The Outcomes of Definitive Radiotherapy in Patients with Prostate Cancer Using Simultaneous Integrated Boost Technique

Abstract

<h3>Purpose/Objective(s)</h3> Previous studies had shown a dose-response relationship in prostate cancer during radiotherapy (RT). The clinical outcomes of prostate cancer patients treated with definitive RT using the simultaneous-integrated boost (SIB) technique were investigated in this study. <h3>Materials/Methods</h3> The clinical data of 556 prostate cancer patients who underwent RT using the SIB technique between September 2012 and September 2021 were retrospectively analyzed. In 39 fractions, patients received 78 Gy to the entire prostate±seminal vesicles and 86 Gy to the intraprostatic lesion (IPL). In addition, high-risk patients received 54 Gy pelvic field irradiation. Diffusion-weighted magnetic resonance imaging was used to define the IPL. Failure from biochemical failure (FFBF) and prostate-cancer specific survival (PCSS) were the primary endpoints. Secondary endpoints were progression free survival (PFS) and toxicity. <h3>Results</h3> The median age of the population was 69 years (range: 47–89 years). According to D'Amico risk categories, there were 175 patients (31.5%) classified as low risk, 186 patients (33.4%) classified as intermediate risk, and 195 patients (35.1%) classified as high risk. 253 patients (54.5%) received androgen deprivation therapy. The median duration of follow-up was 58.2 months (range, 4.7–126.8 months) for the entire cohort. The 5-year FFBF, PCSS, and PFS rates were respectively 93.3%, 98.5%, and 84.1%. In 40 patients (7.2%), progression was observed as biochemical failure in 16 patients, distant metastasis in 2 patients, and both biochemical failure and distant metastasis in 22 patients. Only four patients (0.7%) had a local recurrence. Univariate analysis revealed that the pretreatment PSA value, T and N stages, ISUP score, and D'Amico risk groups were all significant prognostic factors for FFBF and PCSS. PSA levels higher than 20 ng/mL [HR=3.39 (95% CI, 1.28–8.94); p=0.01], nodal metastasis [HR=4.03 (95% CI, 1.61–10.03); p=0.003], high risk disease [HR=6.66 (95% CI, 1.72–25.77); p=0.001], and higher ISUP scores [HR=2.31 (95% CI, 1.53–3.49); p<0.001] were all independent predictors of worse FFBF. In multivariable analysis, the significant predictors of worse PCSS were high risk disease [HR=8.96 (95% CI: 2.13–19.71; p=0.01] and a higher ISUP score [HR=12.21 (95% CI: 1.70–87.74; p=0.004]. Acute gastrointestinal (GI) and genitourinary (GU) system toxicities of grade 2 or greater were observed in 7.4% and 14.0% of patients, respectively. Late GI and GU toxicities of grade 2 or greater were observed in 5.3% and 6.9% of patients, respectively. <h3>Conclusion</h3> The treatment strategy of 78 Gy delivered to the entire prostate with a boost dose of 86 Gy to IPL was effective and safe, with excellent biochemical control and PCSS, and very low toxicity rates. Longer follow-up and randomized trials are needed to validate our findings.