Preclinical studies with the photon radiosurgery system (PRS).

PURPOSE: Determine the radiobiological effectiveness (RBE) for low-energy X-rays (average energy of 23 KeV) produced by the Photon Radiosurgery System (PRS). METHODS AND MATERIALS: RBE values were assessed by comparison with survival data obtained for cells irradiated with either low-energy X-rays from a GE Maxitron 100 machine or high-energy photons from a clinically used Varian 6 MV LINAC. The output of the GE and PRS sources was determined using Baldwin-Farmer and Markus thin window ionization chambers calibrated with 50 kVp X-rays and cross-checked against figures supplied by Photoelectron Corporation. The dose-rate for the PRS was 1.2 Gy/min at a distance of 35 mm with a field flatness of +/-2%. RESULTS: The RBE for the PRS low-energy X-ray source (at 1-mm depth) was greater than either the GE or Varian machines and varied with cell survival. For Chinese hamster ovary (CHO) cells, the PRS was 1.25 and 3.3 times more effective than 90 kVp X-rays and 6 MeV photons at 0.5% cell survival, respectively; by comparison, the PRS was 1.2 and 1.9 times more effective at 0.05% cell survival, respectively. Similar RBE values of 1.4 and 1.2 were obtained for human U373 and T98 glioblastoma cells grown in vitro irradiated with the PRS or GE sources, respectively. Other studies showed that the RBE for the PRS low-energy X-ray source increased with depth. The RBEs for the PRS source at 1-mm and 4-mm depth were 1.2 and 2.5 (0.5% survival) and 1. 2 and 1.9 (0.05% survival). CONCLUSIONS: The biological and physical properties of the PRS low-energy X-rays offer, under the right conditions, a significant advantage for patient treatment over conventional external beam, stereotactic, or brachytherapy treatment.

Outcome in patients with recurrent restenosis after percutaneous transluminal balloon angioplasty.

The records of 1162 consecutive patients undergoing their first percutaneous transluminal coronary angioplasty at a centre between March 1980 and June 1987 were reviewed. Initial angioplasty was successful in 1011 patients (87%). In 202 (20%) symptomatic restenosis developed. Of these, 196 were treated with redilatation; this was successful in 181 (92%). After a second dilatation, restenosis developed in 47 patients (26%). Of these, 41 (87%) were treated with a third angioplasty, with primary success in 38 (93%). A further restenosis developed in 13 of these 38 patients (34%). Eight patients were treated with a fourth angioplasty with restenosis in four (50%). Two of these four patients underwent a fifth angioplasty (with continuing success at long term follow up in both). Overall, 14 of the 47 (30%) patients who developed restenosis twice were eventually treated with coronary bypass surgery. Most patients (33), however, were treated only with repeated angioplasties. Of these 33 patients, 27 were treated with a third angioplasty, four with a fourth procedure, and two with a fifth. Twenty-nine (88%) were symptom free at a mean follow up of 28 (range 8 to 86) months. The combined success rate for a third, fourth, and fifth angioplasty was 94%. These data suggest that most patients with recurrent restenosis after angioplasty may be managed successfully and safely with repeated redilatations.

Factors predicting recurrent restenosis after percutaneous transluminal coronary balloon angioplasty.

To identify factors that predict a second restenosis after repeat percutaneous transluminal coronary balloon angioplasty (PTCA), the records of 196 consecutive patients undergoing redilation for treatment of a first restenosis were reviewed. Repeat PTCA was successful in 181 (92%) of these patients. After a successful second PTCA, 47 patients (26%) developed a second restenosis (recurrent restenosis group, group 1) and 134 (single restenosis group, group 2) did not. The 2 patient groups were compared with respect to clinical, angiographic and procedural factors at second PTCA. Univariate correlates of a second restenosis were younger age (54 +/- 10 vs 57 +/- 9 years, p less than 0.05), interval less than 60 days between initial PTCA and recurrence of anginal symptoms (55% of patients in group 1 vs 25% in group 2, p = 0.001), a greater number of inflations (6.3 +/- 4.2 vs 4.4 +/- 2.5, p less than 0.005) and a shorter maximal balloon inflation time (49 +/- 26 vs 69 +/- 36 seconds, p = 0.0006). With multivariate analysis, the 2 factors that emerged as independent predictors of recurrent restenosis were recurrence of symptoms less than 60 days after initial PTCA (p less than 0.004) and a greater number of inflations (p less than 0.04). These data suggest that younger age and rapid recurrence of anginal symptoms after first PTCA predict an increased likelihood that a second restenosis will occur after repeat PTCA and that certain procedural factors, in particular the greater number of balloon inflations and a shorter maximal balloon inflation time, may play an important role in the development of recurrent restenosis.

Use of percutaneous transluminal coronary angioplasty and bypass surgery despite improved medical therapy for unstable angina pectoris.

To evaluate current strategies for the management of unstable angina, 104 consecutive patients admitted to the coronary care unit with unstable angina during a 6-month period were followed prospectively. Although 58 patients had symptomatic relief with the initiation of intensive medical therapy, 46 (44%) continued to have episodes of angina despite maximal tolerated triple-drug antianginal therapy as well as aspirin or heparin, or both. In-hospital mortality for the 104 patients was 4%. The incidence of myocardial infarction was 8%, and differed (p less than 0.01) for the medically responsive group (3%) vs the medically refractory group (13%). Based on clinical status and coronary anatomy, patients were referred for either bypass surgery (46%), coronary angioplasty (41%) or continued medical therapy (13%). Choice of therapy varied according to the extent of coronary disease, with coronary angioplasty attempted in 72% of patients with 1-vessel disease, 44% of patients with 2-vessel disease and 7% of patients with 3-vessel disease. Angioplasty was performed with an initial success rate of 88%, and compared favorably with bypass surgery in terms of in-hospital mortality (0 vs 11%), late mortality (2.8 vs 7.7%), freedom from angina (62 vs 69%) and subsequent employment (44 vs 27%) at 18 months follow-up. The favorable results of angioplasty in this prospective observational study suggest that additional randomized trials should be conducted in this important patient group.