title: Role of in vivo dosimetry with radiochromic films for dose verification during cutaneous radiation therapy.
abstract: OBJECTIVE
  To evaluate the role of in vivo dosimetry with radiochromic films for dose verification in cutaneous radiation therapy (RT).
  
  
  METHODS
  Five patients with 8 cutaneous or sub-cutaneous malignancies of the face, neck, trunk and extremity receiving RT were included. Orthovoltage, megavoltage photon therapies were applied based on anatomic location. The delivered dose for each target was measured with GAFCHROMIC EBT3TM film. The differences between the prescribed and measured doses in each target were analyzed based on the RT characteristics, target location and custom patient set up. The accuracy of EBT3TM film measurement was verified by measurements in a solid water phantom.
  
  
  RESULTS
  The mean measured dose was -3.2% (-9.6% to +2.3%, P=0.86) lower than prescribed over 23 measurements. A wide range of under dose was detected in orthovoltage therapy when a gap existed between skin and a closed-ended applicator surface. The magnitude of the under dosage was correlated with the degree of the gap (P=0.01). The phantom study confirmed the accuracy of GAFCHROMIC EBT3TM film measurement and found that the low measured dose in orthovoltage therapy was caused by the deviation from the inverse square law (ISL) of the beam output at extended source surface distance (SSD) for closed-ended applicators.
  
  
  CONCLUSIONS
  A significantly low delivered dose for extended SSD orthovoltage therapy was demonstrated during cutaneous RT. The dose fall-off with distance is not completely compensated by the ISL standoff correction for orthovoltage therapy. GAFCHROMIC EBT3™ film is a useful and accurate tool for quality assurance of patients receiving a curative intended cutaneous RT.
authors.affiliation: Central Alberta Cancer Center, 3942-50a Ave, Red Deer, AB, T4N 6R2, Canada. hongwei.liu@albertahealthservices.ca.|Department of Oncology, University of Alberta, Edmonton, AB, Canada. hongwei.liu@albertahealthservices.ca.|Department of Oncology, University of Calgary, Calgary, AB, Canada. hongwei.liu@albertahealthservices.ca.
authors.forename: Hong-Wei
authors.initials: HW
authors.lastname: Liu
authors.affiliation: Tom Baker Cancer Center, Calgary, AB, Canada. james.grafe@albertahealthservices.ca.|Department of Oncology, University of Calgary, Calgary, AB, Canada. james.grafe@albertahealthservices.ca.
authors.forename: James
authors.initials: J
authors.lastname: Gräfe
authors.affiliation: Tom Baker Cancer Center, Calgary, AB, Canada. rao.khan@albertahealthservices.ca.|Department of Oncology, University of Calgary, Calgary, AB, Canada. rao.khan@albertahealthservices.ca.
authors.forename: Rao
authors.initials: R
authors.lastname: Khan
authors.affiliation: Tom Baker Cancer Center, Calgary, AB, Canada. Ivo.Olivotto@albertahealthservices.ca.|Department of Oncology, University of Calgary, Calgary, AB, Canada. Ivo.Olivotto@albertahealthservices.ca.
authors.forename: Ivo
authors.initials: I
authors.lastname: Olivotto
authors.affiliation: Tom Baker Cancer Center, Calgary, AB, Canada. Eduardo.VillarealBarajas@albertahealthservices.ca.|Department of Oncology, University of Calgary, Calgary, AB, Canada. Eduardo.VillarealBarajas@albertahealthservices.ca.
authors.forename: J Eduardo Villarreal
authors.initials: JE
authors.lastname: Barajas
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D005373:Film Dosimetry / Q000295:instrumentation* / Q000379:methods*; D006801:Humans; D008297:Male; D008875:Middle Aged; D019047:Phantoms, Imaging; D017785:Photons; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated; D012878:Skin Neoplasms / Q000532:radiotherapy*