Abstract Book

S1100

ESTRO 37

Developmental Biology- Maastricht Comprehensive Cancer Centre- Maastricht University Medical Centre, Maastricht, The Netherlands 2 Maastricht university, Maastricht Radiation Oncology Maastro- GROW – School for Oncology and Developmental Biology- Maastricht Comprehensive Cancer Centre- Maastricht University Medical Centre MUMC, Maastricht, The Netherlands 3 Maastricht university, Department of Radiotherapy- GROW – School for Oncology and Developmental Biology- Maastricht Comprehensive Cancer Centre- Maastricht University Medical Centre MUMC- Maastricht, Maastricht, The Netherlands Purpose or Objective In radiotherapy for thoracic cancers, dose constraints are determined by lung toxicity. In this study, we evaluated changes in radiomic features on CT obtained from a radiation-induced lung fibrosis (RILF) study in mice, after partial lung irradiation for different dose levels (Granton et.al, 2014). It would help monitoring radiation-induced changes in low dose areas. Material and Methods A total of 61 C57BL/6 adult male mice were used in this study, divided into six groups: the control group (n=12), and five groups with different dose levels of 4 Gy (n=9), 8 Gy (n=8), 12 Gy (n=10), 16 Gy (n=12) and, 20 Gy (n=10). Mice were irradiated using 5-mm circular parallel- opposed fields targeting the upper right lung. After irradiation, all mice were imaged at regular intervals over 39 weeks (i.e., 10 imaging time points). An ROI encompassing the volume of the lung which received maximum dose (cut-off at 80% of maximum lung dose) was delineated on the final CT and used for our analysis. In total, 1384 radiomic features comprising: a) first-order statistics, b) shape and c) filtered texture features were extracted from the ROI. A Wilcoxon rank-sum test was performed to assess the difference in the value of radiomic features across groups. A p-value smaller than 0.05 was considered to be statistically significant. Results We observe statistically significant differences in feature values between the control and irradiated groups. Between 0 and 20 Gy; a total of 459 features were significantly different. For the lowest dose level (4 Gy), significant differences were also found compared to the control group (n=108). Comparing the irradiated groups, we found a statistical difference between 16 and 20 Gy in a total of 188 features, versus 31 features between 8 and 12 Gy(see Table 1). Conclusion This study shows differences in radiomic feature values between groups irradiated with different dose levels. Significant feature differences were observed between the 0 and 4 Gy groups, which were not found using simple CT greyscale difference analysis in previous publications. Changes in radiomic features between baseline CT and follow-up CT scans could potentially be used as non- invasive biomarker to detect changes in the lung after radiation at low dose levels. Longitudinal analysis of earlier time points is currently ongoing.

8 vs 12 Gy 31 16 vs 20 Gy 188

Electronic Poster: Physics track: Intra-fraction motion management

EP-2016 A prospective study developing decision algorithm for respiration controlled radiotherapy E. Kim 1 , E.K. Chie 1 , H.C. Kang 1 , S.Y. Park 1 , C.H. Choi 1 , J.M. Park 1 , J.I. Kim 1 , H.G. Wu 1 1 Seoul National University Hospital, Radiation Oncology, Seoul, Korea Republic of Purpose or Objective The primary goal was to develop patient selection decision algorithm based on pre-treatment clinical factors for patients undergoing radiotherapy to intraabdominal target. A prospective study was carried out to compare the plan quality of volumetric modulated arc therapy (VMAT) with a linear accelerator (LINAC) to that of respiration-gated intensity modulated radiation therapy (IMRT) with magnetic-resonance (MR) image- This study was designed to test the null hypothesis that dose-volume parameter of LINAC and that of tri- 60 Co system plans are the same. The study was designed to test given hypothesis with alpha 0.01 and beta 0.1 using paired T-test. Target accrual was adjusted to incorporate the 20% dropout rate. LINAC plans were generated from 4D CT simulation images with abdominal compression and forced shallow breathing, whereas tri- 60 Co system plans were generated from breath hold fused CT simulation and MR simulation images. Competing plans from each set-up were generated and dose-volumetric parameters from both plans were obtained for analysis. Results A total of 102 patients were enrolled, and 27 patients were excluded due to the innate imbalance in a treatment plan. There were 32 patients with liver tumor (Group A), 21 patients with pancreas or extrahepatic bile duct cancer (Group B), and 22 patients with metastatic abdominal lymph node or adrenal gland tumor (Group C). There were 20 with LINAC plans and 12 with tri- 60 Co plans in Group A, 13 with LINAC plans and 8 with tri- 60 Co plans in Group B, and 14 with LINAC plans and 8 with tri- 60 Co plans in Group C. The average planning target volumes were significantly higher with LINAC vs. tri- 60 Co plans in all groups ( p < 0.001, < 0.001, and 0.001, respectively). In addition, mean doses to liver were increased with tri- 60 Co vs. LINAC ( p = 0.004, < 0.001, and < 0.001, respectively). In Group A, D 1cc of stomach and duodenum were higher in tri- 60 Co vs. LINAC, respectively ( p = 0.004 and 0.045, respectively). In Group B and C, however, D 1cc of stomach and duodenum were not significantly different between two plans. But, mean doses and D 1cc of kidney were significantly higher in tri- 60 Co plan (mean dose, p = 0.049 and 0.003; D 1cc , p = 0.003 and 0.01, respectively). Tri- 60 Co system was selected for patients whose GTV abutted hollow organ in overall patients. In Group B and C, patients with the tumor in contact with hollow organ and small respiratory motion (diaphragm movement < 7mm) showed a trend towards likely to be treated with tri- 60 Co system plan. Conclusion The quality of VMAT plans was superior to that of tri- 60 Co plans for the majority of patients undergoing radiotherapy for an abdominal target. However, respiratory gated image-guided radiotherapy with tri- 60 Co system offered benefits to patients with organs at risk abutted to target. Furthermore, in minority of patients, guided tri- 60 Co system. Material and Methods

Tabel1: The significant features between groups Groups Number of Features (α=0.05)

0 vs 4 Gy 108 0 vs 8 Gy 186 0 vs 12 Gy 78 0 vs 16 Gy 329 0 vs 20 Gy 459 4 vs 8 Gy 151 4 vs 20 Gy 487