title: Assessment of clinically relevant dose distributions in pelvic IOERT using Gafchromic EBT3 films.
abstract: OBJECTIVE
  In IOERT a single dose of radiation is delivered to the tumour site during surgery. Manual dose calculations are used and the irradiation target volume, electron energy and applicator are decided on site by the radiation oncologist. This work assesses the effect that irregular and curved surfaces, typical of pelvic IOERT, may have on the expected dose distribution.
  
  
  METHODS
  The feasibility of using Gafchromic EBT3 films and a slab phantom to obtain 2D dose distributions was investigated. Different set-ups were tested by comparison with water tank measurements, applying the gamma function analysis with 2% and 2 mm criteria. The validated set-up was then used to obtain reference dose distributions, which were converted to colour-coded graphical representations. Phantoms with step-like and curved surfaces were created to simulate typical pelvic IOERT irradiation surfaces, and the dose distributions were obtained and compared with the reference distributions.
  
  
  RESULTS
  Good agreement with water tank measurements was obtained for all applicators below 2 mm, using the chosen setup in reference conditions. In non-reference conditions, the presence of a step-like surface creates an adjacent hotspot, followed by a quick reduction of the dose in depth. With curved surfaces, the dose distribution is shifted forward, becoming curved and deeper, but when the applicator is larger than the hole, hotspots are also observed.
  
  
  CONCLUSIONS
  The shape of the irradiation surfaces alters the dose distribution. Visualization of these effects is important to assess target coverage and interpret in vivo measurements in pelvic IOERT.
authors.affiliation: Medical Physics, Radiobiology and Radiation Protection Group, Research Centre, Portuguese Institute of Oncology, Porto, Portugal.
authors.forename: Filipa
authors.initials: F
authors.lastname: Costa
authors.affiliation: Medical Physics, Radiobiology and Radiation Protection Group, Research Centre, Portuguese Institute of Oncology, Porto, Portugal; Medical Physics Department, Portuguese Institute of Oncology, Porto, Portugal. Electronic address: ssarment@gmail.com.
authors.forename: Sandra
authors.initials: S
authors.lastname: Sarmento
authors.affiliation: Radiation Oncology Department, Portuguese Institute of Oncology, Porto, Portugal.
authors.forename: Olga
authors.initials: O
authors.lastname: Sousa
mesh_terms: D004583:Electrons / Q000627:therapeutic use*; D005373:Film Dosimetry; D006801:Humans; D007432:Intraoperative Period; D008297:Male; D010388:Pelvis / Q000528:radiation effects* / Q000601:surgery*; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D011879:Radiotherapy Dosage; D015203:Reproducibility of Results; D013499:Surface Properties
keywords: Dose distributions; Gafchromic EBT3 films; Pelvic IOERT; Rectal cancer