Biochemical Response After Therapy for Prostate Cancer and the Incidence of Disease Progression Among Patients Treated With Definitive External Beam Radiotherapy at Kenyatta National Hospital: a Retrospective Study

Abstract

Evaluation of the prostate specific antigen levels after radiotherapy predicts biochemical failure, distant metastasis and both cause-specific and overall mortality. PSA nadir in patients treated with radiation therapy may take months to be attained. There is evidence that in most patients a significant and relevant decline in the PSA levels occurs within the first twelve months of completion of treatment. There is paucity of data locally regarding the biochemical response of prostate cancer patients after radiotherapy and how this change relates to the incidence of disease progression and development of metastasis. The main objective of this study was to assess the biochemical (PSA) response in the first 36 months after treatment and the incidence of disease progression among patients with prostate cancer treated at Kenyatta National Hospital with external beam radiation therapy. This retrospective cross-sectional study reviewed the treatment records of 86 prostate cancer patients treated with external beam radiotherapy between 2015–2020 at Kenyatta National Hospital. Data analysis was carried out in R version 4.1.2. Descriptive statistics were used to summarize the data on demographics, baseline PSA, radiotherapy technique and dose, and post-radiotherapy PSA levels. Patient and treatment characteristics were compared based on the PSA levels using Fisher’s exact test. Mann-Whitney U test was used to evaluate the correlation between the post-treatment PSA levels and the likelihood of disease progression. Data was presented using charts and graphs. Results were interpreted at 5% significance level using p values. The mean age at diagnosis was 69 years and 68.6% had NCCN high risk disease. All patients in this study received combined ADT and EBRT via 3DCRT or 2-D technique. 46.5% received a total dose of 66Gy. The median PSA nadir was 0.019ng/ml attained over a median time interval of 12 months after irradiation. 23.3% of the patients had biochemical failure and in 75% of them disease progression was documented. Incidence of biochemical failure was higher among those treated with the 2D (Cobalt) technique than the 3D conformal radiotherapy. There was a statistically significant association between rising PSA and disease progression (Fisher’s test p-value <0.05). From this study we conclude that most of the prostate cancer patients have good biochemical outcome after radiotherapy. The robustness of treatment outcomes can be enhanced by use of more conformal radiotherapy allowing dose escalation and reduced normal tissue toxicity