Abstract
Spine stereotactic body radiation therapy (SBRT) uses high dose per fraction for palliative
pain control. The treatment plans are often heavily modulated due to close proximity
to spinal cord and this can lead to poor plan quality which are susceptible to dose
delivery discrepancy. Therefore, we aim to assess the effectiveness of the monitor
unit (MU) objective tool in Eclipse treatment planning systems in modulating the plan
complexity to improve the plan quality in spine SBRT.
Seven retrospective spine SBRT plans are re-optimized using the MU objective tool
in Eclipse TPS v13.6 and were compared with the original plans. The dose metrics of
the tumor PTV were compared using D1cc. D99%, D95%, D0.03cc, D0.1cc, D0.35cc and D1cc, and that of cord PRV were compared using D0.03cc, D0.1cc, D0.35cc. Four different plan complexities were also calculated for the original and re-optimized
plans to quantify the impact of the tool on the modulation. Patient specific quality
assurance measurements were performed with Stereophan and SRS MapCheck, and analyzed
using the 1%/1-mm and 2%/2-mm criteria with gamma analysis.
The dose metrics of the PTV and cord PRV of the re-optimized and original plans are
similar and still meet the planning dose constraints. In particular, the PTV dose
coverage has a small percentage difference of (0.15 ± 1.33)% and (0.01 ± 1.04)% for
D99% and D95%, respectively. The 4 calculated plan complexity metrics consistently show that the
re-optimized plans are quantitatively less complex than the original plan. The gamma
passing rate of the re-optimized plans improved from (92.2 ± 2.0)% to (94.2 ± 1.6)%
with the 1%/1-mm criterion, and (98.7 ± 1.0)% to (99.5 ± 0.3)% with the 2%/2-mm criterion.
Overall, the re-optimized plans achieve at least a 10% MU reduction (11.7% to 24.6%).
Our study shows that optimization with the MU objective tool can reduce plan complexity
and improves dose delivery accuracy, while not compromising the dose distribution.
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Article info
Publication history
Published online: October 21, 2022
Accepted:
September 20,
2022
Received in revised form:
August 25,
2022
Received:
June 26,
2022
Identification
Copyright
© 2022 American Association of Medical Dosimetrists. Published by Elsevier Inc. All rights reserved.
