Treatment Outcomes of Simultaneous Integrated Boost to Intraprostatic Lesions with External Beam Radiotherapy in Localized Prostate Cancer Patients.

Abstract

To evaluate the treatment outcomes and toxicity of definitive radiotherapy (RT) for prostate cancer (PC) patients using the simultaneous integrated boost (SIB) technique to intraprostatic lesion (IPL). All the patients received 78 Gy for their prostate ± seminal vesicles and 86 Gy for the IPL using the SIB technique. High-risk patients received pelvic nodal irradiation. The pelvic lymphatic field received 46-54 Gy of radiation. Univariable and multivariable analyses were conducted of the prognostic factors for freedom from biochemical failure (FFBF), progression-free survival (PFS), and PC-specific survival (PCSS) of 619 PC patients who received definitive RT between September 2012 and August 2021. Predictors of late Grade ≥ 2 genitourinary (GU) and gastrointestinal (GI) toxicities were also identified using logistic regression. The median age of the entire cohort was 69 years (range, 47-89 years). Most of the patients (82.7%) had tumors with a GS of 6 or 7, 134 (21.6%) had PC with a GS of 3 + 4, 126 (20.4%) had PC with a GS of 4 + 3, and only 9% had clinical nodal metastasis. The median follow-up time for the entire cohort was 68.5 months (95% CI, 64.4-72.6 months). The 5-year FFBF, PFS, and PCSS rates were 93.2%, 83.2%, and 98.6%, respectively. They were predicted by the serum prostate specific antigen (PSA), Gleason score (GS), clinical nodal stage, and D'Amico risk group. Only 45 patients (7.3%) developed disease recurrence 41.9 months after RT. Of these patients, 12 (1.9% of the total) had BF only, 31 (5.3%) had both BF and distant metastasis, and 2 (0.3%) had distant metastasis only. The 5-year FFBF rates for low-, intermediate-, and high-risk disease were 98.0%, 93.1%, and 88.5%, respectively (p < 0.001). The 5-year PFS and PCSS rates according to risk groups were 91.0%, 82.1%, and 77.4% (p < 0.001), and 99.2%, 96.4%, and 95.9% (p = 0.03), and respectively. GS > 7 and lymph node metastasis negatively predicted FFBF and PCSS in multivariable analysis. Lymph node metastasis was associated with poor PFS, but only marginally (p = 0.06). Ninety (14.6%) and 44 (7.1%) patients had acute Grade ≥ 2 GU and GI toxicities, respectively, and 42 (6.8%) and 27 (4.4%) patients had late Grade ≥ 2 GU and GI toxicities, respectively. Diabetes (OR = 2.61; 95% CI = 1.29-5.26; p = 0.007) and transurethral resection of prostate (OR = 6.75; 95% CI = 3.37-13.54; p = 0.001) independently predicted late Grade ≥ 2 GU toxicity, but no significant predictor of late Grade ≥ 2 GI toxicity was found. Localized PC was effectively and safely treated with definitive RT using the SIB technique to deliver 86 Gy to the IPL in 39 fractions without severe late toxicity. This finding must be validated with long-term results.