Lua and sequences

Hi,

I use a Lua RetrieveResultConverter to adapt archived RT data from Helax TMS to newer treatment planning without modifying the archived data.
Now I run into a problem in sequences:
Some sequences like '(300a,00b6)-BeamLimitingDeviceSequence' are of unknown length.
I did not succeed with Lua functions like
'bldmax=#Data.ExposureSequence[ex].BeamLimitingDeviceSequence' or
'bldmax=table.getn(Data.ExposureSequence[ex].BeamLimitingDeviceSequence)'
because of type 'userdata'.
To point out the problem I used this Lua function as RetrieveResultConverter for RTIMAGE from our linac

function rrc0()	writedicom(Data,Data.SOPInstanceUID..'-before')	if Data.Modality=='RTIMAGE' then		print('RTImage from',Data.RadiationMachineName)		ex=0		while Data.ExposureSequence		and Data.ExposureSequence[ex]		and Data.ExposureSequence[ex].BeamLimitingDeviceSequence do			print(' Exposure #',ex,' Frame=',Data.ExposureSequence[ex].ReferencedFrameNumber) 			bld=0			while Data.ExposureSequence[ex].BeamLimitingDeviceSequence			and Data.ExposureSequence[ex].BeamLimitingDeviceSequence[bld]			and Data.ExposureSequence[ex].BeamLimitingDeviceSequence[bld].RTBeamLimitingDeviceType do				print(' BeamLimitingDevice #',bld,'=',Data.ExposureSequence[ex].BeamLimitingDeviceSequence[bld].RTBeamLimitingDeviceType)				bld=bld+1			end -- BeamLimitingDeviceSequence			ex=ex+1		end -- ExposureSequence	end	writedicom(Data,Data.SOPInstanceUID..'-after')end

There is no explicit modification of 'Data' in the lua function, but the dump of the dicom file saved at the end of the function shows additional empty sequence elements:

| (3002,0026) : DS   Len: 4      RTImageSID                     Value: [1000]
 | (3002,0030) : SQ   Len: 542    ExposureSequence               Value: [SEQUENCE]
 |  | DATASET
 |  |  | (300A,00B6) : SQ   Len: 504    BeamLimitingDeviceSequence     Value: [SEQUENCE]
 |  |  |  | DATASET
 |  |  |  |  | (300A,00B8) : CS   Len: 4      RTBeamLimitingDeviceType       Value: [MLCX]
 |  |  |  |  | (300A,00BA) : DS   Len: 4      SourceToBeamLimitingDeviceDistance Value: [359 ]
 |  |  |  |  | (300A,00BC) : IS   Len: 2      NumberOfLeafJawPairs           Value: [29]
 |  |  |  |  | (300A,00BE) : DS   Len: 112    LeafPositionBoundaries         Value: [-200\-135\-125\-115\-105\-95\-85\-75\-65\-55\-45\-35\-25\-15\-5\5\15\25\35\45\55\65\75\85\95\105\115\125\135\200...]
 |  |  |  |  | (300A,011C) : DS   Len: 264    LeafJawPositions               Value: [0\0\0\0\0\0\-51\-50.57\-50.57\-50.57\-50.57\-50.57\-50.57\-50.32\-50.32\-50.32\-50.32\-50.32\-50.32\-50.32\-50.08\-50.08\-50.08\0\0\0\0\0\0\0\0\0\0\0\0\56.6\55.71\54.83\53.94\53.06\52.18\51.29\50.41\50.01\50.01\50.01\50.01\50.01\50.01\50.01\50.01\50.01\0\0\0\0\0\0...]
 |  |  |  | END-OF-DATASET
 |  |  |  | DATASET
 |  |  |  |  | (300A,00B8) : CS   Len: 6      RTBeamLimitingDeviceType       Value: [ASYMY ]
 |  |  |  |  | (300A,00BA) : DS   Len: 4      SourceToBeamLimitingDeviceDistance Value: [271 ]
 |  |  |  |  | (300A,00BC) : IS   Len: 2      NumberOfLeafJawPairs           Value: [1 ]
 |  |  |  |  | (300A,011C) : DS   Len: 10     LeafJawPositions               Value: [-82\80.07 ]
 |  |  |  | END-OF-DATASET
 |  |  |  | DATASET
 |  |  |  | END-OF-DATASET
 |  |  | (300A,00F0) : IS   Len: 2      NumberOfBlocks                 Value: [0 ]
 |  | END-OF-DATASET
  |  | DATASET
 |  | END-OF-DATASET
 | (300A,00B3) : CS   Len: 2      PrimaryDosimeterUnit           Value: [MU]

If the receiving system is another conquest, I can't see these empty elements in the header dump of the gui, but they are sent over the network and Masterplan chokes on RTPLANs containing such sequence elements reporting parsing errors.
Access to the not existing 'Data.ExposureSequence[1]' in line 7 of the function doesn't give result 'nil' but generates an empty sequence element as I further tested. It is not possible to destroy the empty element after the loop by 'Data.ExposureSequence[ex]=nil' after line 18.

What is the recomended way to parse sequences without this result?

Gerald

Hi Marcel,

probably it's not the right syntax I used.
I tried
print(Data['ExposureSequence']) -> userdata:... may be, this really exists
print(Data['ExposureSequence.0.BeamLimitingDeviceSequence.0.RTBeamLimitingDeviceType']) -> userdata:... I expected 'MLCX' in the example above
print(Data['ExposureSequence.1']) -> userdata:... this sequence element doesn't exist, I expected 'nil'
print(Data['ExposureSequence.5.BeamLimitingDeviceSequence']) -> userdata:...

There are no more empty sequence elements in Data but also no information about existing and non-existing elements.
Please correct me.

Gerald

Hi,

thank you, this way it works.

Gerald