Following institutional review board (IRB) approval, we conducted a retrospective review of 24 patient cases encompassing 29 treatment courses for patients with MCC of multiple body parts, including H&N, lower extremity, upper extremity, and trunk treated in the initial or recurrent setting. From this cohort, 8 received post-operative RT at 2 Gy per fraction, 8 received post-operative RT at 4 Gy per fraction (adjuvant nodal radiation received standard fractionation radiation if indicated), 5 received RT at 2 Gy per fraction and 2 received RT at 4 Gy per fraction (no nodal radiation received for hypofractionated patients) in the definitive setting, and 6 received 8 Gy SFRT in the palliative setting. Some overlap was observed in patients receiving RT in a definitive setting, which were later treated for recurrences. Patients’ respective treatment details and outcomes were analyzed until the most recent follow-up. Pertinent patient characteristics such as age, gender, performance status, prior surgical and systemic therapy history, and tumor-related characteristics, including histology, location, stage, and nodal status, were recorded. In addition, treatment parameters such as target and RT field size, patient outcomes, namely, Radiotherapy Oncology Group (RTOG) acute toxicities, as well as recurrence and survival results, were collected. RT was delivered using one of 3 modalities: 3D photons, electrons, and protons.

The toxicity and cumulative incidence of local and distant failures were estimated, with death as a competing risk. Time to failure, either local or distant, was calculated from the date of RT simulation. Local failures were defined by local or regional tumor growth within treatment field or nodal marginal failures adjacent to the treatment field. Distant failures were defined when a malignancy was identified beyond the regional nodal drainage sites. Upon treatment completion, patients entered on surveillance, consisting of follow-up visits including physical examination and body imaging, approximately two to three months post-treatment completion and prior to each clinic visit per investigator’s discretion. The first 12 months post-treatment follow up clinic visits were every three months, after which patients were seen every three to six months.

Patient’s demographic and clinical characteristics were described using descriptive statistics such as frequencies and percentage for categorical variables and median and range for continuous variable. Patient characteristics were compared between patient all groups and also between adjuvant 2 Gy/fx and adjuvant 4 Gy/fx groups using Chi square or Fishers exact test for categorical variables and Mann-Whitney U or Kruskal-Wallis test for continuous variables. Time to event was also compared between patient groups. Kaplan Meier estimates were used to compare time to event analysis using log rank test. One year survival rates were also calculated using Kaplan Meier estimates. All statistical analysis were done using SAS version 9.4 (ASA Inc, Cary, NC). Statistical significant was set at p < 0.05.