title: Assessment and clinical validation of margins for adaptive simultaneous integrated boost in neo-adjuvant radiochemotherapy for rectal cancer.
abstract: OBJECTIVE
  An adaptive concomitant boost (ACB) for the neo-adjuvant treatment of rectal cancer was clinically implemented. In this study population margins M(90,90) considering rectal deformation were derived for 10 consecutive patients treated at 18 × 2.3Gy with Helical Tomotherapy (HT) and prospectively validated on 20 additional patients treated with HT, delivering ACB in the last 6 fractions.
  
  
  METHODS
  Sectorial margins M(90,90) of the whole and second treatment parts were assessed for 90% population through a method combining the 90% coverage probability maps of rectal positions (CPC90%) with 3D local distance measurements between the CPC90% and a reference rectal contour. M(90,90) were compared with the margins M(90,90)(95%/99%), ensuring CPC90% coverage with 95%/99% confidence level. M(90,90) of the treatment second part were chosen as ACB margins which were clinically validated for each patient by means of %volume missing of CPC5/6 excluded by the ACB margins.
  
  
  RESULTS
  The whole treatment M(90,90) ranged between 1.9 mm and 9 mm in the lower-posterior and upper-anterior sectors, respectively. Regarding ACB, M(90,90) were 7 mm in the anterior direction and <5 mm elsewhere. M(90,90)(95%/99%) did not significantly differ from M(90,90). The %volume excluded by the ACB margin was<2% for all male and <5% for 9/10 female patients. The dosimetry impact on R_adapt for the patients with the largest residual error was negligible.
  
  
  CONCLUSIONS
  Local deformation measurements confirm an anisotropic motion of rectum once set-up error is rigidly corrected. Margins of 7 mm anterior and 5 mm elsewhere are adequate for ACB. Female patients show a slightly larger residual error.
authors.affiliation: Medical Physics, San Raffaele Scientific Institute, Milano, Italy.
authors.forename: Roberta
authors.initials: R
authors.lastname: Raso
authors.affiliation: Istituto di Bioimmagini e Fisiologia Molecolare, CNR, Segrate, Milano, Italy.
authors.forename: Elisa
authors.initials: E
authors.lastname: Scalco
authors.affiliation: Medical Physics, San Raffaele Scientific Institute, Milano, Italy. Electronic address: fiorino.claudio@hsr.it.
authors.forename: Claudio
authors.initials: C
authors.lastname: Fiorino
authors.affiliation: Medical Physics, San Raffaele Scientific Institute, Milano, Italy.
authors.forename: Sara
authors.initials: S
authors.lastname: Broggi
authors.affiliation: Medical Physics, San Raffaele Scientific Institute, Milano, Italy.
authors.forename: Giovanni Mauro
authors.initials: GM
authors.lastname: Cattaneo
authors.affiliation: Medical Physics, San Martino-IST Scientific Institute, Genova, Italy.
authors.forename: Stefania
authors.initials: S
authors.lastname: Garelli
authors.affiliation: Medical Physics, San Raffaele Scientific Institute, Milano, Italy.
authors.forename: Marco
authors.initials: M
authors.lastname: Pagliazzi
authors.affiliation: Radiotherapy, San Raffaele Scientific Institute, Milano, Italy.
authors.forename: Najla
authors.initials: N
authors.lastname: Slim
authors.affiliation: Radiotherapy, San Raffaele Scientific Institute, Milano, Italy.
authors.forename: Nadia
authors.initials: N
authors.lastname: di Muzio
authors.affiliation: Istituto di Bioimmagini e Fisiologia Molecolare, CNR, Segrate, Milano, Italy.
authors.forename: Giovanna
authors.initials: G
authors.lastname: Rizzo
authors.affiliation: Medical Physics, San Raffaele Scientific Institute, Milano, Italy.
authors.forename: Riccardo
authors.initials: R
authors.lastname: Calandrino
authors.affiliation: Radiotherapy, San Raffaele Scientific Institute, Milano, Italy.
authors.forename: Paolo
authors.initials: P
authors.lastname: Passoni
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D059186:Chemoradiotherapy, Adjuvant / Q000379:methods*; D019583:Dose Fractionation, Radiation; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011880:Radiotherapy Planning, Computer-Assisted; D050397:Radiotherapy, Intensity-Modulated; D012004:Rectal Neoplasms / Q000532:radiotherapy / Q000628:therapy*; D055815:Young Adult
keywords: Adaptive radiotherapy; Margins; Rectal cancer; Tomotherapy