Observation of grating diffraction radiation at the KEK LUCX facility.

The development of linac-based narrow-band THz sources with sub-picosecond, [Formula: see text]-level radiation pulses is in demand from the scientific community. Intrinsically monochromatic emitters such as coherent Smith-Purcell radiation sources appear as natural candidates. However, the lack of broad spectral tunability continues to stimulate active research in this field. We hereby present the first experimental investigation of coherent grating diffraction radiation (GDR), for which comparable radiation intensity with central frequency fine-tuning in a much wider spectral range has been confirmed. Additionally, the approach allows for bandwidth selection at the same central frequency. The experimental validation of performance included the basic spectral, spatial and polarization properties. The discussion of the comparison between GDR intensity and other coherent radiation sources is also presented. These results further strengthen the foundation for the design of a tabletop wide-range tunable quasi-monochromatic or multi-colour radiation source in the GHz-THz frequency range.

Dosimetric and radiobiological comparison of simultaneous integrated boost and sequential boost of locally advanced cervical cancer.

Introduction Some patients with locally advanced cervical cancer (LACC) cannot undergo brachytherapy (BT). Possible treatment includes two-stage external beam radiotherapy (sequential boost - SEQ) or single-stage external beam radiotherapy (simultaneous integrated boost - SIB). The goal of this paper was to carry out dosimetric and radiobiological comparison of these techniques with respect to tumour and organs-at-risk (OARs) irradiation. Methods The anatomic data of six patients with LACC were used for this study. The single-stage SIB-VMAT (25, 27 or 30 fractions) and double-stage SEQ-VMAT (25 + 6 fractions) plans were developed to deliver EQD2=50 Gy to the pelvic region and EQD2=90 Gy to the tumour. The developed plans were compared with respect to an EQD2 dose delivered to a tumour and to the OARs, expected tumour control probability and normal tissue complications probability. Results The developed SIB-VMAT and SEQ-VMAT plans had physical coverage of the CTV tumours with more than 95% of the prescribed dose delivered to more than 95% of the volume. The irradiation of the tumour for both SIB-VMAT and SEQ-VMAT has comparable EQD2 values close to 87-88 Gy. SIB-VMAT treatment plans provided lower levels of irradiation of OARs than SEQ-VMAT plans. The optimal number of fractions for SIB-VMAT was 27. Conclusion SIB-VMAT is a better treatment option for patients with LACC that are not eligible for BT. Results show that both SIB-VMAT and SEQ-VMAT allowed good coverage of the tumour and high-quality dose delivery. SIB-VMAT allowed minimising irradiation of OARs and shortening the overall treatment time by a week.

Influence of SBRT fractionation on TCP and NTCP estimations for prostate cancer.

INTRODUCTION: Stereotactic body radiation therapy is widely used for the hypofractionated treatment of prostate cancer. The range of total doses used in different clinical trials varies from 33.5 to 50 Gy delivered in 4 or 5 fractions. The choice of an optimal total dose value and fractionation regimen for a particular patient can be carried out using the integral radiobiological criteria, namely tumour control probability (TCP) and normal tissue complication probability (NTCP). In this study, we have investigated the dependence of simulated TCP/NTCP values on total dose in the range of 30-40 Gy delivered in 4 or 5 fractions for patients with low-risk prostate cancer in order to find the optimal total dose value and fractionation regimen. METHODS: The anatomic data (DICOM CT images) of 12 patients with low-risk prostate cancer, who were treated at Tomsk Regional Oncology Centre, were used for the calculation. Dosimetric treatment plans for all patients were simulated using VMAT with 2 arcs in the Monaco treatment planning system v5.10 (Elekta Instrument AB, Stockholm) with a total dose equal to 36.25 Gy. The dosimetric plans were rescaled in the dose range of 30-40 Gy. The TCP and NTCP values were calculated based on differential dose volume histograms using the Niemierko model for both TCP and NTCP, and the Källman-s model for NTCP calculations. The TCP calculation was carried out using the uncertainty of well-known tumour radiobiological parameters values, including α/ß value. NTCP was calculated for an anterior rectal wall, which was the most irradiated organ at risk due to its close contact with the planning target volume. RESULTS: The TCP and NTCP calculations for VMAT of the prostate cancer have shown that the optimal total dose ranges were equal to 32-34 Gy delivered in 4 fractions or 35-38 Gy delivered in 5 fractions. At doses lower than the optimal ones, the TCP values were lower than 95%, while TCP uncertainties were significant (as low as 80%). This fact might bring unexpectedly poor treatment results. At doses higher than optimal ones, the probability of toxicity to the anterior rectal wall became significant. CONCLUSION: The optimization of radiation therapy regimen based on TCP/NTCP criteria could help to determine an optimal total dose and a number of fractions for a particular patient depending on patient-specific anatomic features and planned dose distribution.

Spatial resolution improvement for an optical transition radiation monitor by asymmetric light collection.

The applicability of optical transition radiation (OTR) for measurements of micron sized transverse electron beam profiles is limited not only by the optical system resolution which has a fundamental limit imposed by the uncertainty principle. In the case of OTR generation, a single electron crossing the boundary between vacuum and screen cannot be considered as a single emitting point with isotropic angular distribution. On the contrary, the radiation is emitted from an area with a transverse range that is defined by the radial extension of the electron's Lorentz contracted Coulomb field and is typically estimated as γλ (with γ the Lorentz factor and λ the wavelength of observation). The OTR angular distribution has a characteristic "funnel" shape. As a result the one-dimensional image of a single electron measured with an ideal thin lens has a double lobe shape, and the resolution of any OTR based imaging system is determined by this double lobe function which is also known as OTR Point Spread Function (PSF). As a consequence, the reconstruction of micron sized electron beam profiles is hampered not only due to the fundamental diffraction limit, but also due to the PSF lobe shape. In this paper we present two approaches to improve the spatial resolution of an OTR monitor based on asymmetric light collection using a traditional optical system which allows blocking of one of the lobes. With such a scheme, an OTR PSF can be achieved that is comparable to the one of an ideal point source (Airy distribution).

Tomsk Polytechnic University cyclotron as a source for neutron based cancer treatment.

In this paper we present our cyclotron based neutron source with average energy 6.3 MeV generated during the 13.6 MeV deuterons interactions with beryllium target, neutron field dosimetry, and dosimetry of attendant gamma fields. We also present application of our neutron source for cancer treatment.