Highlights
- •The PB plans that passed the Gamma testing did not yield smaller dose errors compared to the plans that failed the Gamma testing.
- •The MU scaling technique leads to an overall smaller dose error.
- •MU scaling, however, for some DVH evaluation point, worsened some cases.
Abstract
Purpose
To investigate, in proton therapy, whether the Gamma passing rate (GPR) is related
to the patient dose error and whether MU scaling can improve dose accuracy.
Methods
Among 20 consecutively treated breast patients selected for analysis, two IMPT plans
were retrospectively generated: (1) the pencil-beam (PB) plan and (2) the Monte Carlo
(MC) plan. Patient-specific QA was performed. A 3%/3-mm Gamma analysis was conducted
to compare the TPS-calculated PB algorithm dose distribution with the measured 2D
dose. Dose errors were compared between the plans that passed the Gamma testing and
those that failed. The MU was then scaled to obtain a better GPR. MU-scaled PB plan
dose errors were compared to the original PB plan.
Results
Of the 20 PB plans, 8 were passed Gamma testing (G_pass_group) and 12 failed (G_fail_group).
Surprisingly, the G_pass_group had a greater dose error than the G_fail_group. The
median (range) of the PTV DVH RMSE and PTV ΔDmean were 1.36 (1.00–1.91) Gy vs 1.18
(1.02–1.80) Gy and 1.23 (0.92–1.71) Gy vs 1.10 (0.87–1.49) Gy for the G_pass_group
and the G_fail_group, respectively. MU scaling reduced overall dose error. However,
for PTV D99 and D95, MU scaling worsened some cases.
Conclusion
For breast IMPT, the PB plans that passed the Gamma testing did not show smaller dose
errors compared to the plans that failed. For individual plans, the MU scaling technique
leads to overall smaller dose errors. However, we do not suggest use of the MU scaling
technique to replace the MC plans when the MC algorithm is available.
Keywords
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Article info
Publication history
Published online: August 13, 2020
Accepted:
August 5,
2020
Received in revised form:
June 26,
2020
Received:
April 2,
2020
Identification
Copyright
© 2020 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.
