Theoretical investigation of the impact of different timing schemes in hypofractionated radiotherapy.

PURPOSE: This study compares the effectiveness of three fractionation schemes of equal fraction size, comprising five fractions of SBRT over 5 days, 10 days, or 15 days, respectively. METHOD: This comparative study is based on two tumor-control-probability (TCP) models that take into account tumor cell re-sensitization and repopulation during treatment; the Zaider-Minerbo-Stavreva (ZMS) and the Ruggieri-Nahum (RN) models. The ZMS model is further modified to include also re-sensitization according to the ß mechanism of the linear-quadratic (LQ) model of cell killing. The modified version of the ZMS model is verified through fitting to the experimental data set of Fisher and Moulder. The study applies an idea used in a plan ranking methodology developed for the case when the specific values of the model parameters are not known. RESULTS: The TCPs of the compared regimens are calculated for various values of the model parameters and for two different values of the dose per fraction. The TCPs are presented as 2-D functions of two of the model parameters for each model correspondingly. The differences between the TCPs of each of the prolonged regimens and the TCP of the every week day regimen are also calculated for each model. CONCLUSIONS: Both models predict that the prolonged regimens are superior in terms of TCP to the every week-day one for most of the studied cases; however this is shown to exist to a different degree by the two models. It is shown again to a different degree that reversed situations where the every week day schedule is better than the prolonged regimens are also possible. It is concluded that a 30% TCP difference observed in a clinical study in favor of the fifteen-day regimen is theoretically possible. However, the fifteen-day regimen is outperformed in terms of TCP by the every week day regimen in more cases than the regimen lasting ten days. Therefore the choice of a prolongation in time must be made with care.

Complications in total hip replacement.

AIM: THE PURPOSE of the present study was to present the most common treatment failures and complications associated with total hip replacement. MATERIAL AND METHODS: Between 1986 and 2002, 486 total hip replacements (THR) in 403 patients were performed at the Clinics of Orthopedic and Trauma Surgery (St. George University Hospital, Plovdiv). 315 (61.8%) of the patients underwent THR for coxarthrosis, 171 (35.1%)--for traumatic or pathologic subcapital femoral neck fractures. 312 (64.2%) of the patients were women and 174 (35.8%) were men. Right and left arthroplasties were carried out. Patients' age was in the range of 28 to 53 years (median age 59.6). Complications were diagnosed in 97 (19.9%). Late postoperative complications (53.6%) as aseptic loosening of the prosthetic components, superficial and deep hematogenous infections, prosthetic dislocations and heterotopic ossifications were predominant. RESULTS: Complications were categorized as intraoperative, postoperative and late--a finding, consistent with the data in the literature. Among the intraoperative complications most common were malposition of the capsule (7 patients) and of the stem (4 patients) and longer stem (in 1 patient), but they caused no complaints. The postoperative complications consisted of hematomas and seromas wich were treated with early revision surgery. The main causes for late complications were postoperative ossification in 28 patients. Aseptic loosening of the prosthesis was seen in 11 patients. 8 of them complained of acetabular and 3 of thigh pain. Capsule dislocation was registered in 3 patients. CONCLUSIONS: Complications in THR are not infrequent. Their avoidance is largely dependent on the skill and qualification of the team and the quality of hospital care. Adequate risk assessment and prophylaxis are essential in disease outcome.