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Evaluation of Rotational Set Up Errors in Intensity Modulated Proton Therapy (IMPT) and Feasibility of Six Dimensional (6D) Robust Optimization

M Noufal*, D Sharma, K Patro, A Manikandan, G Krishnan, R Thiyagarajan, R Jalali, Apollo proton cancer centre, Chennai, Tamil Nadu,

Presentations

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

Room: AAPM ePoster Library

Purpose:
To assess dose delivery errors due to rotational uncertainties in IMPT plans and investigate on the proposal of 6D robust optimization to mitigate all uncertainties.


Methods:
The planning CT and structures of a head and neck anthropomorphic phantom were rotated for ±1° and ±2° separately in three rotational axes {Roll(R), Pitch(P) and Yaw(Y)} using an in-house MatLab analytical program. Robustly optimized nominal IMPT (IMPT-N) plans, which incorporated three translational error and range uncertainty, were projected on to these rotated image datasets to access variation in dosimetric parameters. Subsequently, 6D robust optimization IMPT (6D-IMPT) plans were carried out using the rotational CT datasets. After thorough validation, same investigation was extended to eight previously treated chordoma/chondrosarcoma patients. For each IMPT-N plan, 12 rotational error simulated plans (P+1,P-1,P+2,P-2,R+1,R-1,R+2,R-2,Y+1,Y-1,Y+2,Y-2) were carried out and robustness of each error plans were assessed by voxel worst (VW) increase in D1% for proximal OARs and VW decrease in D95% for targets.

Results:
The phantom study demonstrate accuracy of our analytical programme for image rotation and feasibility of 6D robust optimization. The presence of patient rotation did not show any appreciable changes in target coverage. However variations up to 20% were observed in D1% depending on degree of rotation and position of OARs . 6D-IMPT plans reduces maximum D1% VW case in all OARs .

Conclusion:
The proposed 6D robust optimized IMPT plans showed better robustness for both translational and rotational uncertainties.

Download ePoster [PDF]

Keywords

Setup Errors, Systematic Errors, Protons

Taxonomy

TH- External Beam- Particle/high LET therapy: Proton therapy – dose optimization

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