kindly support with this dropna function not working

[gheevarpaulosejobs]

file_name = "C:/Users/Gheevar/Documents/PYTHON CLASS/home study/PRACTICE WORK BOOK.xlsx"
sheet = "Sheet1"  ###Sheet name

import pandas as pd   ##pandas
df = pd.read_excel(io=file_name, sheet_name=sheet)

df['SPECIALITY'] = df['SPECIALITY'].str.lower()   ##convering specality to lower case
pd.set_option('display.max_columns', None)        ##to display all columns below
pd.set_option('display.max_rows', None)

df.replace({"SPECIALITY":["pediatric trauma","trauma surgery","ortho_trauma"]}, "trauma")

df.dropna(subset = ['DOCUMENTED'], inplace=True)

df.pivot(index= 'DOCUMENTED', columns='SPECIALITY', values="PT URN")