ESTRO 2023 - Abstract Book

S1734

Digital Posters

ESTRO 2023

Vagina accumulated vox min D98 was >94% for 8/10 VMAT and for 9/10 IMPT treatments. In two reCTs for PT4, a large rectum volume was observed, which would not have been acceptable for treatment delivery. This resulted in shifted deformed reCT doses, which unfortunately had a larger contribution to the accumulated dose (2/4 instead of 2/5), since PT4 had only 4 reCTs made. The doses in the OARs associated with bowel and bone marrow toxicity (bowel bag, rectum and bone marrow) were overall lower with IMPT (Figure 1A, 1C and D) and significantly lower for clinically relevant DVH parameters (Table 1). Conclusion IMPT showed great potential in bone marrow and bowel bag sparing in comparison to VMAT. Rectal volume variations during treatment have to be evaluated to avoid target underdosage for both VMAT and IMPT.

PO-1968 Knowledge-based planning for intensity-modulated proton therapy of the brain and base-of-skull

R. Kaderka 1 , N. Vu 1 , M. Butkus 1

1 University of Miami, Radiation Oncology, Miami, USA

Purpose or Objective Knowledge-based planning (KBP) automates treatment planning with a focus on efficiency, quality and reducing plan variability. We developed and evaluated a KBP model for brain and base-of-skull (BOS) targets treated with intensity modulated proton therapy (IMPT). Materials and Methods Commercial software was used to build a KBP model that creates dose predictions and optimization objectives. The model was trained with 89 patient plans treated at our institution, all optimized to a CTV employing robust optimization. In the training set, n=78 received 46-60Gy and n=11 were re-treats prescribed ≤ 35Gy. While KBP predicts dose distributions, previous literature shows that fine-tuning optimization objectives and priorities in the model can substantially increase resulting plan quality. 20 patients were chosen for re-planning and subsequent iterative adjustment of optimization parameters. The final model was then tested by re-planning an independent set of 27 patients that were not included in training. Plan quality was evaluated by comparing dosimetric parameters of body, CTV, brainstem, cochlea, eye, hippocampus, lens, optic chiasm/nerves, pituitary and skin of the KBP plans to the manual clinical reference. Paired t-tests tested for significance (p<0.05). Results The KBP model was finalized after two iterations to objectives and priorities. This model created clinically acceptable plans for all 27 test plans. The only significant differences between the manual and the KBP plans were CTV D0.03cc (mean manual: 108.4%, mean KBP: 110.0%, p=0.001), CTV Dmin (84.6%/80.4%/p=0.009), and pituitary gland D0.03cc (2181cGy/1792cGy/p=0.021). No other parameters were significant. CTV D0.03cc, DMin and V100% parameters for all patient plans are shown in Fig. 1. The x-value of each point represents the manual plan value and the y-value the KBP plan. It visualizes the lower CTV min doses and higher hot spots for KBP plans but indicates the same overall target coverage as measured by the V100% parameter.