Waveguide-integrated silicon T centres.

The performance of modular, networked quantum technologies will be strongly dependent upon the quality of their quantum light-matter interconnects. Solid-state colour centres, and in particular T centres in silicon, offer competitive technological and commercial advantages as the basis for quantum networking technologies and distributed quantum computing. These newly rediscovered silicon defects offer direct telecommunications-band photonic emission, long-lived electron and nuclear spin qubits, and proven native integration into industry-standard, CMOS-compatible, silicon-on-insulator (SOI) photonic chips at scale. Here we demonstrate further levels of integration by characterizing T centre spin ensembles in single-mode waveguides in SOI. In addition to measuring long spin T1 times, we report on the integrated centres' optical properties. We find that the narrow homogeneous linewidth of these waveguide-integrated emitters is already sufficiently low to predict the future success of remote spin-entangling protocols with only modest cavity Purcell enhancements. We show that further improvements may still be possible by measuring nearly lifetime-limited homogeneous linewidths in isotopically pure bulk crystals. In each case the measured linewidths are more than an order of magnitude lower than previously reported and further support the view that high-performance, large-scale distributed quantum technologies based upon T centres in silicon may be attainable in the near term.

Prostate-specific Antigen Bounce After Stereotactic Body Radiotherapy for Prostate Cancer: A Pooled Analysis of Four Prospective Trials.

AIMS: We conducted a pooled analysis of four prospective stereotactic body radiotherapy (SBRT) trials of low- and intermediate-risk prostate cancer to evaluate the incidence of prostate-specific antigen (PSA) bounce and its correlation with the time-dose-fraction schedule. The correlation between bounce with PSA response at 4 years (nadir PSA < 0.4 ng/ml) and biochemical failure-free survival (BFFS) was also explored. MATERIALS AND METHODS: The study included four treatment groups: 35 Gy/five fractions once per week (QW) (TG-1; n = 84); 40 Gy/five fractions QW (TG-2; n = 100); 40 Gy/five fractions every other day (TG-3; n = 73); and 26 Gy/two fractions QW (TG-4; n = 30). PSA bounce was defined as a rise in PSA by 0.2 ng/ml (nadir + 0.2) or 2 ng/ml (nadir + 2.0) above nadir followed by a decrease back to nadir. Patients with fewer than three follow-up PSA tests were excluded from the pooled analysis. RESULTS: In total, 287 patients were included, with a median follow-up of 5.0 years. The pooled 5-year cumulative incidence of bounce by nadir + 2.0 was 8%. The 2-year cumulative incidences of PSA bounce by nadir + 0.2 were 28.9, 21, 19.6 and 16.7% (P = 0.12) and by nadir + 2.0 were 7.2, 8, 2.7 and 6.7% (P = 0.32) for TG-1 to TG-4, respectively. Multivariable analysis revealed that for nadir + 2.0, pre-treatment PSA (odds ratio 0.49; 95% confidence interval 0.26-0.97) correlated with PSA bounce. Although PSA bounce by nadir + 0.2 (odds ratio 0.10; 95% confidence interval 0.04-0.24) and nadir + 2.0 (odds ratio 0.29; 95% confidence interval 0.09-0.93) was associated with a lower probability of PSA response at 4 years, there was no association between bounce by nadir + 0.2 (hazard ratio 0.36; 95% confidence interval 0.08-1.74) or nadir + 2 (hazard ratio 1.77; 95% confidence interval 0.28-11.07) with BFFS. CONCLUSION: The incidence of PSA bounce was independent of time-dose-fraction schedule for prostate SBRT. One in 13 patients experienced a bounce high enough to be misinterpreted as biochemical failure, and clinicians should avoid early salvage interventions in these patients. There was no association between PSA bounce and BFFS.

Long-term Toxicity and Health-related Quality of Life after Single-fraction High Dose Rate Brachytherapy Boost and Hypofractionated External Beam Radiotherapy for Intermediate-risk Prostate Cancer.

AIMS: To report health-related quality of life (HRQOL) and toxicity in prostate cancer patients treated with single-fraction high dose rate (HDR) brachytherapy boost and external beam radiotherapy (EBRT). MATERIALS AND METHODS: Patients with intermediate-risk prostate cancer were accrued to a phase II clinical trial of 15 Gy HDR boost and EBRT to a dose of 37.5 Gy in 15 fractions. HRQOL (Expanded Prostate Cancer Index Composite [EPIC]), urinary symptoms (International Prostate Symptom Score [IPSS]), erectile function (International Index of Erectile Function [IIEF]) and toxicity (Common Terminology Criteria for Adverse Events [CTCAE], version 3.0) were monitored prospectively. Univariate and multivariate logistic regression analysis was used to investigate associations between HRQOL/toxicity and baseline covariates. RESULTS: The median follow-up time was 5.2 years. The change in the median EPIC scores from baseline to year 5 in the urinary domain was from 91 to 85 (P = 0.0028), in the bowel domain was from 98 to 96 (P = 0.03), in the sexual domain was from 63 to 35 (P < 0.0001) and the hormonal domain remained unchanged at 95 (P = 0.93). Fifty-nine per cent and 46% of the patients with normal erectile function at baseline remained potent at year 1 and year 5, respectively. Late genitourinary toxicity grade 1, 2 and ≥3 occurred in 29, 59 and 4% of patients, respectively. The rates of late gastrointestinal toxicity grade 1, 2 and ≥3 were documented as 45, 19 and 0%, respectively. On multivariate logistic regression analysis, patients with larger prostates were more likely to develop a urinary late toxicity grade ≥2 (P = 0.01). The dose to 10% of the urethra was the only factor associated with a decline in the EPIC urinary domain score (P = 0.012). Prostate volume >43 ml was associated with higher late genitourinary toxicity grade ≥2. CONCLUSIONS: Single 15 Gy HDR brachytherapy with EBRT has a low rate of late genitourinary and gastrointestinal toxicities. Late urinary morbidity may be minimised by limiting the dose to the urethra, particularly for patients with larger prostates.

Accelerated hypofractioned postoperative radiotherapy for prostate cancer: a prospective phase I/II study.

AIMS: To present the initial findings of a single institution, phase I/II study investigating hypofractionated radiotherapy in patients undergoing post-prostatectomy treatment. MATERIALS AND METHODS: Patients requiring postoperative radiotherapy were prospectively enrolled. Dose was prescribed to the prostate bed with 51 Gy in 17 daily fractions. Androgen deprivation was optional. Acute and late gastrointestinal/genitourinary toxicity were assessed using the National Cancer Institute Common Terminology Criteria for Adverse Events version 3.0 and quality of life was assessed using the Expanded Prostate Cancer Index Composite evaluation tool. Prostate-specific antigen (PSA) was evaluated at every follow-up. RESULTS: Thirty patients were enrolled between 2009 and 2011. The median age was 65 years and most had Gleason 7 disease (86%) with pT2c or pT3a (82%). Positive margins were documented in 67% of the patients. The median pre-treatment PSA was 0.12 ng/ml. The median follow-up was 24 months. Overall toxicity was low, with >80% of patients having ≤ grade 1 acute toxicity in both genitourinary and gastrointestinal realms. Similarly, only two patients (6%) experienced grade 2/3 late gastrointestinal/genitourinary toxicity. Quality of life scores were also indicative of a well-tolerated treatment. PSA failure was seen in five patients (17%). CONCLUSIONS: We present a hypofractionated schedule of postoperative prostate radiotherapy that is both well tolerated in terms of both toxicity and quality of life measures. Initial PSA control is encouraging. Further evaluation with a longer follow-up and a larger cohort is warranted.

Intra-fraction motion during extreme hypofractionated radiotherapy of the prostate using pre- and post-treatment imaging.

AIMS: To determine intra-fraction displacement of the prostate during extreme hypofractionated radiotherapy using pre- and post-treatment orthogonal images with three implanted gold seed fiducial markers. MATERIALS AND METHODS: In total, 265 image pairs were obtained from 53 patients who underwent extreme hypofractionated radiotherapy to a dose of 35 Gy in five fractions on standard linear accelerators. Position verification was obtained with orthogonal X-rays before and after treatment and were used to determine intra-fraction prostate displacement. RESULTS: The mean intra-fraction prostate displacements were -0.03 ± 0.61 mm (one standard deviation), 0.21 ± 1.50 mm and -0.86 ± 1.73 mm in the left-right, superior-inferior and anterior-posterior directions, respectively. The mean intra-fraction displacement during the first two fractions was moderately correlated with the displacement in the remaining three fractions, with correlation coefficients of 0.63 (95% confidence interval 0.43-0.77) and 0.47 (95% confidence interval 0.22-0.65) in the superior-inferior and anterior-posterior directions, respectively. There was no significant correlation in the left-right direction with a coefficient of -0.04 (95% confidence interval -0.31-0.23). CONCLUSIONS: The mean intra-fraction prostate displacement during a course of extreme hypofractionated radiotherapy is small. A strategy using the first two fractions to predict future displacements >5 mm warrants further validation.