ESTRO 2023 - Abstract Book

S1325

Digital Posters

ESTRO 2023

P. Caricato 1 , S. Trivellato 1 , R. Pellegrini 2 , M.C. Daniotti 1 , B. Bordigoni 1 , S. Meregalli 3 , E. Bonetto 3 , V. Faccenda 1 , D. Panizza 1 , S. Arcangeli 3,4 , E. De Ponti 1,4 1 ASST Monza, Medical Physics Department, Monza, Italy; 2 Elekta AB, Medical Affairs, Stockholm, Sweden; 3 ASST Monza, Department of Radiation Oncology, Monza, Italy; 4 University of Milan Bicocca, School of Medicine and Surgery, Milano, Italy Purpose or Objective This study aims to fully investigate the capability of a not yet commercially available fully automated lexicographic optimization (LO) planning tool, called mCycle (Elekta AB, Stockholm, Sweden), to further improve performances of an already tested Wish-List (WL) to increase OAR sparing for a retrospectively selected cohort of cervical cancer patients. Materials and Methods Twenty-four mono-institutional consecutive cervical cancer treatment VMAT plans delivered between November 2019 and April 2022 (50 Gy/25 fractions) have been retrospectively selected. In the mCycle planning system (Monaco TPS research v5.59) the LO planning algorithm was combined with the a-priori multi-criterial optimization (MCO). The mCycle fluence map optimization is designed as a two-pass automated LO: MCO progressively optimizes constraints and goals in accordance with an a-priori assigned priority WL. Two versions of WL have been defined. The first one (WL1) aimed to reproduce manual plans, while the second one (WL2) to improve the organs-at-risk (OAR) sparing without affecting target coverage and plan delivery accuracy. Robust WLs have been tuned using a subset of 4 randomly selected patients. The remaining selected treatment plans have been automatically re-planned by using the designed WLs. Manual plans (MP) and mCycle plans (mCP01 and mCP02) were compared in terms of dose distributions, complexity, delivery accuracy, and clinical acceptability. Furthermore, two senior radiation oncologists independently performed a blind clinical evaluation. Finally, an overall quality index has been developed to gather the assessment of the plan quality into a single score. Results The two WLs tuning were performed on the same 4 randomized selected patients requesting 5 and 3 working days for the WL01 and the WL02, respectively. The re-planning of the remaining 20 patients took in both cases 3 working days. mCP01 best performed in terms of target coverage (PTV V95% (%): MP 98.0 [95.6–99.3], mCP01 99.2 [89.7–99.9], mCP02 96.9 [89.4– 99.5]). On the other hand, mCP02 results pointed out a large OAR sparing improvement (e.g ., Rectum D50% (Gy): MP 41.7 [30.2–47.0], mCP01 40.3 [31.4–45.8], mCP02 32.6 [26.9–42.6]). An increase in plan complexity has been registered in mCPs without affecting plan delivery accuracy (Gamma Passing Ratio (3%/3mm): MP 97.0 [92.7–99.2], mCP01 97.2 [95.0–98.6], mCP02 96.7 [94.4–98.2]). In the blind comparisons, all mCPs were considered clinically acceptable and were preferred over MP in 90% of cases with a preference for WL2 over WL1 due to the possible lesser toxicity. Globally, mCPs reported plan quality scores at least comparable to MP. Conclusion This first feasibility retrospective study demonstrated the novel mCycle auto-planning capability to generate high-quality VMAT cervical treatment plans according to the site-specific institutional protocol and the capacity to generate even more demanding WL to potentially decrease toxicities compared to Manual Plans. 1 ASST Monza, Medical Physics Department, Monza, Italy; 2 Elekta AB, Medical Affairs, Stockholm, Sweden; 3 University of Milan Bicocca, School of Medicine and Surgery, Milano, Italy Purpose or Objective In this study, a not yet commercially available fully-automated lexicographic optimization (LO) planning system, called mCycle (Elekta AB, Stockholm), was validated for intracranial stereotactic radiosurgery (SRS). Materials and Methods Forty-four consecutive SRS treatment plans (21 Gy/1 fx) delivered between November 2019 and August 2022 were retrospectively selected and automatically re-planned by mCycle (Monaco research version 5.59.13). Twenty-five of them has 1 lesion, 13 had 2 lesions, 4 had 3 lesions, and 2 had 4 lesions. An a-priori assigned priority list, a so-called Wish List (WL), was used to define the sequential LO: four patient sets (WL tuning set) were necessary to tune each robust WL, for single lesion-plans (SLp) and multiple lesion-plans (MLp). While in manual plans (MP), the arc setup is freely chosen by the planner, the WL was tuned to use 2 coplanar arcs of 140° and 360° for SLp and MLp, respectively. A 0° and 90° collimator rotation was set for counter-clockwise and clockwise arcs, respectively. The fluence optimization is followed by a Monte Carlo calculation (MCc) with a 1 mm-dose grid and 0.5%-statistical uncertainty. A target coverage as high as possible was requested, with at least 80% of the prescription dose covering 99% of the PTV. The main criteria for SLp approval was a brain volume receiving more than 12 Gy less than 10 cm ³ (V12Gy<10 cm ³ ). In MLp this criterion can be overcome to get the minimum target coverage. Manual plans (MP) and mCycle plans (mCP) were compared in terms of dose-volume constraints, conformality, and monitor units (MUs). Statistical significance was assessed by performing the Wilcoxon-Mann-Whitney test and plan delivery accuracy was verified by pre-treatment QA. Results Each WL tuning took 3 days. The median optimization and MCc time can be estimated at 8 hours and 3 hours per MP and mCP, respectively. Results are summarized in Table 1. Statistically significant increases in mCP target coverage and PTV Paddick’s conformity index were registered for both SLp and MLp. Although not statistically significant, mCP showed a PO-1630 Lexicographic optimization-based planning for brain metastasis radiosurgery with coplanar arcs S. Trivellato 1 , P. Caricato 1 , R. Pellegrini 2 , M. Daniotti 1 , G. Montanari 1 , D. Panizza 1 , V. Faccenda 1 , S. Arcangeli 3 , E. De Ponti 1