Treatment of the neck in head and neck mucosal squamous cell carcinoma: what our experience teaches.
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Carcinoma, Squamous Cell↗
Biomedical subjects
V A Marcial-Vega
Publications and source records attributed to V A Marcial-Vega.
Improved linac dose distributions for radiosurgery with elliptically shaped fields.
Stereotactic radiosurgery techniques for a linear accelerator typically use circular radiation fields to produce an essentially spherical radiation distribution with a steep dose gradient. Target volumes are frequently irregular in shape, and circular distributions may irradiate normal tissues to high dose as well as the target volume. Improvements to the dose distribution have been made using multiple target points and optimizing the dose per arc to the target. A retrospective review of 20 radiosurgery patients has suggested that the use of elliptically shaped fields may further improve the match of the radiation distribution to the intended target volume. This hypothesis has been verified with film measurements of the radiation distribution obtained using elliptical radiation beam in a head phantom. Reductions of 40% of the high dose volume have been obtained with elliptical fields compared to circular fields without compromising the dose to the target volume.
Humans↗
Cervical metastases from unknown primaries: radiotherapeutic management and appearance of subsequent primaries.
Between 1964 and 1986, 72 patients who presented with squamous or undifferentiated metastatic carcinoma to neck nodes, where the primary tumor could not be found by standard clinical procedures, were treated at the Mallinckrodt Institute of Radiology. These cases were managed in the following manner: biopsy and radiotherapy in 46 out of 72 patients, radiotherapy (RT) and a planned neck dissection in 14 out of 72, and neck dissection after failure to achieve a complete response (CR) with RT in 12 out of 72. Minimum follow-up was 2 years. The initial CR rates for stages N1, N2a, N2b, N3a, and N3b were 83%, 93%, 61%, 50%, and 33%, respectively. The long-term neck tumor control for the same stages was 83%, 71%, 67%, 44%, and 50%, respectively. One patient had soft tissue necrosis and two had carotid artery ruptures, one of which left no symptomatic sequelae. Twenty-one out of 72 patients developed subsequent primary tumor. Only one of these patients survived. This incidence was not affected significantly by prophylactic treatment of the mucosal areas except in patients with bilateral neck nodes, undifferentiated or poorly differentiated histologies, and/or posterior cervical node involvement. A multivariate analysis showed that prognosticators of an improved disease-free survival were: a complete clearance of tumor by the end of radiotherapy (p less than 0.0009) and no appearance of a subsequent primary tumor (p = 0.035). The only factor that correlated with an increased loco-regional control was having a complete response by the end of radiotherapy (p less than 0.00009). The recommended management and possible ways of preventing the appearance of subsequent primaries will be discussed.
Adult↗
Prevention of hypothyroidism related to mantle irradiation for Hodgkin's disease: preparative phantom study.
To decrease the incidence of hypothyroidism related to mantle irradiation for Hodgkin's disease, we initiated a study designed to protect the thyroid gland using a phantom. A thyroid phantom was filled with technetium-99m. The thyroid phantom was placed inside of its corresponding anterior neck position in a whole body phantom. An anterior scintiscan of the head and neck region demonstrated the radioactivity in the simulated thyroid. A mantle port included a focused block that would shield the thyroid from the anterior port. The phantom was exposed (4 MeV) to 180 cGy (AP-PA) at midplane with lithium fluoride dosimeters in the position of the thyroid. The thyroid received an average of 12 cGy from the anterior field and 48 cGy from the posterior field for a total of 60 cGy per treatment or 30% of the prescribed dose. A complete mantle field course of radiation of 4000 cGy would lead to a thyroid dose of 1200 cGy at a daily fractional dose of 60 cGy. We elected not to block the thyroid from the posterior field to prevent shielding and potential underdosage of involved nodal sites. The present study suggests a method of safe and effective thyroid shielding which needs to be tested clinically to determine whether it would reduce the incidence of chemical and clinical hypothyroidism or simply extend the period until occurrence.
Hodgkin Disease↗
Treatment of supratentorial high grade gliomas with split course high fractional dose postoperative radiotherapy.
Ninety-two patients with malignant supratentorial gliomas diagnosed from 1977 to 1983 received split course external beam radiotherapy. The initial course of radiation consisted of 3000 cGy whole brain in ten fractions 5 days a week. After a 2-week rest, treatment was continued to a portal restricted to the computerized tomography scan demonstrated abnormality plus a margin for an additional 2100 cGy (total 5100 cGy/17 fx/36 days). The optic chiasm and hypothalamus were excluded from the high dose region. Following review of all pathologic specimens, three patients with grade II glioma, three lacking histologic confirmation, two unbiopsied and eleven not receiving the prescribed treatment were excluded from the survival analysis. No patients were lost to follow-up. Surviving patients were followed 85 months (median); range 68-125 months. All remaining patients were followed until death. The median actuarial survival for 73 grade III and IV patients was 12.5 months. The 5-year actuarial survival was 10%. The median survival for 54 grade IV patients was 10 months. The 5-year survival was 4%. For 19 grade III patients the median survival was 22.5 months. The 5-year survival was 26%. There was one long-term grade IV survivor (68 mos.) and four long-term grade III survivors (76, 85, 108, 125 mos). No patient developed optic nerve or chiasm injury. One patient, an 85 months survivor, had biopsy documented radionecrosis and hemiparesis. The incidence of necrosis among 62 patients alive 6 months or more (and therefore at risk of brain necrosis) is 1/62 (2%). The incidence among survivors is 1/5. The nominal standard dose for this regimen is 1749 ret. The predictive value of the "nominal standard dose" and "equivalent dose" formulae for brain necrosis is explored. We conclude (a) that this regimen provides a survival probability equivalent to conventional treatment for grade III and IV supratentorial gliomas, (b) that neither the equivalent nor nominal standard doses predicted the incidence of brain necrosis, (c) that the time dose schedule is well tolerated and has an acceptable risk-benefit ratio, (d) that its advantage to the patient is decreased time requirement and cost.
Adolescent↗
Stereotactic radiosurgery: dose-volume analysis of linear accelerator techniques.
Stereotactic radiosurgery of the brain may be accomplished with a linear accelerator by performing several noncoplanar arcs of a highly collimated beam focused at a point. The shape of the radiation distribution produced by this technique is affected by the beam energy, field size, and the number and size of the arcs. The influence of these parameters on the resulting radiation distributions was analyzed by computing dose volume histograms for a typical brain. Dose volume functions were computed for: (a) the energy range of 4-24 MV x rays; (b) target sizes of 1-4 cm; and (c) 1-11 arcs and dynamic rotation. The dose volume histograms were found to be dependent on the number of arcs for target sizes of 1-4 cm. However, these differences were minimal for techniques with 4 arcs or more. The influence of beam energy on the dose volume histogram was also found to be minimal.
Brain↗