dd command create iso9660

Hi
Env Debian 9.9
using my script to create usb bootable pen from gparted live iso
i downloaded last amd64 version
my script use

dd bs=4M if=$input_file of=$usb_dev status=progress oflag=sync

it run error free ...
but i'm unable to boot ...
infact
lsblk -f gparted.iso reports iso9660 filesystem
dd process overrides any filesystem i create on the pen

here file descriptiom
fdisk -l gparted.iso
Disk gparted.iso: 355 MiB, 372244480 bytes, 727040 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x1b0f7507

Device Boot Start End Sectors Size Id Type
gparted.iso1 * 64 727039 726976 355M 17 Hidden HPFS/NTFS

any help will be appreciated
Maurizio