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A Novel Technique for Three Dimensional Dose Reconstructions From a Single Planar Dose Measurement in Patient Specific Quality Assurance of Intensity Modulated Proton Therapy Plans

A Manikandan*, S Koushik, Ganapathy K, K Patro, M Noufal, R Thiyagarajan, D Sharma, Apollo proton cancer centre, Chennai, Tamil NaduIN,

Presentations

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

Room: AAPM ePoster Library

Purpose:
Patient specific quality assurance (PSQA) in pencil beam scanning based intensity modulated proton therapy (IMPT) plans consume significant machine time owing to the requirement of planar dose verification at multiple depths per field. In this study an algorithm was developed to reconstruct 3D dose distribution of each field from planar dose fluence (PDF) measured at a single depth and validated in clinical environment.

Methods:
A mathematical algorithm was formulated and incorporated in an in-house scripted MATLAB code to reconstruct 3D dose distribution from PDF measured at 3g/cm2 depth in solid water phantom using iMatriXX-PT 2D ionization chamber array. PDF at multiple random depths were extracted from the 3D reconstructed dose distribution and compared with the corresponding PDF calculated by the Raystation TPS. The proposed PSQA technique was validated by comparing a)reconstructed and measured PDFs and b)TPS calculated and measured PDFs for 60 arbitrarily chosen depths from 17 treatment fields of ten clinical IMPT plans delivered in Proteus-235 proton therapy system.

Results:
The ?% obtained using the proposed technique was >95% in all analyzed planes except one. The ?% was <95% only in three depths for the reconstructed vs measured. The overall mean (SD) of ?% was 98.64%(1.79%), 98.84% (1.49%) and 99.3% (1.25%) for reconstructed vs measured, reconstructed vs TPS calculated and TPS calculated vs measured respectively.

Conclusion:
The proposed novel PSQA technique is accurate and robust to predict PDF at any depth. It also simplifies measurement setup and eliminates multiple depths measurement. PSQA time was reduced from around 65 minutes with the existing method to around 17 minutes per plan. The proposed technique thus meets the advantages of log file based QA and is more reliable being measurement based procedure. 3D gamma analysis is also found to be possible from a 2D planar measurement using this technique.

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