High dose rate brachytherapy after EBRT effective, safe for Asian prostate cancer patients
In Asian patients with localized prostate cancer, high dose rate (HDR) brachytherapy following an external beam radiotherapy (EBRT) achieves effective disease control while minimizing toxicity, a recent Singapore study has shown.
“These outcomes are comparable to internationally published data and demonstrate reproducibility of this approach in our unique Asian population,” the researchers noted.
The research team reviewed medical records of 75 prostate cancer patients (median age 70 years) who were treated with EBRT, delivered via intensity modulated radiotherapy (IMRT), followed by HDR brachytherapy. Patients were recruited from the National Cancer Institute at the National University Hospital in Singapore.
At each follow-up, participants underwent testing for prostate-specific antigen (PSA) levels, which were then used to determine biochemical failure, defined as PSA levels 2.0 ng/mL above the nadir values. The principal study outcomes were disease control, defined as biochemical disease-free survival, prostate cancer-specific survival and overall survival. Treatment-related toxicities were also recorded.
Biochemical failure was reported in 14.7 percent (n=11) of the participants, of whom six were found with distant metastasis and one with seminal vesicle involvement. All of these patients were high-risk. The median time to PSA failure was 3 years. [Asia Pac J Clin Oncol 2017;doi:10.1111/ajco.12819s]
The overall 5-year biochemical control in the cohort was 85.2 percent, while in high-risk patients, the corresponding value was 80.5 percent. In comparison, all of the intermediate-risk patients achieved biochemical control at 5 years.
Univariate analysis showed that ethnicity was predictive of biochemical failure, with Indians (odds ratio [OR], 9.33; 95 percent CI, 1.11 to 78.79) and those of ethnicities other than Malay and Chinese (OR, 9.33; 1.11 to 78.79) having higher risks of failure.
Notably, demographic, biochemical and tumour variables, such as T-stage, baseline PSA levels, risk group, medication doses, age and duration of androgen deprivation therapy, were all unrelated to disease control.
There were two prostate cancer-related deaths and four from other causes, resulting in a 5-year cancer-specific and overall survival rates of 97.3 and 92.0 percent, respectively.
“To our knowledge, this is the first report of the outcomes of combined modality treatment in Southeast Asia. Our centre first adopted HDR brachytherapy boost of 21 Gy in two fractions, subsequently 19 Gy in two fractions and currently 15 Gy in a single fraction. Our study shows that these schedules are effective in disease control and is safe in our population,” the researchers said.
In terms of toxicities, 3 percent (n=2) of the participants experienced grade 3 genitourinary toxicity. No grade 4 or 5 toxicities were reported. The most common adverse event was acute grade 1 diarrhoea, observed in 32 percent (n=24) of the patients. This was followed by acute (28 percent) and late (23 percent) grade 1 cystitis.
Because of Singapore’s multiracial population, bolstered by the inclusion of study participants from neighbouring countries, the researchers noted that the study findings “are likely to represent the outcomes of the patients in [Southeast Asia].”
Moreover, the researchers said that the recent findings may contribute to alternative, more economical prostate cancer treatment regimens, adding that “[f]rom a patient's perspective, this approach marries efficacy and convenience. For patients who desire a shorter treatment course, this is a safe consideration.”