ESTRO 2023 - Abstract Book

S1743

Digital Posters

ESTRO 2023

Conclusion Fraction-based 4D dose reconstruction enables the estimation of target dose reduction due to interplay effects. For most patients evaluated in this study, PBS particle therapy with gated beam delivery provides reasonable target dose coverage. MA, RD, and γ -PR are sensitive to the target dose reduction. It seems that 4D dose reconstruction not necessarily has to be performed on a daily basis.

PO-1975 effects of nuclear interaction correction and trichrome fragment spectra modelling in CIRT planning

A. Bazani 1 , J. Brunner 2 , S. Russo 1 , A. Carlino 3 , D.S. Colomar 4 , M. Ciocca 1 , M. Stock 3 , P. Fossati 5 , E. Orlandi 6 , L. Glimelius 4 , S. Molinelli 1 , B. Knäusl 2,3 1 CNAO National Center for Oncological Hadrontherapy, Medical Physics Unit, Pavia, Italy; 2 Medical University of Vienna, Department of Radiation Oncology, Vienna, Austria; 3 MedAustron Ion Therapy Center, Medical Physics Unit, Wiener Neustadt, Austria; 4 Raysearch Laboratories, Physics, Stockholm, Sweden; 5 MedAustron Ion Therapy Center, Radiation Oncology Unit, Wiener Neustadt, Austria; 6 CNAO National Center for Oncological Hadrontherapy, Radiation Oncology Unit, Pavia, Italy Purpose or Objective To assess the effects of nuclear interaction correction (NIC) and trichrome (TRI) fragment spectra modelling on the RBE weighted dose (DRBE) and dose-averaged LET (LETd) distributions for clinical carbon ion dose calculation. Materials and Methods Thirty clinically applied carbon ion radiotherapy (CIRT) plans, previously optimized with local effect model (LEM) I (nominal plans) in the clinical available version of Raystation TPS were recalculated including NIC, applying TRI spectra modelling and the combination of both NIC+TRI (evaluation plans) in version 11B-DTK (PBv4.4), respectively. Plans were grouped according to treatment sites: prostate adenocarcinoma (PCa, 6), head and neck (H&N, 10), pancreatic adenocarcinoma (LAPC, 9), sacral chordoma (SC, 5). Dosimetric parameters were compared for the CTV and ring-dose regions retrieved from the nominal plan, namely the volume between CTV and 90% isodose (iso90%), 90% and 40% isodose (iso40%), 40% and 10% isodose (iso10%). • global gamma analyses restricted to dose regions with 1% dose difference (DD) – 1 mm distance to agreement (DTA), with no dose threshold. • median LETd values for CTV and ring-dose regions, with the addition of the volume included between 10% and 0.5% isodoses (iso0.5%). Median percentage dose and LETd deviations and interquartile (IQ) ranges with respect to the nominal plans ( Δ D% and Δ LETd) and mean gamma passing rates ( γ ) were reported for NIC+TRI plans, grouped for the different treatment sites. Results For CTV, iso90% and iso40%, median Δ D% were within ±1% and mean γ -values were ≥ 95% (Table 1), while changes up to - 1.5% were observed for iso10%, exemplarily shown in figure 1 together with the LETd distribution. • CTV coverage (D98%, D50% and D2%) • median dose to ring-dose regions

CTV

PCa

H&N

LAPC

SC

Δ D98% (IQ) Δ D50% (IQ) Δ D2% (IQ)

0.18 (0.02) 0.00 (0.18) -0.10 (0.23) -0.39 (0.24) 0.22 (0.61) 0.05 (0.11) -0.07 (0.21) -0.33 (0.21) 0.23 (0.24) 0.03 (0.19) -0.05 (0.20) -0.24 (0.21)

iso90%