A four-arc coplanar volumetric modulated arc therapy plan may provide target coverage and dose conformity comparable to a more complex non-coplanar approach in patients receiving hippocampal avoidance whole-brain radiotherapy, according to a technical study published in Radiological Physics and Technology on July 15, 2026.
The retrospective planning study compared several coplanar and non-coplanar VMAT configurations using a Monte Carlo-based treatment planning system. The findings suggest that adding coplanar arcs can improve treatment-plan quality while avoiding some of the delivery challenges associated with non-coplanar techniques.
Protecting Memory During Whole-Brain Radiotherapy
Whole-brain radiotherapy remains an important treatment option for patients with brain metastases and other selected clinical indications. However, radiation exposure to the hippocampus has been associated with damage to neural precursor cells and a decline in memory and cognitive function.
Hippocampal avoidance whole-brain radiotherapy is designed to reduce radiation exposure to this sensitive region while maintaining adequate treatment of the remaining brain tissue. Achieving this balance requires highly conformal treatment planning, particularly because the hippocampi are surrounded by tissue that must still receive the prescribed therapeutic dose.
VMAT has become an important technique for this purpose because it allows radiation intensity and beam shape to change continuously as the treatment machine rotates around the patient. Nevertheless, the optimal number and orientation of treatment arcs continue to be evaluated.
Four Planning Strategies Put to the Test
Surendran Jagadeesan and colleagues evaluated treatment plans from 10 patients who were retrospectively replanned using the Monaco treatment planning system.
Four VMAT techniques were compared
- A two-arc coplanar configuration
- A three-arc coplanar configuration
- A four-arc coplanar configuration
- A combined coplanar and non-coplanar configuration
All plans were designed to deliver a total dose of 30 Gy in 10 fractions to the planning target volume.
The investigators assessed target coverage, dose conformity, dose homogeneity, hippocampal exposure, doses to other organs at risk, monitor units, and estimated treatment-delivery time.
More Coplanar Arcs Improved Plan Quality
The analysis showed that increasing the number of coplanar arcs progressively improved target coverage and dose homogeneity.
Among the coplanar techniques, the four-arc configuration produced the strongest overall dosimetric performance. Its planning target volume coverage, conformity, and homogeneity were comparable to those achieved with the combined coplanar and non-coplanar approach.
All four techniques met the required protocol constraints for the hippocampi and other organs at risk. This finding indicates that each evaluated configuration was capable of producing an acceptable hippocampal avoidance whole-brain radiotherapy plan within the parameters of the study.
Non-Coplanar Planning Achieved the Lowest Hippocampal Doses
Although the four-arc coplanar technique performed similarly across several major planning measures, the non-coplanar approach produced the lowest absolute radiation doses to the hippocampi.
Non-coplanar treatment uses beam paths from different planes rather than restricting all arcs to a single rotational plane. This additional geometric flexibility can improve dose avoidance around small and centrally located structures such as the hippocampi.
However, the dosimetric advantage came with practical trade-offs. The non-coplanar plans required more monitor units and longer treatment-delivery times than the coplanar techniques.
Non-coplanar delivery may also involve additional patient-positioning steps, couch rotation, collision checks, and increased attention to setup accuracy. These considerations can influence workflow, particularly in busy radiotherapy departments or centers where equipment and staffing resources are limited.
A Balance Between Precision and Efficiency
The study highlights an important consideration in radiotherapy planning: the most complex technique may not always provide the most practical overall solution.
While non-coplanar VMAT achieved the greatest reduction in absolute hippocampal dose, four-arc coplanar VMAT produced comparable target coverage, conformity, and homogeneity with more efficient treatment delivery.
The findings therefore support four-arc coplanar VMAT as a practical alternative in centers where non-coplanar treatment is difficult to implement or routinely unavailable.
A coplanar strategy may also reduce the operational demands associated with couch rotation while preserving the plan quality required for hippocampal avoidance treatment.
Findings Remain Focused on Treatment Planning
The results should be interpreted within the scope of the study. This was a retrospective dosimetric analysis involving 10 patients, rather than a prospective clinical trial assessing cognitive outcomes, tumor control, survival, or treatment-related toxicity.
The study demonstrates that the four-arc coplanar technique can produce competitive treatment plans within the Monaco system. However, it does not establish that the technique is clinically superior or equivalent in terms of long-term patient outcomes.
Additional evaluation in larger patient groups and different treatment-planning environments may help determine whether the findings can be consistently reproduced across institutions, equipment platforms, and clinical workflows.
A Practical Route to Hippocampal-Sparing Treatment
As hippocampal avoidance becomes increasingly incorporated into whole-brain radiotherapy planning, treatment centers must balance dose precision with reproducibility, safety, and delivery efficiency.
The findings from Jagadeesan and colleagues indicate that four-arc coplanar VMAT may achieve this balance. By producing plan quality comparable to a non-coplanar strategy while requiring fewer monitor units and shorter treatment times, the technique may offer a more accessible route to hippocampal-sparing radiotherapy.
The study was conducted by researchers affiliated with Burjeel Cancer Institute and Burjeel Medical City in Abu Dhabi, King Saud Bin Abdulaziz University for Health Sciences and Princess Noorah Oncology Center in Jeddah, the Emirates Oncology Society, Dana-Farber Cancer Institute and Harvard Medical School, and Ras Al Khaimah Medical and Health Sciences University.
Written by Nare Hovhannisyan, MD
Stay informed with more articles like this on OncoDaily