ESTRO 2023 - Abstract Book

S1801

Digital Posters

ESTRO 2023

Robustness of plans were assessed using the built-in tool in Varian Eclipse Treatment Planning System, by estimating perturbed doses induced by patient setup offset in the range of 4 mm. The plan quality metrics of the different delivery strategies were compared through two-tailed paired Student’s t-test, with a significance level of 0.05, once their normality was ensured. Results PTV coverage comparison between SF and VMAT plans showed significant increases for coverage (P<0.05) in VMAT technique; no statistically significant differences were observed regarding target homogeneity index, contra-lateral breast and lung DVHs. For organs at risks (OAR), statistically significant differences (P<0.05) were observed in terms of better ipsi-lateral lung V10% with SF, and of heart V20% and LAD maximum and mean dose with VMAT. Robustness analysis showed that the perturbed doses were less variable for VMAT than SF plans (P<0.05) in terms of target coverage, maximum and mean dose to OARs. Total number of MU was lower for VMAT for each patient, and mean delivery time (equal to breath old period for each patient) was lower for VMAT than SF plans: 62.5 ± 8.2 seconds vs 78.5 ± 9.8 seconds. Conclusion This study showed that VMAT DIBH treatments are safe in the framework of 1-week hypofractionated treatments for left EBC, without compromising patient compliance in terms of session duration.

[1] doi.org/10.1016/j.radonc.2020.09.038 0167-8140 [2] doi.org/10.1016/ S0140-6736(20)30932-6 [3] doi.org /10.1002/acm2.12908

PO-2027 Dose comparison study for left-sided breast cancer patients based on different planning techniques

A. Saini 1 , E. Samsøe 2

1 Zealand University Hospital, Department of clinical oncology and palliative care, Næstved, Denmark; 2 Zealand University Hospital, Department of clinical oncology and palliative care, Næstved, Denmark Purpose or Objective Planning breast cancer targets including lymph nodes with conventional technique is challenging in terms of organ at risk (OAR) sparing. Advanced planning techniques, such as VMAT provides better sparing of OARs at high-intermediate dose levels and better target homogeneity. However, in the absence of toxicity data after long-term follow-up, the spread of low dose to the contralateral side and increased spread to ipsilateral OARs should be optimized. The purpose of this study is to find an optimal planning technique for treating breast cancer with the aim to preserve the benefits of both conventional and VMAT technique and to improve the compromises of the two techniques. Materials and Methods Ten left-sided patients with breast cancer and lymph node irradiation (including IMN) scanned in deep inspiration breath hold (DIBH) were retrospectively selected. Dose plans using short tangential arc VMAT (STA), standard long arc VMAT (sVMAT) and conventional tangential field-in-field (CONV) were generated for each patient in Varian Eclipse planning system. STA plans were compared against sVMAT and CONV. The arc length and range of angles in STA affected the OAR doses the most and showed to yield the lowest OAR doses. Evaluation was performed using dose indices for both lungs, contralateral breast, heart, CTVbreast and CTVnodal. Results Coverage criteria of V95% ≥ 98% for CTVbreast and V90% ≥ 98% for CTVnodal were satisfied in all three techniques. STA achieved the lowest Dmean to the heart (2.43 ± 0.99Gy) compared to sVMAT (3.46 ± 0.37Gy; p=0.003) and CONV (3.53 ± 2.07Gy; p=0.037). For ipsilateral lung, STA achieved lower V5Gy compared to sVMAT (p=0.034) and lower V17Gy and Dmean compared to CONV with p=0.001 and p ˂ 0.001 respectively. STA also achieved lower V5Gy and Dmean to contralateral breast and lung compared to sVMAT. Contralateral breast’s V5Gy reduced to 2.38 ± 2.49% vs 15.45 ± 8.68% (p=0.001) and Dmean to 0.65 ± 0.42% vs 3.13 ± 0.85% (p ˂ 0.001). Right lung received 1.16 ± 2.03% vs 16.41 ± 8.02% (p ˂ 0.001) and 0.65 ± 0.30% vs 2.98 ± 0.51% (p ˂ 0.001) for V5Gy and Dmean, respectively. The results for contralateral organs were comparable to the results using conventional technique (CONV). In terms of delivery efficiency, STA achieved lower beam-on time (p=0.016) and total number of MUs (p ˂ 0.001) compared to sVMAT whereas the values were comparable with CONV. Conclusion STA technique achieved lower OAR doses at high-intermediate range compared to CONV technique and significantly reduced the spread of low dose bath in the ipsilateral and contralateral OARs without compromising target coverage. Thus, STA may provide an optimal solution in difficult cases where the CONV technique is not sufficient.

PO-2028 External contour optimization and its influence on Brainlab Exactrac Dynamic

R. Astudillo 1 , R. Fabregat Borras 1 , F. Gomez Enriquez 1 , P.I. Valverde Pascual 2 , M. Martin Veganzones 2 , S. Ruiz Arrebola 1 , M. Gutierrez Ruiz 1 , J. Alonso Muriedas 1 , U.A. Corro Verde 1 , V. Cañon Garcia 1 , J.T. Anchuelo Latorre 1 , M.T. Pacheco Baldor 1 , M. Ferri Molina 1 , P.A. Navarrete Solano 1 , A. Reguilon Martin 3 , G. Camacho de la Vega 3 , D. Bruzos Lopez 1 , M. Garcia Lamela 1 , F. Pinto Guevara 1 , J. Albendea Roch 1 , A.L. Rivero Perez 1 , J.A. Vazquez Rodriguez 1 , J.I. Raba Diez 1