Affiliations: University of Oklahoma Health Sciences Center,
Oklahoma City, USA | Wayne State University School of Medicine, Detroit,
USA | Aspirus Regional Cancer Center, Wisconsin, USA | British Columbia Cancer Agency, Victoria, Canada
Note: [] Corresponding author: Salahuddin Ahmad, Ph.D., University of
Oklahoma Health Sciences Center, Department of Radiation Oncology, 825 N.E.
10th, Suite 1430, Oklahoma City, Oklahoma, OK 73104, USA. Tel.: +1 405 271
5641; Fax: +1 405 271 8297; E-mail: [email protected]
Abstract: The objective of this work was to assess the relative impact of
radiobiological parameters and radiation dose escalation on Tumor Control
Probability for prostate cancer patients treated with radiation.
Radiobiological parameters included α/β ratios, cell surviving
fraction at 2 Gy (SF_{2}) and clonogenic cell density (CCD). Using the
Niemierko method, TCP was calculated in ten prostate cancer patients as a
function of increasing radiation doses (70–140 Gy), α/β ratios
(1.5–20), SF_{2} (0.3–0.7) and CCD (10–20 million cells/cm^{3}). At 70
Gy and CCD of 10 million/cm^{3}, TCP was above 99% for SF_{2} of 0.3 or
0.4, 97.4%–98.6% for SF_{2} of 0.5 and less than 2% for SF_{2} of
0.6 or 0.7. With dose escalation, TCP values above 99% were demonstrated at
80 Gy for SF_{2} of 0.5 and 100 Gy for SF_{2} of 0.6. For SF_{2} of 0.7,
TCP above 99% was demonstrated with 100 Gy and CCD of 10^{4}
cells/cm^{3} or 140 Gy and CCD of 10^{7} cells/cm^{3}. TCP decreased with
lower α/β of 1.5, but at a much smaller scale compared to
SF_{2} changes. TCP modeling predicts that SF_{2} and CCD are dominant
predictors of radioresistance in prostate cancer. Radiation doses of 100 Gy or
greater may be required for tumors with SF_{2} of 0.6 or above. Relating
clinical tumor prognostic indicators such as Gleason score and PSA to
radiobiological parameters will allow us to identify subsets of patients in
need of higher radiation doses and adjuvant therapy to maximize treatment
outcomes.
Keywords: Tumor control probability (TCP), prostate cancer, dose escalation, radiation therapy
