Equivalent whole brain dose for patients undergoing gamma knife for multiple lesions

Area of Science:

• Neurosurgery
• Radiation Oncology
• Medical Physics

Background:

• Advancements in radiosurgery allow treatment of numerous brain metastases.
• The cumulative dose to the whole brain from fractionated radiosurgery is not well-defined.
• Assessing equivalent whole-brain dose aids clinical decision-making for multiple brain lesions.

Purpose of the Study:

• To investigate the relationship between the number and volume of brain metastases and the mean whole brain dose (MWBD) after radiosurgery.
• To determine thresholds for lesion number and volume that result in significant MWBD.
• To inform individualized treatment planning for patients with multiple brain metastases.

Main Methods:

• Retrospective analysis of 12 patients treated with Leksell Gamma Knife Perfexion for multiple brain metastases.
• Contouring of the entire brain and calculation of MWBD for each treatment plan.
• Outlining of all enhancing tumors to record total tumor volume.

Main Results:

• A median of 8 lesions (range 1-41) were treated per patient across 33 total treatments.
• Median MWBD per treatment was 1.4 Gy (range 0.2-7.6 Gy), with median total tumor volume of 4.3 cm³.
• Patients treated for >25 lesions or with >10 cm³ cumulative tumor volume exceeded 4 Gy MWBD.

Conclusions:

• Both the number and volume of brain metastases significantly influence MWBD.
• Thresholds of >25 lesions or >10 cm³ tumor volume per session are associated with MWBD >4 Gy.
• Individualized treatment planning considering tumor location and proximity to critical structures is essential.