ESTRO 2022 - Abstract Book

S1043

Abstract book

ESTRO 2022

study purpose. Dosimetric parameters including D95%, D75%, D2% of PTV and CTV, homogeneity index (HI), conformity index (CI), IMN D95%, V20Gy, V5Gy and mean and maximal doses of lung and V40Gy, V35Gy, V25Gy and mean and maximal doses of heart and LAD were compared between 3D-CRT and VMAT. The Wilcoxon signed-rank test was used for dosimetric comparison. Multiple regression analysis was performed to evaluate the factors associated with a higher reduction rate of heart V40Gy and total lung V20Gy dose by VMAT. Results 16 patients (67%) received IMN irradiation. Mean PTV and CTV coverage (D95%, D75%) was significantly higher for VMAT (PTV: 48 Gy, 50 Gy and CTV: 41 Gy, 49 Gy) compared to 3D-CRT (PTV: 32 Gy, 48 Gy and CTV: 32 Gy, 46 Gy), respectively (all P < 0.01). Mean PTV HI and CI were better for VMAT (1.1 and 1.1 in VMAT, 1.7 and 2.7 in 3D-CRT, P < 0.01). Mean total and ipsilateral lung V20 Gy was lower for VMAT versus 3D-CRT (11.4% and 25.5% versus 14.3% and 31.8%, P < 0.01), whereas mean total and ipsilateral lung V5 Gy were higher for VMAT (30.9% and 60.3% versus 21.2% and 46.2%, all P < 0.01). Mean V40Gy, V35Gy, V25Gy of heart and LAD were significantly lower in VMAT (heart: 0.7%, 1.4%, 2.7% in VMAT, 3.4%, 4.3%, 5.8% in 3D-CRT, all P < 0.01, and LAD: 19.6%, 27.2%, 41.7% in VMAT, 36%, 41.8%, 50.5% in 3D-CRT, P = 0.02 (V25Gy), P < 0.01 (others)). In multivariate regression analysis, IMN irradiation and lower BMI were associated with increased reduction rate of lung V 20 Gy and heart V40Gy by VMAT (P = 0.01, < 0.05). Conclusion VMAT for left-sided breast radiotherapy with RNI had better target coverage and lowered lung V20 Gy and heart V40 Gy. Patients with IMN irradiation and lower BMI may be the optimal candidates for VMAT. 1 Jena University Hospital, Department of Radiotherapy and Radiation Oncology, Jena, Germany; 2 Jena University Hospital, Institute for Medical Statistics, Computer Science and Data Science (IMSID), Jena, Germany Purpose or Objective Consistent deformable image registration (DIR) is the first step for reliable dose deformations. The current study aimed to test whether a commercially available DIR algorithm can reproducibly and consistently deform structures within the same patient between free breathing (FB) and deep inspiration breath hold (DIBH) breast cancer patients datasets. Materials and Methods The study includes 73 patients diagnosed with left sided breast cancer with CTs in FB and DIBH. Breast clinical target volumes (CTV) according to ESTRO, the heart, the left anterior descending artery (LAD), both lungs were contoured in FB and DIBH in the RayStation (RaySearch Laboratories, Stockholm, Sweden). DIR was performed taking the structure set of the FB to be deformed on the DIBH (FB → DIBH) and vice versa (DIBH → FB). Further, DIR was performed focusing on the whole image (“no focus”- DIR_none), the CTV (DIR_CTV), the heart (DIR_heart) or on the surgical clip in the tumor bed (DIR_clip), respectively. Volume differences ( ∆ V) and a dice similarity index (DSI) were calculated. DSI= 2xCV / (mROI_V+dirROI_V); CV- common volume of mROI_V and dirROI_V; mROI_V - manually contoured region of interest volume; dirROI_V - by DIR automatically generated volume. Generalized estimating equations were used to assess the statistical effect of the different DIR focuses on the DSI. PO-1236 Deformable image registration for breast cancer radiotherapy M.N. Duma 1 , L. Pargmann 1 , M. Böhm 2 , A. Wittig 1

Results Table 1 depicts the volume differences ( ∆ V in %) between manually and automatically contoured structures exemplary for the CTV breast and the heart.

The highest DSI for the CTV was achieved by DIR_CTV (p<0.05) regardless of DIR direction (FB → DIBH or DIBH → FB); there was no statistical difference between DIR_clip and DIR_none for the DSI CTV. The DSI of the heart was the highest when focusing on the heart. There are no significant effects of breast size on DSI CTV_breast, ∆ V breast left or ∆ V heart. Patients with smaller breasts achieved higher DSI of the heart compared to those with larger breasts. By every inhaled 100cm ³ the