ESTRO 37 Abstract book

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ESTRO 37

Preoperative chemoradiation is a complex treatment which allows several administration strategies and possibilities intensifications offering opportunities to tailor the treatment according to tumor presentation.

Debate: This house believes that 5x5 Gy offers more opportunities for tailor made treatment than conventional chemoradiotherapy in rectal cancer patients

SP-0345 For the motion seconder D. Sebag-Montefiore University of Leeds, Leeds, the United Kingdom

SP-0343 For the motion F. Peters LUMC, Leiden, the Netherlands

Abstract not received

SP-0346 Against the motion seconder Conventional chemoradiotherapy offers more opportunities for tailor made treatment than 5 x 5 Gy C. Rödel 1 1 Klinikum der Johann Wolfgang Goethe Univ, Academic Department of Radiation Oncology, Frankfurt, Germany Abstract text Current standard of neoadjuvant treatment for rectal cancer is either preoperative short-course radiotherapy (5 x 5 Gy) with immediate or delayed surgery or preoperative, conventionally fractionated radiotherapy with continuous infusion 5-FU or capecitabine (CRT), followed by total mesorectal excision surgery six to eight weeks thereafter. The monolithic approaches, however, to either apply the same schedule of preoperative 5-FU- based CRT or preoperative short-course RT to all patients with TNM stage II and III need to be questioned. Identifying and selecting patients for their most appropriate treatment alternatives based on tumor TN stage and MRI features (e.g., subgrouping of T3, mrCRM), location, molecular profiles, response, and to patients’ risk factors and preferences is mandatory. In this regard, CRT allows for tailor made treatment much better than 5 x 5 Gy as any combination with concurrent systemic treatment as well as RT dose adaption strategies (e.g., by use of SIB, contact RT boost) have been mainly established in combination with CRT. Tailor made alternatives include omission of radical surgery, e.g., for early, low-lying, CRT-responsive tumors that would otherwise require an abdominoperineal resection, but also omission of radiotherapy, e.g., for mid-/high lying tumors without threatened circumferential resection margins. Further treatment algorithms that need to be validated include neoadjuvant chemotherapy alone, or induction and consolidation chemotherapy before or after CRT, and the use of targeted agents for more advanced tumors. Thus, clinicopathological and molecular features as well as accurate imaging and response monitoring during treatment will take an integrative part in the multimodality management of rectal cancer patients. SP-0347 Differences in dosimetry, treatment planning, and equieffective dose A. Haworth 1 1 Institute of Medical Physics School of Physics A28, School of Physics, The University of Sydney, Australia Abstract text In appropriately selected prostate cancer patients treated with low dose rate (LDR) brachytherapy there is long term evidence of high clinical efficacy. High dose rate brachytherapy (HDR), when delivered as a single fraction provides an alternative treatment approach, though long term clinical efficacy data is lacking. As clinical trials develop to compare the outcomes of different treatment approaches, it is important to Symposium: Prostate brachytherapy: LDR seeds versus HDR monotherapy

Abstract not received

SP-0344 Against the motion M.A. Gambacorta 1 , G. Chiloiro 1 , A. Re 1 1 Università Cattolica del Sacro Cuore, Radiation Oncology, Rome, Italy

Abstract text Introduction

Preoperative radiotherapy represents the standard treatment in locally advanced rectal cancer. Two main modalities of delivery are currently used: short course radiotherapy and long course chemoradiation. Both these modalities have as main objective to decrease the rate of local failure. The standard way to deliver preoperative chemoradiation is administration of a 45-50 Gy approximately 5 weeks, with a standard fractionation of 1.8-2Gy a day, with concomitant 5FU based chemotherapy. From the technical point of view standard chemoradiation can be delivered on the tumor and elective CTV with a single field or on the elective CTV followed by a boost directed to the tumor. After 6-8 weeks the patient is re- staged and undergo to radical surgery. Material and methods The standard chemoradiation, due to its characteristic of delivery, permits to achieve tumor downstaging as well as decreasing local failure. This allows to treat more advanced tumor leading to higher possibility of surgery with clear margin. Moreover, tumor response to treatment, may add important information to stratify patients at different prognosis. As an example there is a 15-20% of complete responder tumors at pathology. In these subgroup of patients, retrospective pooled analyses, showed better long term outcomes compared to the not complete responders. Tumor response may be finally attributed to total dose, concomitant chemotherapy intensification and interval between the end of chemoradiation and surgery. These characteristics of chemoradiation can be used to tailor the treatment according tumor presentation and expected results. I.e. studies tried to improve tumor response by adding a second drug to concomitant chemotherapy achieving good results in several phase 2 trials, although not completely confirmed in phase 3 trials, some other studies obtained better results in term of pathological complete response by the intensification of radiotherapy dose both with concomitant or simoultaneous integrated boost, nowadays several phase 2 studies are focusing on the prolongation of interval between chemoradiation and surgery to achieve better response overall demonstrating higher response after 14-16 weeks compared with the standard 6-8 weeks. Other field of research are trying to achieve not only better response but also better DFS in patients at higher risk of metastases or to treat oligometastatic patients. By the addiction of chemotherapy in the neoadjuvant setting both before than after chemoradiation (TNT: Total Neoadjuvant Therapy), researchers are trying to decrease the rate of distant relapses that since now still represents the major cause of tumor death in rectal cancer or to conteporraly treat patients of the primary tumor site and on the

distant site. Conclusion