Search

Background: Breast-conservation surgery is=now commonly used to treat breast cancer. Postoperative breast irradiation reduces cancer recurrence in the breast. There is still controversy concerning the necessity of irradiation of the breast in all patients. Purpose: We present an update of results from a randomized clinical trial designed to examine the efficacy of breast irradiation following conservation surgery in the treatment of women with axillary lymph node-negative breast cancer. The patients were enrolled from April 1984 through February 1989. Initial results were published in 1992 after a median follow-up time of 43 months. It was reported that recurrence of cancer in the breast occurred in 5.5% of the patients who received breast irradiation compared with 25.7% of those who did not. No difference in survival was detected between the two treatment groups. Now that the median patient follow-up has reached 7.6 years, the trial end points have been re-examined and an attempt has again been made to identify a group of patients at low risk for recurrence of cancer in the breast. Methods: Eight hundred thirty-seven patients with node-negative breast cancer were randomly assigned to receive either radiation therapy (n = 416) or no radiation therapy (n = 421) following lumpectomy and axillary lymph node dissection. The cumulative local recurrence rate as a first event, distant recurrence (i.e., occurrence of metastasis) rate, and overall mortality rate for the treatment groups were described by the Kaplan-Meier method and compared with the use of the logrank test. The Cox proportional hazards model was used to adjust the observed treatment effect for the influence of various prognostic factors (patient age, tumor size, estrogen receptor level, and tumor histology) at study entry on the outcomes of local breast recurrence, distant recurrence, and overall mortality. All P values resulted from the use of two-tailed statistical tests. Results: One hundred forty eight (35%) of the nonirradiated patients and 47 (11%) of the irradiated patients developed recurrent cancer in the breast (relative risk for patients in the former versus the latter group = 4.0; 95% confidence interval = 2.83-5.65; P2 cm), and tumor nuclear grade (poor) continued to be important predictors for local breast relapse. On the basis of these factors, we were unable to identify a subgroup of patients with a very low risk for local breast cancer recurrence. Tumor nuclear grade, as previously reported, and tumor size were important predictors for mortality. Conclusions: Breast irradiation was shown to reduce cancer recurrence in the breast, but there was no statistically significant reduction in mortality. A subgroup of patients with a very low risk for local breast recurrence who might not require radiation therapy was not identified.

Background: Although the conservation management of breast cancer has become a routine method of treatment in most centers, there is still considerable controversy surrounding the ultimate minimum treatment required for node-negative breast cancer to achieve adequate local control. Purpose: Our purpose was to assess the value of breast irradiation in reducing breast relapse following conservation surgery for node-negative breast cancer. We attempted to define low-risk groups of women for breast and distant site relapse (i.e., recurrence outside the breast) who might be spared breast irradiation or adjuvant systemic therapy. Methods: Eight hundred thirty-seven patients were randomly assigned to receive radiation therapy or no radiation therapy following lumpectomy and axillary dissection for node-negative breast cancer. Results: Breast irradiation reduced relapse in the breast from 25.7% in the controls to 5.5% in the irradiated patients. There was no difference in survival between the two groups (median follow-up, 43 months). A low-risk group (2 cm), age (

An InP-based normally-off superlattice-insulated-gate field-effect transistor (SIGFET) with a T-shaped gate structure has been developed using an angled self-aligned implant process. The spacing to the n+ source/drain regions created with this new process increases the breakdown voltage and lowers the gate capacitance. It also reduces the short channel effect while a high gm value is maintained. A cutoff frequency fT of 45 GHz was obtained for the SIGFET with 0.56 µm gate length.

A single-transistor dynamic random access memory circuit using a GaAs/AlGaAs structure as the storage cell and modulation-doped field-effect transistors for memory accessing and output sensing has been developed. The functionality of the memory is demonstrated and a storage time of 5.4s is measured at room temperature.

A new enhancement-mode GaAs pseudomorphic high-electron-mobility transistor (pHEMT) with a low-temperature-grown (LTG) GaAs gate insulator has been developed. The source and drain are doped by self-aligned implant and no gate recess is needed. The LTG-GaAs gate insulator drastically reduces the gate leakage current, allowing a maximum drain current of 390 mA/mm obtained at 3 V of forward gate bias. The maximum transconductance is 330 mS/mm and the cutoff frequency is 31 GHz for pHEMTs with a 0.5 µm gate length.

GaAs complementary metal insulator semiconductor field effect transistors (MISFETs) with a low temperature grown GaAs gate insulator were fabricated using the same epitaxial layer structure. Self-aligned Si and Be implants were used for the source/drain region in n- and p-channel MISFETs, respectively. With a 1.5 µm gate length, the maximum drain current is 40 and 120 mA/mm for a normally-off n- and p-channel MISFET, respectively. It increases to 500 mA/mm for a normally-on n-channel device.

A SPICE3 model is developed for the resonant-tunnelling diode that combines a physical formulation of the coherent current component between zero bias and the valley point with an empirical formulation for the incoherent, or excess, current at bias voltages beyond the valley. The model is designed for type-I RTDs, such as GaAs/AlGaAs structures, and a fitting procedure is developed to derive the parameters of the model from the experimental current/voltage curve.

Laser-direct-write deposition of tungsten and laser ablation techniques have been successfully used to modify monolithic capacitors and inductors fabricated on GaAs substrates. The properties of the tungsten inductors and capacitors have been characterised at microwave frequencies and are in good agreement with theory. The new techniques permit postfabrication tuning with precision and versatility that are not achievable by any other method

High-resistivity GaAs grown at low temperatures by molecular beam epitaxy was used as the surface passivation layer of MESFETs. When these MESFETs are biased in the saturation region, the frequency dispersions of the transconductance and output resistance are reduced compared to those of a MESFET without a passivation layer.

Selective plasma etching has been used to form via holes in GaAs-on-Si wafers that are superior to the holes formed by conventional methods in semi-insulating GaAs wafers. The plasma etching technique has a variety of potential microwave device applications.

Laser-direct-write deposition of tungsten has been investigated as a technique for postfabrication trimming of GaAs monolithic microwave integrated circuits. Tungsten microstrip lines of 30 μΩ cm resistivity are deposited via a vapour-phase reaction induced by a focused argon-ion laser beam Lines of 1.8 μm thickness and 50μm width written on a semi-insulating GaAs substrate have a loss of 2.6 dB/cm at 16GHz. This trimming technique is proposed as a practical and accurate method for the optimisation of high-frequency GaAs circuits.

A microwave tunable magnetostatic surface-wave delay-line oscillator which employs a single GaAs monolithic amplifier chip in the feedback loop has been developed. No directional coupler is needed, and a single-mode oscillation can be tuned continuously from 4.82 to 6.39 GHz without frequency jumping. At 61 GHz, an output power of 4.4 dBm was measured with a phase noise of —100dBc/Hz at 10kHz offset from the oscillation frequency.

Gun diodes have been fabricated in GaAs, where the implanted doping concentration is varied linearly from one contact to the other. The starting material was semi-insulating GaAs, and Si/sup ++/ ions were implanted at 140 keV. The dose was varied from 1*10/sup 13/ cm/sup -2/ to 3*10/sup 13/ cm/sup -2/ over a distance of 80 mu m. The width of the implant was 10 mu m. The frequency of oscillation could be smoothly tuned from 6 to 23 GHz by varying the bias voltage in the range of 25 to 35 V. Identical-geometry but uniformly doped devices exhibited bias-independent frequency of oscillation. Other doping profiles can yield other functions. A numerical model to solve the conservation equations, coupled with Poisson's equation, has been developed to simulate device performance. The solution is performed in the time domain and allows the domain nucleation, motion, and discharge to be observed. Doping profiles that optimize the diode performance can be predicted.<>