ESTRO 2022 - Abstract Book

S1295

Abstract book

ESTRO 2022

PO-1515 Dose distribution comparison for WBRT with hippocampal sparing using HyperArc and non-coplanar VMAT

V. Tolstoukhova 1

1 BUZ UR "RKOD named after S. G. Primushko MZ UR", Radiotherapy, Izhevsk, Russian Federation

Purpose or Objective The purpose of this work is to compare the dose distribution for whole brain radiotherapy (WBRT) with hippocampal sparing using HyperArc technology and the non-coplanar VMAT method. Materials and Methods A total of 25 patients treated earlier with WBRT in the radiotherapy department were selected for the study, and 50 treatment plans were calculated for them: 25 HyperArc plans and 25 non-coplanar VMAT plans. A comparative analysis of dose distribution for both methods was performed in the Eclipse 16.1 radiotherapy planning system (Varian Medical Systems). The analysis was conducted according to the following criteria: HI homogeneity index, CI conformity index, GI gradient index, dose to the hippocampus at D(Mean), D(95%), D(Max) and D(0,5cm3), time of plan creation, time of plan calculation and optimization, total number of MUs. A verification analysis QA was also performed with various normalizations (Local and Global) and high detectors density using the ArcCHECK dosimetry system with SNC Patient and 3DVH software (SunNuclear Corporation). The conformity and homogeneity of the dose distribution in the target is almost the same for both methods. Outside PTV dose decreases faster with ncVMAT (an average difference between methods is 0.41). The maximum lens dose is best reduced when planning ncVMAT (difference is about 0.45 Gy). The dose to the hippocampus is reduced much better when planning HyperArc (Dmax difference 0.8 Gy). Equipment wear, proportional to the number of monitor units, is the same for both methods. The time of plan calculation and optimization when using the HyperArc technology increases by 9.8 minutes. Gamma analysis: At threshold TH10% ncVMAT gamma passing rate GPR<95% for 2%/2mm and 3%/2mm are 91.7 and 94.4, respectively. Verification at ТН 10% GPR> 95%: HyperArc passes 2%/2mm and 3%/2mm, and ncVMAT passes 2%/3mm and 3%/3mm. Analysis with Local and Global normalization: For Hyperarc with Global normalization, GPR regardless of the comparison criteria (2%/2mm - 3%/3mm, TH5-20%) is 100%. For ncVMAT with Global normalization, GPR is 99.7% on average. Analysis with high detectors density: On average, ncVMAT GPR increases by 0.7%: at thresholds ТН 5-10% (2%/2mm - 3%/3mm) and ТН 5-20% (2%/2mm). With HyperArc, the difference is only 0.1%. The methods satisfy the protocols conditions: HyperArc: TG-119 (3%, 3mm, TH10%, Global), TG-218 (3%, 2mm, TH10%, Global ), TG-244 (2%, 2mm, TH10%, Local). ncVMAT: TG-119 (3%, 3mm, TH10%, Global), TG-218 (3%, 2mm, TH10%, Global). Conclusion In the case of WBRT with hippocampal sparing both methods work equally well and satisfy the RTOG-933 recommendations. The MUs and dose in PTV and critical structures are almost identical. The difference for methods in time of plan calculation and optimization is 10 minutes (HyperArc - 28.5 minutes, ncVMAT - 18.7 minutes). HyperArc passes verification much better even on the most stringent TG-244 requirements (2%, 2mm, TH10%, local). Results Dosimetric analysis: 1 Aichi Cancer Center Hospital, Radiation Oncology, Nagoya, Japan; 2 Gunma Prefectural College of Health Sciences, Graduate School of Radiological Technology, Maebashi, Japan; 3 Yachiyo Hospital, Radiation Therapy Center, Anjyo, Japan Purpose or Objective Stereotactic body radiotherapy for spinal metastases (spine SBRT) is better than conventional palliative radiotherapy at controlling pain in the spine. In spine SBRT cases after spinal fusion surgery, the magnetic resonance (MR) image is difficult to visualize the spinal cord due to the existence of the metal artifact on it; therefore, the CT myelography is used for the visualization as an alternative to the MR imaging. In such cases, another CT without the enhanced contrast is acquired for the dose calculation in order to avoid the influence on the dose distribution due to the enhanced contrast on the CT myelography images; however, the influence has not been quantitatively clarified. In this study, we aimed to quantitatively evaluate the change in the spinal cord dose in spine SBRT treatment planning by the presence or absence of the enhanced contrast on the CT myelography image. Materials and Methods Nineteen patients who had previously undergone the spine SBRT were selected randomly. All patients had scanned the CT myelography a couple of days after the treatment planning CT. The slice thickness of both image sets was 1 mm. The rigid image registration of the CT myelography that aligned at the treatment planning CT was carried out for the vertebra landmarks. The rigid image registration accuracy was evaluated by calculating the normalized mutual information (NMI) and Pearson's correlation coefficient for the vertebra landmarks. After the registration, the original plan on the treatment planning CT image was recalculated on the CT myelography image that was replaced the contrast-enhanced region (spinal PO-1516 Change in spinal cord dose of treatment plan using CT myelography image in spine SBRT H. Shimizu 1 , Y. Koide 1 , K. Sasaki 2 , Y. Watanabe 3 , T. Aoyama 1 , H. Tachibana 1 , T. Iwata 1 , T. Kitagawa 1 , T. Kodaira 1