Validation of dosimetric field matching accuracy from proton therapy using a robotic patient positioning system

Abstract

Large area, shallow fields are well suited to proton therapy. However, due to beam production limitations, such volumes typically require multiple matched fields. This is problematic due to the relatively narrow beam penumbra at shallow depths compared to electron and photon beams. Therefore, highly accurate dose planning and delivery is required. As the dose delivery includes shifting the patient for matched fields, accuracy at the 1–2 millimeter level in patient positioning is also required. This study investigates the dosimetric accuracy of such proton field matching by an innovative robotic patient positioner system (RPPS). The dosimetric comparisons were made between treatment planning system calculations, radiographic film and ionization chamber measurements. The results indicated good agreement amongst the methods and suggest that proton field matching by a RPPS is accurate and efficient.PACS number: 87.55.km

AAPM task group 224: Comprehensive proton therapy machine quality assurance

“…Couch translational motion accuracy should be confirmed for the most extreme movements and should have a tolerance of AE1 mm. [113][114][115] The "trueness" of the couch positioning is defined as the motion of an object in a straight line without any deviation from that line. The couch vertical axis trueness should be verified because the couch can be subject to accidental collisions or to malfunction resulting from wear and tear.…”

Technique for comprehensive head and neck irradiation using 3-dimensional conformal proton therapy

“…We have previously reported a formal assessment of the accuracy of field matching using our robotic patient positioner and found good agreement between treatment planning calculations and radiographic film and ionization chamber measurements. 34 Most published clinical experiences with proton therapy involved 3D conformal treatment planning in which the desired dosimetry is achieved by manual iterative adjustments in the shape of individual field apertures (blocks) and compensators, or patient-specific devices (PSDs). With uniform scanning, as used in our patients, a uniform dose is delivered across the treatment field with a uniform spread-out Bragg peak (SOBP).…”

New horizons in particle therapy systems

“…Parallel beam scanning systems are considered to be more challenging and more expensive to provide than divergent beam scanning systems. Therefore, the following points need to be considered in relation to the perceived advantage of parallel scanning systems: To some extent, by forcing optimization functions to minimize entrance dose, modulated scanning optimization can also be used to reduce skin dose. Unlike the technical and dosimetric challenges of field matching with scattering systems, robust treatment planning optimization for scanning systems (see “Advanced Treatment Planning” 2018 (in this issue)) provides simple and effective field matching for both parallel and divergent beam geometries. The degree of beam divergence from parallelism also depends on the applied field size (smaller approaches parallelism) and SAD (greater approaches parallelism) for divergent beams. …”

“…• Unlike the technical and dosimetric challenges of field matching with scattering systems, 19 robust treatment planning optimization for scanning systems (see "Advanced Treatment Planning" 2018 (in this issue)) provides simple and effective field matching 20 for both parallel and divergent beam geometries.…”