Dosimetric and microdosimetric study of contrast-enhanced radiotherapy with kilovolt x-rays

Kilovolt x-rays are clearly suboptimal compared to MV photon beams for radiotherapy of deep-seated tumours because of the increased attenuation in tissue, causing a rapid dose fall-off. This picture could change drastically when tumours can be labelled with contrast medium, containing high atomic number elements. This causes a significant dose enhancement to the tumour by exploiting the high cross sections for the photo-electric effect for kV x-rays. In this work, we have investigated the dosimetric and microdosimetric characteristics of kV contrast-enhanced radiation therapy (CERT) for different photon energies, contrast-medium concentrations and types (I and Gd). Two idealized patient treatment plans (head and lung) for irradiation with CT-arc beams were calculated. It is shown that the dose enhancement in tumours can be highly significant (up to about sixfold for realistic 80-120 kVp x-ray spectra and an iodine concentration of 50 mg ml-1) but that dose homogeneity in the tumour depends on photon energy, contrast-medium concentration and type, and irradiation scheme. An attempt to optimize the irradiation scheme is discussed. The microdosimetric study of the dose mean lineal energy shows that radiation quality changes in the contrast-medium-labelled region compared to homogeneous tissue are fairly small and limited to 10%. It is concluded that kV-CERT is a promising radiotherapy technique, provided contrast medium can be delivered reliably to tumours.

[1]  T D Solberg,et al.  Dose distributions using kilovoltage x-rays and dose enhancement from iodine contrast agents. , 1999, Physics in medicine and biology.

[2]  F Verhaegen,et al.  Monte Carlo modelling of radiotherapy kV x-ray units. , 1999, Physics in medicine and biology.

[3]  S M Seltzer,et al.  AAPM protocol for 40-300 kV x-ray beam dosimetry in radiotherapy and radiobiology. , 2001, Medical physics.

[4]  F. Verhaegen,et al.  Sensitivity study for CT image use in Monte Carlo treatment planning , 2005, Physics in medicine and biology.

[5]  Gert Moliere,et al.  Theorie der Streuung schneller geladener Teilchen II Mehrfach-und Vielfachstreuung , 1948 .

[6]  Fritz Sauter,et al.  Über den atomaren Photoeffekt in der K-Schale nach der relativistischen Wellenmechanik Diracs , 1931 .

[7]  A. Einstein.  Über einen die Erzeugung und Verwandlung des Lichtes betreffenden heuristischen Gesichtspunkt [AdP 17, 132 (1905)] , 2005, Annalen der Physik.

[8]  J. Fowler,et al.  On cold spots in tumor subvolumes. , 2002, Medical physics.

[9]  A. Einstein.  Über einen die Erzeugung und Verwandlung des Lichtes betreffenden heuristischen Gesichtspunkt [AdP 17, 132 (1905)] , 2005 .

[10]  J. Battista,et al.  Optimal photon energies for IUdR K-edge radiosensitization with filtered x-ray and radioisotope sources. , 1999, Physics in medicine and biology.

[11]  J P Seuntjens,et al.  Correction factors for water-proofing sleeves in kilovoltage x-ray beams. , 1997, Medical physics.

[12]  F. Verhaegen,et al.  Microdosimetric Analysis of Various Mammography Spectra: Lineal Energy Distributions and Ionization Cluster Analysis , 2004, Radiation research.

[13]  E. Rakovitch,et al.  Clinical significance of atomic inner shell ionization (ISI) and Auger cascade for radiosensitization using IUdR, BUdR, platinum salts, or gadolinium porphyrin compounds. , 2003, International journal of radiation oncology, biology, physics.

[14]  M Gambaccini,et al.  Dual-energy tissue cancellation in mammography with quasi-monochromatic x-rays. , 2002, Physics in medicine and biology.

[15]  W. Veigele,et al.  Photon cross sections from 0.1 keV to 1 MeV for elements Z = 1 to Z = 94* , 1973 .

[16]  C. Ma,et al.  Study of dosimetry consistency for kilovoltage x-ray beams. , 1998, Medical physics.

[17]  J. Robar,et al.  Tumour dose enhancement using modified megavoltage photon beams and contrast media. , 2002, Physics in medicine and biology.

[18]  I. Kawrakow.  Accurate condensed history Monte Carlo simulation of electron transport. I. EGSnrc, the new EGS4 version. , 2000, Medical physics.

[19]  J Winter,et al.  Radiation dose enhancement in tumors with iodine. , 1983, Medical physics.

[20]  T. Solberg,et al.  Calculation of radiation dose enhancement factors for dose enhancement therapy of brain tumours. , 1992, Physics in medicine and biology.

[21]  F Verhaegen,et al.  Microdosimetric characterisation of 28 kVp Mo/Mo, Rh/Rh, Rh/Al, W/Rh and Mo/Rh mammography X ray spectra. , 2002, Radiation protection dosimetry.

[22]  D. Burmistrov,et al.  “Trion” code for radiation action calculations and its application in microdosimetry and radiobiology , 1993, Radiation and environmental biophysics.