Application of the pencil-beam redefinition algorithm in heterogeneous media for proton beam therapy.

In proton beam therapy, changes in the proton range due to lateral heterogeneity may cause serious errors in the dose distribution. In the present study, the pencilbeam redefinition algorithm (PBRA) was applied to proton beam therapy to address the problem of lateral density heterogeneity. In the calculation, the phase-space parameters were characterized for multiple range (i.e. proton energy) bins for given pencil beams. The particles that were included in each pencil beam were transported and redefined periodically until they had stopped. The redefined beams formed a detouring path that was different from that of the non-redefined pencil beams, and the path of each redefined beam was straight. The results calculated by the PBRA were compared with measured proton dose distributions in a heterogeneous slab phantom and an anthropomorphic phantom. Through the beam redefinition process, the PBRA was able to predict the measured proton-detouring effects. Therefore, the PBRA may allow improved calculation accuracy when dealing with lateral heterogeneities in proton therapy applications.

Accumulation of sub-100 nm polymeric micelles in poorly permeable tumours depends on size.

A major goal in cancer research is to develop carriers that can deliver drugs effectively and without side effects. Liposomal and particulate carriers with diameters of ∼100 nm have been widely used to improve the distribution and tumour accumulation of cancer drugs, but so far they have only been effective for treating highly permeable tumours. Here, we compare the accumulation and effectiveness of different sizes of long-circulating, drug-loaded polymeric micelles (with diameters of 30, 50, 70 and 100 nm) in both highly and poorly permeable tumours. All the polymer micelles penetrated highly permeable tumours in mice, but only the 30 nm micelles could penetrate poorly permeable pancreatic tumours to achieve an antitumour effect. We also showed that the penetration and efficacy of the larger micelles could be enhanced by using a transforming growth factor-ß inhibitor to increase the permeability of the tumours.

Optical-field-ionization effects on the propagation of an ultraintense laser pulse in high- Z gas jets.

Interaction of an ultraintense, a(0) >>1, laser pulse with an underdense Ar plasma is analyzed via a two-dimensional particle-in-cell simulation which self-consistently includes optical-field ionization. In spite of rapid growth of ion charge Z and, hence, electron density at the laser front, relativistic self-focusing is shown to persist owing to a reduction of the expected plasma defocusing resulting from the weak radial dependence of the ion charge on laser intensity (even for Z/gamma>1 where gamma is the electron relativistic factor).

Radiation damping effects on the interaction of ultraintense laser pulses with an overdense plasma.

A strong effect of radiation damping on the interaction of an ultraintense laser pulse with an overdense plasma slab is found and studied via a relativistic particle-in-cell simulation including ionization. Hot electrons generated by the irradiation of a laser pulse with a radiance of I lambda(2)>10(22) W microm(2)/cm(2) and duration of 20 fs can convert more than 35% of the laser energy to radiation. This incoherent x-ray emission lasts for only the pulse duration and can be intense. The radiation efficiency is shown to increase nonlinearly with laser intensity. Similar to cyclotron radiation, the radiation damping may restrain the maximal energy of relativistic electrons in ultraintense-laser-produced plasmas.