ESTRO 2022 - Abstract Book

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Abstract book

ESTRO 2022

Since 2020, an automatic KB-planning approach using a volumetric technique ViTAT, that mimics conventional Tangential Field (TF) for R-irradiation, was clinically implemented fully replacing manual TF optimization. ViTAT plans consisted of 4 arcs (6MV) optimized with a VMAT technique (Rapid Arc, Varian) with start/stop angles consistent with TF geometry (60°/220°); arcs were completely blocked, apart from the first and last 20° of rotation. The implemented KB-model was based on 80 clinical TF plans (TF-model) and trained by the RapidPlan (RP) tool implemented in the Eclipse TPS (v13.6, Varian): all patients were treated to 40Gy in 15 fractions. The same patients were re-optimized by the Auto-Planning (AP) module implemented in the Pinnacle TPS (Philips) using intensity-modulated fixed 6MV tangential beams, according to an optimized template developed in another Institute. Beam angles were manually chosen for each patient, while planning was done with no further manual intervention. The resulting dose distributions were used to build a new KB-model using RP (AP-model), aiming to stress the performances of ViTAT. Validation tests were performed on 20 new patients for both KB-plans optimized with AP-model (APm-KBP) and TF-model (TFm-KBP). KB-ViTAT plans were compared in terms of OARs/PTVs dose-volume parameters. Wilcoxon-tests were performed to assess statistically significant differences (p<0.05). Results The goodness of the regression model, indicated by the R 2 parameter, was higher for the AP-model for all OARs. Of note, the R 2 for AP-model/TF-model was 0.63/0.60 for the ipsilateral lung; 0.69/0.44 for the heart; 0.53/0.44 for the contralateral breast and 0.61/0.55 for the contralateral lung, reflecting the absence of any inter-planner variability in the AP-model. Concerning planning performances, APm-KBP resulted in a better sparing of the ipsilateral lung with respect to TFm-KBP, while coverage and other OARs were similar (figure 1). PTV V95% was 96.5/96.7% for APm-KBP/TF-m-KBP, respectively; D1% was 41.8/41.9 Gy. The ipsilateral lung V20Gy was 12.8/13.7% (p=0.000007), V35Gy was 4.5/5.5% (p=0.000001) and the mean dose (Dm) was 6.5/7.0Gy (p=0.0001). On average, APm-KBP contralateral OARs were equivalent to TFm-KBP.

Conclusion We demonstrated the possibility of further improving KB-planning for tangential-like whole breast radiotherapy using a model trained with a more consistent and robust technique obtained by auto-plan optimization. The APm-KBP was able to generate automatic plans better than the KB based on clinical ones. Using APm-KBP it was possible to significantly improve the sparing of the ipsilateral lung DVH-tailor, without any compromise of the PTV coverage. Acknowledge: The study is supported by an AIRC grant (IG23150).

MO-0790 Knowledge-Based automatic plan optimization for left-sided whole breast tomotherapy

P.G. Esposito 1 , R. Castriconi 1 , P. Mangili 1 , S. Broggi 1 , A. Fodor 2 , M. Pasetti 2 , A. Tudda 1 , N.G. Di Muzio 2 , A. del Vecchio 1 , C. Fiorino 1 1 San Raffaele Scientific Institute, Medical Physics, Milan, Italy; 2 San Raffaele Scientific Institute, Radiotherapy, Milan, Italy Purpose or Objective To implement a Knowledge-Based (KB) automatic planning approach for left-sided whole breast treatment for the TomoDirect (TD) modality of Tomotherapy. Materials and Methods 69 TD clinical plans were selected to train a KB-model for left sided breast cancer patients using the RapidPlan (RP) tool implemented in the Eclipse TPS (v13.6, Varian Inc). Using the association between dosimetry and anatomy/geometry features, RP generates models for accurate DVH prediction that can be used to automatize plan optimization. As RP works with inverse-planning techniques (like RapidArc, RA), virtual RA-plans were associated to the dose distributions of TD clinical plans, imported from the Tomotherapy planning station (TomoHD system v.2.1.4). The resulting KB-model was used to set an optimized tomotherapy template via Eclipse Scripting API. The template was fine-tuned to optimize pitch, field width, modulation factor, structure importance, objectives position and priority, resulting in individually KB-optimized template. 30 out of 69 patients and 10 new patients were used for internal and external validation respectively. KB fully- automatic TD plans (KB-TD) were generated for the validation tests using the same gantry entrance/number of fields of the corresponding clinical plan. The comparison between KB-TD and the original plans was made in terms of OARs/PTV dose-volume parameters. Wilcoxon-tests were performed to assess statistically significant differences (p<0.05).