Uncertainties in the choice of dose and elective volumes during postoperative radiotherapy for cutaneous squamous cell carcinoma with perineural invasion.

Abstract

Introduction: Post operative radiotherapy (PORT) for resected cutaneous squamous cell carcinoma (CSCC) with perineural invasion (PNI) is controversial. Therefore, we conducted a survey to study the patterns of practice and determine whether there is a consensus among Radiation Oncologists (ROs) regarding prescribed dose to the post-operative bed and elective treatment of lymph nodal regions and neural pathways. We also compared the recommendations of the ROs with the 2010 NCCN guidelines.

Materials & Methods: In March 2011, we contacted all ROs and trainees residing in the USA through their email address listed in the 2009 ASTRO membership directory. Our survey contained clinical vignettes involving Mohs micrographically resected CSCC with microscopic PNI (mPNI) or clinical (symptomatic or radiographic) cPNI, including named nerve PNI (nPNI). For each vignette, physicians indicated if PORT was appropriate and further specified the dose and volume to treat at standard fractionation. Chemotherapy was not allowed. Responses were stratified according to years of post residency experience, special interest in treating head and neck cancers and number of cases treated per year. We defined consensus as 80% concordance.

Results: Three hundred and fifty two responses were completed and analyzed. Approximately 95% recommended PORT for cPNI whereas a mean of 59% recommended PORT for mPNI. There was no consensus regarding dose to the operative bed. Approximately 30% of respondents prescribed 54 Gy or less at standard fractionation, while the NCCN guidelines recommend 60 Gy in 30 fractions. Only 24% were willing to prescribe 66Gy or more in cases of radiographically identified gross residual disease. In cases of mPNI, there was a consensus not to treat elective nodal volumes; on average only 14% treated elective nodal regions. Even in the presence of cPNI, only 40% recommended elective nodal irradiation (ENI). ROs with over ten years’ experience were more willing to offer ENI for cPNI than less experienced ROs (43% vs. 25% p=0.004). For mPNI, there was no consensus for elective neural pathway irradiation (ENP); whereas for cPNI a clear consensus emerged with over 90% recommending ENP. The NCCN guidelines do not have specific recommendations for ENI or ENP. Stratification based on years of post residency experience (<10 vs. 10+ yrs), number of cases treated per year (0-7 vs. 8+ cases per year) and special interest in treating head and neck cancers did not yield any other statistically significant differences.

Conclusions: Our data from 2011 demonstrates a lack of consensus among ROs regarding radiation dose to the post-operative bed and designation of elective targets (i.e. nodal regions and neural pathways) for resected CSCC with PNI. In contrast to the NCCN guidelines, nearly 30% of ROs under-dosed the post-operative bed. Majority of ROs omitted elective nodal irradiation even in cases of cPNI. While there was a consensus to treat ENP for cPNI, there was wide variability for treating ENP for mPNI. Since this survey was conducted, several guidelines have been published to educate radiation oncologists regarding electively targeting the neural pathways. Updated More data to evaluate the impact of these guidelines is needed in this setting to guide ROs and achieve homogenous practice patterns.