ESTRO 2022 - Abstract Book

S182

Abstract book

ESTRO 2022

Conclusion Low SMI appear to be a resourceful and economic biomarker for nCRT compliance, in terms of RT interruption; furthermore, in the setting of obese patients, a low SMI significantly affects OS. By the analysis of this feature, easily obtainable from the simulation CT, result the possibility to improve the patient's compliance and the survival of the obese patient, personalizing patient’s nutritional support before and during the treatment.

MO-0224 Simultaneous integrated boost in short-course radiotherapy; a novel approach for rectal cancer

S. Vieira 1 , O. Parés 1 , J. Stroom 1 , C. Greco 1

1 Champalimaud Foundation, Radiotherapy, Lisboa, Portugal

Purpose or Objective In the era of growing interest for Total Neoadjuvant Treatment (TNT) in rectal cancer several studies show improved oncologic outcomes by intensifying chemotherapy regimens before surgery. However not every patient is fit for such a strategy of chemo-intensification. Another element of the treatment of rectal cancer with potential to be intensified is radiotherapy. We report on a new approach with dose intensification through a simultaneous integrated boost (SIB) in short- course preoperative radiotherapy for rectal cancer patients (SCRT). Materials and Methods Between February 2014 and June 2019, 41 patients with rectal adenocarcinoma (27 male, 14 female; median age 68 years), were treated with SIB-SCRT (fig1). Inclusion criteria for SIB were advanced age, severe comorbidity precluding surgery, or tumor high-risk features requiring prompt systemic therapy. The planning target volume (PTV pelv ) consisted of the mesorectum and lymphatic areas at risk (CTV pelv + 5mm) and received 25 Gy over 5 consecutive days, with a SIB between 27.5-35 Gy on PTV boost (GTV boost +5mm) according to the extent of the disease and proximity to OARs. A 4 arc 10FFF VMAT plan (Eclipse™) was used (fig1). PTV coverage was defined as the volume receiving the prescribed dose. OAR dose constraints were derived from published hypofractionation schemes: D 5cc <19.5Gy, D max 35Gy for small bowel (SB); D 15cc <18.3Gy for bladder (B) and D 20cc <25Gy for sigmoid (S), with D max 38Gy for both; D 10cc <30Gy for femoral heads (FH); and D 5cc <30Gy, D max 32Gy for cauda equina (CE). Pre-treament QA (ArcCheck®) was performed for all patients using gamma (3%/3mm) passing rates >90%. Patients were set-up with CBCT imaging for all fractions.