Optimization of current modulation function for proton spread-out Bragg peak fields

Journal Article · Mon May 15 04:00:00 EDT 2006 · Medical Physics

DOI:https://doi.org/10.1118/1.2188072· OSTI ID:20775200

Lu, H -M; Kooy, Hanne ^[1]

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1. Northeast Proton Therapy Center, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts 02115 (United States)

Proton treatments with spread-out Bragg peak (SOBP) fields often use a rotating modulation wheel of varying thickness to modulate the pristine Bragg peak in depth and intensity. The technique of modulating also the beam current independently over the wheel rotation provides an additional control over the intensities of the pulled-back Bragg peaks. As a result, a single wheel can be used over a large range of energies and SOBP parameters and field-specific wheels are no longer necessary. An essential task in commissioning a particular treatment depth is the determination of this current modulation function. We have developed a method for the optimization of the current modulation function. The basic idea is to treat the entire beam nozzle, housing the various beam scattering and modulating components, as a whole and to characterize its effect as a transformation from a modulating beam current to a depth-dose distribution. While this transformation is difficult to calculate theoretically due to the complex scattering paths in the nozzle and the phantom, it can, however, be determined by time-resolved dose measurements. Using this transformation, we can calculate SOBP depth-dose distributions for any current modulation function and optimize it by a simple numerical optimization. We have applied the new method to a number of proton beams with satisfactory results.

• OSTI ID: 20775200
• Journal Information: Medical Physics, Journal Name: Medical Physics Journal Issue: 5 Vol. 33; ISSN 0094-2405; ISSN MPHYA6
• Country of Publication: United States
• Language: English

Related Subjects

62 RADIOLOGY AND NUCLEAR MEDICINE
BEAM CURRENTS
BRAGG CURVE
COMMISSIONING
DEPTH DOSE DISTRIBUTIONS
DOSIMETRY
MODULATION
OPTIMIZATION
PHANTOMS
PROTON BEAMS
RADIATION DOSES
RADIOTHERAPY
TIME RESOLUTION