Question about strange data in RTDose dicom file exportet from Monaco (Elekta)

[PiotrLesniak86]

Hello everyone!

I have created simple plan in Monaco (SSD=90 cm, FS= 10x10 cm, 100MU, CT scan of 50x50x50 model of water phantom with uniform density). After that I have exported RTDose file and used it to generete plot of each slice using this code:

import pydicom as pd
import numpy as np
from matplotlib import pyplot as plt 
dcm = pd.dcmread("50x50x50_Test1_Dose_RxA_Bm12.dcm", force = True)

dcm.file_meta.TransferSyntaxUID = pd.uid.ImplicitVRLittleEndian 
for i in range(167):
    plt.imshow(dcm.pixel_array[i])
    plt.show()

The plot from the middle looks ok

But a few slices on the begin look like this:

Have you got any idea what is that?

Thank you in advance for your help!

[darcymason]

Is it possible this is through the beam penumbra? And perhaps the graph auto-scales the colors depending on the maximum intensity. Might help to look at some absolute values in each slice.

[darcymason]

Just re-read the original post, with 10x10 it does sound like this would be penumbra (edit, likely outside penumbra, in low dose region). I believe Monaco stores the dose for a certain distance outside the beam edge, and the calc is noisy in low dose regions.

[PiotrLesniak86]

And perhaps the graph auto-scales the colors depending on the maximum intensity.

It's looks like you are right!

I changed my code - set intensity scale :

max = dcm.pixel_array.max()
min = dcm.pixel_array.min()
plt.imshow(dcm.pixel_array[i], vmin=min, vmax=max, cmap='jet', aspect='auto')

and a few first slices look like this

Slice from the middle:

Thank you!