Controlling brain metastasis with localized radiotherapy.

This study evaluated the impact of radiotherapy (RT) on controlling brain metastasis (BM). The study suggested that a single dose of RT was effective in controlling small BM. Larger BM could be controlled more effectively with multiple rounds of RT.

The spread of cancer from the original tumor to other parts of the body is called metastasis. BM are reported in patients with different types of cancer. Though therapies for many types of cancer are improving, it is hard for them to enter the brain. BM can be treated with RT. However, RT to the whole brain can result in severe side effects.

Stereotactic radiosurgery (SRS) delivers RT to the area of the brain that contains the tumor using 3D imaging. This can avoid side effects to healthy brain tissue. SRS can be given in one dose or can be broken down into fractions of the dose, called fractionated SRS (fSRS).

The dose of RT given during SRS depends on the size of the tumor. The appropriate dose of RT for SRS that completely removes the BM is not yet clear.

The study included data from 56 trials. The most common types of cancer included were lung cancer, melanoma, renal cell carcinoma, and breast cancer. 44% of patients had previously been given whole brain RT (WBRT). Patients received RT as SRS or fSRS. The dose of RT was calculated based on the size of the tumor. The margin around the tumor that was included in the calculation depended on the study. The study evaluated whether RT controlled the BM 1 year after SRS or fSRS.

For RT given in one dose (SRS), 18Gy and 24Gy were the doses that gave 85% and 95% control of small BM (2 cm or smaller). An SRS dose of 18Gy was associated with a 75% control rate of medium BM (2.1-3 cm). An SRS dose of 15Gy was associated with a 69% control rate of larger BM (3.1-4 cm). 

For medium-to-large BMs (2.1-4 cm), 3-5 fractions (doses) of fSRS around 27-35Gy gave 80% tumor control of BM.

The study concluded that for large tumors, fSRS should be used. For smaller tumors, SRS doses of 18Gy were associated with the best outcome.

This article analyzed studies with different protocols. There was no clear definition of what ‘control of the tumor’ meant between trials. The study did not evaluate the impact that RT had on patient outcomes. Also, the study did not evaluate any side effects associated with SRS.