title: Spatial dose distributions in solid tumors from 186Re transported by liposomes using HS radiochromic media.
abstract: OBJECTIVE
  A procedure for the measurement of spatial dose rate distribution of beta particles emitted by 186Re-liposomes in tumoral tissue, using HS GafChromic films, is presented.
  
  
  METHODS
  HNSCC xenografts were intratumorally injected with 3.7 or 11.1 MBq of 186Re-liposomes, and planar gamma camera images were acquired to determine the liposome retention in the tumor. After imaging, rats were sacrificed and tumors were excised and processed in slices; HS film sections were placed between slices and the tumor lobe was reassembled. Tumors and films were kept in the dark at 4 degrees C for 18 h. After irradiation, films were removed and response was read using a transmission scanner. Films were analyzed to determine two-dimensional spatial dose rate distributions and cumulative dose volume histograms. Dose rate distributions were quantified using a 60Co calibration curve, the 186Re physical half-life, and a perturbation factor that takes into account the effect of the film protective layer.
  
  
  RESULTS
  Dose rate distributions are highly heterogeneous with maximal dose rates about 0.4 Gy h(-1) in tumors injected with 3.7 MBq and 1.3 Gy h(-1) in tumors injected with 11.1 MBq. Dose volume histograms showed dose distributed in more than 95% and 80% of the tumor when injected with the lower and the higher activity, respectively.
  
  
  CONCLUSIONS
  The described procedures and techniques have shown the potential and utility of HS GafChromic film for determination of dose rate distributions in solid tumors injected intratumorally with 186Re-liposomes. The film's structure and the liposomes' biodistribution must be taken into account to obtain quantitative dose measurements.
authors.affiliation: Instituto de Fisica, UNAM, A.P. 20-364, Mexico 01000 D.F., Mexico. medina@fisica.unam.mx
authors.forename: Luis A
authors.initials: LA
authors.lastname: Medina
authors.forename: Beth
authors.initials: B
authors.lastname: Goins
authors.forename: Mercedes
authors.initials: M
authors.lastname: Rodríguez-Villafuerte
authors.forename: Ande
authors.initials: A
authors.lastname: Bao
authors.forename: Arnulfo
authors.initials: A
authors.lastname: Martínez-Davalos
authors.forename: Vibhudutta
authors.initials: V
authors.lastname: Awasthi
authors.forename: Olga O
authors.initials: OO
authors.lastname: Galván
authors.forename: Cristina
authors.initials: C
authors.lastname: Santoyo
authors.forename: William T
authors.initials: WT
authors.lastname: Phillips
authors.forename: María-Ester
authors.initials: ME
authors.lastname: Brandan
mesh_terms: D000818:Animals; D002294:Carcinoma, Squamous Cell / Q000378:metabolism* / Q000532:radiotherapy; D004337:Drug Carriers / Q000737:chemistry; D005373:Film Dosimetry / Q000379:methods*; D006801:Humans; D008081:Liposomes / Q000737:chemistry*; D008297:Male; D011868:Radioisotopes / Q000008:administration & dosage / Q000493:pharmacokinetics*; D019275:Radiopharmaceuticals / Q000008:administration & dosage* / Q000493:pharmacokinetics; D011879:Radiotherapy Dosage; D051381:Rats; D011923:Rats, Nude; D012062:Relative Biological Effectiveness; D012211:Rhenium / Q000008:administration & dosage* / Q000493:pharmacokinetics*; D014018:Tissue Distribution
chemical_list: D004337:Drug Carriers; D008081:Liposomes; D011868:Radioisotopes; D019275:Radiopharmaceuticals; D012211:Rhenium