ESTRO 36 Abstract Book

S53 ESTRO 36 _______________________________________________________________________________________________

complementary to molecular and genetic biomarkers if they exist. Our recent studies in neurotoxicity reveal a few interesting findings. For example, a maximum dose effect in white matter fiber bundles is found using longitudinal diffusion tensor imaging and fiber tracking technique. Also, gEUD doses with large α-values (e.g., 14 and 50) received in the brain are associated with late neurocognitive declines, suggesting a maximum dose effect on cognitive function. These results suggest that responses of brain tissue, critical structure, and cognitive function to radiation doses and dose distribution are more complex than we originally thought. Liver is another organ that is sensitive to radiation. Recent studies show that liver function is a predominant predictor for overall survival for patients with intrahepatic cancer and cirrhosis regardless of intervention. Radiation effects on the liver function have been investigated and modeled using dynamic contrast enhanced MRI and HIDA SPECT. To safely treat intrahepatic cancers, both regional and global liver function measures are needed. Can a single test provide regional and global liver function measurements and allow for liver function management during therapy planning? Gadoxetic-acid is widely available liver-specific MRI contrast and is routinely used in clinical MRI. The routine clinical MRI scans with Gadoxetic-acid that are temporally sparse-sampled challenge quantification of liver function using the dual-input tow-compartment model. We have developed a robust algorithm to quantify regional and global liver function from dynamic gadoxetic- acid enhanced MRI. Using regional liver function maps created by our method, we can assess the dose-response of hepatic function in the individual patients, which can be used for optimizing the dose distribution in the liver and thereby minimizing risk of liver function failure. Also, the liver function distribution quantified by this method can be used for assessing liver function preserve by determining the liver functional volume (LFV) for support of clinical decision making for intrahepatic cancer therapy. In this presentation, recent development of imaging and analysis techniques in brain and liver as well as implications of new findings using the techniques will be discussed. SP-0110 Imaging tumour response to neoadjuvant treatment in GI tumours G. Meijer 1 1 UMC Utrecht, Department of Radiation Oncology, Utrecht, The Netherlands Trimodality treatments are often the preferred treatment option in the curative management of cancers in the gastrointestinal tract. Here a combined radiotherapy and chemotherapy regimen are administered prior to the surgical resection of the primary tumor and involved lymph nodes. Typically the primary aim of the neoadjuvant regimen is to downstage the tumor to facilitate negative resection margins at surgery. Interestingly, although these neoadjuvant treatment regimens are not optimized for obtaining local control, pathology reports regularly reveil a complete pathologic response (i.e. no viable tumor left in resection specimen) in particularly rectum and esophageal cancer patients. This opens the window to more tailored treatments where only patients are operated upon that really benefit from the surgery. However, this can only be accomplished if we have accurate means to predict the pathologic outcome prior to surgery. Many research groups have investigated the potential of pre-surgical clinical assessments (e.g. biopsies, endoscopies) to predict the outcome with moderate success. More recently, quantitative imaging techniques like FDG-PET, dynamic contrast enhanced (DCE) MRI, diffusion-weighted (DW) MRI, have shown more potential.

The physical pattern of energy deposition and the enhanced relative biological effectiveness (RBE) of charged particles compared to photons offer unique and not fully understood or exploited opportunities to improve the efficacy of radiation therapy. Variations in RBE within a pristine or spread out Bragg peak and between particle types may be exploited to enhance cell killing in target regions without a corresponding increase in damage to normal tissue structures. In addition, the decreased sensitivity of hypoxic tumors to photon-based therapies may be partially overcome through the use of more densely ionizing radiations. These and other differences between particle and photon beams may be used to generate biologically optimized treatments that reduce normal tissue complications. In this presentation, the biological basis of various models of RBE will be reviewed. In addition, the impact of the RBE of charged particles on measurable biological endpoints, treatment plan optimization, and the prediction or retrospective assessment of treatment outcomes will be examined. In particular, an AAPM task group was formed to critically examine the evidence for a spatially-variant RBE in proton therapy. Current knowledge of proton RBE variation with respect to proton energy, dose, and biological endpoint will be reviewed. The clinical relevance of these variations will be discussed. Recent work focused on improving simulations of radiation physics and biological response in proton, helium, and carbon ion therapy will also be presented. In addition to the physical advantages of protons and more massive ions over photons, the future application of biologically optimized treatment plans has the potential to provide higher levels of local tumor control and improved normal tissue sparing. SP-0108 New horizons in radiobiology: from Relative Biological Effectiveness to “new biology” M. Durante 1 1 University of Trento, Povo, Italy The era of precision medicine has a strong impact on radiotherapy. Treatment planning is now moving from purely physical dose calculation toward biological optimization. Several studies on biomarkers and combined treatments are currently modifying the treatment plan and the design of clinical trials in oncology. In particle therapy, most of the discussion focus on the exploitation of the RBE, which is commonly done in heavy ion therapy and not yet in protontherapy. RBE assessment may improve plan optimization and prevent some side effects that seem to be related to the physical properties, both electromagnetic and nuclear, of protons. Charged particles can however elicit a gene response qualitatively different from that caused by X-ray exposure, and thus open new opportunities. The combination of particles and immunotherapy is particularly promising. Symposium: Imaging for therapeutic response / toxicity evaluation SP-0109 Functional imaging as biomarker for toxicity response Y. Cao 1 1 University of Michigan, Radiation Oncology - Physics, Ann Arbor, USA Population based models for radiation effects on normal tissue and organ function have played a role for minimizing risk of organ injury during treatment planning. However, precision individualized medicine requests to understand individual patient response and sensitivity to radiation doses. Quantitative functional imaging is a powerful tool to assess regional information, and understand local response to radiation doses, which is