ESTRO 2020 Abstract book

S986 ESTRO 2020

supports the role of serial functional imaging during chemoradiation as a biomarker, and will inform our protocols when commissioned on the MRL which has a similar 1.5T magnet to the diagnostic MR used in this study. References 1 Wang JZ, Mayr NA, Zhang D et al. Sequential magnetic resonance imaging of cervical cancer: the predictive value of absolute tumor volume and regression ratio measured before, during, and after radiation therapy. Cancer 2010;116(21):5093–5101. 2 Papadopoulou, I., Stewart, V., Barwick, T. D., Park, W. H. E., Soneji, N., Rockall, A. G., & Bharwani, N. Post– radiation therapy imaging appearances in cervical carcinoma. Radiographics 2016; 36 (2):538–553. 3 Fu, Z. Z., Peng, Y., Cao, L. Y., Chen, Y. S., Li, K., & Fu, B. H. Value of apparent diffusion coefficient (ADC) in assessing radiotherapy and chemotherapy success in cervical cancer. Magnetic Resonance Imaging 2015;33(5), 516–524 PO-1697 Radiotherapy for prostate cancer: Effects of fiducial gold marker on diffusion-weighted MR imaging O. Tanaka 1 , R. Maejima 1 , T. Taniguchi 1 , K. Ono 1 , C. Makita 2 , E. Yama 3 , M. Matsuo 2 1 Asahi University Hospital, Department of Radiation Oncology, Gifu, Japan ; 2 Gifu University Hospital, Department of Radiology, Gifu, Japan ; 3 Gifu Municipal Hospital, Division of Radiation Service, Gifu, Japan Purpose or Objective IMRT has been increasingly performed using fiducial gold markers as means of CT/MRI fusion. In addition, increasing number of studies have reported that results of diffusion- weighted imaging (DWI) and apparent diffusion coefficient (ADC) of MRI are associated with prostate-specific antigen (PSA) in the assessment of efficacy of RT for prostate cancer. Meanwhile, when fiducial markers are placed in the prostate, their size and iron content may affect image quality. DWI is easily affected by metals, and no study has compared the quality of DWI before and after fiducial marker placement in the prostate. Moreover, change in ADC before and after marker placement has not been evaluated properly. In other words, change in the background of DWI after marker placement before RT may hinder evaluation. Therefore, we prospectively assessed effects of fiducial gold marker on DWI during RT for prostate cancer. Material and Methods Twenty-one patients in whom two gold markers were placed on the prostate with abnormal signal intensity on DWI were evaluated. No patients received hormonal therapy or neoadjuvant chemotherapy either before or during the course of IMRT. Contouring, prostate volume measurements, and OAR determination were performed by the same radiation oncologist. MRI was performed in all patients and two gold fiducial markers were placed in the prostate 3 weeks before the CT/MRI fusion setting. CT was performed, followed by MRI within 20 min. MRI was obtained using a five-channel cardiac coil (3-mm section thickness, with no intersection gap, and 16-cm field of view). Parameters for DWI were as follows: spin echo planner image (EPI) [TR/TE in ms]: (2264/70); NSA: 8 times; PES: 103; FES:128; TPR; frequency/phase: 2.58/3.21; and a diffusion b-factor of 1000 s/mm 2 . A radiologist and medical physicist evaluated each image independently. The following were evaluated: Image quality on a scale of 1–5: 5 points indicate no change in the quality of DWI before and after marker placement; 4 points Poster: Physics track: Imaging acquisition and processing

week 2 (p=0.012, p=0.015), baseline v e

(p=0.006), and

baseline ktrans (p=0.047). Conclusion

Hypoxic and non-hypoxic tumor regions differed significantly regarding mpMRI-based diffusion and perfusion parameters ADC, ve, and ktrans, linking these MRI parameters to the tumor oxygenation status. Further studies are warranted to specify the role of mpMRI parameters as possible surrogate for hypoxia PET imaging. PO-1696 Quantitative analysis of mean ADC in cervix cancer patients during chemoradiotherapy A. Datta 1 , M. Dubec 1 , A. Cree 2 , H. Mistry 1 , C. West 3 , A. Choudhury 2 , P. Hoskin 2 1 The University of Manchester, Division of Cancer Sciences, Manchester, United Kingdom ; 2 The Christie NHS Foundation Trust, Radiotherapy Related Research, Manchester, United Kingdom ; 3 The University of Manchester, Translational Radiobiology, Manchester, United Kingdom Purpose or Objective A pilot study to evaluate changes in mean apparent diffusion coefficient (ADC) as a quantitative imaging biomarker during chemoradiotherapy prior to implementation on the MR Linac (MRL). Material and Methods A sample of 6 patients undergoing curative-intent concurrent chemoradiotherapy (CRT) for locally advanced cervical cancer (LACC) were enrolled into a prospective observational imaging study. Sagittal T2 weighted (T2W) and diffusion weighted imaging (DWI) sequences were obtained at three time points during external beam radiotherapy (EBRT). These were in addition to the regular imaging protocol. Conventional ADC maps were calculated and co-registered to the T2W images. A radiologist delineated the tumour volume of interest on the T2W sequences and mean ADC values were calculated. Patients with serial tumour volume reduction at diagnostic MR imaging were classified as imaging-based responders using the Response Evaluation Criteria in Solid Tumors (RECIST) criteria 1,2 Results

Figure 1: Temporal relationship of mean ADC values within the locally advanced cervical tumour during chemoradiotherapy. Day 0 represents the first day of EBRT. Patients 1-5 were all responders and patient 6 was a non- responder. The responders demonstrate a serial increase in mean ADC values during chemoradiotherapy with a positive correlation (Spearman’s r s = 0.69; t=3.42; p=0.005). CRT affects the tumour microarchitecture and integrity of cell membranes. ADC, which measures the rate of water mobility, increases after successful therapy because cell density decreases and reflects cell death 3 .The solitary non-responder (Patient 6) did not demonstrate this trend with a fall in mean ADC value at the third time point. This tumour was a high grade, poorly differentiated, adenosquamous carcinoma which may explain the poor response. Conclusion During CRT, cervical tumour mean ADC values serially increase in those patients responding to treatment. This pattern was not seen in the non-responding patient. This