Left hippocampus sparing whole brain radiotherapy (WBRT): A planning study

Area of Science:

• Radiation Oncology
• Neuro-oncology
• Cognitive Neuroscience

Background:

• Whole brain radiotherapy (WBRT) can lead to cognitive decline, particularly affecting verbal memory.
• Bilateral hippocampus avoidance (HA-WBRT) is investigated to mitigate these effects.
• Unilateral sparing of the dominant (left) hippocampus is a potential alternative strategy.

Purpose of the Study:

• To perform a dosimetrical comparison between HA-WBRT and left hippocampus sparing radiotherapy (LHA-WBRT) plans.
• To evaluate the feasibility of LHA-WBRT in maintaining target coverage and sparing the left hippocampus.

Main Methods:

• HA-WBRT plans for 10 patients were created based on the RTOG 0933 trial protocol.
• Two types of LHA-WBRT plans were generated: "BEST PTV" (maintaining left hippocampus dosimetry) and "BEST LH" (maintaining overall PTV dosimetry).
• Dosimetric parameters including conformity index, homogeneity index, and dose to critical structures were analyzed.

Main Results:

• All HA-WBRT plans met RTOG 0933 criteria.
• LHA-WBRT plans demonstrated improved homogeneity index (31.2% reduction) and reduced optic pathway dose.
• The "BEST LH" LHA-WBRT plans significantly reduced the mean dose to the left hippocampus (D100% by 11.2%, Dmax by 10.9%).

Conclusions:

• LHA-WBRT plans offer potential for improved target coverage and further dose reduction to the spared left hippocampus.
• Further clinical trials are necessary to determine the clinical significance of the observed dose reductions in the left hippocampus.