Technique for verifying treatment fields using portal images with diagnostic quality.

The image quality of portal films for megavoltage photon beams, when using the double-exposure technique, is poor compared to diagnostic quality, X ray images. A technique is described to record on a single film a megavoltage portal image superimposed upon a diagnostic X ray image, which provides the radiotherapist with "diagnostic quality" portal images. The technique uses a commercially available X ray tube mounted on the head of a 60Co unit. The alignment procedure, which uses a leveling device to ensure that the X ray focal spot and 60Co source are at the same location for each exposure, is confirmed by registering on film the image of an alignment marker. An evaluation of film-screen combination showed therapy verification film in a rare earth intensifying screen cassette to be best suited for this technique. The relationship between off-axis dose and the penumbral region of the portal image has been evaluated and should be useful in the interpretation of portal verification film relative to the treatment volume.

Results of irradiation in the squamous cell carcinomas of the anterior faucial pillar-retromolar trigone.

Between January 1966 and August 1981, 159 patients with previously untreated squamous cell carcinomas of the anterior faucial pillar or retromolar trigone received definitive radiation therapy at The University of Texas M. D. Anderson Hospital and Tumor Institute. All except 11 patients were treated by external radiation including combination of electron beams with high-energy photons or 60Co to doses ranging from 60 Gy to 75 Gy. In the N0 patients, as a rule, only the ipsilateral subdigastric nodes were treated electively to a dose of 50 Gy. The 5-year determinate survival rate for the overall group was 83%. The cumulative recurrence rate showed that 92% of the patients had recurrence by 2 years. Therefore, all patients except those who died with no evidence of local disease less than 2 years after treatment were evaluated for local control. The failure rate for the evaluable patients was 29% for T1 lesions, 30% for T2 lesions, 24% for T3 lesions, and 40% for T4 lesions. After salvage surgery, which consisted of intraoral resection in one-third of the patients and of a composite operation in the other two-thirds, the ultimate failure rate was 0% for T1 lesions, 6% for T2 lesions, 8% for T3 lesions, and 20% for T4 lesions. Whereas stage was a poor indicator for treatment outcome, there was a significantly higher failure rate for infiltrative and/or ulcerated lesions (35%) than for exophytic or superficial lesions (15%). Histologic grade was of no prognostic significance, nor was there any significant difference in the failure rate for lesions originating on the anterior faucial pillar versus that for lesions on the retromolar trigone. Following radiotherapy, 30% of the patients developed some degree of bone exposure but only 5.6% (9 patients) required a segmental mandibular resection. The probability of bone exposure was not dose related and more likely reflected tumor location on the mucoperiosteum. Of the whole group, 16 patients (10%) experienced a neck failure with 8 ultimate failures after salvage surgery. Among the 16 patients who had neck failures, 13 were originally staged N0; 6 of these patients had failures that occurred in the electively treated ipsilateral subdigastric area, but the field was too small to cover the nodes adequately. Aspects of the radiotherapy techniques with combined electron and photon beams that may influence the treatment outcome are discussed.

Concomitant boost radiotherapy for advanced squamous cell carcinoma of the head and neck.

The concomitant boost technique is a variant of accelerated fractionation whereby the boost is delivered as a second daily fraction during the basic treatment course to reduce the total duration of treatment. From April 1972 through June 1983, 53 patients with advanced squamous cell carcinoma of various sites in the head and neck region were treated for cure at U.T. M. D. Anderson Hospital with this technique. In 12 patients, the concomitant boost was used because of rapid recurrence following surgical resection either before or after initiation of planned postoperative radiotherapy; the remaining patients had rapidly growing untreated or recurrent disease in the primary site, neck, or both. In most cases, the concomitant boost was delivered in fractions of 120-150 cGy, separated by 3-6 h from the basic daily treatment of 180-200 cGy. The boost treatments were given 2-3 times a week for 3-5 weeks, delivering an average of about 17 Gy in 12 fractions. Two different treatment techniques were used. Patients with predominantly neck disease (30) were treated with glancing AP and PA fields or with appositional electron beam portals to spare the mucous membranes, while those with advanced or rapidly progressive primary lesions, with or without nodal disease (23), received their concomitant boost through lateral photon or high energy electron beams to include the primary tumor site. As expected, the acute mucosal reactions were most severe in the latter group, but only three patients required interruption of treatment because of severe mucositis.(ABSTRACT TRUNCATED AT 250 WORDS)

Determination of electron beam output factors for a 20-MeV linear accelerator.

The demands of a busy clinic require that basic machine calculations be performed as accurately, rapidly, and simply as possible. For the electron beam of the Therac 20 Saturne linear accelerator, a method suitable for a programmable calculator is described to predict the dose output from the measurement of selected fields. One-dimensional output factors were measured; these are defined as output factors of rectangular fields where one side is always equal to the side of the square reference field. The output of an arbitrary rectangular field X, Y is given by the product of the output factors OF(X,Y) = OF(X,10) X OF(10,Y), where 10 is the side of the square reference field. The measured data indicate that the output of very large rectangular and square fields is underestimated using this method for the lower energies. A correction factor of the form CF = C X [(X - 10)(Y - 10)/(X - 10)(Y - 10) 1/2] results in agreement with measured data to within 1.5% for all energies.

Improving the therapeutic ratio of craniospinal irradiation in medulloblastoma.

Radiation therapy delivered to the entire cerebrospinal axis is indicated for a number of pediatric brain tumors, especially medulloblastoma. Improved radiotherapy techniques have changed the near fatal prognosis for children with medulloblastoma to a 50%, 5-year survival. Nevertheless, the treatment results in substantial acute toxicity, and many survivors have serious sequelae. Further improvement in survival with optimal surgery and radiotherapy is not expected unless chemotherapy is added. Refinements in radiotherapy technique, however, can improve the therapeutic ratio of the treatment by lowering its side effects. In the last year children who required craniospinal irradiation at M. D. Anderson Hospital were treated with 6 MV photons to the brain and primary tumor and with 15-17 MeV electrons to the spinal canal. The elective dose to the whole brain was 30 Gy in 17 fractions and 30 Gy in 20 fractions to the spine. The primary tumor received an additional 20-25 Gy. An electron-beam dose distribution was drawn on a computerized tomography (CT) reconstructed sagittal plane. The electron energy was selected so that the 90% isodose line was at least 3 mm anterior to the cord after correction for bone heterogeneity. The treatment was well tolerated in the first five patients. It is projected that the current technique will cause fewer late effects and improve the tolerance to chemotherapy.

Treatment of squamous carcinoma of the retromolar trigone.

Since squamous carcinoma of the retromolar trigone is unusual, there is a paucity of information in the world's literature to use as a reference for selecting treatment and determining pertinent factors affecting prognosis. Consequently, an analysis of the medical records of 110 patients with biopsy proven squamous carcinoma originating in the retromolar trigone, seen and treated entirely at The University of Texas M.D. Anderson Hospital and Tumor Institute at Houston from 1965-1977, with at least 5 years of follow-up, was completed and constitutes the substance of this study. Local-regional control and survival were correlated with age, sex, presenting signs and symptoms, dental status, T and N classification, histologic grading, surgical findings, and the various modalities of treatment. Seventy lesions were staged T1-T2 and 77 patients had N0 necks. Thirty-five patients received a planned combination of surgery and x-ray therapy to the primary and/or neck. A composite resection was performed in 48 patients with the closure accomplished primarily or with a skin graft. The various surgical approaches are critiqued with a favorable emphasis on the marginal resection of the mandible and a modification of the radical neck dissection. The ultimate failure in the primary and the neck was 7% (8/110) and 10% (11/110) respectively. Single modality treatment whether it is surgery or irradiation appears equally adequate regardless of the T or N Stage. However, more T3-T4 cancers were treated initially with surgery. Thirty-six patients developed a second primary cancer of which 29 were in the upper aerodigestive tract. The low 5-year survival of 20% (29/110) reflects a poor salvage of the second primary and a high incidence of intercurrent disease in this elderly group of patients.

Dosimetric evaluation of a pencil-beam algorithm for electrons employing a two-dimensional heterogeneity correction.

The accuracy of a pencil-beam algorithm for electrons employing a two-dimensional heterogeneity correction is demonstrated by comparing calculation with measurement. Ionization measurements have been made in a water phantom for a variety of non-standard geometries. Geometries to demonstrate the effect of an extended treatment distance, a sloping skin surface, and an irregular skin surface have been selected. Additionally, thermoluminescent dosimeters have been used to measure distributions in tissue-substitute phantoms, which were designed from individual patient computerized tomographic scans. Three patient scans have been selected: (1) diffuse hystiocytic lymphoma of the left buccal mucosa and retromolar trigone; (2) squamous cell carcinoma of the nose at the columnella ; and (3) carcinoma of the maxillary antrum. Results demonstrate the algorithm's ability to simultaneously account for the isodose shifting as a result of internal heterogeneities and for sidescatter non-equilibrium caused by lateral discontinuities of the skin surface and internal anatomy. The algorithm is shown to generally be accurate to within +/- 4% in the treatment volume or +/- 4 mm in regions of sharp dose gradients as found in the penumbra and distal edge of the beam. Examples of greater disagreement are shown and their physical interpretation discussed.