General Considerations in the Radiation Treatment of Skin Cancer in the Region of the Eye*
Post on 09-Feb-2017
GENERAL CONSIDERATIONS IN THE RADIATION TREATMENT OFSKIN CANCER IN THE REGION OF THE EYE*
WILLIAM L. WATSON, M.D., F.A.C.S. AND WILLIAM WUESTER, M.D.New York
The purpose in presenting the followingreport is to discuss very briefly some ofthe technical factors to be considered inthe irradiation treatment of skin cancerin the immediate vicinity of the eye. Inas-much as there is a wide variance in thearmamentarium available to individualtherapists, several types will be consid-ered.
Probably one of the oldest methods,and one commonly used on the Continentfor skin cancer, is the radon or radiumplaque. Radium in this applicator is fil-tered through approximately three milli-meters of brass, and is usually applied ata distance of one centimeter from the skin
*From the Head and Neck Department,Memorial Hospital, Service of Dr. Hayes E.Martin.
surface. The intervening distance is main-tained by balsa wood of this thickness.Such a plaque gives a depth dose of ap-proximately 30 percent at one centimeterin the tissue. The skin surrounding thelesion is protected by a 2 to 3 mm. leadshield. The entire unit is held in place withadhesive tape.
There are more than theoretical objec-tions to the use of plaques for treatmentabout the orbit. The duration of applica-tion, depending upon the amount of radi-um or radon available, varies between 1and 20 hours. The difficulty in accurateapplication to convoluted surfaces is ap-parent. The eye cannot be absolutely pro-tected. It is well known that one centi-meter of lead removes but 50 percent ofthe gamma rays. Figure 1 shows the cal-
Fig. 1 (Watson and Wuester). Showing the percentage depth dose received by the deepstructures of the eye when a cancer of the eyelid is treated by one of the usual radium plaquesfiltered by 3 mm. of brass at a distance of 1 em.
262 WILLIAM L. WATSON AND WILLIAM WUESTER
culated percentage depth dose received byvarious structures of the eye with thisform of treatment.
The gold radon seed, 4.0 x 0.75 mm. insize, is widely used interstitially for smallskin lesions. Figure 2 shows the advantageof the gold seed over the plaque. Theseeds, being small, are inserted with theminimum amount of trauma. They are
Fig. 2 (Watson and Wuester). Showing theadvantages of the gold-radon-seed method oftreatment, which reduces the depth dose re-ceived by the lens to 10 percent.
considered permanent implants, althoughin some cases in which the lesion is verysuperficial, they may be extruded severalweeks after insertion. It is not possiblefor the patient to wear an adequate eyeshield for the duration of activity of theradon implant. Furthermore, since thegold seed has 0.3 millimeter gold filtration,91.2 percent of the irradiation is gamma,8.8 percent beta, the latter being almostcompletely absorbed in the first half centi-meter of tissue. Therefore, lead, in thethickness that would be required, offers in-complete protection from the gamma rays.
In using radium-element-eyed needles,size is an objectionable factor. The nee-dles most commonly used have been the17-mm. Treves and the ll-mm. Martinneedle. The objection to size has been par-tially overcome by the 7 X 1 mm. remov-able radium-element seeds recently intro-duced into this country.
The irradiation of normal tissue in closeproximity or contiguity cannot beavoided, especially if the lesion is smalland only large needles are available. Thesame objections pertaining to the goldradon seed hold true here, plus the addedtrauma incident to the insertion of theselarger needles.
The use of the moulage of either dentalmodeling compound or wax, which holdsthe radium or radon tubes or seeds indirect contact with the lesion, has a lim-ited but definite use. This type of therapymust of necessity be limited to very super-ficial lesions of not more than 1 to 2 milli-meters in thickness. Its use has practicallythe same restrictions as has the gold radonseed.
A good deal of clinical evidence is avail-able to support the opinion that no onemethod has so many advantages and sofew disadvantages as a single massivedose of lightly filtered low voltage X ray.Using 100 KV., 25-30 cm. target skin dis-tance and 0.3 millimeters aluminum filtra-tion, one millimeter lead removes over99.5 percent of the radiation. With a 10X 10 ern, field, the depth dose with unfil-tered radiation is approximately 70 per-cent at one centimeter.
The irradiated area should be restrictedto the cancer-bearing area by means of alead shield, one millimeter in thickness,which will completely protect the sur-rounding normal skin. Instead of an openport, the X-ray beam is limited by a cylin-der chosen both to maintain the targetskin distance and to keep the lead shieldand patient in a set position. One mustremember that diminishing the size of theirradiated field decreases both the surfaceand depth dose. Correspondingly higher"r" dosages must be given to the smallerfields.
If any portion of the beam is directedtoward the eye, these structures may beprotected by an oval, curved, lead eye
TREATMENT OF SKIN CANCER NEAR EYE
lead shield(paraffin coated)
Fig. 3 (Watson and Wuester). Showing the present method of treatment by low-voltage,unfiltered X ray. The tumor receives 100 percent and the lens and cornea are completely pro-tected froni harmful effects of the rays.
shield, one millimeter in thickness, coatedwith paraffin to remove the secondaryradiation and offer a less abrasive surfaceto the cornea (fig. 3). This shield is in-serted under the lids under topical anes-thesia. By this means lesions of the eyelidsmay be treated without fear of secondarychanges in the lens or cornea.
From an economic standpoint, the lowercost of therapy, the ease of application,and the short duration of the treatmenttime, all commend themselves.
1. Various considerations in regard tothe treatment of skin cancer in the regionof the eye are discussed. Low-voltage Xray is the means of choice, advocated forits efficiencyand for the safety factors andeconomic considerations offered.
2. No dosage factors are given, foreach case presents its own specific prob-lem of management.
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