Linear Accelerator Treatment of Multiple Metastases in a Single Session
Single Session Multiple Metastasis Treatment
Powerful software optimizes LINAC multi-leaf collimator motion to maximize treatment to each metastasis, while sparing healthy tissue around the tumors. The system delivers the desired amount of radiation dose to all metastases at the same time in a single treatment.
There are two radiosurgery approaches to treat multiple brain metastases in a single session: treat each metastasis individually or treat all metastases at once. The first option requires the patient to be repositioned for every metastasis, which can be time-consuming. The second, more efficient alternative is to treat all metastases at once, which requires a LINAC equipped with a multi-leaf collimator.
For more information on how the multi-leaf collimator works, visit What is Linear Accelerator Stereotactic Radiosurgery.
Dedicated Multiple Brain Metastasis Software
During the LINAC rotations, the leaves of the multi-leaf collimator are in constant motion, carefully balancing the shielding of healthy tissue with delivering treatment dose to the brain metastases.
A complete patient treatment involves several LINAC rotations around the patient’s head to deliver the total radiation dose to all brain metastases. During the LINAC rotations, the leaves of the multi-leaf collimator are in constant motion to shield the healthy tissue surrounding all the metastases. For the treatment of all metastases at once, powerful software determines LINAC leaf motion to carefully balance shielding the healthy tissue with delivering dose to the metastases.
One approach to the simultaneous treatment of multiple brain metastases employs a sophisticated computer algorithm to optimize multi-leaf collimator motion and spare the healthy tissue around the tumors. This technique is designed to spare a maximum amount of healthy tissue while treating multiple brain mets at the same time. For every rotation of the linac gantry, this algorithm selects an optimized grouping of brain metastases that will involve the least exposure of healthy brain tissue. If it is not possible to deliver dose to all metastases without exposing healthy tissue, an additional rotation, or arc, of the linac will be added to the treatment plan. Although several arcs are required to complete the treatment, each arc requires less than a minute to deliver so the speed of the treatment is not compromised but the quality is increased. [1] By the end of treatment delivery, all brain metastases have received their required radiation dose, and healthy brain tissue has been optimally spared. This technique is called Elements Multiple Brain Mets SRS and is compatible with most LINACs and therefore could be made available at most hospitals or cancer centers.
Adapted Conventional Technologies
Other technologies have been adapted from conventional radiotherapy in the body to be used in the brain. These systems prioritize exposing the brain metastases to radiation over shielding the healthy tissue. This means that the multi-leaf collimator leaves deliver the desired radiation dose to all the metastases during every linac rotation. However, this technique creates an effect called dose spillage, which is when radiation overflows the targeted tumor area into healthy tissue areas, which can cause issues. [2] This solution also uses these algorithms to control the radiation intensity and speed of the linac as it rotates around the patient. This delivery technique was originally created to deliver radiation to tumors with complex shapes, but is most commonly used in cases with just one tumor. [3].
[1] References and calculations on file with Brainlab.
[2] Lee, S. H. et al. Clinical application of RapidArc volumetric modulated arc therapy as a component in whole brain radiation therapy for poor prognostic, four or more multiple brain metastases. Radiat. Oncol. J. 30, 53–61 (2012).
[3] Huang, Y. et al. Radiosurgery of multiple brain metastases with single-isocenter dynamic conformal arcs (SIDCA). Radiother. Oncol. 112, 128–32 (2014).
