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Figure 1.
3D printed patient-specific head phantom filled
with dosimetric gel during the treatment planning
process.
Results
Results from mono-energetic irradiation of the cubic
phantoms showed proton range agreement to the TPS
within 1 mm for 90 MeV and 115 MeV, supporting the SPR
gel characterization accuracy. Dose-response linearity was
confirmed for the delivered dose range, except at the
Bragg peak position where a LET dependence was
revealed. Gamma index and relative dose distribution
profiles showed good agreement between TPS and gel, as
shown in in Figure 2.
Figure 2.
(A) Slice of the 3D SFUD dose distribution
converted from a T2 relaxation map obtained from MR
scanning
the irradiated 3D printed head phantom filled with
polymer gel. The PTV is indicated in white. (B) Gel
(RTsafe) and
TPS
dose profiles along the path marked in red in (A). (C)
3%/2mm gamma index along the profile.
Conclusion
In this work we have shown that patient-specific 3D
polymer gel dosimetry is applicable to PT using PBS.
Further characterization and correction of the LET
dependence and comparison to MC dose calculations will
be carried out and presented.
Acknowledgements:
DFG-MAP
PO-0810 Absolute dose pre-treatment Portal Dosimetry
using the Varian MAASTRO implementation
A. Taborda
1
, J. Stroom
1
, C. Baltes
2
, A. Seabra
1
, K.
Dikaiou
2
, C. Greco
1
1
Champalimaud Centre for the Unknown, Clinical
Department, Lisboa, Portugal
2
Varian Medical Systems, Varian Medical Systems Imaging
Laboratory, Baden-Dättwil, Switzerland
Purpose or Objective
Current clinical portal dosimetry from Varian evaluates
dose using calibrated units (CU). This work assesses the
quality of the first Varian implementation of the MAASTRO
algorithm for pre-treatment absolute portal dosimetry (in
Gy) of 6X-FF fields.
Material and Methods
To achieve the proposed goal, a comparison was made
between the gamma analysis results obtained using both
Varian’s clinical portal dosimetry (PDIP v10.0.28) and the
MAASTRO algorithm [1] implementation made available
for the authors in the Portal Dosimetry (PD) application
accessible through the Varian Citrix Research Environment
(CRE). For this study, 10 breast IMRT breast plans and 10
VMAT prostate plans were chosen from the patients’
database. In total, 71 IMRT fields and 40 VMAT arcs were
compiled for analysis. Each plan was recalculated with
gantry zero on a water-equivalent slab phantom, for later
comparison of absolute dose at 5cm depth. Verification
plans were created for irradiation with 6X-FF beams at the
Varian Edge LINAC in order to measure the doses at the
Electronic Portal Imaging Device (EPID) level. For each
field/arc, the measured doses and the calculated doses
were compared by gamma analysis in CU for PDIP and in
absolute dose values (Gy) for the PD system on the CRE.
[1] Nijsten SM et al, 'A global calibration model for a-Si
EPIDs used for transit dosimetry”, Med. Phys. 34(10):
3872-84, 2007
Results
Table 1 presents the summary of the gamma analysis
results obtained in the comparison between the measured
dose at the EPID and the calculated dose using the
MAASTRO algorithm implementation and PDIP. The results
show that the analyzed IMRT plans using the MAASTRO
algorithm obtained, on average, a higher gamma pass
rate, lower mean gamma values and lower dose
differences than while using PDIP. The same is observed
for VMAT plans. Figure 1 shows the graphical comparison
between the gamma passing rate obtained using the
MAASTRO algorithm and PDIP, where the black circles
represent the comparison of the gamma passing rates for
IMRT plans (averaged over all beams) and the open
triangles represent the comparison of the gamma passing
rates for VMAT plans (averaged over all arcs). One can see
that the gamma pass rate obtained using the MAASTRO
algorithm is consistently higher than the one obtained
using PDIP.
Table
1