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Analysis of Two Overall Biological Effective Dose (OBED) Calculation Methods and Their Impact On the Accurate Determination of the Maximum Biological Effective Dose (BED) in Multi-Phase Treatment Plans

K Kauweloa*, N Papanikolaou, S Stathakis, C Esquivel, R Crownover, P Mavroidis, University of Texas HSC SA, San Antonio, TX

SU-E-T-714 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: To evaluate the accuracy of calculating the overall biological effective dose ₍OBED₎ distribution of multi₋phase treatment plans by summing up the physical doses of the individual beam configurations prior their conversion to BED.

Methods: MATLAB 2010a was used to calculate the OBED using the dose distribution matrices of a patients initial and boost treatment plans from Pinnacle. The OBED was calculated using two different methods. Method₋A adds the physical doses from the initial and boost treatment plans, and then converts those values into BED to produce an approximate OBED. Method₋B converts the physical doses for each plan into BED before adding them to produce the true OBED. The latter method uses the true mathematical approach and hence will be used as reference when comparing the results acquired by the two methods. Mathematically, if the average dose per fraction ₍ADPF₎ for the initial ₍ADPF1₎ and boosting ₍ADPF2₎ plans are equal, then the approximate OBED should be equal to the true OBED. However, the larger the difference between the ADPFs is, the larger the difference between the OBEDs will be.

Results: ADPF1 was 1.59 Gy and ADPF2 was 1.34 Gy hence the percent difference between the OBEDs was ₋0.09 ± 0.09 percent. The average, maximum, and minimum values within the OBED for method₋A were 56.6 Gy, 67.2 Gy, and 53.2 Gy while those values within the OBED for method B were 56.7 Gy, 67.3 Gy, and 53.3 Gy.

Conclusion: Method₋A can produce accurate approximations to the true OBED if the ADPF of each plan is approximately equal. This leads to an accurate determination of the maximum BED limit when optimizing multi₋phase treatment plans. Current treatment planning systems do not have the capability to perform calculations based on method₋B, but using the dose volume histograms, method₋A can be performed manually.

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