Merkel cell carcinomaPlanning study for Merkel cell carcinoma based on the relapse pattern

PurposeTo develop a technique for radiation (RT) of in-transit path ways (IT) in Merkel cell carcinoma.MethodIn the planning study, IT were ink-marked on the skin during sentinel lymphscintigraphy and wire-marked in planning-CT. Pre- and post-operative planning-CTs were acquired. The clinical target volume (CTV) included tumor bed plus safety margin, IT and draining nodes, the planning volume (PTV) the CTV plus 0.5-1 cm margin. VMAT plans with 2-3 arcs were analyzed.ResultsA planning study was performed for five pts. including two pts. with primary tumor (PT) in head and neck, 1 pt. each with PT of elbow, forearm and upper leg respectively. Plans showed satisfactory PTV coverage: Dmean 100% ± 0%, D98% 92.4% ± 2.24%, homogeneity index (HI) 0.095 ± 0.01, conformation number (CN) 0.84 ± 0.01 and conformality index (CI) 0.95 ± 0.01.ConclusionThe planning study confirms feasibility of highly conformal irradiation of IT pathways based on individualized target delineation. Currently, patients referred for non-metastatic MCC are encouraged to enroll in a prospective clinical study that evaluates the feasibility of radiation of IT pathways.