Susan F. Dunbar

Image fusion for stereotactic radiotherapy and radiosurgery treatment planning.

PURPOSE We describe an image fusion application that addresses two basic problems that previously limited the use of magnetic resonance imaging (MRI) for geometric localization in stereotactic radiosurgery (SRS) and stereotactic radiotherapy (SRT). The first limitation is imposed by the use of a relocatable, MRI-incompatible, stereotactic frame for stereotactic radiotherapy. The second limitation is an inherent lack of geometric fidelity in current MRI scanners that invalidates the use of MRI for stereotactic localization. METHODS AND MATERIALS We recently developed and implemented a novel automated method for fusing computerized tomography (CT) and MRI volumetric image studies. The method is based on a chamfer matching algorithm, and provides a quality assurance procedure to verify the accuracy of the fused image set. The image fusion protocol removes the need for stereotactic fixation of the patient for the MRI study. RESULTS The image fusion protocol significantly improves on the spatial accuracy of the MRI study. We demonstrate the effect of distortion and the effectiveness of the fusion with a phantom study. We present two case studies, an acoustic neurinoma treated with SRS, and a pilocytic astrocytoma treated with SRT. CONCLUSION The image fusion protocol significantly improves our logistical management of treating patients with radiosurgery and makes conformal therapy practical for treating patients with SRT. The image fusion protocol demonstrates both the superior diagnostic quality and the poor geometric fidelity of MRI. MRI is a required imaging modality in stereotactic therapy. Image fusion combines the superior MRI diagnostic quality with the superior CT geometric definition, and makes the use of MRI in stereotactic therapy possible and practical.

Gorham's massive osteolysis : the role of radiation therapy and a review of the literature

PURPOSE This paper reviews the natural history and management of patients with Gorhams disease and presents four cases treated at The Massachusetts General Hospital since 1965. Gorhams disease is characterized by localized endothelial proliferation which results in destruction and resorption of bone. The etiology is undefined. There is no evidence of a malignant, neuropathic, or infectious component. This disease is progressive in most patients, but in occasional instances the process has been noted to be self-limited. The principal treatment modalities are surgery and radiation therapy. METHODS AND MATERIAL Since 1965, four patients with Gorhams Disease have been treated at the Massachusetts General Hospital. Three received definitive radiation therapy in doses ranging from 31.5 to 45 Gy. The fourth patient underwent surgery primarily. RESULTS Three patients are currently alive and fully functional with no evidence of disease at last follow-up. The fourth patient died of progressive disease despite treatment with both radiation therapy and surgery. CONCLUSION The prognosis for patients with Gorhams disease is generally good unless vital structures are involved. Due to the rarity of this entity, there is no standard therapy. Definitive radiation therapy in moderate doses (40-45 Gy in 2 Gy fractions) appears to result in a good outcome and few long-term complications.

Stereotactic radiotherapy for pediatric and adult brain tumors : preliminary report

PURPOSE Stereotactic radiotherapy is a new modality that combines the accurate focal dose delivery of stereotactic radiosurgery with the biological advantages of conventional radiotherapy (1.8-2.0 Gy/day using 25-30 fractions). The modality requires sophisticated treatment planning, dedicated high-energy linear accelerator, and relocatable immobilization devices. We report here our early experience using stereotactic radiotherapy for intracranial neoplasms. METHODS AND MATERIALS Between June 1992 and September 1993, we treated 82 patients with central nervous system lesions using stereotactic radiotherapy, delivered from a dedicated 6 MV stereotactic linear accelerator. A head fixation frame provided daily relocatable setup using a dental plate for all patients over 8 years of age. A modified head frame, which does not require a mouthpiece, was used for children requiring anesthesia. The patients ranged in age from 9 months to 76 years. Thirty-three patients were children less than 21 years of age. Selection criteria for the protocol included: (a) focal, small (< 5 cm) radiographically distinct lesions known to be radiocurable (pituitary adenoma, craniopharyngioma, meningioma, acoustic neuroma, pilocytic astrocytoma, retinoblastoma), and (b) lesions located in regions not amenable to surgery or radiosurgery such as the brain stem or chiasm. Standard fractionation and conventional doses were delivered. Patients with low-grade astrocytoma, oligodendroglioma, or ependymoma were treated using a dose escalation regime consisting of conventional doses plus a 10% increase. RESULTS Although follow-up is 16 months (range 3-16 months), posttreatment radiographic studies in 77 patients have been consistent with changes similar to those found after conventional radiation therapy. To date, reduction of up to 50% of the original volume has been noted in 19 out of 77 patients, and 4 patients had a complete response, 2 with dysgerminoma, and 1 each with astrocytoma and retinoblastoma. In 56 patients disease was either stable or the follow-up was too short for evaluation. While the follow-up is relatively short, there have been no in-field or marginal recurrences. The only unexpected radiographic findings were in three patients with pilocytic astrocytomas, who developed asymptomatic edema in the treatment volume. Accuracy in daily fractionation was excellent. In over 2000 patient setups with 41,000 scalp measurements, reproducibility was found to be within 0.41 mm (median) of baseline readings, allowing for precise immobilization throughout the treatment course. The treatment in all cases was well tolerated with minimal acute effects. Our stereotactic radiotherapy facility can provide fractionated therapy for 10-12 patients a day efficiently and accurately. CONCLUSIONS The treatment and relocatable stereotactic head frames were well tolerated with minimal acute effects. No long-term sequelae have been noted, although the observation period is short. To fully define the role of stereotactic radiotherapy, we are conducting prospective studies to evaluate neurocognitive and neuroendocrine effects. We expect that this innovative approach will make a significant impact on the treatment of intracranial neoplasms, particularly in children.

Conjunctival lymphoma: Results and treatment with a single anterior electron field. A lens sparing approach☆

Lymphoma of the conjunctiva is rare. It presents in older patients as a mass lesion and usually remains localized. Surgery is limited to biopsy, and radiation therapy is the definitive treatment of choice. The entire conjunctiva is treated. Relatively high doses (approximately 30 Gy) are required for local control, which may lead to cataract formation. Twelve patients with conjunctival lymphoma were treated at the Massachusetts General Hospital between 1979 and 1988. Ten of 12 patients presented with a unilateral lesion; 2 of 12 with bilateral lesions. Two of 12 patients were found to have systemic disease at the time of presentation. One patient developed conjunctival lymphoma 5 years after the diagnosis of generalized disease. Using electron beam, all patients were treated with a single anterior circular field to total doses ranging from 24 Gy to 30 Gy delivered in 8 to 16 fractions over 9 to 20 days. In all cases, the lens was shielded by a specially designed plastic contact lens bearing a 12 mm diameter lead shield. The lens dose was determined at varying depths beneath the shield for 6 MeV and 9 MeV electron beams and ranged from a minimum of 5% to an absolute maximum of 18% of the total dose delivered to the tumor. Local control was maintained in all patients with follow-up to 9 1/2 years. One patient relapsed distantly 3 years after treatment. One of 12 patients died of systemic disease 4 years after treatment of the ocular lesion. Two patients developed cataracts 4 and 5 years after treatment; one had bilateral cataract, although only one eye had been treated. Both patients were over 75 years old. In both cases, the cataracts were felt to be senile cataracts which are ophthalmologically and radiographically distinguishable from radiation induced lesions.

Radiologic determination of the caudal border of the spinal field in cranial spinal irradiation

PURPOSE The purpose of this paper is to determine the inferior border of the caudal sac which dictates the placement of the lower border of the spinal field in Cranial Spinal Irradiation. METHODS AND MATERIALS We have reviewed the pre-treatment craniospinal Magnetic Resonance Imaging studies of 24 evaluable children with seeding central nervous system tumors who were treated at our institution with Cranial Spinal Irradiation since 1988. RESULTS The Magnetic Resonance Imaging studies demonstrated significant variation in the terminal location of the caudal sac, ranging from S2 to S4. The most frequent termination was at S2 (12/24). In four patients (4/24), termination was at mid S1 and in eight others (8/24), it was found to be at or below S3. In addition, the presence of spinal metastases may displace the distal limit even further inferiorly. CONCLUSION Rather than arbitrarily placing the inferior field edge at S2, we recommend individualizing the required margin for the spinal field which should be determined using sagittal T1-weighted images of the lumbosacral spine. This is particularly important in patients who present with spinal metastases, since tumor may extend the dural sac termination distally.

Stereotactic Radiotherapy: A Technique for Dose Optimization and Escalation for Intracranial Tumors

Stereotactic radiosurgery offers the ability to treat relatively small volume intracranial lesions with single fraction, high dose radiotherapy while sparing surrounding tissue due to rapid fall off of dose outside of the treatment volume. Conventional radiotherapy takes advantage of the sparing effects of dose fractionation, but includes relatively large amounts of normal brain in the treatment volume the tolerance of which is dose-limiting. For some intracranial lesions it may not be optimal to treat with large single fractions due to tumor location or size. Conventional fractionated radiotherapy may not be optimum in all cases due to the necessary inclusion of normal structures. Through the development of relocatable head frames, the precision of stereotactic techniques and the biologic advantages of fractionation may be combined in stereotactic radiotherapy (SRT). We report on the treatment of 68 patients with intracranial lesions using a dedicated stereotactic linear accelerator to deliver SRT between June 1992 and June 1993. SRT was used either in order to optimize dose distribution and spare normal tissues in patients with excellent prognosis or in order to increase the dose to tumor while keeping doses to normal tissues below tolerance levels in patients with poorer prognosis (dose escalation). Histologies treated included meningioma, low grade astrocytoma, pituitary adenoma and acoustic neuroma. The most common treatment sites were the parasellar region and cavernous sinuses. Most patients (79%) had surgical debulking prior to SRT. 10-12 patients were treated daily. Patient positioning using relocatable stereotactic frames was highly precise. Acute and subacute side effects were minimal and radiographic responses have been similar to those expected with conventional radiotherapy.(ABSTRACT TRUNCATED AT 250 WORDS)

Connective tissue tumors in patients with cutaneous melanoma

BACKGROUND A possible relation between cutaneous melanoma and connective tissue tumors has been described. OBJECTIVE After the observation that a group of our patients had both cutaneous melanoma and a soft tissue sarcoma, we elected to review this formally. Eleven patients with both diagnoses were identified and are described. METHODS A computer search through the Medical Records Department and the Tumor Registry of the Massachusetts General Hospital identified seven men and four women with the diagnoses of melanoma and malignant bone or soft tissue sarcoma. The medical records and pathology specimens of all tumors were reviewed. RESULTS In three patients, the two tumors were diagnosed within 1 year of each other, in seven, the diagnosis of melanoma was made first, and in one, melanoma was diagnosed after the connective tissue lesion. The interval between the two diagnoses ranged up to 13 years. Although the locations and types of melanoma were typical, some of the connective tissue tumors were unusual; there were two sacral chordomas. In two instances, the melanoma and connective tissue tumor were anatomically close; the sarcoma developed at the edge of the resection of the prior melanoma in one patient. None of the tumors developed in previously irradiated tissues, and in no instance did the second tumor appear to be caused by the therapy received for the first. None of the patients had a family history of melanoma. Four patients had other cancers in addition to the melanoma and connective tissue tumor. CONCLUSION Although these patients were seen in a referral center, it is our impression (based on the total number of patients with connective tissue tumors seen and the incidence of melanoma in the general population) that observing 11 patients with both types of tumors is greater than would be expected by chance.