LAUSR

Simple Summary The lymph node clinical target volume (CTV_LN) contour in total marrow and lymph node irradiation (TMLI) is extremely complex and time-consuming, involving the delineation of numerous lymph node chains. Furthermore, as few patients per year are usually treated, inter- and intraobserver variability pose a difficult challenge in CTV_LN definition. Currently, there is no globally accepted consensus on lymph node chain delineation for TMLI. In this study, we evaluated the impact of the introduction of internal guidelines for the lymph node contouring process in TMLI treatments. Both topological and dosimetric analyses were performed. Guidelines allowed for the reduction of variability in inter- and intra-CTV_LN delineation. Abstract Background: The total marrow and lymph node irradiation (TMLI) target includes the bones, spleen, and lymph node chains, with the latter being the most challenging structures to contour. We evaluated the impact of introducing internal contour guidelines to reduce the inter- and intraobserver lymph node delineation variability in TMLI treatments. Methods: A total of 10 patients were randomly selected from our database of 104 TMLI patients so as to evaluate the guidelines’ efficacy. The lymph node clinical target volume (CTV_LN) was recontoured according to the guidelines (CTV_LN_GL_RO1) and compared to the historical guidelines (CTV_LN_Old). Both topological (i.e., Dice similarity coefficient (DSC)) and dosimetric (i.e., V95 (the volume receiving 95% of the prescription dose) metrics were calculated for all paired contours. Results: The mean DSCs were 0.82 ± 0.09, 0.97 ± 0.01, and 0.98 ± 0.02, respectively, for CTV_LN_Old vs. CTV_LN_GL_RO1, and between the inter- and intraobserver contours following the guidelines. Correspondingly, the mean CTV_LN-V95 dose differences were 4.8 ± 4.7%, 0.03 ± 0.5%, and 0.1 ± 0.1%. Conclusions: The guidelines reduced the CTV_LN contour variability. The high target coverage agreement revealed that historical CTV-to-planning-target-volume margins were safe, even if a relatively low DSC was observed.