Bernice Palos

Two‐dimensional dose distribution of 125I seeds

Two-dimensional dose distribution has been measured for the new (model 6711) 125I seeds used in interstitial implants. Two independent methods, using a silicon diode or thermoluminescent dosimeters, yielded identical results. At any given distance r from the seed center, the dose varies with theta, the angle relative to the seeds axis. Similarly, the r dependence of the dose distribution is different at various theta values. These observations can be qualitatively understood in terms of several factors, namely, source encapsulation, geometrical relationship, and attenuation and scatter. Empirical expressions which approximate the measured results have been developed to facilitate clinical dose distribution calculations.

The Metal/Tissue Interface Effect in Irradiation of the Oral Cavity

Metal dental prostheses or overlays may lead to increased mucosal reactions of adjacent tissue surfaces during intensive irradiation of the oral cavity. The dosimetry of this phenomenon was investigated by irradiating dental phantoms with 4-and 6-MeV photons. Gold and amalgam interfaces may produce local mucosal doses as high as 150-170% depending on the beam geometry, but doses of 111-126% for gold crowns and about 109-118% for amalgam fillings were found for opposed-beam configurations. 2-4 mm of tissue-equivalent absorber is sufficient to re-establish a homogeneous dose distribution and should be employed throughout therapy whenever dental extraction is unwarranted. The radiobiological exaggeration of the interface effect in treatment with opposed beams using one field per day is discussed.

Sterilization of 125I seeds encased in vicryl sutures for permanent interstitial implantation

Abstract Based on chemical and biological indicators and cultures of Vicryl sutures containing dummy metallic seeds similar in size and shape to 125 I seeds, we found that the Stanford technique for re-sterilizing this material was effective. Therefore our technique for intra-operative interstitial implantation of malignant tumors may be used safely without risking insertion of potentially contaminated material into tissues.

A method of interstitial tonsillo-palatine implants

Abstract A modified after-loading method of interstitial tonsillo-palatine implantation using 192 Ir ribbons is described. Removal of the ribbons is simplified by attaching sutures to the metallic clips which maintain the position of the implant. By this safe and apparently effective technique, increased doses of radiation can be delivered to oropharyngeal cancers after external beam radiotherapy. At the same time, radiation injury to the adjacent normal tissues can be minimized, since they receive only a negligible additional dose of radiation from the interstitial implant.

Combined continuous ultra low dose rate irradiation and radiofrequency hyperthermia in the C3H mouse

Intradermally inoculated RIF tumors and normal skin of male C3H mice were implanted with variable activities of Iodine 125 seeds or dummy seeds enclosed in Vicryl sutures, and subjected to 0, 1, 2 or 3 local radiofrequency heat treatments for 30 minutes. Each treatment raised the tumor volume to 44 degrees C. Gastrointestinal toxicity (assessed by weight change), skin reaction, tumor growth delay, and tumor cure were assessed. Neither radiofrequency treatment alone or continuous ultra low dose rate irradiation up to 16,000 rad over 180 days alone was successful in curing these tumors; however, combined modality treatments employing doses as low as 8,000 rad over 180 days plus two radiofrequency treatments did effect cures. Gastrointestinal toxicity was best correlated with hyperthermia treatments, while skin reactions secondary to hyperthermia were prolonged by continuous ultra low dose rate irradiation. Implications for clinical usage are discussed.

A method for inserting i-125 seeds into absorbable sutures for permanent implantation in tissue

Abstract A useful and efficient method is described and illustrated in detail for inserting I-125 seeds into absorbable sutures for intra-operative implantation in tumors. This method of suture preparation and our resterilization technique provide convenient and safe procedures for enabling the use of this versatile method of interstitial implantation. These procedures are used routinely at the Stanford University Medical Center.

Clinical dosimetry for negative pi mesons.

The authors describe a multichannel negative pi meson source for radiation therapy. A series of treatment plans was developed, using only parameters within the design capabilities of this device. The pion-equivalent isodose contours demonstrate a remarkable ability to limit the high-dose region to the tumor target volume, with a rapid fall-off in dose to the normal surrounding tissues.