Direct action of radiation on mummified cells: modeling of computed tomography by Monte Carlo algorithms

Dosimetric assessment of the exposure of radiotherapy patients due to cone-beam CT procedures

Cone-beam computed tomography (CBCT) is widely used for pre-treatment verification and patient setup in image-guided radiation therapy (IGRT). CBCT imaging is employed daily and several times per patient, resulting in potentially high cumulative imaging doses to healthy tissues that surround exposed target organs. Computed tomography dose index (CTDI) is the parameter used by CBCT equipment as indication of the radiation output to patients. This study aimed to increase the knowledge on the relation between CBCT organ doses and weighted CTDI (CTDI_W) for a thorax scanning protocol. A CBCT system was modelled using the Monte Carlo (MC) radiation transport program MCNPX2.7.0. Simulation results were validated against half-value layer (HVL), axial beam profile, patient skin dose (PSD) and CTDI measurements. For organ dose calculations, a male voxel phantom ("Golem") was implemented with the CBCT scanner computational model. After a successful MC model validation with measurements, a systematic comparison was performed between organ doses (and their distribution) and CTDI dosimetry concepts [CTDI_W and cumulative dose quantities f₁₀₀(150) and [Formula: see text]]. The results obtained show that CBCT organ doses vary between 1.2 ± 0.1 mGy and 3.3 ± 0.2 mGy for organs located within the primary beam. It was also verified that CTDI_W allows prediction of absorbed doses to tissues at distances of about 5 cm from the isocentre of the CBCT system, whereas f₁₀₀(150) allows prediction of organ doses at distances of about 10 cm from the isocentre, independently from its location. This study demonstrates that these dosimetric concepts are suitable methods that easily allow a good approximation of the additional CBCT imaging doses during a typical lung cancer IGRT treatment.

Risk to fragmented DNA in dry, wet, and frozen states from computed tomography: a comparative theoretical study

Computed tomography represents the gold standard in forensic and palaeopathological diagnosis. However, the X-rays used may affect the DNA quality through fragmentation and loss of genetic information. Previous work showed that the effects of ionizing radiation on dry DNA are non-significant with P < 10(-8), which cannot be detected by means of polymerase chain reaction methods. In the present paper, complete analytical model that characterizes radiation effects on fragmented DNA in dry, wet, and frozen states is described. Simulation of radiation tracks in water phantom cells was performed using the Geant4-DNA toolkit. Cell hits by electrons with energies between 5 and 20 keV were simulated, and the formation of radiolytic products was assessed at a temperature of 298 K. The diffusion coefficient and the mean square displacement of reactive species were calculated by Stokes-Einstein-Smoluchowski relations at 273 K. Finally, DNA fragment damage was estimated using the density distribution of fragments calculated from atomic force microscopy images. The lowest probability of radiation-induced DNA damage was observed for dry state, with a range from 2.5 × 10(-9) to 7.8 × 10(-12) at 298 K, followed by that for frozen state, with a range from 0.9 to 4 × 10(-7) at 273 K. The highest probability of radiation-induced DNA damage was demonstrated for fragmented DNA in wet state with a range from 2 to 9 × 10(-7) at 298 K. These results significantly improve the interpretation of CT imaging in future studies in forensic and palaeopathological science.

Invasive versus Non Invasive Methods Applied to Mummy Research: Will This Controversy Ever Be Solved?

Advances in the application of non invasive techniques to mummified remains have shed new light on past diseases. The virtual inspection of a corpse, which has almost completely replaced classical autopsy, has proven to be important especially when dealing with valuable museum specimens. In spite of some very rewarding results, there are still many open questions. Non invasive techniques provide information on hard and soft tissue pathologies and allow information to be gleaned concerning mummification practices (e.g., ancient Egyptian artificial mummification). Nevertheless, there are other fields of mummy studies in which the results provided by non invasive techniques are not always self-explanatory. Reliance exclusively upon virtual diagnoses can sometimes lead to inconclusive and misleading interpretations. On the other hand, several types of investigation (e.g., histology, paleomicrobiology, and biochemistry), although minimally invasive, require direct contact with the bodies and, for this reason, are often avoided, particularly by museum curators. Here we present an overview of the non invasive and invasive techniques currently used in mummy studies and propose an approach that might solve these conflicts.