Reduction of Late Urinary Toxicity from Prostate Cancer Radiotherapy via Intrafractional MV-kV Image Guidance

PURPOSE/OBJECTIVE(S)

Prostate cancer localization during radiotherapy is difficult and introduces positional variability during treatment. Here we evaluate the impact on treatment toxicities of an in-house system that uses MV and kV imaging guidance (MKIG) to track implanted fiducials during stereotactic body radiotherapy (SBRT) for localized prostate cancer.

MATERIALS/METHODS

A 3D MKIG platform that tracks prostate implanted fiducials in real-time was built and clinically translated to replace a prior commercial approach called intrafraction motion review (IMR), which tracks thefiducials in 2D kV view only. MKIG has been shown to correct both superior-inferior and anterior-posterior (AP) motions that are harmful to critical organs and is superior to IMR for intrafractional motion management, which is less sensitive to AP motions. From 2017 to 2019, 150 patients with localized prostate cancer were treated with SBRT to 40 Gy in 5 fractions. During the delivery of volumetric modulated arc therapy, orthogonal MV-kV pairs were simultaneously acquired at every 20° gantry rotation and rigidly registered to the reference image templates created from the planning CT. Calculated 3D translations of implanted fiducials were used to localize the prostate and alert the therapist to interrupt and reposition the prostate when exceeding a 1.5-2 mm threshold. A comparison cohort of 121 prostate patients was treated from 2015 to 2016 with the same prescription dose and treatment technique but instead managed by IMR, where the therapist interrupted treatment based on a 2mm expansion of the fiducial contours superimposed on the kV images. Statistics of intrafractional interruptions, patient shifts, and overall delivery time were collected to evaluate the efficacy of the clinical workflow. The incidence of late grade ≥2 toxicities was analyzed to assess clinical complications. The median follow-up time was 5.5 years (range of 3.6 to 8.0 years).

RESULTS

The MKIG cohort had more interruptions per fraction (1.09 vs. 0.28) and longer average delivery time per fraction (579±205s vs. 357±117s) than IMR. 75% of shifts resulting from MKIG were less than 3mm, compared to 51% in IMR, indicating that MKIG tended to detect and correct smaller deviations (p<0.001). The baseline International Prostate Symptom Score was 7.9 in the MKIG cohort vs. 8.4 in IMR (p = 0.41). The incidence of late grade ≥2 urinary toxicity was lower in the MKIG than IMR cohort: 10.7% vs. 19.8% (p = 0.05). One grade ≥2 rectal toxicity was observed in the IMR cohort but none in MKIG.

CONCLUSION

Wehave demonstrated that MKIG is a clinically practical and effective method for monitoring and correcting prostate positional deviations during SBRT of prostate cancer. MKIG is better suited than 2D IMR to localize the prostate and trigger patient repositioning during treatment. A statistically and clinically significant reduction in urinary toxicity was observed. The potential expansion of MKIG to other clinical sites and translation to other centers should be considered.

Mechanistic Studies on the Self-Assembly of PLGA Patchy Particles and Their Potential Applications in Biomedical Imaging

Currently, several challenges prevent poly(lactic-co-glycolic acid) (PLGA) particles from reaching clinical settings. Among these is a lack of understanding of the molecular mechanisms involved in the formation of these particles. We have been studying in depth the formation of patchy polymeric particles. These particles are made of PLGA and lipid-polymer functional groups. They have unique patch-core-shell structural features: hollow or solid hydrophobic cores and a patchy surface. Previously, we identified the shear stress as the most important parameter in a patchy particle's formation. Here, we investigated in detail the role of shear stress in the patchy particle's internal and external structure using an integrative experimental and computational approach. By cross-sectioning the multipatch particles, we found lipid-based structures embedded in the entire PLGA matrix, which represents a unique finding in the PLGA field. By developing novel computational fluid dynamics and molecular dynamics simulations, we found that the shear stress determines the internal structure of the patchy particles. Equally important, we discovered that these particles emit a photoacoustic (PA) signal in the optical clinical imaging window. Our results show that particles with multiple patches emit a higher PA signal than single-patch particles. This phenomenon most likely is due to the fact that multipatchy particles absorb more heat than single-patchy particles as shown by differential scanning calorimetry analysis. Furthermore, we demonstrated the use of patchy polymeric particles as photoacoustic molecular probes both in vitro and in vivo studies. The fundamental studies described here will help us to design more effective PLGA carriers for a number of medical applications as well as to accelerate their medical translation.

Maximal motor unit discharge rates in the quadriceps muscles of older weight lifters

Although the existence of "neural factors" is regularly cited as an important contributor to muscular strength, we have little specific knowledge regarding the existence of such neural factors or how they contribute to the expression of muscular force.

PURPOSE

The present investigation sought to assess maximal motor unit discharge rates in older, highly resistance-trained adults to determine whether maximal motor unit discharge rates might be one such neural contributor to maximal strength production.

METHODS

Subjects consisted of seven well-trained older weight lifters (ages 67-79 yr) and five untrained age-matched older adults. While subjects performed 50 and 100% maximal voluntary knee extensor contractions (MVC), recordings from groups of motor units were obtained from the rectus femoris muscle by using an indwelling electrode. Off-line analysis was performed to identify individual motor unit firing occurrences and to compute maximal motor unit discharge rates.

RESULTS

As expected, knee extension strength in the trained weight lifters (367.0 +/- 72.0 N) was significantly greater than that in the control subjects (299.9 +/- 35.9 N; P < 0.05). Motor unit discharge rates were similar in the two subject groups at the 50% MVC force level (P > 0.05), but maximal (100% MVC) motor unit discharge rate in the weight lifters (23.8 +/- 7.71 pps) was significantly greater than that in the age-matched controls (19.1 +/- 6.29 pps; P < 0.05).

CONCLUSION

Motor unit discharge rates may comprise an important neural factor contributing to maximal strength in older adults.

Impact of an aggressive stenting strategy on initial and one-year follow-up costs in patients undergoing coronary angioplasty

BACKGROUND

Although stents have been shown in randomised trials to reduce restenosis rates compared with balloon angioplasty, there are concerns regarding the cost-effectiveness of an aggressive stenting strategy. Stents were shown to increase medical costs over 12 months in the early trials.

AIM

Our aim was to determine the economic impact of an aggressive stenting strategy using current stenting techniques compared with a conservative stenting strategy.

METHODS

Initial and one year follow-up costs were determined in all patients who underwent successful revascularisation during June to December 1996 (aggressive stenting, n = 401), and compared to all patients treated in the corresponding months in 1995 (conservative stenting, n = 347). All patients had clinical follow-up for one year.

RESULTS

The proportion of patients receiving a stent increased from 22.5% in 1995 to 66.1% in 1996 (p < 0.0001). Requirement for repeat procedures in the 1995 group compared with 1996 was coronary angiography in 31% vs 16% (p < 0.001), coronary angioplasty in 11% vs 6% (p = 0.0044) and bypass surgery in 4.8% vs 2.5% (p = 0.054). The mean initial cost of the procedure was higher in the aggressive stenting group ($4319 +/- 1276 in 1995 vs $5131 +/- 1491 in 1996, p < 0.0001), but after 12 months follow-up, total medical costs were equivalent ($5975 +/- 4143 in 1995 vs $5994 +/- 3476 in 1996, p = NS).

CONCLUSION

An aggressive coronary stenting strategy is associated with higher initial costs compared with a conservative strategy, but lower costs during follow-up due to reduced need for repeat procedures, resulting in equivalent one year total medical costs.

Behaviour therapy in psychiatric outpatients

In a prospective study of fifty consecutive outpatients (30 men and 20 women) attending the Behaviour Therapy Clinic at a general hospital, the commonest conditions were obsessive compulsive disorders (n = 16), phobic disorders (n = 11) and generalised anxiety disorders (n = 9). Three-quarters of the referrals were from psychiatrists and family physicians. The patients received between 2 to 10 sessions of behaviour treatment; most had 4 to 6 sessions with a mean of 4.7, SD 1.82. The commonest behavioural techniques administered were exposure therapy with response prevention and relaxation therapy. Initially, treatment was therapist-aided, but subsequently self-help was encouraged with regular reviews of the patient's homework. After one month, 42 patients (84%) were assessed to have improved somewhat, with 20 (40%) showing moderate improvement. After three months, 41 (82%) continued to improve, with 33 (66%) showing moderate to great improvement. Nine patients were considered to have failed in therapy-six defaulted and three were non-responders. The reasons for defaulting treatment were unwillingness to bear with the discomfort involved in exposure therapy, lack of motivation or returning to own hometown in Malaysia. Sixteen patients (n = 32%) were treated solely with behavioural techniques while the rest had a combination of behaviour therapy and drugs, especially anxiolytics and antidepressants. However, at the end of treatment, the dosages of most medications were reduced or else discontinued completely.

A collaborative evaluation of seven alternatives to the Draize eye irritation test using pharmaceutical intermediates

Much of the data which have been generated on in vitro alternatives to the Draize eye irritation test have dealt with compounds within a specific chemical class or product category. However, in the pharmaceutical industry, it is often necessary to evaluate materials which are not related in structure or properties. It was thus decided to evaluate a diverse series of chemicals in seven in vitro methods for estimating ocular irritation. Thirty-seven test materials were chosen to represent a broad range of pH, solubility, and in vivo irritation potential. Assays were chosen to include as many different types of end points as practical. The group of assays was composed of TOPKAT (assessing structure-activity relationships), bovine corneal opacity-permeability (BCO-P; corneal opacity/toxicity), Eytex (protein coagulation), neutral red uptake (cytotoxicity), MTT in living dermal equivalent (cytotoxicity), Microtox (cytotoxicity in bacteria), and CAMVA (inflammation/toxicity). The results of the study indicated that, in general, the cytotoxicity end points did not correlate well with the in vivo data. The BCO-P, CAMVA, and Eytex assays had the best overall concordance (88.9, 75.8, and 75.0%, respectively) with this set of compounds. Estimation of irritation potential based on structure-activity (TOPKAT) was possible for only approximately 50% of the compounds; however, the assay showed 100% sensitivity (i.e., no false negatives), but low specificity (i.e., negatives correctly identified only 54.5% of the time). These data suggest that for screening of chemicals of diverse structure and properties, the more mechanism-based assays, as opposed to general cytotoxicity assays, hold more promise and should be further evaluated.