A pre-treatment patient specific QA alternative approach for HyperArc treatments.
PO-1639
Abstract
A pre-treatment patient specific QA alternative approach for HyperArc treatments.
Authors: Nina Cavalli1, Elisa Bonanno2, Giuseppe Stella3, Giuseppina Borzì1, Lucia Zirone1, Martina Pace1, Carmelo Marino1
1Humanitas-Istituto Clinico Catanese, Medical Physics Department, Misterbianco, Italy; 2Humanitas-Istituto Clinico Catanese, Medical Physics Department, Misterbianco , Italy; 3University of Catania, Physics and Astronomy "E. Majorana" Department, Catania, Italy
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Purpose or Objective
Mobius3D
system was validated with the purpose to use it as a modern second – check
dosimetry system. Our objective has been to determine the appropriateness of
M3D as pre-treatment patient specific QA for HyperArc (HA) treatments, establishing
if Mobius3D can safely replace the measurements based patient specific QA for
this kind of treatments.
Material and Methods
30 Stereotactic
Radiosurgey (SRS) HA plans for brain were delivered across the ionization
chamber located inside homogeneous Mobius Verification Phantom (MVP).
The measured
dose inside the MVP was compared with M3D calculated dose and then with TPS
calculated one.
In a second
step for all 30 plans, dose distributions calculated on the patient’s CT-
dataset by Mobius and our algorithm (AcurosXB
v.15.6) were compared using the following metrics: target Dmean
percent difference, target D90% percent difference and global 3D
gamma passing rate over the entire dataset. The used gamma criteria were 3%-2mm.
All 30 plans
were then delivered across radiochromic film (EBT3) and electronic portal imaging
device (EPID) and analysed with Portal Dosimetry (PD), in terms of gamma
analysis (3%-2mm). Results were evaluated considering a gamma passing rate
>90 %.
The appropriateness of M3D as an alternative to
measurement-based patient specific QA, was evaluated as the percentage of
verified plans that passing 3D global gamma analysis with Mobius3D and the
conventional methods at the indicated level.
Results
All 30 analyzed
plans showed good agreement between MVP measured point dose and dose calculated
by M3D and Eclipse TPS. In fact, the average point dose difference on MVP
between our algorithms and measurements with ionization chamber was 1.85 % [min
1.16%-max 2.55%], while concerning M3D, the average point dose difference was 2.32
% [min 1.05%-max 3.44%].
Concerning
comparison on the CT-dataset between TPS and Mobius3D we found an average
target Dmean percent difference of 1.83% [min 1.16%-max 2.55%]. The
average D90% difference was 2.83% [min 2.6%-max 3.1%]; 3D global
gamma passing rate ranged from 89.2% to 99.6 % at the specified gamma criteria.
Tab I shows results about plans with a gamma
passing rate >90% and about the agreement between M3D gamma evaluation (3%-2mm)
and conventional methods.
Plans passing gamma analysis with M3D system were the same plans that passing radiochromic film and portal dosimetry pre-treatment QA.
Conclusion
The study shows Mobius3D
to be a suitable alternative to conventional measured based QA methods for SRS
HyperArc treatments when using the 3%/2mm gamma criterion.
The evaluation based on M3D system has the advantages
to be resource and time sparing.