Radioactive Plaque Research Articles

Accuracy of Diagnosis of Choroidal Melanomas in the Collaborative Ocular Melanoma Study

In the 3-year period during which patients were enrolled into the Collaborative Ocular Melanoma Study, 413 eyes with clinical diagnoses of choroidal melanoma were examined histopathologically as of December 31, 1989. Four hundred eleven of these eyes were found to be diagnosed correctly. One eye, removed after preoperative external beam radiation, was found to have a hemangioma. The second eye, removed after radioactive iodine plaque placement, was described as a magnocellular nevus (melanocytoma) by four of the five pathologists on the Collaborative Ocular Melanoma Study Pathology Review Committee. The Collaborative Ocular Melanoma Study misdiagnosis rate of 0.48% is the lowest ever reported. The major challenge with regard to posterior uveal melanomas is no longer that of correct diagnosis but rather determination of the optimal treatment.

Treatment of choroidal melanoma: MR imaging in the assessment of radioactive plaque position.

Verification of the position of an episcleral iodine-125 gold plaque in relation to underlying choroidal melanoma is essential during early radiation therapy to ensure accurate plaque placement and thus optimum dose delivery. The authors used magnetic resonance (MR) imaging to examine 15 patients with choroidal melanoma after plaque placement to assess tumor coverage. The relationship of the plaque to the tumor was well defined in all cases, including two tumors anterior to the ora serrata. MR imaging measurements of the plaques were within 1 mm of the actual plaque sizes, while tumor measurements were within 2 mm of the preoperative ultrasound estimations of tumor dimensions. Tumors as small as 3 mm thick were readily visualized with MR imaging. Associated subretinal effusion was demonstrated in seven cases.

Episcleral Radioactive Plaque Therapy

Between 1983 and 1987, 56 patients with choroidal melanoma were treated at the University of Southern California with episcleral plaque (RPT). There were 29 female and 27 male patients, with a mean age of 59 years. Tumor stage at diagnosis was T2 in 18 (32%) and T3 in 38 (68%) patients. The tumor height ranged from 2.9 to 15 mm (mean 6.8 mm). Radial dimensions ranged from 5 to 25 mm (mean 13.2 mm), and circumference ranged from 7 to 23 mm (mean 12.3 mm). Most (77%) patients had posteriorly located tumors, including 18% that were juxtapapillary. Custom-designed gold plaques were utilized in this study. Radioactive isotopes used were 125I for 26 procedures or 192Ir for 31 procedures. A total of 56 patients were treated, with one patient having two procedures. Radiation doses at the tumor apex ranged from 29.8 to 165.4 Gy (mean 94.5 Gy), with the dose at 5-mm depth ranging from 70.5 to 430 Gy (mean 161.5 Gy). Follow-up ranged from 29 to 57 months (mean 39 months). The overall 4-year survival was 96%, with a 91% incidence of free-of-disease progression at 4 years. The majority (84%) of patients experienced a decrease in tumor height, with 27 (48%) patients having greater than 50% decrease. Increase in tumor height was noted in 5 (9%) and no change in 4 (7%) patients. Useful vision (greater than 5/200) was observed in 59% of patients, including 21% who had improved vision. Metastatic tumor occurred in 5 (9%) patients, with a mean time to metastases of 14 months. There was a good correlation between radial tumor dimension and metastatic disease, p less than 0.001. Treatment complications were observed in 34 (61%) patients, with cataract and retinopathy being the most common. Enucleation was performed in 11 (20%) patients, with a mean time to enucleation of 14.5 months. Causative factors for enucleation were treatment complications in 6 and tumor progression in 5 patients. Enucleations were required primarily in patients with tumors greater than 8 mm in height (p = 0.009). Improved RPT techniques with three-dimensional dosimetry are needed to reduce the overall incidence of treatment complications. Adjuvant hyperthermia is being investigated in an attempt to improve tumor control in patients with larger tumors.

Magnetic resonance imaging of juxtapapillary plaques in cadaver eyes.

Adequate treatment of juxtapapillary melanomas with episcleral plaque brachytherapy using lower energy radiation sources may be difficult because of uncertainties regarding the relationship of the plaque to the optic nerve and tumour base. We obtained magnetic resonance images of a dummy plaque placed in a juxtapapillary location in cadaver specimens. Although it is possible to place a plaque in close association with the optic nerve sheath, a tissue barrier exists which may prevent actual contact between the plaque and nerve. Posterior tilting of the plaque may also occur. Because of these uncertainties regarding plaque placement, juxtapapillary melanomas should be considered a distinct subgroup when evaluating the efficacy of radioactive plaque brachytherapy in the treatment of choroidal melanoma.

Ultrasound Determination of the Relationship of Radioactive Plaques to the Base of Choroidal Melanomas

There is an assumption that radioactive plaques placed at surgery are, and will remain, in proper relationship to the base of the tumor. The plaque dose is calculated based on this assumption. In fact, factors such as loose sutures, improper diameter estimations, pressure from adjacent rectus muscles, and intervening tissue (oblique muscles) can compromise this relationship. Ultrasound provides a practical method of imaging the tumor and plaque simultaneously. The authors have used postoperative ultrasound to monitor the accuracy of iodine-125 plaque placement in nine cases. Detection of eccentrically placed and malpositioned plaques provides valuable insight which can be used to refine surgical technique. Detection of plaque tilting by oblique muscles can serve as a basis for recalculating dosage. The relationship of plaque margins to vital ocular structures such as the optic nerve can also be determined by ultrasound.

Echographic verification of radioactive plaque position in the treatment of melanomas.

Visualization of the position of an episcleral plaque in relation to the underlying choroidal melanoma during the early radiation treatment period reconfirms accurate plaque location and may help assure optimal treatment. We used high-resolution B-scan echography to confirm the position of the episcleral plaque in 16 consecutive cases of choroidal melanoma. The technique is most useful for well-defined tumors as small as 3 mm in height whose anterior border does not extend beyond the ora serrata.

Should I Enroll in a Randomized Clinical Trial? A Critical Commentary

rid the body of cancer provided it has not spread. The second patient is attracted to the radioactive plaque because it offers about the same threeto-five year life expectancy as surgery, and there is no point in removing the eye if there is no guarantee that it is going to let the patient live longer. The third patient claims that the other two Have it all wrong. He argues that since neither my doctor nor any other doctor knows which treatment is better there surely is no way for me to know. He defends the randomization process by appealing to altruistic considerations: a desire to find an answer and make the world a little better. The device of presenting an imaginary patient conversation is an interesting one. Explaining to patients the justification of randomization is difficult. I am convinced, however, that the message conveyed in this conversation-especially the claim that if the doctors cannot know which treatment

Effect of gold shielding on the dosimetry of an 125I seed at close range.

Radioactive 125I plaques with gold shields have been used for the treatment of choroidal melanoma. The effect of the gold shield on the dosimetry of a single 125I seed (model 6711) has been investigated in this paper. Increases in dose at close range due to the presence of the shield are observed. Such enhancement is in agreement with Williamson's Monte Carlo calculations.

An Inexpensive Fiberoptic Light Pipe to Aid in Placement of Episcleral Radioactive Plaques

Episcleral plaque placement requires accurate localization of choroidal melanomas. Available fiberoptic light pipes can be fashioned to become scleral markers and transilluminators. The equipment is available wherever posterior segment surgery is performed. Surgical technique and equipment modifications are described.

Helium Ion Therapy for Choroidal Melanoma

Eighty-two patients with choroidal melanomas were treated with helium ion charged particle irradiation. Seventy-eight of 82 patients have either remained stable or demonstrated tumor shrinkage. Forty-five of 46 patients followed for at least 1 year after therapy have demonstrated tumor regression with a mean tumor shrinkage of approximately 31%. No tumor-related mortality has been observed. The most effective method of choroidal melanoma management is unclear. Charged particle external beam irradiation may be more applicable and have less ocular morbidity than either radioactive plaques or photocoagulation.

Helium ion therapy for choroidal melanoma.

Forty patients with choroidal melanomas received radiation therapy with helium ion-charged particles. Thirty-six of 30 patients either remained stable or demonstrated tumor shrinkage. Seventeen of 18 patients followed up for at least one year after therapy demonstrated tumor regression, with a mean tumor shrinkage of approximately 40%. The most effective method of choroidal melanoma management is unclear. Charged-particle external-beam irradiation may be more applicable and have less ocular morbidity than either radioactive plaques or photocoagulation.

Helium Ion Charged Particle Therapy for Choroidal Melanoma

Nine patients with choroidal melanomas were treated with helium ion charged particle irradiation. No patient demonstrated tumor enlargement, and most lesions followed for more than five months have demonstrated tumor shrinkage. The most effective method of choroidal melanoma management is unclear. Heavy charged particle irradiation may be more applicable and have less ocular morbidity associated with it in either radioactive plaques or photocoagulation.

Complications of Cobalt Plaque Therapy of Choroidal Melanomas

We treated a small series of patients with choroidal malanomas with radioactive cobalt plaques. To assess the effectiveness of radiation, we performed radioactive phosphorus (32P) uptake determinations before and after treatment. The 32P results did not tumor destruction. In five of seven patients with posterior pole melanomas, radiation retinopathy developed after treatment with resultant decrease in vision.

Physical aspects of megavolt electron therapy.

Directed streams of electrons with controllable energies in the 1-to 3-Mev range have been found uniquely suitable for the treatment of radiation-sensitive disease at the skin. This new approach to superficial therapy (1, 2) has been under investigation by members of the staff of the Lahey Clinic in Boston and the Massachusetts Institute of Technology during the four-year period commencing August 1951 (3). The present paper will report on the physical aspects of such megavolt electron therapy, including particularly the technics of electron irradiation of small and of extensive skin areas, the dose distribution below the skin, the reduction of accompanying whole-body x-irradiation, and the avoidance of possible accidental overexposure. The effective treatment of radiation-sensitive lesions of the skin presents a variety of often difficult physical requirements. In the simplest case, the lesion may involve a single localized region of moderate size and superficial depth. Control by ionizing energy requires the delivery of an adequate dose and, if the lesion is malignant, the inclusion of an ample margin of healthy peripheral tissue. Such lesions can usually be controlled by conventional low-voltage x-ray therapy or by radioactive plaque technics. Only too commonly these lesions are adjacent to or overlie tissue structure whose tolerance for radiation is small. Figure 1A shows a typical rapidly growing epidermoid tumor near the inner canthus of the eye. On the other hand, many superficial lesions are extensive and involve in varying degree all or nearly all of the skin. This is true of certain stages of mycosis fungoides, inflammatory carcinoma, psoriasis, atopic dermatitis, and generalized exfoliative dermatitis. Such cases, except for palliation of the most troublesome areas, are often outside the capabilities of conventional x-ray therapy and still further beyond the more limited scope of the external radioactive plaque. Figure 2A shows a representative patient with advanced mycosis fungoides involving most of the skin surface. For such cases, the use of large fields of high-energy electrons may offer a uniquely effective method of treatment. Analysis of the wide range of clinical manifestations of superficial disease has shown that most lesions can be effectively irradiated by electrons of constant but controllable energy directed at normal incidence into the skin surface. Such electron therapy offers the hitherto unattained possibility of both limiting the radiation dose to the actual depth of tissue requiring treatment and of reducing the reaction in the radiosensitive skin. Moreover, mono-energetic electron sources can be arranged to irradiate either localized areas or, substantially, the entire skin surface, with short exposure times and with accurate control of the dosage.