Radiation Therapy for Brain Tumors
By John Lee, M.D., Radiation Oncologist, Medical
Director, California Pacific Medical Center Department of Radiology
Radiation therapy is used in the treatment of primary or metastatic brain tumors either alone or in combination with surgery and/or chemotherapy. The two primary forms of administering radiation therapy consist of external beam radiation therapy (EBRT) or stereotactic radiation therapy (SRT). Circumstances unique to each patient’s situation may influence how these treatment options are applied. The potential benefits of combination treatments must be carefully balanced with the potential risks.
For either form of radiation therapy, EBRT or SRT, a treatment planning or simulation appointment is carried out first. The process begins with the patient being fitted with an individualized immobilization mask or head frame. CT scanning and MRI are carried out in this device. The radiation oncologist then defines the target volume (usually the visible tumor on MRI) and a margin to allow for possible extension of disease and to allow for slight variations in the patient’s daily setup. The adjacent critical organs also are contoured.
Then a treatment plan is generated, using computerized planning to accurately focus a high dose of radiation to the brain tumor, while sparing normal tissue.
External Beam Radiation Therapy
EBRT involves linear accelerators producing high-energy radiation beams that penetrate tissues and deliver radiation to a specified target. EBRT is delivered as a daily outpatient treatment in five to ten minutes, five days a week, typically over four to six weeks.
Intensity modulated radiation therapy (IMRT) is a form of EBRT. IMRT delivers a varying intensity of radiation while the head of the linear accelerator assembly is rotating. IMRT is similar to CT scanning, in the sense that during a CT scan a low-energy X-ray beam rotates around the patient, creating a sequence of cross sectional images. IMRT also uses a rotating beam, but the beam delivers higher levels of radiation and at different modulating intensities.
The modulation is achieved with small computer-driven lead “leaves” called multi- leaf collimators (MLCs) in the head of the linear accelerator. IMRT is commonly used for treatment of brain or spinal tumors to maximize radiation dose to the tumor but minimize toxicity to surrounding critical organs, and is an improvement over conventional 3D-conformal treatment plans.(1)
Stereotactic Radiation Therapy
Stereotactic radiation therapy (SRT), also known as SABRknife, is a noninvasive approach to treat brain tumors, using multiple pencil-thin beams of radiation. This focused technique allows radiation to be delivered to an area of the brain or spinal cord that might be considered inoperable. Another advantage of SRT is that radiation treatment is delivered in one to five treatment sessions.
At CPMC, our TRILOGY® linear accelerator has been modified with BrainLab’s Exactrac® Robotic Couch & Tracking System. The patient is positioned on a sliding bed (Exactrac® couch) that the linear accelerator rotates around. This allows delivery of multiple high-energy beams in arcs shaped to the tumor volume. The pattern of the arc is computer-matched to the tumor’s shape. This also minimizes the dose delivered to surrounding normal tissues and is a major improvement over previous, less conformal treatment technologies(2).
Some of the most common SRT indications for treatment include: arteriovenous malformations(3), acoustic neuromas(4), pituitary tumors(5), pineal tumors(6), primary and metastatic brain tumors, trigeminal neuralgia(7), and essential tremors(8).
Treatment Outcomes with Stereotactic Radiation Therapy
Brain metastases: A clinical study involving patients with one to three brain metastases was conducted to compare whole-brain radiation therapy (WBRT) with or without SRT boost. Overall, SRT boost improved median survival among patients who had a solitary metastasis, from 4.9 months to 16.5 months(9). A Mayo Clinic review(10) of patients with a solitary brain metastasis who underwent either surgery or SRT had statistically similar median survivals after treatment but local control was improved for SRT-treated patients—none of the patients treated with SRT had local recurrence versus 58 percent of patients treated with surgery.
Pituitary tumors: Pituitary tumors typically are treated with surgical removal and/or radiation therapy. SRT may decrease high hormonal levels caused by these tumors more quickly than conventional radiation. A review of 34 published studies including 1,567 patients with pituitary tumors that were treated with SRT demonstrated that tumor growth could be controlled in approximately 90 percent of cases(11).
Meningiomas: Most meningiomas are benign and slow-growing. Radiation therapy plays a role when the meningioma cannot be completely removed with surgery, in nonsurgical patients or in surgically inaccessible locations. Long-term (10-year) results of SRT at the University of Pittsburgh indicate that tumor size was reduced in more than half of patients with meningiomas(12).
Conclusions: Treatment of brain tumors is a complex decision-making process. Most treatment plans involve multiple members of the neuro-oncology team: neurosurgery, neurology, radiation oncology and neuroradiologists. Treatment regimen will vary widely according to location of the tumor, its size and type, and patient age and comorbidities. Radiation therapy or stereotactic radiosurgery will play a role in many clinical situations. CPMC and CPNI physicians are proud to offer the newest treatment modalities in radiation therapy and stereotactic radiosurgery for their patients.
- De La Fuente, Herman T, Ahmad And S, Vlachaki MT. Intensity modulated radiation therapy versus three dimensional conformal radiation therapy for treatment of high grade glioma: a radiobiological modeling study. J. Xray Sci Technolology. 2010: 18(4); 393-402.
- Jin JY. Wen N. Ren L. Glide-Hurst C. Chetty IJ. Advances in treatment techniques: arc-based and other intensity modulated therapies. Cancer J. 2011: May-June 17(3); 166-76.
- Yashar P. Arnar AP. Gianotta SL, Yu C, Pagnini PG, Liu CY, Apuzzo ML. Cerebral arteriovenous malformations: issues of the interplay between stereotactic radiosurgery and endovascular surgical therapy. World Neurosurgery. 2011. May-June, 75(5-6); 638-47.
- Roos DE, Potter AE, Zacest AC. Hearing preservation after low dose linac radiosurgery for acoustic neuroma depends on initial hearing and time. Radiotherapy Oncology. 2011: July 7 [Epub ahead of print].
- Park KJ. Kano H. Parry PV. Niranian A. Flickinger JC. Lunsford LD. Kondziolka D. Long-term outcomes after Gamma Knife Stereotactic Radiosurgery for Nonfunctional Pituitary Adenomas. Neurosurgery. 2011.
- Kano H. Parry PV. Niranian A, Kondziolka D, Flickinger JC. Lunsford LD. Role of stereotactic radiosurgery in the management of pineal parenchymal tumors. Prog Neurol Surg. 2009: 23: 44-58.
- Chen JC, Rahimian J, Rahimian R, Arellano A, Miller MJ, Girvigian MR. Frameless image-guided radiosurgery for initial treatment of typical trigeminal neuralgia. World Neurosurgery. 2010 Oct-Nov: 74(4-5_; 538-43.
- Kondziolka D, Ong JG, Lee JY, Moore RY, Flickinger JC. Lunsford LD. Gamma Knife thalamotomy for essential tremors. J. Neurosurgery. 2008 Jan 108(1): 111-7
- Andrews DW, Scott CB, Sperduto PW, et al. Whole brain radiation therapy with or without stereotactic radiosurgery boost for patients with one to three brain metastases: phase III results of the RTOG 9508 randomized trial. Lancet. 2004;363:1665-1672.
- O’Neill BP, Iturria NJ, Link MJ, et al. A comparison of surgical resection and stereotactic radiosurgery in the treatment of solitary brain metastases. International Journal of Radiation Oncology Biology Physics. 2003;55(5):1169-1176.
- Laws ER, Sheehan JP, Sheehan JM, et al. Stereotactic radiosurgery for pituitary adenomas: a review of the literature. Neurooncology. 2004;69(1-3):257-72
- Kondziolka D, Nathooo N, Flickinger JC, et al. Longterm results after radiosurgery for benign intracranial tumors. Journal of Neurosurgery. 2003; 53:815-821.