To fully exploit the prospects presented by the increasing focus on biological approaches for enhancing radiotherapy outcomes, improvements in repeatability and translatability of radiobiological and preclinical studies are required. This requires the development and adoption of appropriate dosimetric standards and reproducible approaches to increase confidence in the studies, enabling inter-laboratory validation and facilitating clinical translation. An Institute of Physics and Engineering in Medicine (IPEM) working party reviewed the current status and challenges associated with dosimetry of medium-energy X-rays and make recommendations with the aim to optimize the potential clinical significance of radiobiological preclinical investigations. The paper discusses the currently available resources with technical recommendations for performing dosimetry in medium-energy X-rays, along with the consequences of lack of standardization and implications of dose inhomogeneity. It is clear that there is still a gap in understanding the needs for standardization of dosimetric aspects of preclinical and radiobiological studies. It is recommended that these radiobiology studies should be conducted in partnership with medical/radiation physicists. This collaboration ensures the correct utilization of suitable dosimetry systems, thus guaranteeing accuracy and consistency of dose delivery. Appropriate calibration and traceability to national/international standards laboratory, along with regular quality assurance of radiation devices, are paramount to reproducibility. Additionally, it is critical that experimental details and associated dosimetry are sufficiently reported to ensure accurate replication that enables reanalysis including evaluation of dose distributions. Increasing awareness among the researchers and the funding bodies was identified as a crucial step to improve translatability and appropriate resources are budgeted to increase the value for money of research proposals. The proposed recommendations will serve as a vital resource for researchers, encouraging uniformity in experimental design and improving the translatability of preclinical research to clinical settings.

Despite well-established dosimetry in clinical radiotherapy, dose measurements in pre-clinical and radiobiology studies are frequently inadequate, thus undermining the reliability and reproducibility of published findings. The lack of suitable dosimetry protocols, coupled with the increasing complexity of pre-clinical irradiation platforms, undermines confidence in preclinical studies and represents a serious obstacle in the translation to clinical practice. To accurately measure output of a pre-clinical radiotherapy unit, appropriate Codes of Practice (CoP) for medium energy x-rays needs to be employed. However, determination of absorbed dose to water (D _w ) relies on application of backscatter factor (B _w ) employing in-air method or carrying out in-phantom measurement at the reference depth of 2 cm in a full backscatter (i.e. 30 × 30 × 30 cm ³ ) condition. Both of these methods require thickness of at least 30 cm of underlying material, which are never fulfilled in typical pre-clinical irradiations. This work is focused on evaluation the effects of the lack of recommended reference conditions in dosimetry measurements for pre-clinical settings and is aimed at extending the recommendations of the current CoP to practical experimental conditions and highlighting the potential impact of the lack of correct backscatter considerations on radiobiological studies.

Purpose Current techniques and procedures for dosimetry in microbeams typically rely on radiochromic film or small volume ionization chambers for validation and quality assurance in 2D and 1D, respectively. Whilst well characterized for clinical and preclinical radiotherapy, these methods are noninstantaneous and do not provide real time profile information. The objective of this work is to determine the suitability of the newly developed vM1212 detector, a pixelated CMOS (complementary metal-oxide-semiconductor) imaging sensor, for in situ and in vivo verification of x-ray microbeams. Methods Experiments were carried out on the vM1212 detector using a 220 kVp small animal radiation research platform (SARRP) at the Helmholtz Centre Munich. A 3 x 3 cm(2) square piece of EBT3 film was placed on top of a marked nonfibrous card overlaying the sensitive silicon of the sensor. One centimemter of water equivalent bolus material was placed on top of the film for build-up. The response of the detector was compared to an Epson Expression 10000XL flatbed scanner using FilmQA Pro with triple channel dosimetry. This was also compared to a separate exposure using 450 mu m of silicon as a surrogate for the detector and a Zeiss Axio Imager 2 microscope using an optical microscopy method of dosimetry. Microbeam collimator slits with range of nominal widths of 25, 50, 75, and 100 mu m were used to compare beam profiles and determine sensitivity of the detector and both film measurements to different microbeams. Results The detector was able to measure peak and valley profiles in real-time, a significant reduction from the 24 hr self-development required by the EBT3 film. Observed full width at half maximum (FWHM) values were larger than the nominal slit widths, ranging from 130 to 190 mu m due to divergence. Agreement between the methods was found for peak-to-valley dose ratio (PVDR), peak to peak separation and FWHM, but a difference in relative intensity of the microbeams was observed between the detectors. Conclusions The investigation demonstrated that pixelated CMOS sensors could be applied to microbeam radiotherapy for real-time dosimetry in the future, however the relatively large pixel pitch of the vM1212 detector limit the immediate application of the results.

Image-guided small animal irradiation platforms deliver small radiation fields in the medium energy x-ray range. Commissioning of such platforms, followed by dosimetric verification of treatment planning, are mostly performed with radiochromic film. There is a need for independent measurement methods, traceable to primary standards, with the added advantage of immediacy in obtaining results. This investigation characterizes a small volume ionization chamber in medium energy x-rays for reference dosimetry in preclinical irradiation research platforms. The detector was exposed to a set of reference x-ray beams (0.5–4 mm Cu HVL). Leakage, reproducibility, linearity, response to detector’s orientation, dose rate, and energy dependence were determined for a 3D PinPoint ionization chamber (PTW 31022). Polarity and ion recombination were also studied. Absorbed doses at 2 cm depth were compared, derived either by applying the experimentally determined cross-calibration coefficient at a typical small animal radiation platform ‘user’s’ quality (0.84 mm Cu HVL) or by interpolation from air kerma calibration coefficients in a set of reference beam qualities. In the range of reference x-ray beams, correction for ion recombination was less than 0.1%. The largest polarity correction was 1.4% (for 4 mm Cu HVL). Calibration and correction factors were experimentally determined. Measurements of absorbed dose with the PTW 31022, in conditions different from reference were successfully compared to measurements with a secondary standard ionization chamber. The implementation of an End-to-End test for delivery of image-targeted small field plans resulted in differences smaller than 3% between measured and treatment planning calculated doses. The investigation of the properties and response of a PTW 31022 small volume ionization chamber in medium energy x-rays and small fields can contribute to improve measurement uncertainties evaluation for reference and relative dosimetry of small fields delivered by preclinical irradiators while maintaining the traceability chain to primary standards.