ESTRO 38 Abstract book

S68 ESTRO 38

possibly associated with concomitant chemotherapy, followed by a boost either by brachytherapy (BT) or external beam radiotherapy (EBRT). Pulsed Dose-Rate technique (PDR) has become a standard modality, with high local control rates, but questions are remaining regarding patient’s selection and predictive factors for local control and toxicities. Material and Methods Between 2005 and 2017, 179 consecutives patients with an anal canal cancer (all histological types), received PDR-BT as a boost after EBRT (+/- concomitant chemotherapy) in our institution. 159 were available for the analysis. Previously reported prognostic factors were analysed in univariate and multivariate analyses with a focus on the local extent of the tumour (T stage; circumference and anal margin and/or rectal mucosa involvement). Local control response was clinically assessed at the time of brachytherapy, then every 3 months for 2 years (MRI every 6 months), then every 6 months. Late toxicities after BT were classified according to the CTCAE-v5.0. Results The main characteristics of tumours and treatments are detailed in table 1. With a mean follow-up of 44.5 months, the 5-years loco- regional control and Progression Free Survival (PFS) were respectively 89% (95%CI 86-92) and 82% (95%CI 78-86). Overall Survival (OS) rate was respectively 84% (±4) and 76% (±7) at 5 and 10 years. Sixteen patients underwent abdominoperineal resection for local recurrence (14) or severe local toxicity (2). 14.5% experienced mucosal grade >=2 late toxicity. In multivariate analysis, local control response at the time of BT (HR=4.46 for Partial Response rate); EBRT technique (HR = 3.25 for IMRT vs 3D conformal), histology and diabetes were significantly associated with PFS. In that series, gap between EBRT and BT was not significant, but was significantly greater in patients treated with 3D conformal EBRT (30.3 vs 17.6 days, p=0.002). Local extent of the tumour at the initial staging did not significantly influence the PFS in univariate and multivariate analyses. Only tumour recurrence was significantly associated with overall survival (OS). No significant factors was identified for grade >=2 late toxicity.

considered for further boost. A planning MRI scan with a multiple channel surface applicator in place was taken within 3 weeks of NACTRT completion. Residual tumour / fibrotic regions were contoured (CTV), dose prescribed at periphery of the residual tumor (7 - 10 mm) depending on depth of invasion and isodose distribution generated for 2- 3 channels in closest proximity to the CTV. Plan evaluation consisted of ensuring that the CTV is completely covered by the 85% isodose cloud, while trying to limit the opposing rectal wall from being covered by the 50% isodose line (Fig. 1). High dose rate brachytherapy was delivered with iridium-192 source to a dose of 4 to 6 Gy in 2 fractions one week apart. Patients were assessed for tumor response at 6 weeks from radiation completion with DRE, rectal MRI scan and direct endoscopic visualization a 12 weeks. Patients with incomplete clinical response at 6 to 12 weeks were sent for immediate surgery. Patients with complete (CR) or near complete clinical response (NCR) were observed.

Results In all, 66 patients underwent NACTRT in the given period and 21 patients were found to be suitable for brachytherapy boost. 1 patient defaulted immediately after completion of brachytherapy. Four (20%) patients having partial response 3 underwent abdominoperineal resection and I had intersphincteric resection. Of these 1 patient had pathological complete response. Of the remaining 20 patients, 15 (75%) had CR to NCR at 12 weeks follow up and were enrolled for the wait and watch approach (Fig. 3). One with nCR underwent local excision. At a median follow up of 27 weeks (range16 – 44 weeks) only no patient has had a local regrowth and all15 (75%) patients continue to be on observation. No rectal toxicity reported. Conclusion Dose escalation with MRI guided endorectal brachytherapy for non operative management of rectal cancer is feasible and can lead to a larger number of patients to achieve complete clinicoradiological response leading to organ preservation. Longer follow up and a larger sample size would be required to weigh the potential benefits of dose escalation with regard to local response, progression free interval, successful salvage and against risk of long term toxicity. PV-0140 Predictive factors and patients’ selection for pulsed dose rate brachytherapy boost in anal cancer T. Brahmi 1 , A.A. Serre 1 , F. Gassa 1 , F. Lafay 1 , M. Sandt 1 , P. Pommier 1 1 Centre Léon Bérard, Radiation Therapy, Lyon, France Purpose or Objective The therapeutic standard of care for localized anal canal cancers is the association of pelvic radiation therapy,

Conclusion PDR-BT is an effective boost modality after EBRT for anal carcinoma patients and may be also indicated in selected patients with a limited involvement of anal margin and rectal mucosa and/or a diameter > 50% (maximal 2/3) of the anal mucosa. The EBRT technique was significantly associated with PFS and IMRT should be applied in these