Merging Orthovoltage X-Ray Minibeams spare the proximal tissues while producing a solid beam at the target

Abstract

Conventional radiation therapy of brain tumors often produces cognitive deficits, particularly in children. We investigated the potential efficacy of merging Orthovoltage X-ray Minibeams (OXM). It segments the beam into an array of parallel, thin (~0.3 mm), planar beams, called minibeams, which are known from synchrotron x-ray experiments to spare tissues. Furthermore, the slight divergence of the OXM array make the individual minibeams gradually broaden, thus merging with their neighbors at a given tissue depth to produce a solid beam. In this way the proximal tissues, including the cerebral cortex, can be spared. Here we present experimental results with radiochromic films to characterize the method’s dosimetry. Furthermore, we present our Monte Carlo simulation results for physical absorbed dose, and a first-order biologic model to predict tissue tolerance. In particular, a 220-kVp orthovoltage beam provides a 5-fold sharper lateral penumbra than a 6-MV x-ray beam. The method can be implemented in arc-scan, which may include volumetric-modulated arc therapy (VMAT). Finally, OXM’s low beam energy makes it ideal for tumor-dose enhancement with contrast agents such as iodine or gold nanoparticles, and its low cost, portability, and small room-shielding requirements make it ideal for use in the low-and-middle-income countries.

Requirements for Designing an Effective Metallic Nanoparticle (NP)-Boosted Radiation Therapy (RT)

“…Even if MV photons are more abundant in cancer therapy, kV photons come again into play with microbeams or minibeams [210]. kV machines are less expensive, require less shielding, and could make NP-induced cancer radiotherapy available to most countries.…”

Iodine nanoparticle radiotherapy of human breast cancer growing in the brains of athymic mice

“…( d ): Monte Carlo simulations comparing unidirectional depth-dose distributions of 6 MV and 320 kVp X-rays with 320 kVp convergent minibeams. Figures ( a ) and ( b ) are from reference 7 and ( d ) is from reference 33 . Although the 320 kVp energy spectrum is different from the 100 kVp used here (more appropriate for mice), this figure is only intended to present a concept adjusted to human use.…”

“…For both mini- and microbeams it was found that blood vessels in the intervening unirradiated segments could repair the irradiated adjacent segments with no consequential residual damage, thus greatly reducing the entrance dose damage 55 . Also, by merging the segmented beams at the tumor, resulting in a damaging broad beam, deep tumors can be selectively irradiated, thus making even unidirectional orthovoltage irradiation superior to megavoltage 33 , 56 (Fig. 6 d).…”

Iodine nanoparticles enhance radiotherapy of intracerebral human glioma in mice and increase efficacy of chemotherapy

“…Even ultrahigh-dose millimeter- and micrometer-wide orthovoltage X-ray beams have surprising yielded minimal normal-tissue damage: intervening minimally irradiated tissues enable almost full repair of many kinds of normal tissues 67 – 69 . The beams can be interlaced or converged at the tumor, providing an even better dose distribution than with MV X-rays 70 . This technique is now being considered for improving synchrotron and proton radiotherapy 71 – 73 .…”