ESTRO 2021 Abstract Book

S351

ESTRO 2021

progression. The majority of studies in this area are retrospective and small case series. Three recent systematic reviews and meta-analysis (Valle LF et al. MASTER Eau Urol 2020;Dec19; Corkum T et al. Adv Radiat Oncol 2020;5:965-77; Munoz F et al. Cancer Treat Rev 2021;95:102176) show that salvage prostatectomy, SBRT and brachytherapy are equally efficacious, with SBRT and brachytherapy having significantly better toxicity profile. Some prospective studies (NCT03438552, ACTRN12617000035325, NCT00851916) are currently ongoing regarding SBRT for the treatment of recurrent prostate cancer. While awaiting the results of ongoing studies, recently completed ESTRO ACROP Delphi consensus on salvage SBRT (Jereczek-Fossa B et al. Cancer Treat Rev in press) may serve as a practical guidance for salvage SBRT and for the design of trials for this promising approach. The ESTRO ACROP consensus was reached regarding some selection criteria, diagnostic procedures and therapeutic indications of salvage SBRT. Instead, the role of biopsies, RT dose and OARs constraints remained critical points and need to be addressed urgently. The proper patient selection and treatment delivery can offer to a good proportion of men with locally recurrent prostate cancer long-term cure with very limited toxicity.

SP-0462 The role of brachytherapy A. Bossi France

Abstract not available

SP-0463 The role of surgery S. Joniau Belgium

Abstract not available

Symposium: New developments in head and neck cancer radiotherapy

SP-0464 Current status of IMPT versus VMAT in head and neck cancer M. Krengli 1 , C. Pisani 1 , P. Franco 1 1 University of Piemonte Orientale, Radiation Oncology, Novara, Italy

Abstract Text The aim of the present report is to clarify the current state of research on the use of protons in head and neck tumors. The current standard of care for head and-neck malignancies is intensity-modulated radiotherapy (IMRT) and its natural evolution, the volumetric modulated arc therapy (VMAT). The advantage of these techniques lies on the possibility to increase dose conformity within the target volume potentially improving the chance to avoid organs-at-risk (OARs). Proton therapy offers further advantages over VMAT because of the unique physical characteristics of the proton beam. Most of the proton radiation dose is deposited across the ‘Bragg peak’, reducing irradiation of normal tissues beyond the tumor. Intensity modulated proton therapy is the most advanced modality of treatment delivery allowing for robust treatment plans and for better sparing of normal tissues. In head and neck cancer treatment, proton beam’s advantage includes sparing of major OARs in close proximity to the tumor, such as major salivary glands, oral cavity structures, pharyngeal mucosa, larynx, spinal cord and brain tissue. This may lead to decreased toxicity profile, improve patients’ quality of life, while potentially offering opportunities for dose-escalation to improve tumor control and prolong survival. A relevant issue should be carefully taken into account with regard to physical dose distribution of protons which are very sensitive to the changes of tissues in the plateau before the Bragg peak: a change in depth of the target due to tissue edema or change in density due to mucous content of an air cavity could affect greatly the dose distribution with the risk of missing the target and overshooting healthy structures. Radiation oncologists, physicists and biologists are collaborating to define the appropriate use of proton beam therapy and generate clinical evidence for its use, to further justify its adoption also in head and neck cancer treatment. Several studies explored the advantages of protons over photons for head and neck tumors. The radiation target for specific head and neck cancers could be limited to one side such as for most salivary gland tumors (without involvement of midline structures) and well-lateralized oral cavity, oropharynx, or skin cancers. Proton therapy can offer excellent organ sparing with minimal exit dose compared to VMAT in treating unilateral head and neck targets. Reduced dose to these OARs might decrease acute toxicities, with respect to mucositis, dysgeusia, nausea or vomiting, and fatigue. Multiple clinical trials are aimed at de-escalation of treatment intensity by reducing radiation dose or volume in oropharyngeal cancer (OPC) HPV-positive. Due to the anatomical complexity and large target volumes often seen in OPC, IMPT is generally recommended to enhance conformality and homogeneity of the radiation plan, while minimizing radiation to OARs. Early dosimetry studies have shown potential advantages of IMPT over IMRT in sparing of OARs and these dosimetry advantages could likely contribute to a favorable toxicity profile of proton therapy in OPC. A randomized phase III trial comparing IMPT vs. IMRT (NTC01893307) is ongoing at MD Anderson Cancer Center. The study aims to demonstrate non-inferiority of IMPT vs. IMRT in terms of oncological outcomes, as well as to clarify the role of IMPT in mitigating treatment related toxicities. Nowadays, a very important issue is to identify criteria to select patients who could benefit from protons. As a matter of fact, a model-based selection has been proposed to potentially qualify patients for IMPT. VMAT plan is created for patients with optimal OARs sparing in NTCP models for a number of toxicities. IMPT plan is created only for pts with NTCP difference between VMAT and IMPT best case scenario. If delta NTCP threshold is exceeded, then a robust IMPT plan is created and patient selected for proton-treatment. Literature data show that around 60% qualify for planning comparison and 35% are selected for proton