length of the source. Values of for 1.0 and 5.0cm long RCPD source in liquid water were found to be 0.663, and 0.235 respectively. A comparison between Monte Carlo simulated F(r, ) for the TG-43U1 recommended minimal radial distances with the values obtained at smaller radial increments is shown in figure 1a. This figure shows the possibility of under estimation if only minimal radial distances recommended by TG-43U1 are utilized. In addition, a comparison of F(r, ) for 5cm long RCPD sources with the values of a 0.5cm long source at 3.0cm radial distance in liquid water is shown in Fig 1b. Conclusions: Results of these investigations indicate a significant differences between the F(r,) of an elongated source and seed type source. In addition, variation in F(r,) at the vicinity of the end of the active length of the source can not be accurately predicted with the use of minimal radial distances recommended by TG-43U1. Therefore, dosimetric characteristics of elongated brachytherapy sources can be determined following TG-43U1 provided that F(r,) is determined at smaller radial increments than that is noted in the T43U1 protocol. Moreover, near the end of the active length of the source F(r,) should be determined at L/2 0.2cm. S700 I. J. Radiation Oncology ● Biology ● Physics Volume 66, Number 3, Supplement, 2006
Transcript of 2867
Conclusions: Because of the shorter radioactive decay half-life of the 131Cs seeds, post-implant dosimetry for 131Cs implantsshould be performed within 10 � 2 days. Additional external beam irradiation of multiple 2-Gy fractions may be needed tocompletely compensate edema-induced dose deficits depending on edema magnitudes.
Author Disclosure: Z. Chen, None; J. Deng, None; K. Roberts, None; R. Nath, None.
2867 Comparison of 131Cs, 103Pd and 125I Isotopes in Preplanning for Permanent Prostate Brachytherapy
F. Trichter, E. Furhang, D. Shasha, R. D. Ennis
St. Luke’s-Roosevelt Hospital Center, Continuum Health Partners, New York, NY
Purpose/Objective(s): A new radioactive isotope, 131Cs (IsoRay Medical Inc., Richland, WA), has recently been introducedfor permanent interstitial brachytherapy treatment of prostate cancer. The nuclear characteristics of 131Cs are: average decayenergy, 29 keV; half-life, 9.7 days. The nuclear characteristics of the commonly used isotopes 103Pd and 125I are, respectively:average decay energy, 20.7 keV and 28.4 keV; half life, 17 days and 59.4 days. This study evaluates implant preplanning usingthe 131Cs isotope and compares it to implant preplanning using 103Pd and 125I.
Materials/Methods: A treatment planning study for 12 patients, who had undergone permanent prostate implant, is presented.The patients were planned using the Variseed (Varian Medical Systems, Palo Alto, CA) treatment planning system usingDose-Optimized placement. Treatment plans utilizing 131Cs, 103Pd and 125I seeds were generated using the ultrasound imagesacquired during the actual implant. The images included contours of the PTV and urethra. The urethra was visualized byinstilling aerated gel before ultrasound image acquisition. Dose prescription was 135Gy for the treatment with103Pd seeds -activity 2.5U, 144Gy for the study with 125I - activity 0.51U and 115Gy in the study with 131Cs. Treatment plans using 131Cswere generated for two source activities: 2.0U and 2.2U (the vendor recommended and maximum activities).
Results: There was a significant difference in the number of seeds needed to achieve the treatment objectives using differentisotopes. The average number of seeds for implants was 10% less using 131Cs-2U, 20% less using 131Cs-2.2U, and 15% lessusing 125I than for implants using 103Pd, with higher differences for larger glands. The difference in the number of needlesbetween each type of isotope was insignificant for all patients. Equivalent PTV coverage resulted in lower V200 and V150 andhigher urethra V150 and V125 for higher energy seeds. The average V200 was 42.1% for 103Pd, 30.1% for 125I, and 26% for131Cs. The average V150 was 74.6% for 103Pd, 67.5% for 125I, and 61% for 131Cs. The PTV D100 was 30% higher for131Cs and 21% higher for 125I seeds. The average urethra V150 was 6.6% for 103Pd, 19.4% for 125I, 8.7% for 131Cs 2Useeds, and 11.5% for 131Cs 2.2U seeds.
Conclusions: The choice of isotope for prostate brachytherapy depends on many variables and treatment philosophy.Preplanning using 131Cs results in more homogeneous dose distribution in the PTV, but higher urethra doses.
Author Disclosure: F. Trichter, None; E. Furhang, None; D. Shasha, None; R.D. Ennis, None.
2868 Novel Recommendations for Dosimetry of Elongated Low Energy Photon Emitter Brachytherapy Sources
S. A. Dini, S. B. Awan, K. Dou, R. Mokhberiosgouei, A. S. Meigooni
University of Kentucky, Lexington, KY
Purpose/Objective(s): Recently, elongated RadioCoilTM 103Pd (RCPD) sources have been introduced to eliminate shortcomings associated with seed type sources such as seed migration and embolization1. For clinical application of this source,the dosimetric characteristic of this source model needs to be evaluated using the AAPM TG-43U1 protocol. This protocol ismainly based on experiences with seed type sources where the variation of the 2D anisotropy function between the twosubsequent radii is minimal. However, for an elongated brachytherapy source, where a significant portion of the treatmentvolume may fall within the active length of source, this assumption may not be valid. In this project the applicability ofTG-43U1 protocol for determination of dosimetric characteristics around elongated RCPD brachytherapy sources beeninvestigated.
Materials/Methods: The new RCPD source design is available in 1.0 to 6.0cm integral lengths with 0.8cm outer diameter.Dosimetric characteristics of the new sources were determined following TG-43U1 recommendations in Solid Water™ materialusing TLD dosimetry and MCNP5 Monte Carlo simulation techniques and in liquid water using Monte Carlo simulationtechnique. F(r,�) of RCPD were determined for angles 0o to 90o Radial dose function, g(r) was measured at radial distancesranging from 0.5cm to 7.0cm and calculated from 0.2cm to 7.0cm.
Results: Dose rate constant of the RCPD source was found to reduce by increasing active length of the source. Values of �for 1.0 and 5.0cm long RCPD source in liquid water were found to be 0.663, and 0.235 respectively. A comparison betweenMonte Carlo simulated F(r, �) for the TG-43U1 recommended minimal radial distances with the values obtained at smallerradial increments is shown in figure 1a. This figure shows the possibility of under estimation if only minimal radial distancesrecommended by TG-43U1 are utilized. In addition, a comparison of F(r, �) for 5cm long RCPD sources with the values of a0.5cm long source at 3.0cm radial distance in liquid water is shown in Fig 1b.
Conclusions: Results of these investigations indicate a significant differences between the F(r,�) of an elongated source andseed type source. In addition, variation in F(r,�) at the vicinity of the end of the active length of the source can not be accuratelypredicted with the use of minimal radial distances recommended by TG-43U1. Therefore, dosimetric characteristics ofelongated brachytherapy sources can be determined following TG-43U1 provided that F(r,�) is determined at smaller radialincrements than that is noted in the T43U1 protocol. Moreover, near the end of the active length of the source F(r,�) shouldbe determined at L/2 � 0.2cm.
S700 I. J. Radiation Oncology ● Biology ● Physics Volume 66, Number 3, Supplement, 2006
