COMS Eye Research Articles

ROPES eye plaque brachytherapy dosimetry for two models of 103Pd seeds

Brachytherapy dose distributions are calculated for 15mm ROPES eye plaque loaded with model Theragenics200 and IR06-(103)Pd seeds. The effects of stainless steel backing and Acrylic insert on dose distribution along the central axis of the eye plaque and at critical ocular structure are investigated. Monte Carlo simulation was carried out with the Version 5 of the MCNP. The dose at critical ocular structure by considering the eye composition was calculated. Results are compared with the calculated data for COMS eye plaque loaded with Theragenics200 palladium-103 seeds and model 6711 iodine-125 seed. The air kerma strength of the IR06-(103)Pd seed to deliver 85Gy in apex of tumor in water medium was calculated to be 4.10 U/seed. Along the central axis of stainless steel plaque loaded with new (103)Pd seeds in Acrylic insert, the dose reduction relative to water is 6.9% at 5mm (apex). Removal of the Acrylic insert from the plaque (replacing with water) did not make significantly difference in dose reduction results (~0.2%). The presence of the stainless steel backing results in dose enhancement near the plaque relative to water. Doses at points of interest are higher for ROPES eye plaque when compared to COMS eye plaque. The dosimetric parameters calculated in this work for the new palladium seed, showed that in dosimetry point of view, the IR06-(103)Pd seed is suitable for use in brachytherapy. The effect of Acrylic insert on dose distribution is negligible and the main effect on dose reduction is due to the presence of stainless steel plaque backing.

WE-D-BRB-06: Treating Ocular Melanoma with Eye Plaque Brachytherapy: COMS Or NAG Eye Plaque?

Purpose: To compare dosimetry characteristics of Nag‐eye plaque with COMS eye plaque using I‐125 and Cs‐131 brachytherapy sources. Material and methods: Monte Carlo technique was used to generate 3D dose distributions of a 16‐mm Nag eye plaque and 16‐mm COMS eye plaque loaded with the I‐125 and Cs‐131 brachytherapy sources separately. The Nag eye plaque is a comparatively simpler eye plaque that uses fewer seeds than the COMS and does not require a Silastic seed carrier. The simulations were carried out with gold alloy plaques. A water equivalent seed carrier was used instead of the Silastic trough designed for the traditional COMS eye plaque. The Nag eye plaque used only eight sources forming two squares; the COMS eye plaque was loaded with thirteen sources forming three isocentric circles. A spherical eyeball 24.6 mm in diameter and an ellipsoid tumor 6 mm in height and 12‐mm in diameter were used to evaluate the doses delivered. Results: The doses along the eye plaque axis and the DVHs of the tumor were calculated. Our results indicated that, to achieve a prescription dose of 85 Gy at 6 mm from the inner sclera edge, the Nag eye plaque required 6.156 U/source for I‐125 and 6.82 U/source for Cs‐131; the COMS eye plaque required 4.015 U/source and 4.433 U/source for the same source types. The doses from two types of eye plaques on the central axis were almost the same at distances greater than 5 mm; the OSU‐Nag plaque gave slightly lager doses than the COMS at distances less than 5 mm. The DVHs of the tumor showed that the NAG plaque tended to create slightly more hot dose regions than the COMS. Conclusion: The dosimetric characteristic of Nag‐eye plaque is comparable to COMS in using either I‐125 or Cs‐131 source.

TU-E-350-04: The Practice of Clinical Therapy Medical Physics

Clinical Therapy Physics is the real “practice” of Medical Physics. Therapy Medical Physics is reimbursed explicitly and implicitly as having direct contribution to specific patient care — the only Medical Physics sub‐field with this advantage. Whether it is in establishing External Beam, IMRT,SRS or SBRT programs with IGRT or providing Brachytherapy (HDR & LDR) programs for cancer therapy, the Clinical Therapy Medical Physicist works in partnership with the Radiation Oncologist to provide quality services in cancer care. Supervision of dosimetrists and therapists, the other members of the radiation oncology team is an important part played by us. Dr. Hevezi was Director of Medical Physics at the Cancer Therapy & Research Center for 15 years and built an important clinical therapy physics program there. A broad range of clinical services there included not only the above mentioned procedures, but procedures like Total Body Photon Therapy, COMS Eye Plaque therapy, and others. He currently serves as Lead CyberKnife Physicist with the South Texas RadioSurgery Associantion in San Antonio and directs Medical Physics graduate students in the University of Texas Health Science Center at San Antonio. Dr. Hevezi has been recently elected to the Board of Chancellors of the American College of Radiology where he serves as Chair of the Medical Physics Commission. He is former Chair of AAPM's Professional Economics Committee and most recent clinical interest is in developing the CyberKnife SBRT treatment modality for cancer therapy. He holds a basic patent in this technology. On completing the session on Meet the Experts, The Practice of Clinical Therapy Medical Physics, the attendee will: 1. Be able to identify the procedures in Clinical Therapy Medical Physics that are germane to the Practice 2. Be able to describe the interactions between the Medical Physicist and the Radiation Oncology team members 3. Be versed in the method of reimbursement currently available for the Medical Physicist in Clinical Therapy Medical Physics 4. Be able to identify the specific quality assurance procedures that the Medical Physicist must know in the Practice of Clinical Therapy Medical Physics 5. Be able to identify the spectrum of activities the Clinical Therapy Medical Physicist may be called on to perform in the Radiation Oncology Department

Monte Carlo simulation of COMS eye plaque brachytherapy

Purpose: Current ABS and AAPM recommendations for COMS eye plaque brachytherapy dose calculations employ a modified TG-43 formalism that forgoes 2D anisotropy function corrections and assumes a homogenous liquid water medium. Monte Carlo (MC) simulations of COMS eye plaques were performed to calculate dose, examine trends, and provide comparisons with brachytherapy treatment planning results.

Three-dimensional CT treatments pre-planning of I-125 COMS eye plaque implant brachytherapy

Purpose: The purpose of this study is to develop a pre-planning method to perform COMS based eye plaque dosimetry planning using a commercially available 3D Brachy RTP, compare dosimetrical aspects between pre-planning using 2D COMS (clinically used) methodology and pre-planning using 3D CT information and asses if the use of 3D CT data benefits pre-planning of eye plaque implants.

TU-E-BRB-04: Meet the Expert - Therapy Clinical

Clinical Therapy Physics is the real “practice” of Medical Physics. Therapy Medical Physics is reimbursed explicitly and implicitly as having direct contribution to specific patient care — the only Medical Physics sub‐field with this advantage. Whether it is in establishing External Beam, IMRT,SRS or SBRT programs with IGRT or providing Brachytherapy (HDR & LDR) programs for cancer therapy, the Clinical Therapy Medical Physicist works in partnership with the Radiation Oncologist to provide quality services in cancer care. Supervision of dosimetrists and therapists, the other members of the radiation oncology team is an important part played by us. Dr. Hevezi was Director of Medical Physics at the Cancer Therapy & Research Center for 15 years and built an important clinical therapy physics program there.A broad range of clinical services there included not only the above mentioned procedures, but procedures like Total Body Photon Therapy, COMS Eye Plaque therapy, and others. He is currently the lead Medical Physicist at the Methodist CyberKnife Center in San Antonio and directs Medical Physics graduate students in the University of Texas Health Science Center at San Antonio. Dr. Hevezi has been recently elected to the Board of Chancellors of the American College of Radiology where he serves as Chair of the Medical Physics Commission. He is current Chair of AAPM's Professional Economics Committee and most recent clinical interest is in developing the CyberKnife SBRT treatment modality for cancer therapy. Educational Objectives: 1. To understand the clinical practice of Therapy Medical Physics. 2. To become familiar with some of the new technologies in Radiation Oncology.

125I eye plaque dose distribution including penumbra characteristics.

The two main purposes of this work are (1) to determine the penumbra characteristics for 125I eye plaque and the relative influence of the plaque and eye-air interface on the dose distribution, and (2) to initiate development of a treatment planning algorithm for clinical dose calculations. Dose was measured in a newly designed solid water eye phantom for an 125I (6711) seed at the center of a 20 mm COMS eye plaque using thermoluminescent dosimeter (TLD) "cubes" and "minichips" inside and outside the eye, in the longitudinal and transverse central planes. TLD cubes were used in most locations, except for short distances from the seed and in the penumbra region. In the presence of both the plaque and the eye-air interface, the dose along the central axis was found to be reduced by 10% at 1 cm and up to 20% at 2.5 cm, relative to the bulk homogeneous phantom case. In addition, the overall dose reduction was greater for larger off-axis coordinates at a given depth. The penumbra characteristics due to the lip collimation were quantified, particularly the dependence of penumbra center and width on depth. Only small differences were observed between the profiles in the transverse and longitudinal planes. In the bulk geometry (without the eye-air interface), the dose reduction due to the presence of the plaque alone was found to be 7% at a depth of 2.5 cm. The additional reduction of 13% observed, with the presence of eye-air interface (20% combined), can be attributed to the lack of backscattering from the air in front of the eye. The dose-reduction effect due to the anterior air interface alone became unnoticeable at a depth of 1.1 cm (1.5 cm from the eye-air interface). An analytic fit to measured data was developed for clinical dose calculations for a centrally loaded seed. The central axis values of the dose rates multiplied by distance squared, Dr2, were fitted with a double exponential function of depth. The off-axis profile of Dr2, at a given depth, was parametrized by a modified Fermi-Dirac function to model both the penumbra characteristics due the plaque lip collimation and the effect of oblique filtration by silastic.