Add shorthand function to merge two pre-existing RTStruct structure s…

…ets (#70)

✨ Add class to merge two pre-existing RTStruct structure sets

rt_utils/__init__.py

@@ -1,2 +1,3 @@
 from .rtstruct import RTStruct
 from .rtstruct_builder import RTStructBuilder
+from .rtstruct_merger import RTStructMerger

rt_utils/rtstruct_merger.py

@@ -0,0 +1,33 @@
+from .rtstruct import RTStruct
+from .rtstruct_builder import RTStructBuilder
+from . import ds_helper, image_helper
+
+class RTStructMerger:
+
+
+    @staticmethod
+    def merge_rtstructs(dicom_series_path: str, rt_struct_path1: str, 
+        rt_struct_path2: str) -> RTStruct:
+        """
+        Method to merge two existing RTStruct files belonging to same series data, returning them as one RTStruct
+        """
+
+        rtstruct1 = RTStructBuilder.create_from(dicom_series_path, rt_struct_path1)
+        rtstruct2 = RTStructBuilder.create_from(dicom_series_path, rt_struct_path2)
+
+        for roi_contour_seq, struct_set_roi_seq, rt_roi_observation_seq in zip(rtstruct1.ds.ROIContourSequence, rtstruct1.ds.StructureSetROISequence, rtstruct1.ds.RTROIObservationsSequence):
+            roi_number = len(rtstruct2.ds.StructureSetROISequence) + 1
+            roi_contour_seq.ReferencedROINumber = roi_number
+            struct_set_roi_seq.ROINumber = roi_number
+            rt_roi_observation_seq.ReferencedROINumber = roi_number
+
+            # check for ROI name duplication
+            for struct_set_roi_seq2 in rtstruct2.ds.StructureSetROISequence:
+                if struct_set_roi_seq.ROIName == struct_set_roi_seq2.ROIName:
+                    struct_set_roi_seq += "_2"
+
+            rtstruct2.ds.ROIContourSequence.append(roi_contour_seq)
+            rtstruct2.ds.StructureSetROISequence.append(struct_set_roi_seq)
+            rtstruct2.ds.RTROIObservationsSequence.append(rt_roi_observation_seq)
+
+        return rtstruct2