# How to define "Experimantal file slice position" value in the film dosimetry analysis?

**URL:** <https://discourse.slicer.org/t/how-to-define-experimantal-file-slice-position-value-in-the-film-dosimetry-analysis/27993>\
**Category:** Support\
**Created:** [February 22, 2023, 10:30pm UTC](https://discourse.slicer.org/t/how-to-define-experimantal-file-slice-position-value-in-the-film-dosimetry-analysis/27993 "2023-02-22T22:30:32Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![abcxyzooo](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/abcxyzooo/32/18523_2.png) [@abcxyzooo](https://discourse.slicer.org/u/abcxyzooo)\
**Post date:** [February 22, 2023, 10:30pm UTC](https://discourse.slicer.org/t/how-to-define-experimantal-file-slice-position-value-in-the-film-dosimetry-analysis/27993/1 "2023-02-22T22:30:32Z")

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Dear all:  
I am new to the 3D slicer. The purpose of using 3D slicer is to do the gamma analysis using Film Dosimetry Analysis .  
I have created the film calibration curve.  
But I am confused in defining “Experimantal file slice position” in the film dosimetry analysis.  
Here was my exposure setting:  
Total phantom thickness: 10cm, Beam angle: 0, Beam isocenter: depth: 5cm, SAD: 100cm, Field size: 10cm x 10cm, MU: 200.  
I placed the RW3 film in the middle of the phantom(depth 5cm) in the same position of the beam isocenter.

 ![Screenshot 2023-02-22 153505](https://us1.discourse-cdn.com/flex002/uploads/slicer/original/3X/6/9/697bb90b9f8d6957bee3ac0314fd36184fce6447.png)  
So my question is how to define the file slice position? I have tried 173.6 and 19 (the underlined value in the picture). It dosen’t seem to be the correct value.  
Please give me a hint, thanks!