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Radiobiological and Physical Evaluation of the Effect of Metal Artifacts with VMAT and IMPT Plans

T Lee1*, W Hsi2, Y Mekuria3, (1) Indiana University Health Arnett, Lafayette, IN, (2) Radiation Oncology, University of Florida, Gainesville, FL and University Florida Health Proton Radiotherapy Institute, Jacksonville, FL, Morton Grove, IL, (3) St. Joseph University Hospital, Patterson, NJ

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: quantitatively investigate the effect of metal artifacts in prostate cancer treatment plans with - full-arc VMAT and 2-field IMPT on CT images with metal-artifacts (MA) and with Metal Arifacts reduced using previously developed MMAS model.


Methods: prostate cases with metal prosthesis were studied. 2 full-arc VMAT plans with and without defining metal as an avoiding structure and 2 field MPT plans with and without avoiding rotating fields by 25-30 degrees posteriorly from 90 and 270 degrees respectively for each IMPT fields. Optimized plans were created on CT images with metal artifacts and beam parameters were transferred to the CT images with Metal artifacts reduced and the dose was recalculated. 4 plans from each case were created and previously developed RTPET (RadioTherapy Plan Evaluation Toll) was employed to evaluate and compare the plans in terms of TCP, NTCP, Cumulative DVHs, Conformity Index (CI), Dose Homogeneity Index (DHI), as well as dose statistics, e.g. Dmean. TCP/NTCP and DVH plots as well as the table of metrics of each evaluated structure was created for each plans to compare with corresponding plans.


Results: plans were barely affected by the presence of metal artifacts with all evaluation metrics within +/- 2.0% differences, while IMPT plans significantly affected. For VMAT plans, Dmean, CI, DHI were <=+/-1.0% and TCP / NTCP with almost no change. On the other hand, IMPT plans with fields penetrating the metal show Dmean up to 5.5%, CI ~ 90%, TCP ~13.5% decrease, NTCP 13% increase from reference plan, while those with fields avoiding metals show Dmean up to 3%, CI 87%, TCP ~0.0%, NTCP ~ 3.0% increase.


Conclusion: and IMPT plan evaluation and comparisons show that the presence of metal artifact affects dose statistics as well as radiobiological outcomes, e.g. TCP / NTCP if the beams don’t avoid them.

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Keywords

Not Applicable / None Entered.

Taxonomy

TH- Radiobiology(RBio)/Biology(Bio): RBio- general

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