ABSTRACT
OBJECTIVES: To identify risk factors for the long-term persistent genitourinary toxicity (GUT) after stereotactic body radiation therapy (SBRT) for localized prostate cancer (PCa). METHODS: A total of 306 patients who underwent SBRT at our institution between March 2017 and April 2022 were retrospectively evaluated. SBRT was performed at 35 Gy in five fractions over 5 or 10 days. Factors related to the long-term persistence of acute GUT after SBRT were analyzed. RESULTS: During the median follow-up period of 39.1 months, 203 (66%) patients experienced any grade of acute GUT, which remained in 78 (26%) patients 6 months after SBRT. Multivariate analysis revealed that age ≥75 years was consistently a significant independent risk factor for any grade of acute GUT 6, 12, and 24 months after SBRT (hazard ratio [HR] 2.31, p = 0.010; HR 2.84, p = 0001; and HR 3.05, p = 0.009, respectively). Older age was not a significant risk factor for the development of grade ≥2 acute GUT. The duration of acute GUT was significantly longer in the older group than in the nonolder group (median duration = 234 vs. 61 days, p < 0.001), and the incidence of persistent GUT was significantly more frequent in the older group beyond 6 months after SBRT. CONCLUSIONS: Older age is a significant independent risk factor for the long-term persistent GUT after SBRT for localized PCa.
ABSTRACT
Purpose.This study aims to establish a robust dose prescription methodology in stereotactic radiosurgery (SRS) and stereotactic radiotherapy (SRT) for brain metastases, considering geometrical uncertainty and minimising dose exposure to the surrounding normal brain tissue.Methods and Materials.Treatment plans employing 40%-90% isodose lines (IDL) at 10% IDL intervals were created for variously sized brain metastases. The plans were constructed to deliver 21 Gy in SRS. Robustness of each plan was analysed using parameters such as the near minimum dose to the tumour, the near maximum dose to the normal brain, and the volume of normal brain irradiated above 14 Gy.Results.Plans prescribed at 60% IDL demonstrated the least variation in the near minimum dose to the tumour and the near maximum dose to the normal brain under conditions of minimal geometrical uncertainty relative to tumour radius. When the IDL-percentage prescription was below 60%, geometrical uncertainties led to increases in these doses. Conversely, they decreased with IDL-percentage prescriptions above 60%. The volume of normal brain irradiated above 14 Gy was lowest at 60% IDL, regardless of geometrical uncertainty.Conclusions.To enhance robustness against geometrical uncertainty and to better spare healthy brain tissue, a 60% IDL prescription is recommended in SRS and SRT for brain metastases using a robotic radiosurgery system.
