A treatment planning method for sequentially combining radiopharmaceutical therapy and external radiation therapy.
OBJECTIVE
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
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.
Hobbs
Robert F
RF
Johns Hopkins University, Baltimore, MD 21231, USA.
McNutt
Todd
T
Baechler
Sébastien
S
He
Bin
B
Esaias
Caroline E
CE
Frey
Eric C
EC
Loeb
David M
DM
Wahl
Richard L
RL
Shokek
Ori
O
Sgouros
George
G
D000328:Adult; D000465:Algorithms; D003131:Combined Modality Therapy / Q000379:methods; D006801:Humans; D008297:Male; D009942:Organometallic Compounds / Q000627:therapeutic use*; D009943:Organophosphorus Compounds / Q000627:therapeutic use*; D058958:Organs at Risk / Q000528:radiation effects; D012516:Osteosarcoma / Q000532:radiotherapy*; D011832:Radiation Injuries / Q000517:prevention & control; D011868:Radioisotopes / Q000627:therapeutic use*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012062:Relative Biological Effectiveness; D012493:Samarium / Q000627:therapeutic use*; D013116:Spinal Cord / Q000528:radiation effects*; D013125:Spinal Neoplasms / Q000532:radiotherapy*; D015899:Tomography, Emission-Computed, Single-Photon / Q000379:methods; D014057:Tomography, X-Ray Computed / Q000379:methods
D009942:Organometallic Compounds; D009943:Organophosphorus Compounds; D011868:Radioisotopes; D012493:Samarium; C061972:samarium Sm-153 lexidronam