Analyzing data in SPSS using ROC Curve with categorical variables

I have DataSet with the following data:
Case#       Dosage     Result
1               DosagA      healthy
2               DosagA     sick
3               DosagB      sick
4               DosageC    healthy
Dosage is 5 categories.

To analyse Using ROC, I encoded Result as: Healty =1, sick =0

Case# Dosage  Result
1       DosagA  1
2       DosagA  0
2       DosagB  0
4       DosageC 1
When trying to build ROC in SPSS with: Test Variable= result, State variable= Dosage, I get the error message:
String Variable are not allowed in the list
Do I have to Encode Dosage with numeric values?
What is the best solution for ROC Curve using categorical variables?