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Objective. Relative biological effectiveness (RBE) differs between radiation qualities. However, an RBE of 1.0 has been established for photons regardless of the wide range of photon energies used clinically, the lack of reproducibility in radiobiological studies, and outdated reference energies used in the experimental literature. Moreover, due to intrinsic radiosensitivity, different cancer types have different responses to radiation. This study aimed to characterize the RBE of clinically relevant high and low photon energies in vitro for three human cancer cell lines: HCT116 (colon), HeLa (cervix), and PC3 (prostate). Approach. Experiments were conducted following dosimetry protocols provided by the American Association of Physicists in Medicine. Cells were irradiated with 6 MV x-rays, an 192Ir brachytherapy source, 225 kVp and 50 kVp x-rays. Cell survival post-irradiation was assessed using the clonogenic assay. Survival fractions were fitted using the linear quadratic model, and survival curves were generated for RBE calculations. Main results. Cell killing was more efficient with decreasing photon energy. Using 225 kVp x-rays as the reference, the HCT116 RBESF0.1 for 6 MV x-rays, 192Ir, and 50 kVp x-rays were 0.89 ± 0.03, 0.95 ± 0.03, and 1.24 ± 0.04; the HeLa RBESF0.1 were 0.95 ± 0.04, 0.97 ± 0.05, and 1.09 ± 0.03, and the PC3 RBESF0.1 were 0.84 ± 0.01, 0.84 ± 0.01, and 1.13 ± 0.02, respectively. HeLa and PC3 cells had varying radiosensitivity when irradiated with 225 and 50 kVp x-rays. Significance. This difference supports the notion that RBE may not be 1.0 for all photons through experimental investigations that employed precise dosimetry. It highlights that different cancer types may not have identical responses to the same irradiation quality. Additionally, the RBE of clinically relevant photons was updated to the reference energy of 225 kVp x-rays. [ABSTRACT FROM AUTHOR]

Background Purpose Methods Results Conclusions Large reported variability in the material composition and geometrical components of the Xoft electronic high‐dose‐rate brachytherapy Causes inter‐source discrepancy in the source output. This variability is due to the manual manufacturing and assembly of the sources.This study aimed to develop a dosimetry software tool called E‐Brachy to characterize the Xoft source and quantify the discrepancies in its photon spectrum and dosimetric properties.E‐Brachy is based on the Geant4 Monte Carlo toolkit and consists of two parts. In part one, the geometry and material composition for the source received in the computer‐aided design format from the vendor were converted to the geometry description markup language format using the GUIMesh Python tool and integrated into the E‐Brachy software. There was a large variation in material composition and thickness for some of the tube components. The simulation started from electrons and resulted in x‐ray generations in the anode region. Multithreading, a track length estimation, and the uniform bremsstrahlung splitting variance reduction techniques were used to decrease the simulation time and increase the x‐ray production. The photon energy, position, and momentum were saved into a phase space file as the photon exited the source, but before interacting with the external environment. The obtained x‐ray energy spectrum was compared with measurements from the National Institute of Standards and Technology (NIST). In part two, by sampling from the generated photons, the dose rates and dosimetric parameters according to the TG‐43 protocol were calculated for model S7500 and compared to the ones previously calculated for model S700 source, which were deemed identical by the manufacturer.The material composition that resulted in the most similar spectrum as the measured NIST spectrum with Pearson's correlation coefficient of 0.99 and a calculated Euclidean difference of 0.061±0.001$0.061\,\pm \,0.001$ keV was chosen for further dosimetric analysis of the model S7500 source. Characteristic peaks showed the presence of tungsten, yttrium, and silver in the source components. Differences in dose rates between the two source models surpassed 20% for polar angles θ≥150∘$\theta \,\ge \,150^\circ$, reaching a peak at r=3$r\,=\,3$ cm and θ=175∘$\theta \,=\,175^\circ$. The differences in the radial dose function values were within 5%. The relative difference in percentage between the anisotropy function values of the two models was closer to 0 for smaller θ$\theta$ values, but at higher polar angles, they increased to 300%.A software package called E‐Brachy was successfully developed for the characterization and dosimetry of Xoft electronic brachytherapy sources. E‐Brachy can be combined with spectral measurements to investigate the inter‐ and intra‐source variability. The software package was tested by comparing the simulated spectra from the S7500 Xoft source model with NIST measurements and its TG‐43 parameters with the S700 model. The TG‐43 parameters between the two sources significantly exceed the recommendations of TG‐56. [ABSTRACT FROM AUTHOR]

Purpose: To issue consensus recommendations for contact X-Ray brachytherapy (CXB) for rectal cancer covering pre-treatment evaluation, treatment, dosimetric issues and follow-up. These recommendations cover CXB in the definitive and palliative setting., Methods: Members of GEC ESTRO with expertise in rectal CXB issued consensus-based recommendations for CXB based on literature review and clinical experience. Levels of evidence according to the Oxford Centre for Evidence based medicine guidance are presented where possible., Results: The GEC ESTRO ACROP consensus recommendations support the use of CXB to increase the chances of clinical complete remission and cure for patients who are elderly with high surgical risk, surgically unfit or refusing surgery. For palliative treatment, the use of CXB is recommended for symptomatic relief and disease control. The use of CXB in an organ-preservation setting in surgically fit patients is recommended within the setting of a clinical trial or registry., Conclusions: The GEC ESTRO ACROP recommendations for CXB are provided. Recommendations towards standardisation of reporting and prescription are given. Practitioners are encouraged to follow these recommendations and to develop further clinical trials to examine this treatment modality and increase the evidence base for its use. The routine collection of outcomes both clinical and patient-reported is also encouraged., Competing Interests: JP Gerard is the medical advisor of Ariane Medical Systems Company, Derby, UK F Verhaegen, M Berbee and EJ van Limbergen have submitted a patent on an endorectal probe device a patent for effecting radiation treatment of colorectal cancerous tissue in the rectum of a human or animal subject which is pending to Maastricht University. All other authors state they have no conflicts of interest, (© 2021 The Authors. Published by Elsevier B.V. on behalf of European Society for Radiotherapy and Oncology.)