Superiority of 160 kV vs 6 MV Xray 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 nontoxic HZ radiosensitizer or carboplatin
Irradiated with either 6 MV or 160 kV Xrays to test changes in surviving
fraction (SF)
In vitro analysis
Methods and materials
Radiosensitizers:
Pyridine Terpyridine Pt(II) complex
1. (typ-Pt)
- low in vitro toxicity
- allows decoupling
of chemotoxicity and
radiotoxicity
- unexpectedly
cytotoxic in vivo
2. Carboplatin
- common cancer
therapeutic – well
known cytotoxic
range
- going to be used in
in vivo study
Clonogenic assay with Pt-sensitized F98
cells after broadband X-ray irradiation (160
kV Vs 6 MV, 7 Gy)
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 irradiation
varying radiation dose (with carboplatin)
No sig. difference
In vivo experiments
6 MV
10 Gy
103 F98 glioma cells
160 kV
10 Gy
Non – therapeutic dose of carboplatin
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!