VMAT Stereotactic Ablative Radiotherapy for oligometastatic patients: role of FDG PET/CT
PO-1448
Abstract
VMAT Stereotactic Ablative Radiotherapy for oligometastatic patients: role of FDG PET/CT
Authors: SIMONA BORGHESI1, Chiara Gasperi2, Francesca Terziani1, Assunta Simona Curion2, Andrea Rampini3, Paola Pernici1, Silvia Bertocci4, Pietro Giovanni Gennari1, Carmine Iermano5, Roberta De Majo5, Pier Luigi Losardo3, Enrico Tucci1
1Azienda USL Toscana Sud Est, San Donato and S. Maria alla Gruccia Hospital, Radiotherapy Department, Arezzo - Valdarno, Italy; 2Azienda USL Toscana Sud Est, San Donato Hospital, Health Department Staff Medical Physics, Arezzo, Italy; 3Azienda USL Toscana Sud Est, San Donato and S. Maria alla Gruccia Hospital, Radiotherapy Department, Arezzo - Valdarno, Italy; 4Azienda USL Toscana Sud Est, San Donato and S. Maria alla Gruccia Hospital , Radiotherapy Department, Arezzo - Valdarno, Italy; 5Azienda USL Toscana Sud Est, San Donato and S. Maria alla Gruccia Hospital, Radiotherapy Department , Arezzo - Valdarno, Italy
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Purpose or Objective
To
explore the role of FDG positron emission tomography/computed
tomography (FDG PET/CT) in Volumetric-Modulated Arc Therapy (VMAT)
Stereotactic Ablative Radiotherapy (SABR) of oligometastases.
Material and Methods
Seventy
consecutive patients with oligometastases underwent FDG PET/CT
scanning for staging and radiation treatment planning. CT-based gross
tumor volumes (GTVCT) was first delineated using clinical information
and CT imaging data, and after by a gradient autosegmented
PET/CT-based GTVs (GTVPETCT). The mean GTV, proximal and distal
margins were compared. For lung oligometastases, 4D CT was used and
ITV derived for comparison with GTVPET CT. The differences in the
volume, position, matching index (MI) and degree of inclusion (DI) of
the GTVPET CT and GTVCT were investigated. The maximal standardized
uptake value (SUVmax) and metabolic tumor volume (MTV) were
correlated with outcome.
Results
From
December 2014 to September 2018, 70 oligometastatic patients were
treated with VMAT SABR (median dose 45 Gy, range 30-50, in 3-5
fractions) at the Radiotherapy Unit of San Donato Hospital –
Arezzo. Site of oligometastases were lung (28 patients), bone (20),
lymphonodes (22) from lung (30), breast (28) and colorectal cancer
(12). The mean GTVPETCT was significantly smaller than the mean GTVCT
volumes (P = 0.04). Interobserver variability in target delineation
was reduced if FDG PET CT was used. The proximal and distal margins
of GTVCT volumes were altered by a mean of 0.5 ± 0.3 cm and 0.4 ±
0.2 cm, respectively. For 4D CT, ITV encompassed GTVPET CT in most
cases: the GTVPET approximated to the ITV and the spatial mismatch is
apparent between them. After
a median follow up of 15.5 months (range 18.2- 32.8), 2 years local
control (LC) was 90%. MTV and SUVmax did not significantly correlate
with LC (p=0.16 and 0.4 respectively).
Conclusion
FDG
PET/CT for dose planning improved target definition in
oligometastatic patients. If VMAT SABRT is used, PET/TC parameters
did not correlate with outcome. GTVPET CT can not replace ITV in
spatial position and form for lung oligometastases. The advent of 4D
PET/CT will improve the accuracy of contouring the perimeter for
moving targets.