Impact of consensus guidelines on delineation of primary tumor clinical target volume (CTVp) for head and neck cancer: Results of a national review project.

Background And Purpose: A significant interobserver variability (IOV) for clinical target volume of the primary tumor (CTVp) delineation was shown in a previous national review project. Since then, international expert consensus guidelines (CG) for the delineation of CTVp were published. The aim of this follow-up study was to 1) objectify the extent of implementation of the CG, 2) assess its impact on delineation quality and consistency, 3) identify any remaining ambiguities.

Materials And Methods: All Belgian RT departments were invited to complete an online survey and submit CTVp for 5 reference cases. Organs at risk and GTV of the primary tumor were predefined. Margins, volumes, IOV between all participating centers (IOV) and IOV compared to a reference consensus delineation (IOV) were calculated and compared to the previous analysis. A qualitative analysis was performed assessing the correct interpretation of the CG for each case.

Results: 17 RT centers completed both survey and delineations, of which 88% had implemented CG. Median DSC for CTVp_total was 0.80-0.92. IOV and IOV improved significantly for the centers following CG (p = 0.005). IOV for CTVp_high was small with a DSC higher than 0.90 for all cases. A significant volume decrease for the CTVp receiving 70 Gy was observed. Interpretation of CG was more accurate for (supra)glottic carcinoma. 60% of the radiation oncologists thinks clarification of CG is indicated.

Conclusion: Implementation of consensus guidelines for CTVp delineation is already fairly advanced on a national level, resulting in significantly increased delineation uniformity. The accompanying substantial decrease of CTV receiving high dose RT calls for caution and correct interpretation of CG. Clarification of the existing guidelines seems appropriate especially for oropharyngeal and hypopharyngeal carcinoma.