Pictured: Assen S. Kirov

I am an associate attending physicist in the Department of Medical Physics. I have expertise in the physics, calibration and quality assurance of linear accelerators and PET/CT scanners used in the radiation treatment process.  In the past I have performed extensive research in the dosimetry of radioactive sources used for brachytherapy as well as for improving the dosimetric measurement accuracy for Intensity Modulated Radiation Therapy, with special attention on adapting scintillation and other imaging methods for 2D and 3D dosimetry measurements. 

My current research focuses on quantifying and reducing the uncertainties in using PET for targeted therapies and in other aspects of nuclear medicine including internal dosimetry. I have organized and lead a task group within the American Association of Physicists in Medicine (AAPM Task Group No. 211) to standardize the evaluation of PET auto-segmentation methods. Most recently I have initiated a clinical protocol for investigating correlations between the distribution of PET tracer uptake and histopathology findings by performing Quantitative Autoradiography of Biopsy Specimens (QABS) extracted under PET/CT guidance. This work, which was supported in part by a grant from Biospace Lab S.A., has potential to provide useful information for guiding interventional radiology procedures and localized cancer therapies and for in-situ validation of new radiopharmaceuticals with high spatial resolution.

An open-access book chapter, lecture handouts, and a list of selected publications on related topics describing my work can be found below. 


  1. R. K. Valicenti, A. S. Kirov, A. S. Meigooni, V. Mishra and J. F. Williamson, “Validation of Monte Carlo Dose Calculations about a High-Intensity Ir-192 Source for Pulsed Dose-Rate Brachytherapy using Thermoluminescent Dosimetry”, Med.Phys., 22 (1995) 821. [PubMed Abstract]

  2. A. S. Kirov, A. S. Meigooni, Y. Zhu, R. K. Valicenti and J. F. Williamson, “Quantitative Verification of 192Ir Pulsed and High Dose-Rate Source Structure by Pin-hole Autoradiography “, Med.Phys., 22 (1995)1753-1757. [PubMed Abstract]

  3. A. S. Kirov, J. F. Williamson, A. S. Meigooni, and Y. Zhu , “TLD, Diode and Monte Carlo Dosimetry of Ir-192 Source for High Dose-Rate Brachytherapy”, Phys. Med. Biol., 40 (1995) 2015-2036. [PubMed Abstract]

  4. A. S. Kirov, J. F. Williamson, A. S. Meigooni, and Y. Zhu “Measurement and Calculation of Heterogeneity Correction Factors for an Ir-192 High Dose-Rate Brachytherapy Source behind Tungsten Alloy and Steel Shields”, Med.Phys., 23 (1996) 911-919. [PubMed Abstract]

  5. Y. Zhu, A. S. Kirov, V. Mishra, A. S. Meigooni, and J. F. Williamson, “Quantitative Evaluation of Radiochromic Film Response for Two-Dimensional Dosimetry”, Med.Phys., 24 (1997) 223-231. [PubMed Abstract]

  6. R. K. Das, D. Keleti, Y. Zhu, A. S. Kirov, A. S. Meigooni and J. F. Williamson, “Validation of Monte Carlo Dose Calculations near 125I sources in the Presence of Bounded Heterogeneities”, Int. J. Rad. Onc. Biol. Phys., 38 (1997) 843-853. [PubMed Abstract]

  7. A. S. Kirov and J. F. Williamson, “Two Dimensional Scatter Integration Method for Brachytherapy Dose Calculations in 3D Geometry”, Phys. Med. Biol., 42 (1997) 2119-2135. [PubMed Abstract]

  8. G. M. Daskalov , A. S. Kirov, J. F. Williamson, “Analytical approach to heterogeneity correction factor calculation for brachytherapy”, Med.Phys., 25 (1998) 722-735. [PubMed Abstract]

  9. A.S. Kirov, C. Hurlbut, J. F. Dempsey, S. B. Shrinivas, J. W. Epstein, W. R. Binns, P. F. Dowkontt and J. F. Williamson, “Towards two dimensional brachytherapy dosimetry using plastic scintillator: New highly efficient water equivalent plastic scintillator materials “, Med.Phys., 26 (1999) 1515-1523. [PubMed Abstract]

  10. A. S. Kirov, W. R. Binns, J. F. Dempsey, J. W. Epstein, P. F. Dowkontt, S. Shrinivas, C. Hurlbut, and J. F. Williamson, “Towards two dimensional brachytherapy dosimetry using plastic scintillator: Localization of the scintillation process “, Nucl. Instr. Meth., A 439 (2000) 178-188.

  11. J. F. Wiliamson, J. F. Dempsey, A. S. Kirov, J. I. Monroe, W. R. Binns and H. Hedtjärn, “Plastic scintillator response to low energy photons”, Phys. Med. Biol., 44 (1999) 857-871. [PubMed Abstract]

  12. F. Dempsey, D. A. Low, A. S. Kirov, J. F. Williamson, ” Quantitative optical densitometry using scanning film digitizers “, Med.Phys., 26 (1999) 1721-1731. [PubMed Abstract]

  13. A. S. Kirov, S. Shrinivas, C. Hurlbut, J. F. Dempsey, W. R Binns, and J. L Poblete, ” New water equivalent liquid scintillator solutions for 3D dosimetry”, Med. Phys., 27 (2000) 1156-1164. [PubMed Abstract]

  14. F. Dempsey, D. A. Low, S. Mutic, J. Markman, A. S. Kirov, G. H. Nussbaum, and J. F. Williamson, “Validation of a precision radiochromic film dosimetry system for quantitative two-dimensional imaging of acute exposure dose distributions”, Med. Phys., 27 (2000) 2462-2475. [PubMed Abstract]

  15. A. S. Kirov and J. F. Williamson, “Monte Carlo Aided Dosimetry of the Source Tech Medical I-125 Interstitial Brachytherapy Source”, Med. Phys. 28, (2001), 764-772, with corrections published in Med. Phys. 29 (2002) 262-263. [PubMed Abstract]

  16. S. Devic, J. Seuntjens, G. Hegyi, E. B. Podgorsak, C. G. Soares, A. S. Kirov, I. Ali, J. F. Williamson, and Angel Elizondo. “Dosimetric Properties of Improved GafChromic Films for Seven Different Digitizers”, Med. Phys., 31 (9), (2004) 2392-2401. [PubMed Abstract]

  17. S. Jan, G. Santin, D. Strul, K. Assi, D. Autret, S. Avner, R. Barbier, M. Bardi, P. Bloomfield, D. Brasse, V. Breton, P. Bruyndonckx, I. Buvat, A. F. Chatziioannou, Y. Choi, Y. H. Chung, C. Comtat, D. Donnarieix, L. Ferrer, S. J. Glick, C. Groiselle, S. Kerhoas-Cavata, A. S. Kirov, V. Kohli, M. Koole, M. Krieguer, D. J. van der Laan, F. Lamare, G. Largeron, C. Lartizien, D. Lazaro, M. C. Maas, L. Maigne, F. Mayet, F. Melot, C. Merheb, C. Morel, E. Pennacchio, J. Perez, U. Pietrzyk, F. R. Rannou, M. Rey, D. R. Schaart, C. R. Schmidtlein, L. Simon, T. Y. Song, S. Staelens, J. M. Vieira, D. Visvikis, R. Van de Walle, E. Wie, “GATE - Geant4 Application for Tomographic Emission: a simulation toolkit for PET and SPECT”, Phys. Med. Biol., 49, (2004), 4543-4561. (Awarded 2009 Prize for Highest Cited paper in Physics in Medicine and Biology for the period 2004-2008) [PubMed Abstract]

  18. Åsa Palm, Assen S. Kirov, and Thomas LoSasso,”Predicting energy response of radiographic film in a 6 MV x-ray beam using Monte Carlo calculated fluence spectra and absorbed dose”, Med. Phys., 31, (2004),3168-3178. [PubMed Abstract]

  19. Azam Niroomand-Rad, Sou-Tung Chiu-Tsao, Christopher G. Soares, Ali S. Meigooni, Assen S. Kirov, “Comparison of Uniformity of Dose Response of Double Layer Radiochromic Films (MD-55-2) Measured at 5 Institutions”, Physica Medica, XXI (2005) 15-21. [PubMed Abstract]

  20. S. Devic, J. Seuntjens, E. Sham, E. B. Podgorsak, C. R. Schmidtlein , A. S. Kirov, and C. G. Soares, “Precise radiochromic film dosimetry using a flat-bed document scanner”, Med. Phys., 32 (2005) 2245-2253. [PubMed Abstract]

  21. Kirov A. S., Piao J. Z., Mathur N. K., Miller T. R., Devic S., Trichter S., Zaider M., Soares C. G., and LoSasso T., “The Three Dimensional Scintillation Dosimetry Method: Test for a 106Ru eye plaque applicator”, Phys. Med. Biol., 50 (2005) 3063-3081. [Full-Text]

  22. C. R. Schmidtlein, A. S. Kirov, Bidaut L., Nehmeh S., Erdi Y., Ganin A., Stearns C. W., McDaniel D. L., Humm J., and Amols H., “Validation of GATE Monte Carlo simulations for the GE Advance/Discovery LS PET scanners”, Med. Phys., 33 (1) (2006) 198-208. [PubMed Abstract]

  23. A. S. Kirov, G. Caravelli, Åsa Palm, Chen Chui, Tom LoSasso, “Pencil Beam Approach for Correcting the Energy Dependence Artifact in Film Dosimetry for IMRT verification”, Med. Phys., 33(10) (2006) 3690-3699. [PubMed Abstract]

  24. D. Visvikis, M. Bardies, S. Chiavassa, C. Danford, A. Kirov, F. Lamare, L. Maigne, S. Staelens, R. Taschereau, “Use of the GATE Monte Carlo package for dosimetry applications”, Nucl. Instr. Meth., A 569 (2006) 335-340.

  25. A. S. Kirov, C Danford, C. Ross Schmidtlein, E. Yorke, J. L. Humm, and H. I. Amols, “PET Quantification Inaccuracy of Non-Uniform Tracer Distributions for Radiation Therapy,” Proceedings paper M13-5, 2007 IEEE Nuclear Science Symposium and Medical Imaging Conference Record, pp. 2838-2841, Oct. 27 - Nov. 3 , 2007, Honolulu, HI, USA. [Full Text]

  26. I. Kawrakow, K. Mitev, G. Gerganov, Y. Madzhunkov, A. Kirov, “Efficient photon transport in positron emission tomography simulations using VMC++”, Journal of Physics: Conference Series, 102 (2008) 012014.

  27. A. S. Kirov, J. Z. Piao, C. R. Schmidtlein, “Partial Volume Effect correction in PET using regularized iterative deconvolution with variance control based on local topology”, Phys. Med. Biol., 53 (2008) 2577-2591. [Full-Text]

  28. Nehmeh, S.A., El-Zeftawy, H., Greco, C., Schwartz, J., Erdi, Y. E., Kirov, A., Schmidtlein, C. R., Gyau, A. B., Larson, S. M, Humm, J. L, “An iterative technique to segment PET lesions using a Monte Carlo based mathematical model.” Med Phys, 2009. 36(10): p. 4803-9. [PubMed Abstract]

  29. K. Mitev, A. Kirov, Y. Madzhunkov, G. Gerganov and I. Kawrakow, “Study of the Influence of Photon Energy Cuts on the PET Simulation Results,” Proceedings of the 2009 IEEE Nuclear Science Symposium and Medical Imaging Conference Record, p. 2873-76, Oct. 25 - 31, 2009, Orlando, FL, USA [Full Text]

  30. C R Schmidtlein, B J Beattie, D L Bailey, T J Akhurst, W Wang, M Gonen, A S Kirov, and J L Humm, Using an External Gating Signal to Estimate Noise in PET with an Emphasis on Tracer Avid Tumors, Phys. Med. Biol. 2010. 55(20): p. 6299-326. [PubMed Abstract]

  31. G. Gerganov, K. Mitev, C. R. Schmidtlein, H. Kang, A. S. Kirov, I. Kawrakow, Detecting Visual Differences in reconstructed Images Using a Region-Based Test for Outliers, 2010 IEEE Nuclear Science Symposium and Medical Imaging Conference Record, Oct.30 - Nov.6 2010.

  32. Terezakis, S. A., Hunt, M. A., Kowalski, A., McCann, P., Schmidtlein, C. R., Reiner, A., Gonen, M., Kirov, A. S., Gonzales, A. M., Schoder, H., & Yahalom, J., ’[(1)F]FDG-positron emission tomography coregistration with computed tomography scans for radiation treatment planning of lymphoma and hematologic malignancies’, Int J Radiat Oncol Biol Phys, 2011,vol. 81, no. 3, pp. 615-22 [PubMed Abstract]

  33. Assen S. Kirov, C. Ross Schmidtlein, Hyejoo Kang and Nancy Lee (2012). Rationale, Instrumental Accuracy, and Challenges of PET Quantification for Tumor Segmentation in Radiation Treatment Planning, in Positron Emission Tomography - Current Clinical and Research Aspects, Chia-Hung Hsieh (Ed.), p.27, ISBN: 978-953-307-824-3, InTech. [Full Text]

  34. Mitev K, Gerganov G, Kirov AS, Schmidtlein CR, Madzhunkov Y, Kawrakow I.,” Influence of photon energy cuts on PET Monte Carlo simulation results”, Med Phys. 2012 Jul;39(7):4175-86. [PubMed Abstract]

  35. Munley, T.M. , Kagadis, G.C., McGee K.P., Kirov, A.S. , Jang, S., Mutic, S. Jeraj, R., Xing, L, “An introduction to molecular imaging in radiation oncology: A report by the AAPM Working Group on Molecular Imaging in Radiation Oncology (WGMIR)”, Medical Physics 40, 101501 (2013); doi: 10.1118/1.4819818 [PubMed Abstract]

  36. Cohen, G. N., Munro, J. J., 3rd, Kirov, A., Losasso, T., Yamada, Y., Williamson, M., Dower, T.L, Zaider, M. (2014). 32P brachytherapy conformal source model RIC-100 for high-dose-rate treatment of superficial disease: Monte Carlo calculations, diode measurements, and clinical implementation. Int J Radiat Oncol Biol Phys, 88(3), 746-752. [PubMed Abstract]

  37. Kirov, A.S, Fanchon, L.M. Pathology-validated PET image data sets and their role in PET segmentation, Clin Transl Imaging (2014) 2:253–267 [Full Text]

  38. Fanchon, L.M., S. Dogan, A.L. Moreira, S. Carlin, C. Schmidtlein, E. Yorke, A. Apte, I. Burger, J. Durack, J.P. Erinjeri, M. Maybody, H. Schoder, R.H. Siegelbaum, C.T. Sofocleous, J.O. Deasy, S. Solomon, J.L. Humm, and A.S. Kirov, (2015), “Feasibility for in situ, High Resolution Correlation of Tracer Uptake with Histopathology by Quantitative Autoradiography of Biopsy Specimens Obtained under FDG PET/CT Guidance”, J Nucl Med,56 (4), p 538-544 [Full text]

  39. M. Maybody, R.K. Grewal, J.H. Healey, C.R. Antonescu, L. Fanchon, S. Hwang, J.A. Carrasquillo, A. Kirov, A. Farooki, “Ga-68 DOTATOC PET/CT-Guided Biopsy and Cryoablation with Autoradiography of Biopsy Specimen for Treatment of Tumor-Induced Osteomalacia,” Cardiovascular and interventional radiology [PubMed Abstract] (2016).