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Superiority of 160 kV vs 6 MV X-ray irradiation combined with
heavy element radiosensitization
By: Sara N. Lim, Anil K. Pradhan, Sultana N. Nahar, Rolf F. Barth, Claudia Turro, Alycia M. Palmer, Erica H. Bell
and Xiaokui Mo
Outline of presentation
Background: X-ray radiotherapy and how can we improve it?
Low energy 160 kV vs 6000 kV (6 MV) X-rays
What is radiosensitization?
enhancing X-ray dose with heavy elements to kill malignant cells
Monte Carlo simulations on radiosensitization using heavy elements (high atomic number Z or HZ – review from earlier presentation).
Experiments: promising in vitro results
In vivo experiments in progress
Current Radiotherapy
6 MV clinical linac (Varian Clinac)
unfiltered spectrum: ~0-6000 keV (6 MeV)
• X-rays can not differentiate between tumor tissues and healthy tissues with or with out radiosensitization
• Reason for use: penetration
What if there was a way to increase the damage to tumor tissues that more than
makes up for the lack of penetration?
There is! With heavy element radiosensitization!
Dose Enhancement Factors
Geant4 results using 7ug/ml Pt for increase in dose deposition as a function of X-ray energy
160 kV
6 MV
In vitro experiments
F98 rat glioma cells:
Radiosensitized with relatively non-toxic HZ radiosensitizer or carboplatin
Irradiated with either 6 MV or 160 kV X-rays to test changes in surviving fraction (SF)
In vitro analysis Methods and materials
Clonogenic assay with Pt-sensitized F98 cells after broadband X-ray irradiation (160 kV Vs 6 MV, 7 Gy)
1.
2.
Radiosensitizers:
Pyridine Terpyridine Pt(II) complex (typ-Pt)
- low in vitro toxicity
- allows decoupling of chemotoxicity and radiotoxicity
- unexpectedly cytotoxic in vivo
Carboplatin
- common cancer therapeutic – well known cytotoxic range
- going to be used in in vivo study
Decrease in malignant cell survival after irradiation
varying amounts of radiosensitizer
no x-ray
6 MV
160 kV
no x-ray
6 MV
160 kV
Increase cell killing: Low Energy VS High Energy
160 kV
6 MV
radiation dose
Decrease in malignant cell survival after irradiationvarying radiation dose (with carboplatin)
No sig. difference
In vivo experiments
Non – therapeutic dose of carboplatin
103 F98 glioma cells
160 kV10 Gy
6 MV10 Gy
So, what will this experiment show?
In vivo experiments
Stay tuned for the sequel
Conclusion
In vitro experiments showed greater cell death with low energy X-rays
Radiosensitized rats treated with low energy X- rays SHOULD live longer
Thanks for listening!