Downloading data with s5cmd
s5cmd is a very fast S3 and local filesystem execution tool, which, as experiments showed, is significantly faster than the Google-provided gsutil.
Unlike gsutil, s5cmd does not currently verify file checksum on download (although, this feature appears to be added to the v2.1.0 milestone). See related discussion in https://github.com/peak/s5cmd/issues/398. If you need help verifying checksum of the downloaded files, please post a question on IDC forum.

Prerequisites

Here is the s5cmd help article that describes how to use it with Google Cloud Storage: https://github.com/peak/s5cmd#google-cloud-storage-support. In the following we summarize the steps as they apply to IDC.
Install s5cmd following the instructions in https://github.com/peak/s5cmd#installation.
Set up the HMAC key following this procedure.
Create a file ~/.aws/credentials with the following content:
[default]
aws_access_key_id=<your HMAC key>
aws_secret_access_key=<your HMAC key secret>
If you want to use s5cmd from a Colab notebook, it might be handy to save the credentials file to the .aws folder in Google Drive, which you can mount to the Colab notebook and copy your credentials in place. See details on using Google Drive with Colab in the IDC Colab cookbook notebook.
You can verify if your setup was successful by running the following command: it should successfully download one file from IDC using s5cmd.
s5cmd --endpoint-url https://storage.googleapis.com cp s3://public-datasets-idc/eae91afc-1977-4728-9d6a-06f782c696d4.dcm .
If the command above completes successfully, you can proceed with download in 2 steps, as before, but with slight modifications.

Step 1: Generate s5cmd compatible manifest

s5cmd manifest should contain the list of command copying individual files from your list that should have the following format (note the s3 URL prefix!):
cp s3://<bucket>/<file1> .
cp s3://<bucket>/<file1> .
You can generate such manifest by just slightly modifying the query for preparing the manifest as described in Downloading data:
SELECT CONCAT("cp ",REPLACE(gcs_url, "gs://", "s3://"), " .")
FROM bigquery-public-data.idc_current.dicom_all
WHERE SeriesInstanceUID = "1.3.6.1.4.1.32722.99.99.298991776521342375010861296712563382046"
Save the query defining the manifest into a file named s5cmd_query.txt, and run the query to save the manifest into a file s5cmd_manifest.txt:
bq query --use_legacy_sql=false --format=csv --max_rows=20000000
< s5cmd_query.txt > s5cmd_manifest.txt

Step 2: Download the files specified in the manifest

The following command will download the files specified in s5cmd_manifest.txt to the current directory:
s5cmd --endpoint-url https://storage.googleapis.com run s5cmd_manifest.txt