ESTRO 2020 Abstract book

S227 ESTRO 2020

Despite the challenges with definition and stability of high uptake areas, several phase III randomized trials are currently investigating the effect of selectively increasing the dose to these areas. These trials are based on various functional imaging modalities and functional markers. In the NARLAL2 trial for locally advanced lung cancer [1], dose is escalated heterogeneously to the areas with high 18F-FDG-PET uptake before treatment start as shown in Fig 1. In the FLAME trial, multiparametic MR defines a tumor sub-volume of the prostate for homogeneous dose escalation [2]. Although most studies have investigated the relation of pre-treatment functional imaging with local recurrence, another approach is to monitor the early response to radiotherapy with functional imaging during the radiotherapy course (see Fig 2). Small studies have shown correlation between the early treatment response and the local recurrence rates as well as overall survival. Thus, functional imaging during treatment might enable early treatment adaptation either as a selective dose escalation based on functional imaging during treatment or as a stratification of patients into different treatment regimens with different levels of dose escalation. The first approach is investigated in the RTOG 1106 lung cancer trial [4], where the dose is escalated in the final part of the treatment course based on a high mid-treatment 18F-FDG- PET uptake.

[1] Møller DS et. al Heterogeneous FDG-guided dose- escalation for locally advanced NSCLC (the NARLAL2 trial): Design and early dosimetric results of a randomized, multi- centre phase-III study. Radiother Oncol. 2017;124:311- 317. [2] Prognostic value of dynamic hypoxia PET in head and neck cancer: Results from a planned interim analysis of a randomized phase II hypoxia-image guided dose escalation trial. Welz S et al.Radiother Oncol. 2017;124:526-532. [3] Monninkhof EM et al. Standard whole prostate gland radiotherapy with and without lesion boost in prostate cancer: Toxicity in the FLAME randomized controlled trial. Radiother Oncol. 2018; 127:74-80. [4] Kong FM et al. Effect of Midtreatment PET/CT-Adapted Radiation Therapy With Concurrent Chemotherapy in Patients With Locally Advanced Non-Small-Cell Lung Cancer: A Phase 2 Clinical Trial. JAMA Oncol. 2017;3:1358- 1365. SP-0393 Audits for IMRT/VMAT: present and future P. Kazantsev 1 1 IAEA - International Atomic Energy Agency, NAHU, Wien, Austria Abstract text The International Atomic Energy Agency has been providing dosimetry audit services for radiotherapy centres around the world for over 50 years. One of the major challenges in this work is to keep up with modern developments in radiotherapy technology such as introduction of multileaf collimators (MLCs), computerized and later inverse treatment planning, and advanced on- board imaging capabilities. Clinical implementation of any new technologies should be accompanied by adequate Symposium: Audits for advanced radiotherapy techniques