Abstract Book

S799

ESTRO 37

EP-1472 Microscopic extension of residual rectal tumor mass post-neoadjuvant chemoradiation: a meta- analysis A. Verrijssen 1 , M. Bellezzo 2 , A. Habr-Gama 3 , R. Perez 3 , J. Guillem 4 , K. Bujko 5 , R. Houben 6 , F. Verhaegen 2 , M. Berbee 7 , E. Van Limbergen 7 1 MAASTRO Clinic, Radiation Oncology, Maastricht, The Netherlands 2 MAASTRO Clinic, Clinical Physics Research, Maastricht, The Netherlands 3 Instituto Angelita & Joaquim Gama, Colorectal Surgery, Sao Paolo, Brazil 4 Memorial Sloan Kettering Cancer Center, Colorectal Surgery, New York City, USA 5 Maria Sklodowska-Curie Memorial Cancer Center, Radiotherapy, Warsaw, Poland 6 MAASTRO Clinic, Data Management, Maastricht, The Netherlands 7 MAASTRO Clinic, Radiotherapy, Maastricht, The Netherlands Purpose or Objective TME surgery is the standard of care for invasive rectal cancer. However, this surgery is associated with significant morbidity, certainly in patients with distal tumors for whom surgery will result in a permanent colostomy. Chemoradiation is used for locally advanced tumors to improve locoregional control. Some patients develop a complete clinical response for which a watch and wait policy can be safely applied. Nonetheless, most patients do not develop such a response and still demonstrate a residual macroscopic tumor mass. Recent studies have shown that dose escalation by a radiation boost increases the complete response rate, which in turn may increase the use of organ sparing strategies. This boost can be given externally or internally, where internal boosting has theoretical benefits due to its steep dose fall-off, allowing for high doses to the residual tumor and low doses to surrounding tissue. To date, the widespread introduction of selective endoluminal radiation techniques is hampered by a lack of evidence based guidelines that describe the radiation treatment volume in relation to the residual tumor mass. In order to reach a complete response it logically seems important to treat all remaining microscopic tumor cells after chemoradiation. With the goal of providing evidence based guidelines that define an appropriate treatment volume and patient selection, we present a meta-analysis based on individual patient data of studies that have assessed the amount or range of submucosal spread of rectal tumors after neoadjuvant chemoradiation. Material and Methods The meta-analysis was executed using the PRISMA Checklist of items to include when reporting a systematic review and meta-analysis 2009. Papers describing microscopic tumor extension for rectal tumors after neoadjuvant chemoradiation were included. Authors were contacted to provide individual patient data. This data was combined into a database and analyzed. Average microscopic extension was calculated. The treatment margin needed to treat all microscopic disease in 85% and 90% of the patients was calculated. Results Eight papers fit our search terms. For four of the articles, we received the individual patient data, resulting in 225 patients for analysis. The average microscopic extension was 4.6 mm. For 85% of patients, microscopic extension outside of the visual lesion was limited to 3mm, whereas for 90% of patients this distance increased to 7.4mm.

Conclusion The majority of patients have limited significant microscopic submucosal or other tumor spread extending outside of the residual tumor mass. Using a margin of 7 mm around the residual tumor mass or residual mucosal abnormality for the radiation boost would account for all microscopic extension in 90% of patients, although a margin of 3 mm could be deemed acceptable, accounting for all microscopic extension in 85% of patients. EP-1473 Prediction of pathologic staging with MRI after neoadjuvant chemoradiation for Rectal Cancer C. De la Pinta Alonso 1 , M. Martín Martín 1 , E. Fernández- Lizarbe 1 , A. Hervás Morón 1 , F. López-Campos 1 , S. Sancho García 1 1 Ramón y Cajal Hospital, Radiation Oncology, Madrid, Spain Purpose or Objective This study was designed to evaluate the role of magnetic resonance imaging (MRI) on preoperative restaging locally advanced rectal cancer after neoadjuvant chemoradiotherapy (CRT), in order to facilitate individualization of surgical management. Material and Methods We analyzed 124 patients who had received neoadjuvant CRT underwent a MRI before and after CRT. All patients underwent restaging MRI followed by surgery after the end of CRT. The primary endpoint of the present study was to estimate the accuracy of post-CRT MRI as compared with pathologic staging. Results Pathologic T classification matched the post-CRT MRI findings in 48(38.7%) of 124 patients. Sensitivity in T0, T1, T2, T3 and T4 was 23%, 17%, 27%, 53% and 83% respectively. Specificity in T0, T1, T2, T3 and T4 were 89%, 94%, 43%, 64% and 83% respectively. Sensitivity in N0 and N1 were 83% and 19% respectively. Specificity was 89% in N0 and 88% in N1. 46(37,1%) of 124 patients were overstaged in T classification. Pathologic N classification matched the post-CRI MRI findings in 78(62,9%)of 124 patients. 21(16,9%)were overstaged in N classification. 28(22.5%) of 124 patients who had been downstaged on MRI after CRT were confirmed on the pathological staging with same stage(T and N). 22p with ypT0 were correlation with MRI after CRT in 5p (22,7%). Conclusion MRI has low accuracy for restaging locally advanced rectal cancer after preoperative chemoradiation so it is currently not consistent enough for clinical application. O. Hernando Requejo 1 , M. Lopez Gonzalez 1 , E. Sanchez Saugar 1 , A. Cubillo Gracian 2 , E. Vicente Lopez 3 , A. Montero Luis 1 , R. Ciervide Jurio 1 , M. Garcia Aranda 1 , J. Valero Albarran 1 , S. Gonzalo Ruiz 1 , R. Alonso Gutierrez 1 , J. Rodriguez Pascual 2 , Y. Quijano Collazo 3 , J. Perez Moreno 4 , P. Fernandez Leton 4 , C. Rubio Rodriguez 1 1 Hospital Universitario Madrid Sanchinarro - Grupo Hospital de Madrid, Radiation Oncology, Madrid, Spain 2 Hospital Universitario Madrid Sanchinarro - Grupo Hospital de Madrid, Medical Oncology, Madrid, Spain 3 Hospital Universitario Madrid Sanchinarro - Grupo Hospital de Madrid, Surgical Oncology, Madrid, Spain 4 Hospital Universitario Madrid Sanchinarro - Grupo Hospital de Madrid, Medical Physics, Madrid, Spain EP-1474 IMRT and Integrated-boost as neoadjuvant chemoradiation for rectal cancer.