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Radiobiological Modeling for Assessing Risk to Patients Using Measurement Acquired DVH During Patient Plan Verification

A Alexandrian

A Alexandrian1*, P Mavroidis2 , K McConnell3 , N Kirby4 , N Papanikolaou5 , S Stathakis6 , (1) ,San Antonio, TX, (2) Univ North Carolina, Chapel Hill, NC, (3) UT Health San Antonio, San Antonio, TX, (4) University of Texas HSC SA, San Antonio, TX, (5) UTHSCSA, Shavano Park, Texas, (6) University of Texas HSC SA, San Antonio, TX


SU-I-GPD-T-219 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To translate the differences observed during IMRT-QA between plan delivery and treatment plan into tumor control and normal tissue complication probabilities (TCP and NTCP). We hypothesize that radiobiological modeling can provide additional insight in terms of patient safety evaluating patient specific IMRT plans than conventional dose delivery verification methods.

Methods: 55 IMRT patients have been selected in this study from five anatomical sites: brain, head and neck, lung, pelvis, and prostate. A PTW Octavius 4D system was used to acquire the delivered doses of the patient plans. The PTW Verisoft with the DVH 4D software was used to construct the individual organ DVHs from the measured doses. Only structures with volumes that could be fit within the ion chamber array measuring volume could be used in the comparison. A radiobiological analysis was performed to calculate the values of TCP and NTCP of the VeriSoft and treatment plan. The total normal tissue complication probability (PI) and the complication-free tumor control probability (P+) was also calculated.

Results: The average differences of TCP were found to be: -3.47%±-0.81% for brain, -4.2%±13.5% for head and neck, 7.5%±18.4% for lung, -2.4%±5.2% for pelvis, and -3.1%±2.7% for prostate. These differences in the NTCP values to the organs at risk were used to calculate the following PI and P+ results: -4.7%±4.1% and -3.9%±5.8% for the brain, -11.3%±17.6% and 4.8%±8.5% for head and neck, -0.4%±1.3% and 7.8%±18.3% for lung, -3.8%±5.7% and 1.0%±6.6% for pelvis, and for prostate -3.6%±1.9% and 0.8%±3.6%, respectively.

Conclusion: It is shown that the translation of the dosimetric differences between IMRT-QA measurements and treatment plan into radiobiological differences gives a better picture of their impact to the expected outcome of the individual organs. Incorporation of radiobiological modeling yields more insight about plan quality than conventional patient specific plan verification metrics.

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