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

Robert F. Hobbs, Todd McNutt, Sébastien Baechler, Bin He, Caroline E. Esaias, Eric C. Frey, David M. Loeb, Richard L. Wahl, Ori Shokek, George Sgouros

Research output: Contribution to journalArticlepeer-review

38 Scopus citations


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 (DRPT) values into a normalized total dose (or equivalent 2-Gy-fraction XRT absorbed dose), NTDRPT map. The BED was calculated numerically using an algorithmic approach, which enabled a more accurate calculation of BED and NTDRPT. 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 NTDRPT to tumor from RPT was 22.6 Gy (range, 1-85 Gy); the maximum spinal cord voxel NTDRPT from RPT was 6.8 Gy. The combined therapy NTDsum to tumor was 71.5 Gy (range, 40-135 Gy) for a maximum voxel spinal cord NTDsum 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.

Original languageEnglish (US)
Pages (from-to)1256-1262
Number of pages7
JournalInternational Journal of Radiation Oncology Biology Physics
Issue number4
StatePublished - Jul 15 2011
Externally publishedYes


  • External beam therapy
  • Radiopharmaceutical therapy
  • Three-dimensional dosimetry
  • Treatment planning

ASJC Scopus subject areas

  • Radiation
  • Oncology
  • Radiology Nuclear Medicine and imaging
  • Cancer Research


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