Non melanoma skin cancer Recommendations for CTV margins in radiotherapy planning for non melanoma skin cancer Luluel Khan a , Richard Choo b , Dale Breen a , Dalal Assaad a , Jefferey Fialkov a , Oleh Antonyshyn a , David McKenzie a , Tony Woo a , Liying Zhang a , Elizabeth Barnes a,⇑ a University of Toronto, Ontario, Canada; b Mayo Clinic, Rochester, MN, USA article info Article history: Received 29 November 2011 Received in revised form 4 June 2012 Accepted 13 June 2012 Available online 31 July 2012 Keywords: Non melanoma Radiotherapy CTV Guidelines Margins abstract Purpose: To provide practice guidelines for delineating clinical target volume (CTV) for radiotherapy planning of non melanoma (NMSC) skin cancers. Methods and materials: 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 microscop- ically 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 sec- tion assisted assessment of resection margins, were accrued. The distance of microscopic tumor exten- sion beyond a gross lesion varied from 1 mm to 15 mm, with a mean of 5.3 mm. 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; 10 mm 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. Ó 2012 Elsevier Ireland Ltd. All rights reserved. Radiotherapy and Oncology 104 (2012) 263–266 Non melanoma skin cancer (NMSC) is the most common malig- nancy worldwide [1]. Surgical excision is often the primary treat- ment for malignant skin tumors but may be accompanied with cosmetic or functional deficits due to tumor size or location. In such cases, radiotherapy (RT) constitutes an effective alternative [2]. Radiotherapy outcome is dependent on whether the micro- scopic tumor extension, the clinical target volume (CTV), is ade- quately covered in the treatment volume. Too stringent a margin can lead to inadequate tumor coverage and local failure, whereas too generous a margin will increase the amount of normal tissue treated and can unnecessarily increase morbidity, depending on location. Though delineating the CTV can be challenging as little data are available, some studies have shown good outcomes using CTV from GTV (gross tumor volume) expansions of 5 mm to 1 cm in relatively large patient cohorts [3,4]. After preliminary analyses [5], a margin of 10 mm was required to provide a 95% chance of obtaining clear resection margins. The microscopic tumor extent was positively correlated with the size of the gross lesion, but not with other variables such as histology or the number of surgical attempts required to obtain clear resec- tion margins, although there was a trend toward significance. It was thought that the lack of statistical significance was due to the sample size. Now at study completion, with over double the sample, we attempt to provide guidelines for CTV margin delinea- tion for specific tumor sizes and subtypes of NMSC. Methods and materials The non melanoma skin cancer (NMSC) clinic at the Odette Can- cer Center is a multidisciplinary clinic and includes a radiation oncologist, plastic surgeon and dermatologist also board certified in pathology [6]. Surgical excision with histologic assessment of resection margins based on frozen section is usually reserved for high risk lesions, such as: those with poorly defined clinical bor- ders, diameters larger than 2 cm, histopathologic features showing 0167-8140/$ - see front matter Ó 2012 Elsevier Ireland Ltd. All rights reserved. http://dx.doi.org/10.1016/j.radonc.2012.06.013 ⇑ Corresponding author. Address: Department of Radiation Oncology, Odette Cancer Centre, Sunnybrook Health Sciences Centre, 2075 Bayview Avenue, Toronto, Ontario, Canada M4N 3M5. E-mail address: toni.barnes@sunnybrook.ca (E. Barnes). Radiotherapy and Oncology 104 (2012) 263–266 Contents lists available at SciVerse ScienceDirect Radiotherapy and Oncology journal homepage: www.thegreenjournal.com