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SU‐FF‐T‐312: Dosimetry for Radiobiological Evaluation of the Active Beam Scanning System at Loma Linda University Medical Center
Author(s) -
Wroe A,
Rightnar S,
Ghebremedhin A,
Schulte R,
Lesyna D,
Patyal B,
Slater J,
Gridley D,
Slater J
Publication year - 2009
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.3181792
Subject(s) - dosimetry , pencil beam scanning , proton therapy , nuclear medicine , medical physics , beam (structure) , proton , radiation treatment planning , radiation therapy , optics , physics , medicine , nuclear physics , radiology
Purpose: Active beam scanning is a new and important innovation in proton therapy, potentially allowing for a more conformal proton treatment through dynamic manipulation of proton pencil beams. Active beam scanning thus requires accurate online dosimetry to track the proton pencil beam both in space and time, whilst at the same time monitoring dose delivered to a given point within the patient. Radiobiological validation of this new technology is equally important. Currently, with passive proton beam delivery a uniform RBE of 1.1 is assumed, and this has lead to satisfactory clinical results both in terms of tumor control and side effects. However, it is unclear whether this RBE value is also appropriate for active beam scanning treatments. Methods and Materials: To investigate this, researchers at Loma Linda University Medical Center are utilizing a multilayered system to evaluate radiobiological parameters at multiple positions within a water tank along the depth dose profile. The results obtained are being compared with identical experiments completed with Co‐60 photons and passively delivered protons. As a prerequisite for accurate and meaningful comparisons, precise dosimetry ensuring compatibility of dose rate, depth dose profile, dose uniformity and absolute dose have to be performed for all three radiation modalities. This presentation describes in detail the dosimetry methodology associated with the project, including film and ion chamber evaluation of the three radiation modalities. Results: Initial results indicate that the active beam scanning system provides proton radiation fields comparable to that utilizing passive beam delivery with a flatness and symmetry within 3% (TG45) at all positions along the Bragg peak. Further, dose rates experienced with this system are also comparable to that for passive beam delivery. Conclusions: This preclinical work will provide a unique opportunity to discuss both dosimetry‐ and radiobiology‐associated issues of automatic beam scanning in proton therapy.