Abstract Book

S812

ESTRO 37

Purpose or Objective The nature of pulmonary micronodules detected at diagnosis in patients affected by rectal adenocarcinoma is not currently clear. In this retrospective study, we analyzed the incidence and evolution of pulmonary micronodules identified at CT scan during the initial staging. Material and Methods From January 2008 to March 2015, 146 patients affected by LARC were treated with neoadjuvant radiochemotherapy (RTCT) in Pisa University Hospital. All patients underwent staging examinations including chest CT scan with contrast injection. In this retrospective study, we evaluated the percentage of patients with pulmonary micronodules at diagnosis (excluding calcific micronodules), size, number and pulmonary localization of these and their progression in metastatic disease. Results Of the 146 patients treated with RTCT in our center (median age 64 years), 55.5% had at least one pulmonary micronodule at initial chest CT scan. The maximum diameter of micronodules ranged between 3 and 13 mm; 68% of these were > 5mm. After a median follow-up of 66.8 months, 18/81 patients (22%) with pulmonary micronodules at diagnosis developed pulmonary metastasis, 12 (66,6%) of whom progressed from pre- existing micronodules. The data analysis showed a strong correlation between micronodules’s diameter and micronodules’s progression (p=0.0015); instead there was not a correlation between the lung progression and number (p=0.763) or localization (left or right and upper, mean or lower lobe; p=0.595) of the micronodules. Of the 66 patients without lung micronodularity, only 5 (7,7%) developed lung metastasis. Conclusion In patients affected by LARC, the nature of the pulmonary micronodules detected by initial CT scan is not currently clear. Analyzing our data, we can conclude that 14,8% of these lesions tend to evolve into metastasis during the natural history of the disease. This percentage is a bit higher than that reported by other studies that have enrolled not only patients with rectal cancer but also those with colon cancer; this could be explained by the well-known predisposition of rectal cancer to give lung mts. EP-1497 Predictive factors of nodal response to neoadjuvant RTCT in pts affected by LARC S. Montrone 1 , A. Sainato 1 , R. Morganti 2 , B. Manfredi 1 , C. Laliscia 1 , M. Cantarella 1 , A. Gonnelli 1 , S. Ursino 1 , F. Orlandi 1 , A. Cristaudo 1 , D. Baldaccini 1 , F. Pasqualetti 1 , F. Paiar 1 1 OSPEDALE SANTA CHIARA, Radiotherapy, PISA, Italy 2 OSPEDALE SANTA CHIARA, Biostatistical Consulting, PISA, Italy Purpose or Objective Preoperative radiochemotherapy (RTCT) followed by total mesorectal excision (TME) is the standard of cure in patients (pts) with locally advanced rectal cancer (LARC). After neoadjuvant RTCT the rate of complete pathologic response (pCR) range between 15%-30% and many studies are trying to find predictive factors of response in order to select pts who could benefit from intensified loco- regional treatments. The primary endpoint of this retrospective analysis was to analyze the clinical nodal characteristics (stage, size, number) as predictive factors of pathological nodal response to neoadjuvant RTCT.

Material and Methods We analyzed retrospectively the data of 119 pts affected by LARC, treated at Pisa University Hospital with neoadjuvant RTCT, between 2008 and 2015. Based on MRI images, we analyzed nodal characteristics at diagnosis (clinical nodal stage and number of nodes with short axis diameter ≥5mm), trying to correlate these factors with the pathological nodal response. We also analyzed the time between surgery and RTCT (> or < 8 weeks) and its correlation with nodal response. Results All pts completed the planned radiotherapy and underwent surgery. The mean time between the end of RTCT and surgery was 8.6 weeks (range: 4.7-15.1). Twenty-five pts (21%) had metastatic nodes at pathological examination. Our analysis showed no correlation between clinical N-stage (cN0 vs cN+) and pathological N-stage (pN0 vs pN+) (p=0.327). Instead, the initial number of nodes >5mm at MRI resulted to be strongly correlated with the pathological N-stage both as a continuous variable (p=0.004) and as a dichotomous variable (number of lymph nodes <3 vs ≥4) (p<0.0001). When the RTCT-surgery time was analyzed no differences were reported in terms of pN0-ratio (p=0.950). Conclusion Knowing the predictive factors of pathological response in pts affected by LARC treated with neoadjuvant RTCT could be important to decide to modify the loco-regional treatment itself. The study of nodal predictive parameters represents a challenge because of the difficulty in clearly establishing the initial nodal status. Despite the awareness of these difficulties and the limits of our retrospective study, we can assume that a greater number of nodes with short axis diameter > 5mm at diagnosis could be a predictive factor of non-response to neoadjuvant treatment. EP-1498 Efficacy and Safety of SIB Delivered with Helical Tomotherapy and Daily IGRT for Rectal Cancer . S. El Chammah 1 , A. Duhram 1 , B. Pichon 1 , M. Montemurro 2 , D. Hanhloser 3 , B. De Bari 4 1 Centre Hospitalier Universitaire Vaudois, Radiation Oncology, Lausanne, Switzerland 2 Centre Hospitalier Universitaire Vaudois, Medical Oncology, Lausanne, Switzerland 3 Centre Hospitalier Universitaire Vaudois, Surgery, Lausanne, Switzerland 4 Hôpital Univ. Jean Minjoz CHU Minjoz Jeans & Belfort- Montbéliard Hospital, Radiation Oncology, Besançon, France Purpose or Objective To report the results in terms of toxicity and local control of locally-advanced rectal cancer (LARC) patients treated with preoperative simultaneous integrated boost (SIB) delivered with helical tomotherapy (HT), and chemotherapy (CRT) using daily image guidance (IGRT) Data of 77 consecutive LARC patients treated between 12/2009 and 11/2016 were collected and analysed. Radiotherapy (RT) consisted of 45 Gy (1.8 Gy/fraction, 5 days/week for 5 weeks) to the regional lymph nodes, and a SIB up to a total dose of 50 Gy to the tumor and clinically involved nodes (2 Gy/fraction, 5 days/week for 5 weeks). The CTV to PTV margin was 5 mm for both the CTVs. Daily IGRT was performed before each session in order to take into account and correct setup errors. Chemotherapy consisted of capecitabine 850 mg/m2, followed by surgery. Material and Methods