ESTRO 2022

Session Item

Mixed sites/palliation

Session Code: 6026

Session Type: Poster (digital)

Track: Clinical

VMAT Stereotactic Ablative Radiotherapy for oligometastatic patients: role of FDG PET/CT

SIMONA BORGHESI, Italy

Presentation Number: PO-1448

Abstract

Abstract Title:

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.