Factors affecting accuracy and precision in ultrasound guided radiotherapy

BACKGROUND AND PURPOSE

Transperineal ultrasound (TPUS) is used clinically for directly assessing prostate motion. Factors affecting accuracy and precision in TPUS motion estimation must be assessed to realise its full potential.

METHODS AND MATERIALS

Patients were imaged using volumetric TPUS during the Clarity-Pro trial (NCT02388308). Prostate motion was measured online at patient set-up and offline by experienced observers. Cone beam CT with markers was used as a comparator and observer performance was also quantified. The influence of different clinical factors was examined to establish specific recommendations towards efficacious ultrasound guided radiotherapy.

RESULTS

From 330 fractions in 22 patients, offline observer random errors were 1.5 mm, 1.3 mm, 1.9 mm (left-right, superior-inferior, anteroposterior respectively). Errors increased in fractions exhibiting poor image quality to 3.3 mm, 3.3 mm and 6.8 mm. Poor image quality was associated with inconsistent probe placement, large anatomical changes and unfavourable imaging conditions within the patient. Online matching exhibited increased observer errors of: 3.2 mm, 2.9 mm and 4.7 mm. Four patients exhibited large systematic residual errors, of which three had poor quality images. Patient habitus showed no correlation with observer error, residual error, or image quality.

CONCLUSIONS

TPUS offers the unique potential to directly assess inter- and intra-fraction motion on conventional linacs. Inconsistent image quality, inexperienced operators and the pressures of the clinical environment may degrade precision and accuracy. Experienced operators are essential and cross-centre standards for training and QA should be established that build upon current guidance. Greater use of automation technologies may further minimise uncertainties.

In vitro fertilization. The Jamaican experience

In June 2000, twenty-eight infertile couples were treated by in vitro fertilization and embryo transfer at our initial assisted reproduction programme carried out in conjunction with Midland Fertility Services, Aldridge, Birmingham, England. A pre-requisite for treatment was that on day 3 of the menstrual cycle the levels of follicle stimulating hormone (FSH) and oestradiol (E2) should be < 10 i mu/l and < 100 pg/ml respectively in the female partner. The ages of the women ranged from 26 to 42 years with a mean age of 35.5 years. Down regulation was carried out by using buserelin acetate 0.5 microgram subcutaneously from day 21 of the cycle for 21 days. This process was completed when the ovaries and pituitary gland were quiescent and the endometrial thickness < 4 mm in diameter. On completion of down regulation the gonadotrophin hormone, pergonal (dosage of 150-450 units) was used for ovarian hyperstimulation. A total of 294 oocytes (mean of 10.5, range 2-45) were retrieved of which 138 were fertilized (mean of 4.9, range of 0-28). Twenty-four patients each received a mean of two embryos. Five patients (20.8%) had positive pregnancy tests. Three patients (0.1%) developed ovarian hyperstimulation syndrome (OHSS), one had the severe, and two, the mild form of the syndrome. All three cases were treated successfully. The success at the initial IVF controlled ovarian hyperstimulation augers well for the future of infertile couples seeking treatment at the Fertility Management Unit, The University of the West Indies, Jamaica.