A treatment planning method for sequentially combining radiopharmaceutical therapy and external radiation therapy

Int J Radiat Oncol Biol Phys. 2011 Jul 15;80(4):1256-62. doi: 10.1016/j.ijrobp.2010.08.022. Epub 2010 Oct 13.


Purpose: Effective cancer treatment generally requires combination therapy. The combination of external beam therapy (XRT) with radiopharmaceutical therapy (RPT) requires accurate three-dimensional dose calculations to avoid toxicity and evaluate efficacy. We have developed and tested a treatment planning method, using the patient-specific three-dimensional dosimetry package 3D-RD, for sequentially combined RPT/XRT therapy designed to limit toxicity to organs at risk.

Methods and materials: The biologic effective dose (BED) was used to translate voxelized RPT absorbed dose (D(RPT)) values into a normalized total dose (or equivalent 2-Gy-fraction XRT absorbed dose), NTD(RPT) map. The BED was calculated numerically using an algorithmic approach, which enabled a more accurate calculation of BED and NTD(RPT). A treatment plan from the combined Samarium-153 and external beam was designed that would deliver a tumoricidal dose while delivering no more than 50 Gy of NTD(sum) to the spinal cord of a patient with a paraspinal tumor.

Results: The average voxel NTD(RPT) to tumor from RPT was 22.6 Gy (range, 1-85 Gy); the maximum spinal cord voxel NTD(RPT) from RPT was 6.8 Gy. The combined therapy NTD(sum) to tumor was 71.5 Gy (range, 40-135 Gy) for a maximum voxel spinal cord NTD(sum) equal to the maximum tolerated dose of 50 Gy.

Conclusions: A method that enables real-time treatment planning of combined RPT-XRT has been developed. By implementing a more generalized conversion between the dose values from the two modalities and an activity-based treatment of partial volume effects, the reliability of combination therapy treatment planning has been expanded.

Publication types

  • Case Reports
  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Algorithms
  • Combined Modality Therapy / methods
  • Humans
  • Male
  • Organometallic Compounds / therapeutic use*
  • Organophosphorus Compounds / therapeutic use*
  • Organs at Risk / radiation effects
  • Osteosarcoma / radiotherapy*
  • Radiation Injuries / prevention & control
  • Radioisotopes / therapeutic use*
  • Radiotherapy Dosage
  • Radiotherapy Planning, Computer-Assisted / methods*
  • Relative Biological Effectiveness
  • Samarium / therapeutic use*
  • Spinal Cord / radiation effects*
  • Spinal Neoplasms / radiotherapy*
  • Tomography, Emission-Computed, Single-Photon / methods
  • Tomography, X-Ray Computed / methods


  • Organometallic Compounds
  • Organophosphorus Compounds
  • Radioisotopes
  • Samarium
  • samarium Sm-153 lexidronam