Radiation dosimetry changes in radiotherapy treatment plans for adult patients arising from the selection of the CT image reconstruction kernel.

OBJECTIVE: The reconstruction kernel used for a CT scan strongly influences the image quality. This work investigates the changes in Hounsfield units (HUs) which can arise when altering the image reconstruction kernel for planning CT images and the associated changes in dose in the radiotherapy treatment plan if the treatment planning system (TPS) is not re-calibrated. METHODS: Head and neck, prostate and lung CT images from four centres were used. For a specific scan, the base image was acquired using the original reconstruction kernel (used when the TPS was calibrated) and the treatment plan produced. The treatment plan was applied to all images from the other reconstruction kernels. Differences in dose-volume metrics for the planning target volume (PTV) and organs at risk (OARs) were noted and HU differences between images measured for air, soft tissue and bone. RESULTS: HU change in soft tissue had the greatest influence on dose change. When within ±20 HU for soft tissue and ±50 HU for bone and air the dose change in the PTV and OAR was within ±0.5% and ±1% respectively. CONCLUSIONS: When imaging parameters were changed, if HU change was within ±20 HU for soft tissue and ±50 HU for bone and air, the change in the PTV and OAR doses was below 1%. ADVANCES IN KNOWLEDGE: The degree of dose change in the treatment plan with HU change is demonstrated for current TPS algorithms. This adds to the limited evidence base for recommendations on HU tolerances as a tool for radiotherapy CT protocol optimization.

IPEM topical report: the first UK survey of dose indices from radiotherapy treatment planning computed tomography scans for adult patients.

CT scans are an integral component of modern radiotherapy treatments, enabling the accurate localisation of the treatment target and organs-at-risk, and providing the tissue density information required for the calculation of dose in the treatment planning system. For these reasons, it is important to ensure exposures are optimised to give the required clinical image quality with doses that are as low as reasonably achievable. However, there is little guidance in the literature on dose levels in radiotherapy CT imaging either within the UK or internationally. This IPEM topical report presents the results of the first UK wide survey of dose indices in radiotherapy CT planning scans. Patient dose indices were collected for prostate, gynaecological, breast, lung 3D, lung 4D, brain and head and neck scans. Median values per scanner and examination type were calculated and national dose reference levels and 'achievable levels' of CT dose index (CTDIvol), dose-length-product (DLP) and scan length are proposed based on the third quartile and median values of these distributions, respectively. A total of 68 radiotherapy CT scanners were included in this audit. The proposed dose reference levels for CTDIvol and DLP are; prostate 16 mGy and 570 mGy · cm, gynaecological 16 mGy and 610 mGy · cm, breast 10 mGy and 390 mGy · cm, lung 3D 14 mGy and 550 mGy · cm, lung 4D 63 mGy and 1750 mGy · cm, brain 50 mGy and 1500 mGy · cm and head and neck 49 mGy and 2150 mGy · cm. Significant variations in dose indices were noted, with head and neck and lung 4D yielding a factor of eighteen difference between the lowest and highest dose scanners. There was also evidence of some clustering in the data by scanner manufacturer, which may be indicative of a lack of local optimisation of individual systems to the clinical task. It is anticipated that providing this data to the UK and wider radiotherapy community will aid the optimisation of treatment planning CT scan protocols.

Catalytic nanoreactors in continuous flow: hydrogenation inside single-walled carbon nanotubes using supercritical CO2.

One nanometre wide carbon nanoreactors are utilised as the reaction vessel for catalytic chemical reactions on a preparative scale. Sub-nanometre ruthenium catalytic particles which are encapsulated solely within single-walled carbon nanotubes offering a unique reaction environment are shown to be active when embedded in a supercritical CO2 continuous flow reactor. A range of hydrogenation reactions were tested and the catalyst displayed excellent stability over extended reaction times.

Correlation between prostate brachytherapy-related urethral stricture and peri-apical urethral dosimetry: a matched case-control study.

BACKGROUND AND PURPOSE: Radiation dose to the bulbomembranous urethra has been shown to correlate with urethral stricture formation. This retrospective case-control study was designed to explore the relationship between dose to the apical/peri-apical regions of the urethra and development of brachytherapy (BXT)-related urethral stricture. MATERIALS AND METHODS: Cases were patients who developed urethral stricture after treatment with BXT as monotherapy and who had urethral dosimetry post-implant. Each case was matched with a control that had not developed urethral stricture. Dosimetry was compared between cases and controls. RESULTS: Twenty-three cases were pair matched with 23 controls. There were no significant differences between the two groups in terms of age, presenting Prostate Specific Antigen (PSA), International Prostate Symptom Score (IPSS) or Gleason score. The dose delivered to the peri-apical and apical urethra was significantly higher for cases when compared with controls (peri-apical urethra: mean V(150) 1.1 Vs 0.8 cc [p=0.02]; apical urethra: mean dose 200 Vs 174 Gy [p=0.01]). The distance from the prostate apex to isodose lines was also found to be significant in predicting stricture formation. CONCLUSION: There was evidence to suggest that the development of BXT-related stricture was associated with radiation dose at the apical and peri-apical urethra. Attention to the dose delivered to those areas may minimise the risk of developing such morbidity.