pydicomRT

pydicomRT is a Python library for handling Radiation Therapy DICOM files. It provides utilities to create, modify, parse, and validate RTSTRUCT datasets; convert between RTSTRUCT and volumetric masks; and handle spatial/deformable registration and dose. It integrates smoothly with pydicom, numpy, and SimpleITK.

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Project Goals

• Lower the development barrier for RT applications
  Provide intuitive APIs and tools that allow researchers and engineers to work with radiation therapy–related DICOM files more easily, without requiring deep knowledge of the complex DICOM standard.

• Enable seamless integration between Python 3D libraries and pydicom
  Build a robust bridge so that common Python 3D image processing libraries (e.g., numpy, SimpleITK) can work seamlessly with pydicom, accelerating medical imaging and radiotherapy application development.

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Features

• Build RTSTRUCT datasets and manage Regions of Interest (ROIs)
• Convert between 3D numpy masks and DICOM contours
• Validate RTSTRUCT, Spatial REG, Deformable REG, and RTDOSE datasets
• Load and sort DICOM image series with orientation/spacing sanity checks
• Generate RTDOSE datasets and convert RTDOSE DICOM files to SimpleITK images
• Export Spatial (REG) and Deformable Spatial (REG-DR) registrations from SimpleITK transforms
• Parse deformable registration grids into NumPy displacement fields
• SimpleITK helpers for image building, resampling, and registration (rigid, demons, bspline, soft_demons)
• Coordinate transformation utilities between pixel and patient spaces
• CT modality IOD helpers

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Quick Links

• Examples: example/try_demon_reg.py, example/try_sort_dcms.py
• Deformable REG builder demo: test/reg/df_reg_build_test.py
• RTSTRUCT API: src/pydicomrt/rs
• Registration API: src/pydicomrt/reg
• Utilities: src/pydicomrt/utils
• Architecture Doc: docs/architecture.md

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Installation

Dependencies

• Python >= 3.8
• pydicom >= 2.0.0
• numpy >= 1.26.4
• opencv-python >= 4.10.0
• scipy >= 1.10.3
• simpleitk >= 2.5.0

Install via pip

pip install pydicomrt

Install from source

git clone https://github.com/higumalu/pydicomRT.git
cd pydicomRT
pip install .

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Usage Examples

Create an RTSTRUCT Dataset and Add ROI

import numpy as np
from pydicomrt.rs.make_contour_sequence import add_contour_sequence_from_mask3d
from pydicomrt.rs.add_new_roi import create_roi_into_rs_ds
from pydicomrt.rs.builder import create_rtstruct_dataset
from pydicomrt.utils.image_series_loader import load_sorted_image_series

# Load DICOM image series
ds_list = load_sorted_image_series("path/to/dicom/images")

# Create an empty RTSTRUCT dataset
rs_ds = create_rtstruct_dataset(ds_list)

# Create an ROI (Region of Interest)
rs_ds = create_roi_into_rs_ds(rs_ds, [0, 255, 0], 1, "CTV", "CTV")

# Create a 3D mask
mask = np.zeros((len(ds_list), 512, 512))
mask[100:200, 100:400, 100:400] = 1
mask[120:180, 200:300, 200:300] = 0

# Add 3D mask to RTSTRUCT dataset
rs_ds = add_contour_sequence_from_mask3d(rs_ds, ds_list, 1, mask)

# Save the RTSTRUCT dataset
rs_ds.save_as("path/to/output.dcm", write_like_original=False)

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Spatial Registration (Rigid) and DICOM REG Export

This example estimates a rigid transform between two CT series using SimpleITK and stores it in a DICOM Spatial Registration (REG) object.

import numpy as np
import SimpleITK as sitk
from pydicomrt.utils.image_series_loader import load_sorted_image_series
from pydicomrt.utils.sitk_transform import SimpleITKImageBuilder
from pydicomrt.reg.method.rigid import rigid_registration
from pydicomrt.reg.type_transform import affine_to_homogeneous_matrix
from pydicomrt.reg.builder import SpatialRegistrationBuilder

# Load CT series as pydicom datasets
fixed_ds = load_sorted_image_series("/path/to/CT_fixed")
moving_ds = load_sorted_image_series("/path/to/CT_moving")

# Convert to SimpleITK images
fixed_img = SimpleITKImageBuilder().from_ds_list(fixed_ds)
moving_img = SimpleITKImageBuilder().from_ds_list(moving_ds)

# Run rigid registration in physical space (returns sitk.Transform)
rigid_tfm = rigid_registration(fixed_img, moving_img)

# Convert to 4x4 row-major list for DICOM REG
tfm_4x4 = affine_to_homogeneous_matrix(rigid_tfm).astype(np.float32).ravel().tolist()

# Build a DICOM Spatial Registration dataset and save
builder = SpatialRegistrationBuilder(fixed_ds)
builder.set_uid_prefix("1.2.826.0.1.3680043.2.1125.")  # Optional but helps keep UIDs consistent
builder.add_rigid_registration(moving_ds, tfm_4x4)
reg_ds = builder.build()
reg_ds.save_as("/path/to/output_reg.dcm", write_like_original=False)

Notes:

• DICOM stores transforms as a 4x4 row-major matrix in the fixed image frame. Ensure transform directions match your use-case.
• You can set a custom UID root globally via the DICOM_UID_PREFIX environment variable.

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Deformable Spatial Registration (Demons) Export

This workflow performs a rigid pre-align, runs demons registration, and exports the resulting displacement field into a DICOM Deformable Spatial Registration dataset.

import numpy as np
import SimpleITK as sitk
from pydicomrt.utils.image_series_loader import load_sorted_image_series
from pydicomrt.utils.sitk_transform import SimpleITKImageBuilder, resample_to_reference_image
from pydicomrt.reg.method.rigid import rigid_registration
from pydicomrt.reg.method.demons import demons_registration
from pydicomrt.reg.type_transform import affine_to_homogeneous_matrix
from pydicomrt.reg.builder import DeformableSpatialRegistrationBuilder

fixed_ds = load_sorted_image_series("/path/to/CT_fixed")
moving_ds = load_sorted_image_series("/path/to/CT_moving")
fixed_img = SimpleITKImageBuilder().from_ds_list(fixed_ds)
moving_img = SimpleITKImageBuilder().from_ds_list(moving_ds)

# Ensure voxel grids match before registration
moving_img = resample_to_reference_image(fixed_img, moving_img)

# Rigid pre-alignment
rigid_tfm = rigid_registration(fixed_img, moving_img)
rigid_matrix = affine_to_homogeneous_matrix(rigid_tfm).astype(np.float32).ravel().tolist()
moving_rigid = sitk.Resample(
    moving_img,
    fixed_img,
    rigid_tfm,
    sitk.sitkLinear,
    -1000.0,
    moving_img.GetPixelIDValue(),
)

# Demons deformable registration (returns registered image, transform, displacement field)
reg_img, deform_tfm, dvf = demons_registration(fixed_img, moving_rigid, verbose=False)

# Export to DICOM Deformable Spatial Registration
identity = np.eye(4, dtype=np.float32).ravel().tolist()

builder = DeformableSpatialRegistrationBuilder(fixed_ds)
builder.add_deformable_registration(
    moving_ds_list=moving_ds,
    vectorial_field_transform=deform_tfm,
    pre_transform=rigid_matrix,
    post_transform=identity,
)
reg_dr = builder.build()
reg_dr.save_as("/path/to/output_dr.dcm", write_like_original=False)

demons_registration returns a SimpleITK displacement-field transform (deform_tfm) and a DVF image (dvf). The builder converts the transform into the DICOM VectorGridData representation automatically.

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Parse a Deformable Registration Dataset

from pydicom import dcmread
from pydicomrt.reg.parser import get_deformable_reg_list

reg_ds = dcmread("/path/to/output_dr.dcm")
reg_entries = get_deformable_reg_list(reg_ds)
field = reg_entries[0]["DeformableRegistrationGrid"]["VectorGridData"]
print(field.shape)  # (z, y, x, 3) float32 displacement vectors in mm

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Create an RTDOSE Dataset from a SimpleITK Image

import SimpleITK as sitk
from pydicom import dcmread
from pydicomrt.dose.builder import generate_base_dataset, cp_information_from_ds, add_dose_grid_to_ds

reference = dcmread("path/to/reference_ct_or_plan.dcm")
dose_img = sitk.ReadImage("path/to/dose_image.nii.gz")

dose_ds = generate_base_dataset()
dose_ds = cp_information_from_ds(dose_ds, reference)
dose_ds = add_dose_grid_to_ds(dose_ds, dose_img)

dose_ds.save_as("path/to/output_dose.dcm", write_like_original=False)

To convert an RTDOSE DICOM dataset back to SimpleITK, use pydicomrt.dose.sitk_transform.get_dose_sitk_image.

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Extract Contour Information from RTSTRUCT Dataset

from pydicomrt.rs.parser import get_roi_number_to_name, get_contour_dict

# Get ROI mapping
roi_map = get_roi_number_to_name(rs_ds)
print(roi_map)  # Output: {1: 'CTV'}

# Get contour dictionary
ctr_dict = get_contour_dict(rs_ds)

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Validate RTSTRUCT Dataset

from pydicomrt.rs.checker import check_rs_iod

# Check whether the RTSTRUCT dataset conforms to IOD specification
result = check_rs_iod(rs_ds)
print(result)  # Output: {'result': True, 'content': []}

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Convert RTSTRUCT to 3D Mask

from pydicomrt.rs.rs_to_volume import rtstruct_to_mask_dict, calc_image_series_affine_mapping
from pydicomrt.utils.image_series_loader import load_sorted_image_series

# Load DICOM image series
ds_list = load_sorted_image_series("path/to/dicom/images")

# Calculate affine mapping and mask volume shape
affine_mapping, mask_volume_shape = calc_image_series_affine_mapping(ds_list)

# Convert RTSTRUCT to 3D mask dictionary
mask_dict = rtstruct_to_mask_dict(rs_ds, affine_mapping, mask_volume_shape)

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Module Structure

• rs: RTSTRUCT-related functionalities

  • builder: Create RTSTRUCT datasets
  • add_new_roi: Add new ROIs
  • make_contour_sequence: Create contour sequences
  • parser: Parse RTSTRUCT datasets
  • checker: Validate RTSTRUCT datasets
  • rs_to_volume: Convert between RTSTRUCT and volume data
  • packer: Pack contour data
  • contour_process_method: Contour processing methods
  • rs_ds_iod: RTSTRUCT IOD definitions

• reg: Spatial/deformable registration

  • builder: Build DICOM REG / Deformable REG datasets
  • parser: Extract spatial/deformable transforms (e.g., get_deformable_reg_list)
  • check: Validate registration datasets
  • method: SimpleITK registration helpers (rigid, bspline, demons, soft_demons)
  • ds_reg_ds_iod: Deformable spatial registration IOD definitions
  • s_reg_ds_iod: Spatial registration IOD definitions
  • type_transform: Transform conversions (affine → homogeneous, displacement fields → DICOM grids)

• dose: Dose distribution functionalities

  • builder: Create dose datasets
  • sitk_transform: Convert dose datasets to SimpleITK images
  • dose_ds_iod: Dose IOD definitions

• ct: CT image data functionalities

  • ct_ds_iod: CT IOD definitions

• utils: Utility tools

  • image_series_loader: Load and sort DICOM image series
  • coordinate_transform: Coordinate transformation utilities
  • validate_dcm_info: Validate DICOM metadata
  • sitk_transform: SimpleITK conversions, SimpleITKImageBuilder, and resampling helpers
  • rs_from_altas: Build RTSTRUCT datasets from atlas inputs

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Contributing

Issues and pull requests are welcome!

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Reference

• SimpleITK
• pydicom
• RT-Utils
• PlatiPy

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License

This project is licensed under the MIT License - see the LICENSE file for details.

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Author

• Higumalu (higuma.lu@gmail.com)