Larger Brain Metastases
If you have been diagnosed with a brain metastasis that is larger than 3cm in diameter, your doctor may consider a “hypo-fractionated” treatment. Hypo-fractionation combines the accuracy of radiosurgery with conventional radiotherapy by breaking a single treatment into three, five or more sessions, or fractions [1-3]. This treatment method is used when the ‘effective dose’ needed for the size of the tumor is too high for the patient to withstand all at once. The goal is to give enough radiation to kill tumor cells, while allowing the healthy tissue to recover in between sessions. This method is well established for many types of tumors, especially large brain metastases.
In general, the higher the radiation dose aimed at a brain tumor, the higher the likelihood that the dose will destroy all tumor cells. There are, however, limits to the amount of dose that can be safely given. A dose that is too high may cause radiation necrosis—the forming of an area of dead tissue. Necrosis can sometimes cause brain edema (swelling) or the development or worsening of problems with mental function. The challenge is always to deliver a dose high enough to destroy the tumor cells but which is still safe for the patient.
When choosing the radiation dose, specialists also need to consider the consistency of the tumor tissue and type of primary cancer: metastases from melanomas, renal cell carcinoma, and sarcoma are considered resistant to radiation. They also take into account whether the patient has had whole brain radiation therapy beforehand. Clinical studies have established which radiosurgery dose is still safe if delivered after whole brain radiation was delivered previously to the patient. This same dose is usually used for radiosurgery when it is the sole treatment; however, it has shown to not always effectively destroy the tumor. This is especially true for larger tumors that are typically treated with even lower doses to avoid the risk of necrosis. Ask your doctor about radiation dose specifically for your diagnosis and type of brain metastasis.
[1] Inoue, H. K. et al. Optimal hypofractionated conformal radiotherapy for large brain metastases in patients with high risk factors: a single-institutional prospective study. Radiat. Oncol. 9, 231 (2014).
[2] Ernst-Stecken, A., Lambrecht, U., Mueller, R., Sauer, R. & Grabenbauer, G. Hypofractionated stereotactic radiotherapy for primary and secondary intrapulmonary tumors: first results of a phase I/II study. Strahlentherapie und Onkol. 182, 696–702 (2006).
[3] Fahrig, A. et al. Hypofractionated stereotactic radiotherapy for brain metastases–results from three different dose concepts. Strahlentherapie und Onkol. 183, 625–30 (2007).
