Clinical implementation of low-dose total body irradiation using topotherapy technique.

BACKGROUND AND PURPOSE: The topotherapy technique was recently suggested as a robust alternative to helical radiation delivery for total body irradiation (TBI). It allows to deliver a discrete number of beams with fixed gantry. A Topotherapy-based low-dose TBI technique was optimized and clinically implemented. MATERIALS AND METHODS: TBI delivery was split in two parts: the first treating from the head to half thigh and the second the remaining legs. An in-silico investigation aimed to optimize plan parameters was first carried out on four patients. For the upper plan, field width and pitch were fixed to 5 cm and 0.5: the combined impact of five modulation factor (MF) values and different field configurations (6/8/12 fields) was investigated. For the lower plan, two anterior/posterior beams (field width: 5 cm; pitch: 0.5; MF:1.5) were used. After assessing the optimal technique, set-up/quality assurance/image-guidance procedures were defined and the technique clinically implemented: 23 patients were treated up to now. RESULTS: The best compromise between treatment time and planning target volume (PTV) coverage/homogeneity was found for MF = 1.5 and 8 fields. All clinical plans were automatically optimized using an "ad-hoc" plan template: excellent PTV coverage (PTV95%>98.5%) and homogeneity (median SD:4%) were found with a median beam-on time of 17/9 min for the upper/lower plan. All patients were successfully treated and transplanted. CONCLUSIONS: TBI delivered with the topotherapy approach robustly guarantees adequate coverage and dose homogeneity. Semi-automatic clinical plans can be quickly generated and efficiently delivered.

Clinical factors predicting late severe urinary toxicity after postoperative radiotherapy for prostate carcinoma: a single-institute analysis of 742 patients.

PURPOSE: To investigate the clinical factors independently predictive of long-term severe urinary sequelae after postprostatectomy radiotherapy. PATIENTS AND METHODS: Between 1993 and 2005, 742 consecutive patients underwent postoperative radiotherapy with either adjuvant (n = 556; median radiation dose, 70.2 Gy) or salvage (n = 186; median radiation dose, 72 Gy) intent. RESULTS: After a median follow-up of 99 months, the 8-year risk of Grade 2 or greater and Grade 3 late urinary toxicity was almost identical (23.9% vs. 23.7% and 12% vs. 10%) in the adjuvant and salvage cohorts, respectively. On univariate analysis, acute toxicity was significantly predictive of late Grade 2 or greater sequelae in both subgroups (p <.0001 in both cases), and hypertension (p = .02) and whole-pelvis radiotherapy (p = .02) correlated significantly in the adjuvant cohort only. The variables predictive of late Grade 3 sequelae were acute Grade 2 or greater toxicity in both groups and whole-pelvis radiotherapy (8-year risk of Grade 3 events, 21% vs. 11%, p = .007), hypertension (8-year risk, 18% vs. 10%, p = .005), age ≤ 62 years at RT (8-year risk, 16% vs. 11%, p = .04) in the adjuvant subset, and radiation dose >72 Gy (8-year risk, 19% vs. 6%, p = .007) and age >71 years (8-year risk, 16% vs. 6%, p = .006) in the salvage subgroup. Multivariate analysis confirmed the independent predictive role of all the covariates indicated as statistically significant on univariate analysis. CONCLUSIONS: The risk of late Grade 2 or greater and Grade 3 urinary toxicity was almost identical, regardless of the RT intent. In the salvage cohort, older age and greater radiation doses resulted in a worse toxicity profile, and younger, hypertensive patients experienced a greater rate of severe late sequelae in the adjuvant setting. The causes of this latter correlation and apparently different etiopathogenesis of chronic damage in the two subgroups were unclear and deserve additional investigation.

In-gantry or remote patient positioning? Monte Carlo simulations for proton therapy centers of different sizes.

PURPOSE: We estimated the potential advantage of remote positioning (RP) vs. in-room positioning (IP) for a proton therapy facility in terms of patient throughput. MATERIALS AND METHODS: Monte Carlo simulations of facilities with one, two or three gantries were performed. A sensitivity analysis was applied by varying the imaging and setup correction system (ICS), the speed of transporters (for RP) and beam switching time. Possible advantages of using three couches (for RP) or of switching the beam between fields was also investigated. RESULTS: For a single gantry facility, an average of 20% more patients could be treated using RP: ranging from +45%, if a fast transporter and slow ICS were simulated, to -14% if a slow transporter and fast ICS was simulated. For two gantries, about 10% more patients could be treated with RP, ranging from +32% (fast transporter, slow ICS) to -12% (slow transporter, fast ICS). The ability to switch beam between fields did not substantially influence the throughput. In addition, the use of three transporters showed increased delays and therefore a slight reduction of the fractions executables. For three gantries, RP and IP showed similar results. CONCLUSIONS: The advantage of RP vs. IP strongly depends on ICS and the speed of the transporters. For RP to be advantageous, reduced transport times are required. The advantage of RP decreases with increasing number of gantries.