Online-adaptive SRT with automated Organ At Risk contouring for abdominal oligometastases: Results
PO-1658
Abstract
Online-adaptive SRT with automated Organ At Risk contouring for abdominal oligometastases: Results
Authors: Nuyttens|, Joost(1)*[j.nuyttens@erasmusmc.nl];Visani|, Liuca(2);Granton|, Patrick(3);Milder|, Maaike(4);
(1)Erasmus MC Cancer Institute, Radiation oncology, Rotterdam, The Netherlands;(2)Azienda Ospedaliero-Universitaria Careggi- University of Florence, radiation oncology, FLorence, Italy;(3)Erasmus MC Cancer Institute, radiation oncology, Roterdam, The Netherlands;(4)Erasmus MC Cander Institute, Radiation Oncology, Rotterdam, The Netherlands;
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Purpose or Objective
In the phase II prospective STEAL trial, online-adaptive stereotactic radiotherapy (AO-SBRT) with a library of plans is used to treat patients with abdominopelvic lymphnode oligometastases. Here, we report the treatment workflow and plan choice of the first 12 patients.
Material and Methods
Eligible oligometastatic patients with abdominal lymphadenopathies were enrolled in the STEAL trial , and treated with CyberKnifeR with an in-room CT scan (fig 1). Patients were all treated with a total dose of 45 Gy in 5 daily consecutive fractions of 9 Gy. For each patient, a library of 3 plans was created: plan A, based on the planning CT dose prescribed to the 90% isodose-line; plan B, with OARs contours based on their localization on a diagnostic CT scan; and plan C, based on the planning CT scan but with dose prescribed to the 80% isodose-line. Before each fraction, a CT-scan was made with the in-room CT scan and the patient remaining in the treatment position. Automatically, the fraction CT scan was forwarded to the image analysis software (MIM Software Inc. Cleveland) and a workflow initiated. The planning CT scan and the fraction CT scan were rigidly matched to one another according to the tracking method of the Cyberknife. The dose of the three plans and the target volumes (GTV and PTV) were automatically rigidly transferred to the fraction CT. Organs at Risk (OAR) contours from the initial planning CT were transferred to the fraction CT scan by deformable image registration (DIR). For each plan, the relevant DVH parameters such as PTV coverage and dose to bowel (V35) were presented in a pass/fail table. On the basis of a protocol decision tree , the RTT selected the best plan of the day and the patient was treated with the chosen plan. The RTT’s received training in order to perform the whole work flow and to make plan choice.
Fig 1:The CyberKnife with in-room CT scan
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Results
Due to anatomical changes visible on the fraction CT scan, 2 patients needed re-planning: one due to severe constraint violation for both duodenum and stomach, abandoning the plan-of-the-day (POTD) strategy. The other due to inter-fraction movement of the GTV outside the PTV. Plan A was most frequently selected from the library in 68% of the fractions, followed by plan C in 26%. Plan B was chosen in 6%. Plan A was selected in only 5 fractions out of 58 due to a bad correspondence between the contours generated by DIR on the fraction CT and the visible anatomy (fallback option). The time between fraction CT scan and treatment was within 15 minutes for all patients.
Conclusion
Online-adaptive stereotactic radiotherapy with automated organ at risk contouring and a plan-of-the-day strategy to improve OARs sparing in SBRT of lymphadenopathies located in the abdominopelvic region is feasible. Treatment plan selection can be handed over to RTT’s after training.