ESTRO 36 Abstract Book

S72 ESTRO 36 _______________________________________________________________________________________________

lesion controlled was named “oligorecurrence” in Japan, and it is considered to have a better survival than “oligometastases with uncontrolled primary site” (synchronous oligometastases, named by Niibe). There are aggressive cancer cells in the primary lesion from the initial state of synchronous oligometastases, so its prognosis is generally poor. In the oligorecurrence state, cancer cells are seeded in the metastatic site at the control of primary lesion, and Interleukin has been reported to play a key role in progression of micrometastases. Locally radical therapy for oligometastases includes surgical resection, radiofrequency ablation, or radiotherapy, and in particular, stereotactic body radiation therapy (SBRT) is remarked as a promising treatment modality for oligometastases, accompanying not only a high local control rate with a mild toxicity, but also possibility of abscopal effect. In the NCCN guideline for non-small cell lung cancer, it is described that definitive radiotherapy to oligometastases, particularly SBRT, is an appropriate option in such cases if it can be delivered safely to the involved sites. Longer survival would be expected in cases of indolent oligometastatc states such as limited number of metastases and destination organs, metastases to parallel organ, and metachronous or late-onset timing. Though some studies showed good clinical effectiveness of SBRT for patients with oligometastases, further prospective studied are mandatory to address the significance of SBRT for oligometastases and true prognostic factors, and a desirable treatment method according to each kind of primary cancer sites. Recently, drugs for immune checkpoint inhibitor appeared and are expected to have a synergistic effect with radiotherapy to each other, in particular SBRT or particle therapy. Many prospective studies of combined therapy with SBRT and immune checkpoint inhibitors for metastatic disease were just started, but there remains a big problem of high expensive cost of immune checkpoint inhibitors. In this presentation, interpretation and management of oligometastases will be reviewed in order to evaluate and develop the significance of radiotherapy for oligometastases. Stereotactic body radiotherapy (SBRT) is commonly used to treat patients with extracranial oligometastases in clinical settings. In addition, the “abscopal effect”, which is radiotherapy-induced immune-mediated tumor regression at sites distant to the irradiated field, and treatment with a combination of SBRT and immune checkpoint inhibitors have attracted attentions of researchers. According to an international survey of more than 1000 radiation oncologists reported by Lewis SL et al.[1], 61% of responders have been using SBRT for extracranial oligometastases, and the most commonly treated organs were the lung (90%), liver (75%) and spine (70%). Many authors have suggested that surgery for extracranial oligometastases might improve local control and overall survival. With the recent technical developments in SBRT, SBRT is also a promising modality for achieving a high rate of local control with minimal invasiveness. In this lecture, we would like to review the treatment results of SBRT for extracranial oligometastases, such as those located in the lung, liver and spine and discuss comparisons between surgery and SBRT, and cost-effectiveness. 1) SBRT for extracranial oligometastases, such as those located in the lung, liver and spine. 1. Lung Colorectal cancer (CRC) often presents with oligometastases, commonly in the lung and liver, and CRC SP-0148 SBRT for oligometastases T. Kimura 1 , Y. Nagata 1 1 Hiroshima University, Department of Radiation Oncology, Hiroshima, Japan

has a high risk of local failure [2]. The accepted selection criteria include a good performance status (PS), absence of extra-pulmonary disease, control of the primary tumor, 1-5 synchronous or metachronous metastases and adequate respiratory function [3, 4]. Several authors have reported that the 2-year local control rate ranges 49- 96%. The optimal dose is recommended at least 48 Gy in three fractions to achieve greater than 90% 2-year control. 2. Liver The best candidates are patients with a good PS, controlled or absent extra-hepatic disease, ≤3 hepatic lesions, size lesions ≤3 cm, lesion distance from organs at risk >8 mm, good liver function (Childs A) and a healthy liver [5]. Several authors have reported that the 2-year local control rate ranged from 79- 92%.The optimal dose is recommended 48- 60 Gy in three fractions for lesions with a diameter ≤3 cm, while for lesions with a diameter >3 cm a higher prescription dose, such as 60- 75 Gy is necessary to obtain similar local control [5]. 3. Spine The goal of spinal SBRT is local control and pain control. Several authors have reported that the 1-year local control rate ranges 80- 98% and provides pain relief. Therefore, several dose/fractionation schedules, such as 24 Gy in 1 fraction or 27 or 30 Gy in 3 fractions have been used and the optimal dose/fraction schedule is still unclear. 2) Comparison between surgery and SBRT for extracranial oligometastases According to several guidelines, surgery for extracranial oligometastases is still standard practice because of lack of evidence that SBRT has clinical advantages. A retrospective analysis comparing surgery with SBRT for 110 patients with pulmonary oligometastases demonstrated that 3-years overall survival rates were 62% for surgery and 60% for SBRT (p = 0.43) [6]. The authors concluded survival after surgery was not better than after SBRT although SBRT should be the second choice after surgery. However, no randomized trials have been conducted, and prospective randomized studies are required to define the effectiveness of each modality. 3) Cost-effectiveness Extracranial oligometastases have been usually managed with systemic therapy with or without surgery. However, systemic therapy, including molecular targeted drugs, is expensive. A cost-effectiveness analysis using a Markov modelling approach demonstrated that video-assisted thoracic surgery wedge resection or SBRT could be cost- effective in selected patients with pulmonary oligometastases [7]. Increases in medical expenses are a social problem worldwide, but it can be said that SBRT is a promising modality in this aspect. (References) [ 1] Lewis SL, Porceddu S, Nakamura N, et al. Am J Clin Oncol 2015. [2] Shultz DB, Filippi AR, Thariat J, et al. J Thorac Oncol 2014; 9: 1426-1433. [3] Ashworth A, Rodrigues G, Boldt G, et al. Lung Cancer 2013; 82: 197-203. [4] Binkley MS, Trakul N, Jacobs LS, et al. IJROBP 2015; 92:1044-1052. [5] Scorsetti M, Clerici E and Comito T. J Gastrointestes Oncol 2014; 5: 190-197. [6] Widder J, Klinkenberg TJ, Ubbels JF, et al. Radiother Oncol 2013; 107: 409-413. [7] Lester-Coll NH, Rutter CE, Bledsoe TJ, et al. IJROBP 2016; 95: 663- 672.

Proffered Papers: Best of particles

OC-0149 Lateral response heterogeneity of Bragg peak ion chambers for narrow-beam photon &proton dosimetry P. Kuess 1 , T. Böhlen 2 , W. Lechner 1 , A. Elia 2 , D. Georg 1 , H. Palmans 2