Radiotherapy for pediatric brain tumors

Pediatric brain tumors

Brain tumors in children vary with regard to histology, location, gender distribution, and age of onset. The past several decades have witnessed substantial improvements in the diagnosis and treatment. As a result, the number of long-term survivors also has increased continuously. Recent advances in neuroimaging facilitate tumor localization and mapping of brain function by noninvasive techniques and are becoming important in preoperative assessment for brain tumors. Surgery remains the mainstay of treatment of many tumor types. A role for chemotherapy is emerging, particularly for nonresectable tumors and in infants, for whom the adverse effects of radiation therapy are severe. Despite the improved treatments and prognostic data, however, many long-term survivors experience significant neurocognitive and developmental deficits.

Resection Followed by Radiosurgery for Advanced Juvenile Nasopharyngeal Angiofibroma: Report of Two Cases

OBJECTIVE AND IMPORTANCE

Experience with the management of juvenile nasopharyngeal angiofibroma (JNA) by gamma knife radiosurgery is limited. We report control of the disease in two patients with advanced-stage JNA treated with primary resection followed by gamma knife stereotactic radiosurgery of residual disease.

CLINICAL PRESENTATION

An 18-year-old man presented with chronic sinusitis, worsening headaches, diplopia, and left-sided facial numbness. A second patient, a 19-year-old man, presented with recurrent epistaxis and nasal congestion. Magnetic resonance imaging findings and endoscopic evaluation in each patient were consistent with advanced-stage JNA.

INTERVENTION

One patient underwent craniofacial resection with approximately 3.0 cm3of residual tumor in the region of the cavernous sinus. The other patient underwent preoperative embolization followed by a lateral rhinotomy for tumor resection with approximately 4.7 cm3of residual tumor in the right infratemporal fossa. In an attempt to limit radiation to surrounding normal brain, residual tumor in both patients was treated with gamma knife stereotactic radiosurgery. Control of disease was documented by magnetic resonance imaging more than 24 months after treatment.

CONCLUSION

Short-term control of late-stage JNA was achieved by use of a strategy of primary surgical resection followed by gamma knife radiosurgery of residual tumor in two patients. Establishing the effectiveness and safety of this strategy over conventional methods of managing advanced JNA will require future prospective studies.

Gamma-knife radiosurgery in pediatric cerebral and skull base tumors

BACKGROUND

This retrospective study of 12 children with cerebral or skull base tumors was undertaken to evaluate morbidity and outcome after gamma-knife surgery.

PROCEDURE

Twelve consecutive children treated with stereotactic radiosurgery in a curative intent were reviewed. There were five girls and seven boys. The mean age at diagnosis was 5.8 years and at radiosurgical treatment 8.4 years. There were four pilocytic astrocytomas, two craniopharyngeomas, two pineoblastomas, two ependymomas, and two other tumors of high malignancy. We used a 201-source Co60 Leksell gamma knife and all children were treated in general anesthesia.

RESULTS

The mean tumor volume was 3.7 cm(3) and the mean tumor margin dose was 13.8 Gy. Seven patients remained stable after gamma-knife treatment with a mean follow- up of 78.6 months. One patient died during follow-up. The remaining four patients had progressive disease, two within and two outside the irradiated field, and have received further treatment. They are still alive with and without disease with a mean follow-up of 96.8 months.

CONCLUSION

Gamma-knife surgery is an effective treatment in some non-resectable cerebral and skull base pediatric tumors. In most cases, it is used in combination with other therapeutic modalities. It is safe and well tolerated.

Novel techniques in the delivery of radiation in pediatric oncology

The field of radiation oncology continues to develop at a rapid pace, due to concurrent progress in high speed computing, improved sensitivity in diagnostic imaging (both anatomic and physiologic), and the introduction of rational new therapeutics built on solid radiobiologic principles. These innovations will become critically important in the field of pediatric oncology, as they will allow for an increased therapeutic ratio in the developing child. Maximizing the benefit of lower dose radiation through the use of radiation modifiers (hypoxic cell sensitizers, signal transduction pathway inhibitors, concurrent chemotherapy), increasing the tolerance of normal tissues (radioprotectors) and tailoring the target area more closely to the desired critical tissues (IMRT, functional simulation with PET and MRS, radiolabeled monoclonal antibodies) will lessen the short and long term toxicity of radiation and increase its effectiveness.

Innovative therapies for pediatric brain tumors

Success in the treatment of pediatric brain tumors has lagged behind that of other pediatric cancers. This paper highlights many of the advances that have taken place over the past few years in the surgical, radiotherapeutic, and chemotherapeutic approaches to central nervous system lesions that we hope will lead to a dramatic improvement in outcome. Innovations in neurosurgical and radiotherapeutic techniques have resulted in decreasing toxicity although substantial improvement in cure rates has not been observed. Many new techniques such as gene therapy, angiogenesis inhibitors, immunotherapy, and others that have not been part of the classic approach to these lesions are now in clinical trials in the hope that they will impact on the survival of these patients. The scientific basis for these new treatment modalities and preliminary clinical results are discussed.

The radiobiology of radiosurgery and stereotactic radiotherapy

Radiation therapy has evolved into a complex amalgamation of treatment techniques that differ significantly according to the way the radiation is delivered to the patient and coincidentally according to the biologic effects that are observed with each technique. Although there are concepts within radiobiology that unify the field, it is not apparent that the biologic effects with one methodology of treatment resemble those of another. Radiosurgery, although initially developed in the 1950s, has become more commonly used in recent years. This treatment involves high-dose, single-fraction treatments with sharp dose gradients to small volumes of tissue. This contrasts with conventional external-beam radiotherapy which involves small-dose, multiple-fraction, broad-dose-gradient treatment to relatively large volumes of tissue. Stereotactic radiotherapy generally delivers small-dose, multiple-fraction treatments to small or intermediate volumes of tissue with a sharp dose gradient compared with conventional external-beam treatment. A discussion of these technique differences with reference to the radiobiologic implications may help elucidate the potential utility of the techniques in clinical radiotherapy.