Modern Radiotherapy of Brain Tumors

Abstract

   There are many kind of tumors, Brain tumors account for 1.4% of all cancers. Median age of brain cancer is 58 years. Incidence is 6.4 per 100 000  men and women per year. The 5-year survival for localized brain and other nervous system cancers is 36.3%. Brain cancers account for 2.6% of all cancer deaths. Sixty per-cent of all primary brain tumors are glial tumors and two-thirds of these are clinically aggressive, high grade tumors.
   Indications of radiotherapy are High Grade Gliomas, Residual disease, Recurrent disease and Benign Tumors. If we talk about examples of high grade tumors here are some of them: Anaplastic astrocytoma (grade III), Glioblastoma (grade IV), Papillary tumor of pineal region Moderately differentiated parenchymal pineal tumor (grade III), Pineoblastoma (grade IV).
   There are many kinds of benign brain tumors, here are some examples, in particular: Meningioma, Pituitary tumors, Craniopharyngioma,  Hemangioblastoma and Hemangiopericytoma, Glomus Jugular Tumor, Pineocytoma, Chordoma, Vestibular Schwannoma, Ganglioglioma, Central neurocytoma.
   Types of radiotherapy techniques include Conventional  2D approach, 3 dimensional conformal radiotherapy (3DCRT), Stereotactic Radiosurgery and stereotactic Radiotherapy, Brachytherapy and Proton Beam Therapy.
   Two Dimensional planning for Brain Tumors include, firstly contouring target outlines, then place a field, Immobilization, particularly: head rest, thermoplastic mask and base plate.
   Disadvantages of conventional planning: Irradiation of large volumes of brain with normal tissue also, Higher toxicity and side effects, Lack of 3D visualization of tumors and 2D planning of 3D tumors.
   Taking planning CT slices in Neurooncology: Different from diagnostic imaging, Use appropriate immobilization device, Image the patient in treatment position.
   Planning MRI includes following steps: Position ideally in treatment position with orfit & base plate, Transfer images to planning system. Imaging: CT, CT-MR Fusion and PET Scan – limited but emerging role.
   Advantages of 3D planning are that it is ideal for all cases, it is also conformal, it has capability of maximum sparing of normal tissue and lower toxicity.
   There are some advantages of SRS and SRT over 3DCRT for example: High conformity, To treat small lesions not amenable to 3D CRT, Higher tumor dose, Save larger amount of normal tissue.
   Indications for SRS are benign and malignant brain tumors, arteriovenous malformations and well circumscribed targets in a size less than 4 cm in diameter. Indications for SRT are lesions more than 4 cm in size and lesions located near critical structures.
   Radiation therapy includes stereotactic radiotherapy that also includes the following: Gamma Knife, LINAC based and Cyberknife. Gamma knife is designed to provide an overall treatment accuracy of 0.3 mm. Gamma knife has three main components, Spherical source housing, 4 types of collimator helmets and Couch with electronic controls.
   Proton Beam Therapy is used for Low grade & High grade glioma, Benign brain tumors: Vestibular Schwannomas/Acoustic Neuromas, Meningioma, pituitary adenoma, AVM, Skull base tumors: chordoma/Chondrosarcomas, pediatric brain tumors: Medulloblastoma, Germ cell tumors.
   To sum it up, multiple options and techniques are available for treating brain tumors. Need to use the optimum technique, decision to be based on need of patient and available technique.