SU‐E‐T‐36: Sensitivity of Tumor Control Probability to Changes in Radiobiological Parameters

C. Knaup, P. Mavroidis, S. Stathakis, G. Swanson, N. Papanikolaou

Research output: Contribution to journalArticlepeer-review


Purpose: Radiobiological parameters used to calculate tumor control probabilities (TCP) are known to vary among patients. It then becomes important to explore the effects different parameters have on TCP calculations. Here, the effect of different parameter combinations on TCP for several prostate seed implant treatments was explored. Methods: Forty‐four patients were evaluated. All patients were treated with Pd‐103 seeds and were planned on the Spot system. The prescription dose was 120 Gy. A post‐implant CT was taken for each patient and was used to create a tumor DVH. Using this information and different biological parameters, the linear‐quadratic model was used to calculate the biological effective dose (BED). The BED was then used to calculate the TCP. Combinations of the following biological parameters were evaluated: alpha/beta = 2, 3, 4 Gy; D50 = 30, 50, 70 Gy; and maximum normalized dose‐response gradient (gamma) = 2, 3, 4. The TCP for each patient was calculated for each of the twenty‐seven different combinations.Results: Combinations with the highest TCP at a given low BED were those were alpha/beta and gamma were high and D50 was low. Combinations with the lowest TCP at a given high BED levels were those were alpha/beta and gamma were low and D50 was high. Parameter values of alpha/beta = 2 Gy, D50 = 50 Gy and gamma = 4 provided TCP values that are consistent with realistic patient outcomes. These parameters yield an α value that was consistent with newer findings Conclusions: In this work, the sensitivity of TCP calculations on choice of biological parameters was evaluated for prostate seed implant patients. This was done by calculating the BED and TCP for the tumor. The parameters that best matched realistic clinical results were alpha/beta = 2 Gy, D50 = 50 Gy and gamma = 4.

Original languageEnglish (US)
Pages (from-to)3493
Number of pages1
JournalMedical physics
Issue number6
StatePublished - Jun 2011

ASJC Scopus subject areas

  • Biophysics
  • Radiology Nuclear Medicine and imaging


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