--- a/Framework/Loaders/OrthancSeriesVolumeProgressiveLoader.cpp	Tue Jun 02 12:34:27 2020 +0200
+++ b/Framework/Loaders/OrthancSeriesVolumeProgressiveLoader.cpp	Tue Jun 02 13:16:40 2020 +0200
@@ -322,7 +322,7 @@
       {
         std::unique_ptr<OrthancStone::ILoadersContext::ILock> lock(loadersContext_.Lock());
         boost::shared_ptr<IObserver> observer(GetSharedObserver());
-        lock->Schedule(observer, 0, command.release()); // TODO: priority!
+        lock->Schedule(observer, sliceSchedulingPriority_, command.release());
       }
     }
     else
@@ -479,6 +479,33 @@
     SetSliceContent(GetSliceIndexPayload(message.GetOrigin()), message.GetImage(), quality);
   }
 
+
+  void  OrthancSeriesVolumeProgressiveLoader::SetMetadataSchedulingPriority(int p)
+  {
+    medadataSchedulingPriority_ = p;
+  }
+
+  int   OrthancSeriesVolumeProgressiveLoader::GetMetadataSchedulingPriority() const
+  {
+    return medadataSchedulingPriority_;
+  }
+
+  void  OrthancSeriesVolumeProgressiveLoader::SetSliceSchedulingPriority(int p)
+  {
+    sliceSchedulingPriority_ = p;
+  }
+    
+  int   OrthancSeriesVolumeProgressiveLoader::GetSliceSchedulingPriority() const
+  {
+    return sliceSchedulingPriority_;
+  }
+
+  void  OrthancSeriesVolumeProgressiveLoader::SetSchedulingPriority(int p)
+  {
+    medadataSchedulingPriority_ = p;
+    sliceSchedulingPriority_ = p;
+  }
+
   OrthancSeriesVolumeProgressiveLoader::OrthancSeriesVolumeProgressiveLoader(
     OrthancStone::ILoadersContext& loadersContext,
     boost::shared_ptr<OrthancStone::DicomVolumeImage> volume,
@@ -490,6 +517,8 @@
     , volume_(volume)
     , sorter_(new OrthancStone::BasicFetchingItemsSorter::Factory)
     , volumeImageReadyInHighQuality_(false)
+    , medadataSchedulingPriority_(0)
+    , sliceSchedulingPriority_(0)
   {
   }
 
@@ -560,7 +589,7 @@
       {
         std::unique_ptr<OrthancStone::ILoadersContext::ILock> lock(loadersContext_.Lock());
         boost::shared_ptr<IObserver> observer(GetSharedObserver());
-        lock->Schedule(observer, 0, command.release()); //TODO: priority!
+        lock->Schedule(observer, medadataSchedulingPriority_, command.release());
       }
     }
   }

--- a/Framework/Loaders/OrthancSeriesVolumeProgressiveLoader.h	Tue Jun 02 12:34:27 2020 +0200
+++ b/Framework/Loaders/OrthancSeriesVolumeProgressiveLoader.h	Tue Jun 02 13:16:40 2020 +0200
@@ -131,6 +131,12 @@
     
     boost::shared_ptr<ISlicePostProcessor>  slicePostProcessor_;
 
+    /** See priority setters/getters below */
+    int medadataSchedulingPriority_;
+
+    /** See priority setters/getters below */
+    int sliceSchedulingPriority_;
+
     OrthancSeriesVolumeProgressiveLoader(
       OrthancStone::ILoadersContext& loadersContext,
       boost::shared_ptr<OrthancStone::DicomVolumeImage> volume,
@@ -151,6 +157,28 @@
 
     void SetSimultaneousDownloads(unsigned int count);
 
+    /**
+      Sets the relative priority of the requests for metadata.
+      - if p < PRIORITY_HIGH (-1)                 , the requests will be high priority
+      - if PRIORITY_LOW (100) > p > PRIORITY_HIGH , the requests will be medium priority
+      - if p > PRIORITY_LOW                       , the requests will be low priority
+
+      Default is 0 (medium)
+    */
+    void  SetMetadataSchedulingPriority(int p);
+
+    /** @see SetMetadataSchedulingPriority */
+    int   GetMetadataSchedulingPriority() const;
+
+    /** Same as SetMetadataSchedulingPriority, for slices. Default is 0. */
+    void  SetSliceSchedulingPriority(int p);
+    
+    /** @see SetSliceSchedulingPriority */
+    int   GetSliceSchedulingPriority() const;
+
+    /** Sets priorities for all requests. @see SetMetadataSchedulingPriority */
+    void  SetSchedulingPriority(int p);
+
     void SetDicomSlicePostProcessor(boost::shared_ptr<ISlicePostProcessor> slicePostProcessor)
     {
       // this will delete the previously stored slice processor, if any

--- a/Samples/Common/RtViewerApp.cpp	Tue Jun 02 12:34:27 2020 +0200
+++ b/Samples/Common/RtViewerApp.cpp	Tue Jun 02 13:16:40 2020 +0200
@@ -119,6 +119,10 @@
       // "false" means only using hi quality
       // TODO: add flag for quality
       ctLoader_ = OrthancSeriesVolumeProgressiveLoader::Create(*loadersContext_, ctVolume_, true);
+      
+      // better priority for CT vs dose and struct
+      ctLoader_->SetSchedulingPriority(-100);
+
 
       // we need to store the CT loader to ask from geometry details later on when geometry is loaded
       geometryProvider_ = ctLoader_;