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O. Bohoudi
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P2.14 - Radiotherapy (ID 715)
- Event: WCLC 2017
- Type: Poster Session with Presenters Present
- Track: Radiotherapy
- Presentations: 1
- Moderators:
- Coordinates: 10/17/2017, 09:30 - 16:00, Exhibit Hall (Hall B + C)
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P2.14-019 - Magnetic Resonance (MR)-Guided Adaptive Stereotactic Ablative Radiotherapy for Adrenal Metastases (ID 9196)
09:30 - 09:30 | Author(s): O. Bohoudi
- Abstract
Background:
Stereotactic ablative radiotherapy (SABR) can result in high local control rates for adrenal metastases when biological doses of at least 100 Gy~BED10~ are delivered [Chance WW, 2017]. SABR is technically challenging due to respiration-induced displacements of the adrenals and adjacent organs at risk (OAR), both of which are poorly visualised using imaging techniques currently available at linear accelerators. MR imaging enables superior anatomical imaging of both the adrenals and OAR’s. We implemented stereotactic MR-guided adaptive radiotherapy (SMART) using daily on-table re-optimization of pretreatment SABR plans using the anatomy-of-the-day. We studied the impact such daily plan re-optimization for adrenal metastases.
Method:
Since mid-2016, 13 patients with adrenal metastases from lung cancer have undergone video-assisted, respiratory-gated SMART delivery on the MRIdian system (ViewRay Inc.). This entails using visual feedback involving projection of both target volume and safety margins onto a monitor visible to patients. The radiotherapy system automatically shuts-off delivery when the target is outside pre-specified safety margins (3mm). The commonest fractionation scheme delivered was 5-fractions of 10 Gy (in 9 patients). Prior to each fraction, a 17-second MR scan in shallow breath-hold was performed with patient in treatment position, in which the GTV was rigidly registered to that on the baseline MR scan. Setup was performed on the gross tumor volume (GTV), and contour deformation was used to automatically generate OAR’s according to the anatomy-of-the-day. Baseline SABR plans were recalculated on the anatomy-of-the-day (defined as ‘predicted plans’), before being routinely re-optimized.
Result:
The median planning target volume (PTV = GTV + 3mm) was 35.1 cc (range 6.5 – 69.8 cc). Online plan adaptation improved PTV coverage in 78% of all fractions. Re-optimized plans exhibited significantly better sparing of OAR and achieved a reduction in volumes of stomach, bowel and duodenum receiving 33Gy, with respect to predicted plans. All patients completed the planned treatments using repeated breath-holds. The total on-table duration was approximately 50 minutes for each fraction.
Conclusion:
Breath-hold SABR delivery under MR-guidance is advantageous for adrenal tumors. Substantial variations in OAR’s positions were observed at imaging prior to delivery of each fraction, leading to improved target coverage and OAR sparing when on-table plan re-optimization was performed.
