title: Post-radioembolization yttrium-90 PET/CT - part 2: dose-response and tumor predictive dosimetry for resin microspheres.
abstract: BACKGROUND
  Coincidence imaging of low-abundance yttrium-90 (90Y) internal pair production by positron emission tomography with integrated computed tomography (PET/CT) achieves high-resolution imaging of post-radioembolization microsphere biodistribution. Part 2 analyzes tumor and non-target tissue dose-response by 90Y PET quantification and evaluates the accuracy of tumor 99mTc macroaggregated albumin (MAA) single-photon emission computed tomography with integrated CT (SPECT/CT) predictive dosimetry.
  
  
  METHODS
  Retrospective dose quantification of 90Y resin microspheres was performed on the same 23-patient data set in part 1. Phantom studies were performed to assure quantitative accuracy of our time-of-flight lutetium-yttrium-oxyorthosilicate system. Dose-responses were analyzed using 90Y dose-volume histograms (DVHs) by PET voxel dosimetry or mean absorbed doses by Medical Internal Radiation Dose macrodosimetry, correlated to follow-up imaging or clinical findings. Intended tumor mean doses by predictive dosimetry were compared to doses by 90Y PET.
  
  
  RESULTS
  Phantom studies demonstrated near-perfect detector linearity and high tumor quantitative accuracy. For hepatocellular carcinomas, complete responses were generally achieved at D70 > 100 Gy (D70, minimum dose to 70% tumor volume), whereas incomplete responses were generally at D70 < 100 Gy; smaller tumors (<80 cm3) achieved D70 > 100 Gy more easily than larger tumors. There was complete response in a cholangiocarcinoma at D70 90 Gy and partial response in an adrenal gastrointestinal stromal tumor metastasis at D70 53 Gy. In two patients, a mean dose of 18 Gy to the stomach was asymptomatic, 49 Gy caused gastritis, 65 Gy caused ulceration, and 53 Gy caused duodenitis. In one patient, a bilateral kidney mean dose of 9 Gy (V20 8%) did not cause clinically relevant nephrotoxicity. Under near-ideal dosimetric conditions, there was excellent correlation between intended tumor mean doses by predictive dosimetry and those by 90Y PET, with a low median relative error of +3.8% (95% confidence interval, -1.2% to +13.2%).
  
  
  CONCLUSIONS
  Tumor and non-target tissue absorbed dose quantification by 90Y PET is accurate and yields radiobiologically meaningful dose-response information to guide adjuvant or mitigative action. Tumor 99mTc MAA SPECT/CT predictive dosimetry is feasible. 90Y DVHs may guide future techniques in predictive dosimetry.
authors.affiliation: Department of Nuclear Medicine and PET, Singapore General Hospital, Outram Road, Singapore 169608, Singapore. yung.h.kao@gmail.com.
authors.forename: Yung-Hsiang
authors.initials: YH
authors.lastname: Kao
authors.forename: Jeffrey D
authors.initials: JD
authors.lastname: Steinberg
authors.forename: Young-Soon
authors.initials: YS
authors.lastname: Tay
authors.forename: Gabriel Ky
authors.initials: GK
authors.lastname: Lim
authors.forename: Jianhua
authors.initials: J
authors.lastname: Yan
authors.forename: David W
authors.initials: DW
authors.lastname: Townsend
authors.forename: Charley A
authors.initials: CA
authors.lastname: Budgeon
authors.forename: Jan A
authors.initials: JA
authors.lastname: Boucek
authors.forename: Roslyn J
authors.initials: RJ
authors.lastname: Francis
authors.forename: Timothy St
authors.initials: TS
authors.lastname: Cheo
authors.forename: Mark C
authors.initials: MC
authors.lastname: Burgmans
authors.forename: Farah G
authors.initials: FG
authors.lastname: Irani
authors.forename: Richard Hg
authors.initials: RH
authors.lastname: Lo
authors.forename: Kiang-Hiong
authors.initials: KH
authors.lastname: Tay
authors.forename: Bien-Soo
authors.initials: BS
authors.lastname: Tan
authors.forename: Pierce Kh
authors.initials: PKh
authors.lastname: Chow
authors.forename: Somanesan
authors.initials: S
authors.lastname: Satchithanantham
authors.forename: Andrew Eh
authors.initials: AE
authors.lastname: Tan
authors.forename: David Ce
authors.initials: DC
authors.lastname: Ng
authors.forename: Anthony Sw
authors.initials: AS
authors.lastname: Goh