ESTRO 38 Abstract book

S226 ESTRO 38

Material and Methods 60 patients with clinical approved IMRT plans for cervical cancer were selected into establishing a knowledge-based model by linear fitting the equivalent uniform dose (EUD, a=1) and equivalent uniform distance (EUL, a=1), developed from the overlap volume histograms (OVH) method. Another 20 patients were used as the test group. By integrating the EUD-EUL model with Auto-Planning module, a fully automated hybrid IMRT planning platform was developed based on Pinnacle scripts and python codes. IMRThy plans, generated this hybrid planning platform, were compared with corresponding IMRTap plans, generated by Auto-Planning module with default pre-setting objectives from a template. The quality and consistency of IMRThy plans produced by this hybrid planning platform were evaluated by dose/volume indices and EUD-EUL metrics. Results The linear regression between EUD and EUL for bladder and rectum of 60 previous clinical approved plans were shown in figure 1. Therefore, correlation functions between EUD and EUL for bladder and rectum were obtained:

Conclusion The fully automated hybrid IMRTplanning platform, combining knowledge-based model and Auto-Planning module, could generate clinical accepted plans and significantly improve the quality and consistency of IMRT plans.

Proffered Papers: BT 6 : Innovative and uncommon indications

OC-0431 Esophageal brachytherapy: Institut Gustave Roussy’s experience M. Kissel 1 , E. Chirat 1 , P. Annede 1 , P. Burtin 2 , I. Fumagalli 1 , E. Bronsart 1 , F. Mignot 1 , A. Schernberg 1 , I. Dumas 1 , C. Haie-Meder 1 , C. Chargari 1 1 Institut Gustave Roussy, Radiotherapy, Villejuif, France; 2 Institut Gustave Roussy, Gastroenterology, Villejuif, France Purpose or Objective Esophageal cancer is characterized by its propension to local evolution, which conditions prognosis but also quality of life. Brachytherapy may be a therapeutic option for all stages of esophageal cancer, especially for This retrospective unicentric study included all consecutive patients treated for an esophageal high dose rate brachytherapy in our institution from 1992 to 2018. Results 90 patients were included. They were treated in four distinct indications : exclusive (7 patients), boost after external beam radiotherapy (41), reirradiation (36) or palliative aim (6). Most frequently prescribed schemes were 3x5Gy (boost) or 6x5Gy (exclusive treatment and reirradiation). At the end of follow-up, 50% of patients had presented with local recurrence : 46% in the boost setting, 71% for exclusive brachytherapy, 47% for reirradiation and 100% for palliative treatment. 17% of patients had a metastatic relapse. Median overall survival (OS) was 15 months in the whole cohort : 22 months in the boost setting, 25 months for exclusive brachytherapy, 15 months for reirradiation and only 2 months for palliative treatment. Tumor length at brachytherapy, brachytherapy dose and interfraction response were significantly associated to OS. 40% of patients presented with grade 2+ toxicity, mostly esophagitis, including 3 toxic deaths. Conclusion Phase III trial RTOG9405, showing the absence of dose- effect on esophageal cancer, has led teams to progressively give up the technique in the boost setting. Although local control outcomes are still poor, one must remember that patients are unfit for any curative therapeutic option and that palliative chemotherapy offers mediocre results. The most promising setting probably is reirradiation since brachytherapy offers a remarkable dose gradient allowing best OAR sparing. Esophageal brachytherapy deserves to be further investigated since some patients, even unfit, may benefit from it in some indications, with acceptable toxicity. Prospective studies are warranted. OC-0432 Endoluminal brachytherapy with induction chemotherapy and definitive chemoradiation in Ca.Esophagus S. Raghunath 1 , R. Tiwari 1 , G. Narayanan 1 , B. Vishwanathan 1 , R. Sultana 1 1 Vydehi Institute of Medical Sciences and Research Center, Radiation Oncology, Bangalore, India inoperable patients. Material and Methods

EUDbla = 45.37 – 5.78*EULbla with R2 = 0.79 EUDrec = 44.23 – 5.38*EULrec with R2 = 0.69

The dose/volume indices of IMRThy plans and IMRTap plans were listed in table 1. For PTV, V95 of IMRThy plans were a little worse than that of IMRTap plans with significant differences (IMRThy: 95.38±0.92%, IMRTap: 96.04±0.73% with p=0.02). While HI and CI of IMRThy and IMRTap plans were very similar without significant differences. Considering bladder and rectum, the organs predicted by the EUD-EUL model, dose/volume indices including V20, V30, V40 and Dmean of IMRThy plans were dramatically reduced than IMRTap plans with significant differences. While V50 and V60 of IMRThy plans were lower than that of IMRTap plans without significant differences. For femoral heads, which were not considered in the predicting model, all dose/volume indices were comparable between these two type plans.