Radiation dose intensification in pre-operative chemo-radiotherapy for locally advanced rectal cancer

To assess the role of radiation dose intensification with simultaneous integrated boost guided by 18-FDG-PET/CT in pre-operative chemo-radiotherapy (ChT-RT) for locally advanced rectal cancer.

A prospective study was approved by the Internal Review Board. Inclusion criteria were: age >18 years old, World Health Organization performance status of 0-1, locally advanced histologically proven adenocarcinoma of the rectum within 10 cm of the anal verge, signed specific informed consent. High-dose volumes were defined including the hyper-metabolic areas of 18-FDG-PET/CT of primary tumor and the corresponding mesorectum and/or pelvic nodes with at least a standardized uptake values (SUV) of 5. A dose of 60 Gy/30 fractions was delivered. A total dose of 54 Gy/30 fractions was delivered to prophylactic areas. Capecitabine was administered concomitantly with RT for a dose of 825 mg/mq twice daily for 5 days/every week.

Between September 2011 and July 2015 fortypatients were recruited. At the time of the analysis, median follow up was 20 months (range 5-51). The median interval from the end of ChT-RT to surgery was 9 weeks (range 8-12). Thirty-seven patients (92.5 %) were submitted to sphincter preservation. Tumor Regression Grade (Mandard scale) was recorded as follows: grade 1 in 7 (17.5 %), grade 2 in 17 (42.5 %), grade 3 in 15 (37.5 %) and grade 4 in 1 (2.5 %). Post-surgical circumferential resection margin was negative in all patients. A tumor downstaging was reported in 62.5 % (95 % CI: 0.78-0.47). A nodes downstaging was registered in 85 % (95 % CI: 0.55-0.25). 18-FDG-PET/CT was not able to predict pCR. No correlation was found between pre-treatment SUV-max values and pCR. A metabolic tumor volume >127 cc was related to ypT ≥2 (p 0.01). Patients with TRG >2 had higher tumor lesion glycolysis values (p 0.05).

Preliminary results did not confirm some advantages in terms of primary tumor downstaging/downsizing compared to conventional schedules reported in historical series. The role of 18-FDG-PET/CT in neoadjuvant rectal cancer management needs to be confirmed in further investigations. Long terms results are necessary.