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Stereotactic body radiation therapy (SBRT) with extreme hypofractionation is replacing prostatectomy mostly in case of low risk prostate cancer.However, in selected cases of intermediate/high risk, it could be a justified treatment.This study evaluated safety and efficacy of Linac-based SBRT in elderly patients affected by prostate cancer(PC).

Men ≥70 years with localized PC were enrolled.The SBRT schedule was 35 Gy in 5 fractions administered with Volumetric Modulated Arc Therapy (VMAT) in 1 or 2 weeks based on target volume and urinary symptoms.According to risk group, androgen deprivation therapy(ADT) was prescribed in adequate cases. Urinary symptoms were evaluated at baseline using the International Prostate Symptom Score (IPSS).Toxicity was assessed at the end of treatment, 2 weeks after SBRT and during follow-up using the Common Terminology Criteria for Adverse Events(CTCAE).PSA values were recorded before treatment and during follow-up as biochemical response criteria.

Between July 2019-September 2021, 111 patients were treated.Median age was 77 years (range 70-86); 33% were low-risk, 48% favorable/unfavorable intermediate-risk and 19% high-risk group. Median pre-treatment PSA was 6.61 ng/ml(range 0.2-40 ng/ml). ADT was administrated in 58 patients.Median PTV was 99.5cc(range 51-192.2).Median baseline IPSS was 6(range 0-19).At the end of treatment, no acute genitourinary(GU) or gastrointestinal(GI) toxicities ≥G2 were observed.At 2-3 weeks after treatment, 3 patients reported G2 subacute GU toxicity (urinary frequency, urinary tract pain and urinary retention), while 14 patients referred GI toxicity (rectal tenesmus).During the last follow up, 26 and 2 patients reported, respectively, G1 and G2 GU toxicity, while 22 and 1 cases described, respectively, G1 and G2 GI toxicity.No late toxicities ≥G3 were recorded.At a median follow up of 23 months(range 8-35), excellent biochemical disease control was achieved in all cases (median PSA 0.5 ng/ml(range 0-6.46)).The univariate analysis showed a statistically significant relationship between GU toxicity and the following variables: IPSS(p 0.03), PTVvolume(p 0.05), Dmax PTV(0.01), urethra-sparing (p 0.03) and late-toxicity_GI(0.03). The multivariate analysis confirmed statistically significant association for urethra-sparing (OR 0.39[95%CI 0.013-1] p 0.05) and late-toxicity_GI(OR 2.44[95%CI 6.3-9.4] p 0.04).Regarding to GI toxicity, the univariate analysis showed a statistically significant relationship with the following variables: IPSS(p 0.002), day RT (p 0.02) and late-toxicity_GU(p <0.001).The multivariate analysis confirmed statistically significant association for late-toxicity_GU(OR 43.2[95%CI 10-182] p <0.001)and a correlation with Dmax rectum (OR 0.23[95%CI 0.05-1] p 0.05).

Linac-based SBRT in elderly patients affected by localized PC is feasible and well tolerated with excellent biochemical disease control.Longer follow-up is needed to assess late toxicity and long-term clinical outcome.