Basic Physics of Proton Therapy - AAPM proton vs photon lateral penumbra • the proton penumbra depends on system design and setup parameters • in general, the proton penumbra is not significantly sharper than the photon penumbra • the low-dose ‘tails’ of the proton field are not as pronounced as for photon fields
Proton beam therapy - The University of Toledo • At shallower depths, proton penumbra (both 20%–80% and 50%–95%) is smaller than that of photon beams • It increases rapidly with depth and becomes larger than the 15-MV photon beam for depths greater than 17 cm for 20%–80% and 22 Lateral beam profiles in the penumbra region for cm for 50%–95%
Physics of Particle Beams - ptcog. site Lateral Penumbra Changes in Depth Photons: • Photons interact with electrons by Compton scattering • Scattered photons get out of beam • Remaining photons have almost same energy spectrum • No change over depth in the energy and momentum distribution of the electrons from Compton scattering • Therefore no change in lateral buildup
Photon Dose Distributions - Oncology Medical Physics Key Point: Energy (in addition to collimator design, field size, and SAD) has an impact on penumbra Lower energies tend to cause less transmission penumbra but have greater lateral scatter than higher energies These competing effects yield the smallest physical penumbra at about 10MV in soft tissue
Comparison of Measured and Computed Lateral Penumbra for a by . . . - FLVC The lateral penumbra of a proton pencil beam scanning system (PBS) is of great importance in sparing of organs at risk and normal tissue when treating patients The purpose of this current work is to measure the lateral penumbra of the Ion Beam Applications (Ion Beam Applications, Louvain‐la‐Neuve, Belgium) ProteusPLUS PBS
Proton Therapy - SpringerLink Per ICRU-78 , “for depths typically up to ~17–18 cm in tissue, the lateral dose falloff is steeper than that for photon beams ” At larger depths, scattering in the patient increases the lateral penumbra such that it is generally larger than that for photon beams
Proton Treatment Planning • Protons have a sharp lateral beam penumbra which decreases with increasing beam energy and, hence, depth of penetration • Proton beam penumbra is widest in the Bragg peak region where the proton energy is least • Penumbra is narrower for proton then photon beam for penetrations up to 17‐18 cm
Capstone Practice Test 2 Flashcards - Quizlet The lateral penumbra of a proton field is _____ as compared to a photon field a slightly less b less c slightly greater d about the same
Comprehensive investigation of lateral dose profile and output factor . . . Results: Quantification of the lateral penumbra broadening and signal reduc-tion at the fields center revealed that measurements in the pencil beam scanning fields are only compromised slightly even by large volume ionization chambers with maximum differences in the lateral penumbra of 0 25 mm and 4% signal reduction at the field center