Stereotactic ablative radiotherapy is a very promising approach for the treatment of patients with prostate cancer. The aim of this study was to evaluate the clinical tolerance, effectiveness, patterns of failure; and attempt to define predictive factors based on our experience. The cohort consists of 264 low-risk and 236 intermediate-risk consecutive patients treated at one institution. Prostate-specific antigen (PSA), adverse effects, and androgen deprivation therapy (ADT) usage are note.

Stereotactic ablative radiotherapy

The average lifespan of men in our country has increase by almost 19 years since our institution is establish (1951). The steadily increasing life expectancy conveys a need for both an efficient and effective modality of treatment but also well tolerated in terms of early and late toxicity since we can expect our patients to live up to 10 to 20 years on average; after radical treatment. The concept of hypofractionation in prostate cancer patients (PCP) dates back to the late 20th century; although back then; the intent was most likely cost-efficiency.

The main concern was the treatment toxicity; but due to an improvement in irradiation and imaging techniques allowing us to achieve excellent dose conformity; (3-dimensional conformal radiation therapy; intensity-modulated radiation therapy; image-guided radiation therapy; and finally stereotactic ablative radiotherapy [SABR] along with CyberKnife [CK]); the toxicity of high fraction doses is becoming less and less of an issue.

Irradiation and imaging

That said; this modality could hardly be called a novelty, but the quantity of single-center experience studies and phase II trials is limited; while phase III research is still ongoing. As described in the 2.2019 NCCN Guidelines for Prostate Cancer; “longer follow-up (FU) and prospective multi-institutional data are required to evaluate long-term results.” A treatment process should be regarded in 3 aspects: curability; adverse effects, and the convenience of the treatment itself. Radiobiologically, the α/β ratio of prostate cancer is very low compared to adjacent healthy tissues, approximately 1.5 Gy according to Fowler.

It allows us to achieve a very high biological effective dose through escalation of fraction dose compared to conventionally fractionated regimens, which could translate into a more effective local control of the tumor. Due to the very high dose conformity of CK SABR treatment, the dose delivered to organs at risk can be greatly reduced; and therefore, both the acute and the late toxicity can theoretically be maintained at mild and acceptable levels.

Moreover, compared to conventional fractionation schemes, SABR requires only 5 treatment sessions over 10 days, instead of 20 to 39 sessions over 4 to 8 weeks of treatment. The main aim of this study was to evaluate the tolerance and effectiveness of SABR in PCP and assess whether CK SABR can be a standard procedure for a selected group of patients. The second purpose was to analyze treatment failures and an attempt to define predictive factors.