Dosimetric comparison of Intraoperative Radiotherapy and SRS for liver metastases
PO-1530
Abstract
Dosimetric comparison of Intraoperative Radiotherapy and SRS for liver metastases
Authors: Davide Scafa1, Gustavo R. Sarria1, Frank A. Giordano1, David Koch1, Thomas Muedder1, Jasmin A. Holz1, Younéss Nour1, Stephan Garbe1, Maria A. Gonzalez-Carmona2, Georg Feldmann3, Tim O. Vilz4, Mümtaz Köksal1, Leonard Christopher Schmeel1
1University Hospital Bonn, Department of Radiation Oncology, Bonn, Germany; 2University Hospital Bonn, Department of Internal Medicine I, Bonn, Germany; 3University Hospital Bonn, Department of Internal Medicine III, Bonn, Germany; 4University Hospital Bonn, Department of Surgery, Bonn, Germany
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Purpose or Objective
Purpose/Objectives
To perform a dosimetric comparison between kilovoltage intraoperative radiotherapy (IORT) and stereotactic radiosurgery (SRS) simulating both deep-inspiration breath-hold (DIBH) and free-breathing (FB) modalities for patients with liver metastases.
Material and Methods
Methods/Materials
Diagnostic computed-tomographies (CT) of patients carrying one or two lesions < 4 cm and who underwent surgery were retrospectively screened and randomly selected for the study. For DIBH-SRS, a gross target volume (GTV) plus planning target volume (PTV) were delineated. For FB-SRS, a GTV plus an internal target volume (ITV) and PTV were defined. Accounting for the maximal GTV diameters, a modified GTV (GTV-IORT) was expanded circumferentially to simulate a resection cavity. The best suitable round-applicator size was thereafter selected. All treatment plans were calculated homogeneously to deliver 40 Gy. Doses delivered to organs at risk (OAR) and target volumes were compared for IORT vs. both SRS modalities.
Results
Results
Eight patients encompassing 10 lesions were included in the study. The mean liver volume was 2,050.97 cm3(SD 650.82) and mean GTV volume 12.23 cm3 (SD 12.62). As for target structures, GTV-IORT (19.44 cm3 [SD 17.26]) were significantly smaller than both PTV DIBH-SRS (30.74 cm3 [SD 24.64], p=0.002) and PTV FB-SRS (75.82 cm3 [SD 45.65], p=0.002). The median applicator size was 3 cm (1.5 – 4.5) and the mean IORT simulated delivery time was 45.45 min (SD 19.88). All constraints were met in all modalities. Liver V9.1 showed significantly smaller volumes with IORT (63.39 cm3 [SD 35.67]) when compared to DIBH-SRS (150.12 cm3[SD 81.43], p=0.002) or FB-SRS (306.13 cm3 [SD 128.75], p=0.002). No other statistical or dosimetrically relevant difference was observed for stomach, spinal cord or biliary tract. Mean IORT D90 was 85.3% (SD 6.05), whereas D95 for DIBH-SRS and FB-SRS were 99.03% (SD 1.71, p=0.042) and 98.04% (SD 3.46) p=0.036), respectively.
Conclusion
Conclusion
Kilovoltage IORT bears the potential as novel add-on treatment for resectable liver metastases, significantly reducing healthy liver exposure to radiation in comparison to SRS. Prospective clinical evidence is required to confirm this hypothesis.