title: Recommendations for CTV margins in radiotherapy planning for non melanoma skin cancer.
abstract: OBJECTIVE
  To provide practice guidelines for delineating clinical target volume (CTV) for radiotherapy planning of non melanoma (NMSC) skin cancers.
  
  
  METHODS
  A prospective, single arm, study. Preoperatively, a radiation oncologist outlined the boundary of a gross lesion, and drew 5-mm incremental marks in four directions from the delineated border. Under local anesthesia, the lesion was excised, and resection margins were assessed microscopically by frozen section. Once resection margins were clear, the microscopic tumor extent was calculated using the presurgical incremental markings as references. A potential relationship between the distance of microscopic tumor extension and other variables was analyzed.
  
  
  RESULTS
  A total of 159 lesions in 150 consecutive patients, selected for surgical excision with frozen section assisted assessment of resection margins, were accrued. The distance of microscopic tumor extension beyond a gross lesion varied from 1mm to 15 mm, with a mean of 5.3mm. The microscopic tumor extent was positively correlated with the size of gross lesion, histology and number of surgical attempts required to obtain a clear margin. To provide a 95% or greater chance of covering microscopic disease we make the following recommendations for CTV margins; 10mm for BCC less than 2 cm, 13 mm for BCC greater than 2 cm, 11 mm for SCC less than 2 cm, and 14 mm for SCC greater than 2 cm.
  
  
  CONCLUSIONS
  Tumors greater than 2 cm and SCC histology required larger margins to adequately cover the microscopic extent of disease. This information is crucial in radiation planning of NMSC. Clinicians should be cautioned, as these guidelines may not offer optimum treatment for patients with extremely large or small lesions.
authors.affiliation: University of Toronto, Ontario, Canada.
authors.forename: Luluel
authors.initials: L
authors.lastname: Khan
authors.forename: Richard
authors.initials: R
authors.lastname: Choo
authors.forename: Dale
authors.initials: D
authors.lastname: Breen
authors.forename: Dalal
authors.initials: D
authors.lastname: Assaad
authors.forename: Jefferey
authors.initials: J
authors.lastname: Fialkov
authors.forename: Oleh
authors.initials: O
authors.lastname: Antonyshyn
authors.forename: David
authors.initials: D
authors.lastname: McKenzie
authors.forename: Tony
authors.initials: T
authors.lastname: Woo
authors.forename: Liying
authors.initials: L
authors.lastname: Zhang
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Barnes
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000704:Analysis of Variance; D002280:Basal Cell Carcinoma / Q000473:pathology / Q000532:radiotherapy* / Q000601:surgery; D002294:Carcinoma, Squamous Cell / Q000473:pathology / Q000532:radiotherapy* / Q000601:surgery; D015331:Cohort Studies; D005260:Female; D005500:Follow-Up Studies; D005629:Frozen Sections; D006801:Humans; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D009361:Neoplasm Invasiveness / Q000473:pathology; D009367:Neoplasm Staging; D009360:Neoplastic Cells, Circulating / Q000473:pathology / Q000528:radiation effects; D017410:Practice Guidelines as Topic; D011446:Prospective Studies; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D018570:Risk Assessment; D012878:Skin Neoplasms / Q000473:pathology* / Q000532:radiotherapy* / Q000601:surgery; D016896:Treatment Outcome; D047368:Tumor Burden / Q000528:radiation effects