ESTRO 38 Abstract book

S239 ESTRO 38

sides of the neck (with the exception of T1 laryngeal and small lateralized tonsillar fossa carcer), in order to reduce the risk of contralateral RF (cRF). Meanwhile, there is slowly growing evidence that the incidence of cRF in well- selected HNSCC is very low (<5%). Furthermore, unilateral ENI will result in significant decrease in the incidence and severity of acute and late toxicity and improve QoL. In different studies, large treated volumes, chemoradiation and bilateral neck irradiation were the most important predictors for radiation-related toxicity. Therefore, there is increasing need for selection tools to expand the indication for unilateral ENI to reduce toxicity and improve QoL. As a consequence of the improved prognosis and increased incidence of HPV-positive oropharyngeal cancer among young people, these issues are becoming increasingly important since these young patients will live longer with the burden of troublesome late toxicities. At the Dutch Cancer Institute, we initiated a proof-of- concept study, the SUSPECT study (mapping of sentinel lymph node drainage using SPECT to tailor ENI in node- negative neck of patients with head and neck cancer) (ClinicalTrials.gov Identifier NCT02572661). The aim of this study was to investigate the role of SPECT/CT for the lymph drainage mapping (LDM) and to explore the incidence of cRF in patients electively treated to one side of the neck, based on SPECT/CT-guided LDM. In this study, 50 patients with primary HNSCC, T1‐3N0-2bM0 located in the oral cavity, oropharynx, larynx (except T1 glottic), and hypopharynx, not crossing the midline and planned for treatment with (chemo)radiotherapy in curative setting, were included. LDM was performed using SPECT/CT scan 2-4 hours after injection of the primary tumor with radioactive Tc-Albumin (80MBq). Patients without any contralateral drainage, only the ipsilateral neck was electively irradiated. In case a contralateral tracer accumulation was identified, the elective treatment included the ipsilateral neck and only the level containing tracer accumulation, instead of the whole contralateral neck. The preliminary results are very promising. The dosimetric analysis showed highly significant reduction of dose to the salivary glands, swallowing muscles, speech structures, larynx, supraglottic region and thyroid glands. These dosimetric advantages was translated in significant reduction of the frequency, severity, and duration of acute and late toxicities such as grade 3 dysphagia (tube- feeding) and dry mouth, compared to a historical cohort of 50 consecutive patients treated bilaterally, outside the framework of the study. The first 40 patients included have meanwhile a follow-up time of at least 1 year. Only one patient with cRF was seen (2.5%). This patient was successfully salvaged by ND and is still alive with NED, 1.5 years after treatment. SP-0465 Adapting RT in soft tissue sarcoma: the influence of anatomy, biology and response B. O'Sullivan 1 1 Princess Margaret Cancer Centre, Radiation Oncology, Toronto, Canada Abstract text Traditional combined modality approaches to the local management of soft tissue sarcoma have used post- operative radiotherapy (RT) in a “shrinking field” concept to deliver an elective dose (e.g. 50 Gy) to a clinical target volume (CTV2) encompassing potential microscopic involvement beyond the original location of the gross tumour volume (GTV) and a higher dose to the originally site of the GTV (CTV1). These CTVs can be treated simultaneously or sequentially and generally are facilitated by the use of IMRT to deliver a dose of 60-66 Gy to the combined volume. Alternatively, pre-operative RT to CTV2 alone is often favored with RT reserved for CTV1 as a “boost” if involved resection margins occur at the resection. However, adequate and safe RT administration may not be feasible in some sites such as

patients (≥70 years with tumours ≤2 cm, clinically node- negative, oestrogen-positive). Both studies showed significantly higher rates of local relapse in the endocrine therapy alone arms; though these differences, the addition of whole-breast radiation therapy did not result in differences in breast cancer–specific survival. The BASO II trial confirmed that patients treated with either exclusive adjuvant radiotherapy or endocrine therapy with tamoxifen had an equivalent local relapse rate per annum of 0.8%. These data suggest that radiation or endocrine therapy alone resulted in excellent disease control in older women with early breast cancer, and that the combination of treatments may have less benefit than expected. A direct comparison between radiation or endocrine therapy omission as adjuvant treatment is lacking in the existing literature [11-13]. The use and dose of a boost on the tumour bed has been largely investigated. In a phase 3 randomised controlled trial, the effect of a radiation boost of 16 Gy on overall survival, local control, and fibrosis for patients with stage I and II breast cancer compared with patients who received no boost has been evaluated. At a 20-year follow- up time, a radiation boost has no effect on long-term overall survival, but can improve local control, with the largest absolute benefit in young patients, although it increases the risk of moderate to severe fibrosis. Conversely, boost can be avoided in most patients older than age 60 [14,15]. References [1]. Yarnold J, Ashton A, Bliss J, et al. Radiother Oncol. 2005;75:9–17. [2]. Owen JR, Ashton A, Bliss JM, et al. Lancet Oncol. 2006;7:467–71. [3]. START Trialists’ Group. Bentzen SM, Agrawal RK, et al. Lancet Oncol. 2008;9:331–41. [4]. START Trialists’ Group. Bentzen SM, Agrawal RK, et al. Lancet. 2008;371:1098–107. [5]. Haviland JS, Owen JR, Dewar JA, et al. Lancet Oncol. 2013;14:1086–94. [6]. Whelan TJ, Pignol JP, Levine MN, et al. N Engl J Med. 2010;362:513–20. [7]. Coles CE, Griffin CL, Kirby AM, et al. Lancet. 2017;390(10099):1048–1060. [8]. Meattini I, Livi L, Pallotta S, Marrazzo L. Breast. 2018;38:98–100. [9]. Polgar C, Van Limbergen E, Potter R et al. Radiother Oncol 2010;94:264-73. [10]. Correa C, Harris EE, Leonardi MC et al. Pract Radiat Oncol 2017;7:73-9. [11]. Kunkler IH, Williams LJ, Jack WJL, et al. Lancet Oncol. 2015;16:266-273. [12]. Hughes KS, Schnaper LA, Bellon JR, et al. J Clin Oncol. 2013;31:2382-2387. [13]. Blamey RW, Bates T, Chetty U, et al. Eur J Cancer. 2013;49:2294-2302. [14]. Vrieling C, van Werkhoven E, Maingon P, et al. JAMA Oncol. 2017;3:42-48. [15]. Bartelink H, Maingon P, Poortmans P, et al. Lancet Oncol. 2015;16:47-56. SP-0464 Image-guided elective neck irradiation in head and neck cancer A. Al-Mamgani 1 1 Netherlands Cancer Institute, Department of Radiaition Oncology, Amsterdam, The Netherlands Abstract text Because of the rich lymphatic supply of the head and neck region, head and neck squamous cell carcinoma (HNSCC) has the tendency to metastasize to the regional lymph nodes, also to the contralateral side. The concept of elective nodal irradiation (ENI) was introduced in the sixties by Fletcher and supported later on by others. Since then, there is a long-standing empirical convention to irradiate the vast majority of HNSCC electively to both