MRI-assisted radiosurgery: A quality assurance nomogram for palladium-103 and iodine-125 prostate brachytherapy

Brachytherapy. 2020 Jan-Feb;19(1):38-42. doi: 10.1016/j.brachy.2019.10.002. Epub 2019 Dec 4.


Purpose: We sought to develop an activity nomogram for magnetic resonance (MR)-planned permanent seed prostate brachytherapy to improve quality assurance through a secondary dosimetric check.

Methods and materials: Patients undergoing MRI-assisted radiosurgery (MARS), whereby MRI is used for preoperative planning and postimplant dosimetry, were reviewed from May 2016 to September 2018. Planned activity (U) was fitted by MR-prostate volume (cc) via simple linear regression. Resulting monotherapy nomograms were compared with institutional nomograms from an ultrasound-planned cohort. Dosimetric coverage and external urinary sphincter (EUS) dose were also assessed for MR-planned patients.

Results: We identified 183 patients treated with MARS: 146 patients received palladium-103 (103Pd; 102 monotherapy and 44 boost), and 37 received iodine-125 (125I) monotherapy. Median prostate volume was 28 cc (interquartile range: 22-35). Lines of best fit for implant activity were U = 4.344 × (vol) + 54.13 (R2: 95%) for 103Pd monotherapy, U = 3.202 (vol) + 39.72 (R2: 96%) for 103Pd boost and U = 0.684 (vol) + 13.38 (R2: 96%) for 125I monotherapy. Compared with ultrasound, MR-planned nomograms had lower activity per volume (p < 0.05) for both 103Pd monotherapy (∼6%) and 125I monotherapy (∼11%), given a median size (30 cc) prostate. Across all MARS implants, postimplant dosimetry revealed a median V100% of 94% (interquartile range: 92-96%). Median EUS V125 was <1 cc for all patients, regardless of isotope.

Conclusions: We developed a quality assurance nomogram for MR-planned prostate brachytherapy. When compared with ultrasound-planned, MR-planned monotherapy resulted in a lower activity-to-volume ratio while maintaining dosimetric coverage, likely secondary to EUS-sparing and reduced planning target margins.

Keywords: Brachytherapy; Iodine; Magnetic resonance (MR); Nomogram; Palladium; Prostate.

Publication types

  • Comparative Study
  • Research Support, N.I.H., Extramural

MeSH terms

  • Brachytherapy / methods*
  • Brachytherapy / standards*
  • Humans
  • Iodine Radioisotopes
  • Magnetic Resonance Imaging
  • Male
  • Nomograms*
  • Organ Size
  • Palladium
  • Prostate / pathology
  • Prostatic Neoplasms / diagnostic imaging
  • Prostatic Neoplasms / radiotherapy*
  • Quality Assurance, Health Care*
  • Radiation Dosage
  • Radioisotopes
  • Radiometry
  • Radiosurgery
  • Radiotherapy Dosage
  • Radiotherapy Planning, Computer-Assisted / methods
  • Radiotherapy Planning, Computer-Assisted / standards
  • Ultrasonography
  • Urethra


  • Iodine Radioisotopes
  • Radioisotopes
  • Palladium
  • Palladium-103
  • Iodine-125