Film dosimetry analyses on the effect of gold shielding for Iodine-125 eye plaque therapy for choroidal melanoma

Journal Article · Sat Sep 01 04:00:00 EDT 1990 · Medical Physics; (USA)

DOI:https://doi.org/10.1118/1.596556· OSTI ID:6140878

Wu, A ^[1]; Krasin, F ^[2]

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1. Department of Radiation Oncology, University of Pittsburgh, School of Medicine, Joint Radiation Oncology Center and Pittsburgh Cancer Institute, Pittsburgh, PA (USA)
2. Department of Radiation Oncology, Tufts University School of Medicine, New England Medical Center, Boston, MA (USA)

One of the methods currently being used to treat choroidal melanoma employs an episcleral plaque containing I-125 radioactive seeds. However, comprehensive dosimetry studies on the plaque are scarce and controversial. For this work, we use film to study the dosimetry outside the lip of the gold shield of the eye plaque. This lip around the gold shield was made to protect the critical structures behind and adjacent to the lesion. Since the changes of energy spectrum of I-125 in tissue are negligible, film dosimetry seems to be a logical choice because of high spatial resolution required around the lip of the gold plaque. For this study, we first established an H and D curve with dose expressed in a unit of specific dose rate constant. This avoids absolute dose measurements. All film density measurements are made with a 1-mm aperture scan, normalized to the density at the prescription point for tumor of 3--5-mm apical height, i.e., 5 mm from the interior surface of sclera, and converted to percentage isodose curves. With a gold shield, it is found that when the plaque is placed against the optical nerve, the optical disk and macula, located at 2 mm outside the lip, on the exterior surface of sclera, may receive 85% of the prescription dose for a 12-mm plaque and 58% for a 16-mm plaque. For tumors of 8-mm apical height, the optical nerve would receive more than the prescription dose.

• OSTI ID: 6140878
• Journal Information: Medical Physics; (USA), Journal Name: Medical Physics; (USA) Vol. 17:5; ISSN MPHYA; ISSN 0094-2405
• Country of Publication: United States
• Language: English

Related Subjects

560151* -- Radiation Effects on Animals-- Man
63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTANT EFFECTS ON LIVING ORGS. AND BIOL. MAT.
BETA DECAY RADIOISOTOPES
BODY
BODY AREAS
DAYS LIVING RADIOISOTOPES
DISEASES
DOSIMETRY
ELECTRON CAPTURE RADIOISOTOPES
ELEMENTS
EYES
FACE
FILM DOSIMETRY
GOLD
HEAD
IMPLANTS
INTERMEDIATE MASS NUCLEI
IODINE 125
IODINE ISOTOPES
ISODOSE CURVES
ISOTOPES
MATERIALS
MEDICINE
MELANOMAS
METALS
NEOPLASMS
NUCLEAR MEDICINE
NUCLEI
ODD-EVEN NUCLEI
ORGANS
RADIATION DOSE DISTRIBUTIONS
RADIATION SOURCE IMPLANTS
RADIATION SOURCES
RADIOISOTOPES
RADIOLOGY
RADIOTHERAPY
SENSE ORGANS
SHIELDING MATERIALS
THERAPY
TRANSITION ELEMENTS