Direct observation of a nuclear spin excitation in Ho2Ti2O7.

A single nondispersive excitation is observed by means of neutron backscattering, at E_{0}=26.3 microeV in the spin ice Ho2Ti2O7 but not in the isotopically enriched 162Dy2Ti2O7 analogue. The intensity of this excitation is rather small, less, similar0.2% of the elastic intensity. It is clearly observed below 80 K but resolution limited only below approximately 65 K. The application of a magnetic field up to micro_{0}H=4.5 T, at 1.6 K, has no measurable effect on the energy or intensity. This nuclear excitation is believed to perturb the electronic, Ising spin system resulting in the persistent spin dynamics observed in spin ice compounds.

Frustrated spin correlations in diluted spin ice Ho(2-x)La(x)Ti(2)O(7).

We have studied the evolution of the structural properties as well as the static and dynamic spin correlations of spin ice Ho(2)Ti(2)O(7), where Ho was partially replaced by non-magnetic La. The crystal structure of diluted samples Ho(2-x)La(x)Ti(2)O(7) was characterized by x-ray and neutron diffraction and by Ho L(III)-edge and Ti K-edge extended x-ray absorption fine structure (EXAFS) measurements. It is found that the pyrochlore structure remains intact until about x = 0.3, but a systematic increase in local disorder with increasing La concentration is observed in the EXAFS data, especially from the Ti K edge. Quasi-elastic neutron scattering and ac susceptibility measurements show that, in x≤0.4 samples at temperatures above macroscopic freezing, the spin-spin correlations are short ranged and dynamic in nature. The main difference with pure spin ice in the dynamics is the appearance of a second, faster, relaxation process.

Active minimisation of radiation scatter during breast radiotherapy: management implications for young patients with good-prognosis primary neoplasms.

BACKGROUND AND PURPOSE: Radiotherapy is used to reverse or prevent local tumour growth but is also a carcinogen in its own right. A recent audit of post-radiotherapy second malignancies in this institution revealed a striking preponderance of tumours originating near the outside edge of the treatment field. Since this finding suggests the existence of a critical subtherapeutic dose range predisposing to tumourigenesis, we attempted to define and reduce this radiation scatter dose. MATERIALS AND METHODS: We undertook a dosimetric review of 6 MV scatter from a linear accelerator in sites matching the putative tumourigenic region, and then extended this analysis to patients and tissue phantoms. RESULTS: A wide range of radiation scatter doses was confirmed-for example, doses 3 cm from the field edge varied from 1.7 to 22% of the therapeutic dose depending upon the field parameters. Scatter doses were then assessed in a sample of eight patients undergoing standard breast radiotherapy. Contralateral breast sites 4-12 cm from the midline received 4-10% of the therapeutic dose, or 200-500 cGy for a 50 Gy treatment, approximating historical estimates of the tumourigenic range. The deep component of this scatter dose from medial field breast irradiation was reduced 19% simply by replacing the 15 degrees medial tangential field wedge with a 30 degrees lateral wedge. Other manoeuvres which reduced contralateral breast dose by up to 46% included making the posterior field edges co-planar and shielding the breast during medial field irradiation. CONCLUSIONS: These results suggest that the risk of radiogenic second malignancies could be significantly decreased by careful attention to the treatment details. Greater awareness of these measures may prove particularly relevant to the conservative management of young patients with good-prognosis breast neoplasms such as ductal carcinoma in situ.

Treating the vaginal vault in carcinoma of the endometrium using the Buchler afterloading system.

The advent of high-dose-rate afterloading intracavitary radiotherapy has implications for both staff safety and the possibility of convenient, outpatient-based treatment for the patient. We have carried out a retrospective analysis of its use with high-activity iridium 192 and the Buchler machine to treat the vaginal valut in patients with adenocarcinoma of the endometrium, most of whom also received external-beam radiotherapy to the pelvis. We have compared the survival, complication and local control rates with a comparable group of historical controls treated with low-dose-rate intracavitary caesium ovoids. Complication rates, which included vaginal stenosis not volunteered by the patient, were 16% (95% confidence intervals 6-26%) in the study group and 28% (95% confidence intervals 17-41%) in the control group, with no serious complications requiring surgery. The actuarial survival was 92% at 5 years in the study group, and 94% at 5 years in the control group. Local control was 94% at 5 years in the control group and 98% at 5 years in the study group. The authors suggest that the use of high-dose-rate intracavitary radiotherapy, with the Buchler afterloading system, for vaginal vault irradiation in carcinoma of the endometrium is a convenient, safe and quick method, which does not necessitate admission or sedation of the patient. In addition it provides complete radiation protection for staff.

Total lymphoid irradiation preceding bone marrow transplantation for chronic myeloid leukaemia.

Between August 1985 and October 1987 we treated 35 patients with chronic myeloid leukaemia (CML) by high dose chemotherapy, total body irradiation (TBI) (1000 or 1200 cGy, n = 31) and total lymphoid irradiation (TLI) (800 or 600 cGy, n = 35) preceding allogeneic bone marrow transplantation (BMT). Both TBI and TLI were given at 200 cGy/fraction. Twenty-three patients had HLA-identical sibling donors, nine patients had HLA-matched but unrelated donors, and three partially HLA-mismatched donors. Twenty-two patients received T-cell depleted marrow. The addition of TLI to the standard protocol did not add greatly to the toxicity. Four patients had recurrent leukaemia before engraftment was evaluable. The other 31 patients engrafted and no graft failed. Twenty-two patients survive at a median time from transplant of 305 days (range 81-586 days). Fourteen have no evidence of disease; eight have or had only cytogenetic evidence of leukaemia. We conclude that the addition of TLI to pretransplant immunosuppression increases the probability of reliable engraftment in patients receiving T-cell depleted marrow. This benefit is not associated with significantly increased toxicity.

Oedema of the neck after ablation of the thyroid with radioactive iodine.

Six out of 30 patients who underwent thyroid ablation with 131I during the period 1975-85 developed acute oedema of the neck within 48 h of the therapeutic dose. The condition was painless and responded well to treatment with corticosteroids. The early onset and absence of pain distinguish this complication from radiation thyroiditis. Dosage calculations and thermoluminescent-dosimeter measurements of the dose at various points on the anterior surface of the neck of a patient with a toxic adenoma of the thyroid treated with 131I were in fairly good agreement with one another and confirmed that the oedema of the neck could not be a direct effect of irradiation on the extrathyroidal tissues. It is suggested that this phenomenon may be a hypersensitivity reaction associated with massive destruction of thyroid tissue.

A device for interstitial therapy of low pelvic tumours--the Hammersmith perineal hedgehog.

The freehand production of accurate volume or multiplane implants for interstitial therapy is difficult. The size of tumour that may be treated in this fashion is therefore limited. A solution to this problem is to use a perspex template to guide the implant and maintain its configuration during treatment. We describe our experience using such a template (the Syed-Neblett template) in treating pelvic tumours. The device has been adapted for use with the iridium wire available in the UK. Two new templates have been designed which are more versatile for treating tumours in this area. Ten patients have been treated and with appropriate analgesia, antibiotic cover and nursing care the implant was well tolerated.

Fractionation of whole body irradiation before bone marrow transplantation for patients with leukaemia.

Thirty patients in various stages of acute leukaemia or chronic granulocytic leukaemia (CGL) were treated with cytotoxic drugs followed by whole body irradiation (TBI) administered in 200 cGy fractions twice daily to a total of 1000 or 1200 cGy. The immediate toxicity of fractionated TBI administered in this way was negligible and patients required only minor premedication and little treatment subsequently for complications attributable to TBI. Fourteen (47%) patients have died, ten of the 12 transplanted with active disease, and four of the 18 subjected to transplantation in remission of acute leukaemia or in chronic phase of CGL. Though the duration of follow-up is still short, no patient in the latter group (follow-up of survivors ranging from six to 146 weeks) has yet relapsed with any evidence of recurrent leukaemia. We conclude that this method of fractionating TBI reduced toxicity for the patient without necessarily reducing its antileukaemic effect.