Health-Related Quality of Life after Combined External Beam and Either High Dose Rate (HDR) or Low Dose Rate (LDR) Brachytherapy: Does the Rectal Dose from the LDR Brachytherapy Make a Difference?

PURPOSE/OBJECTIVE(S)

The recently reported randomized Phase III trial comparing health related quality of life (HRQOL) after combined external beam radiation therapy (EBRT) and either HDR or LDR brachytherapy (BT) found a significant decline in the EPIC Bowel domain HRQOL score at 24- 48 months after treatment in the LDR arm of the trial. As all patients in the trial received the same EBRT dose, and HDR rectal dose was strictly controlled to be <9.5 Gy to 1cc of rectal wall (RD1cc), we investigated whether the variable rectal dose from the LDR component of treatment was related to the decline in Bowel HRQOL for these patients.

MATERIALS/METHODS

A total of 195 men with upper tier intermediate or high-risk prostate cancer were assigned by a random number generator to receive either an HDR (15 Gy, n = 108) or LDR (110Gy, n = 87) brachytherapy boost combined with 46Gy/23 fractions EBRT. All LDR patients had 1 month post implant quality assurance using CT-MRI fusion. The Expanded Prostate Cancer Composite (EPIC) questionnaire was used to evaluate HRQOL at baseline, q3 mo for 1 year, q6mo for 3 yr and then annually. A multivariate linear regression model was used to investigate the dose-response relationship between EPIC bowel domain score at 24- 48 months and RD1cc.

RESULTS

With a median follow up of 48 months, the previous analysis confirmed the expected time course of acute bowel/urinary symptoms, with LDR showing more prolonged decline in HRQOL bowel domain at 3 and 6 months, but equivalence to HDR by 12 months. HRQOL urinary domain remained equivalent from 12-60 mo. The decline in the HRQOL bowel domain observed for LDR patients from 24-48 mo was analyzed for the 79 patients with sufficient data. The mean baseline HRQOL bowel domain score was 92 and fell on average to 85 at 24-48 mo. Mean RD1cc for the LDR patients was 82Gy (SD 22 Gy), with a maximum value of 129 Gy. In this range of rectal doses, a 20Gy increase in RD1cc, was associated on average with a 1.5-point decrease in EPIC HRQOL bowel domain score (p = 0.21).

CONCLUSION

The rectal dose received by the LDR patients showed a non-significant dose-response with the EPIC Bowel domain HRQOL score. This confirms the accepted rectal dose constraints for LDR brachytherapy but does not explain the observed decline in bowel scores from 24-48 months.

Quorum sensing affects biofilm formation through lipopolysaccharide synthesis in Klebsiella pneumoniae

Biofilm formation by Klebsiella pneumoniae is modulated by quorum sensing through the synthesis of interspecies AI-2 autoinducers. We characterized in K. pneumoniae the genes homologous to those described in Escherichia coli involved in AI-2 transport, and created two isogenic mutants deleted of lsrCD and tqsA. The levels of extracellular AI-2 with lsrCD and tqsA knockout mutants showed increased and lowered concentrations of AI-2, respectively. The level of transcripts of luxS, the gene responsible for AI-2 synthesis, was increased in sessile cells of the tqsA mutant. In contrast, the expression of the AI-2 import regulator genes lsrR and lsrK was decreased. In addition, the two mutants lsrCD and tqsA formed biofilms with greater biomass but impaired architecture. Since exopolysaccharides play a main role in K. pneumoniae biofilm formation, we investigated their relationship with AI-2 synthesis. None of the mutations in luxS and the AI-2 transport systems affected the expression of three capsule polysaccharide-related genes (wzi, wza and wzx), but all induced an increase in the expression of two lipopolysaccharide (LPS)-synthesis-related genes, wbbM and wzm. AI-2 therefore seems to act as a regulator of biofilm formation and LPS synthesis in sessile K. pneumoniae cells.

Genomic diversity in Staphylococcus xylosus

Staphylococcus xylosus is a commensal of the skin of humans and animals and a ubiquitous bacterium naturally present in food. It is one of the major starter cultures used for meat fermentation, but a few strains could potentially be hazardous and are related to animal opportunistic infections. To better understand the genetic diversity of S. xylosus intraspecies, suppressive and subtractive hybridization (SSH) was carried out with the S. xylosus C2a strain, a commensal of human skin, used as the driver for three tester strains, S04002 used as a starter culture, S04009 isolated from cow mastitis, and 00-1747, responsible for mouse dermatitis. SSH revealed 122 tester-specific fragments corresponding to 149 open reading frames (ORFs). A large proportion of these ORFs resembled genes involved in specific metabolisms. Analysis of the distribution of the tester-specific fragments in 20 S. xylosus strains of various origins showed that the S. xylosus species could be divided into two clusters with one composed only of potentially hazardous strains. The genetic content diversity of this species is colocalized in a region near the origin of replication of the chromosome. This region of speciation previously observed in the Staphylococcus genus corresponded in S. xylosus species to a strain-specific region potentially implicated in ecological fitness.