Given a passage with a context and an answer, construct a question on the basis of the information present in the passage. Construct the question in such a way that (i) it is unambiguous, (ii) it is answerable from the passage, (iii) its answer is unique (iv) it answer uses text phrases from the passage. Avoid creating questions that (i) can't be answered correctly without actually understanding the passage and (ii) uses the same words or phrases given in the passage.

Context: To investigate a putative increased risk of rectal cancer subsequent to prostatic radiotherapy.', 'In an analysis of the Surveillance, Epidemiology, and End Results registry, we compared men who had radiotherapy for prostatic carcinoma with those treated surgically and those treated with neither modality. Kaplan-Meier analyses for the time to failure from rectal cancer were performed between age-matched subgroups of the three cohorts. Cox proportional hazards analyses were performed to ascertain what influences might affect the incidence of subsequent rectal cancer.', 'In all, 33,831 men were irradiated, 167,607 were treated surgically, and 36,335 received neither modality. Rectal cancers developed in 243 (0.7%) of those irradiated (mean age, 70.7 years), 578 (0.3%) of those treated surgically (68.7 years), and 227 (0.8%) of those treated with neither modality (74.2 years). When age effects and the differences between the surgical and untreated cohorts were controlled for, we were unable to demonstrate any significant increased incidence of rectal cancer in men irradiated for prostatic cancer.
Answer: An increased frequency of rectal cancer after prostatic irradiation, apparent on crude analysis, could be attributed to age confounding and other unmeasured confounders associated with prostate cancer treatment and rectal cancer risk.
Is prostatic irradiation associated with any measurable increase in the risk of subsequent rectal cancer?

Context: Guanidinoacetic acid (GAA) is an experimental dietary additive that might act as a creatine source in tissues with high-energy requirements. In this case study, we evaluated brain levels of creatine in white matter, gray matter, cerebellum, and thalamus during 8wk oral GAA administration in five healthy men and monitored the prevalence and severity of side effects of the intervention.', 'Volunteers were supplemented daily with 36mg/kg body weight (BW) of GAA for the first 4wk of the intervention; afterward GAA dosage was titrated 60mg/kg BW of GAA daily. At baseline, 4, and 8wk, the participants underwent brain magnetic resonance spectroscopy, clinical chemistry studies, and open-ended questionnaire for side-effect prevalence and severity.', 'Brain creatine levels increased in similar fashion in cerebellum, and white and gray matter after GAA supplementation, with an initial increase of 10.7% reported after 4wk, and additional upsurge (7.7%) from the weeks 4 to 8 follow-up (P<0.05). Thalamus creatine levels decreased after 4wk for 6.5% (P=0.02), and increased nonsignificantly after 8wk for 8% (P=0.09). GAA induced an increase in N-acetylaspartate levels at 8-wk follow-up in all brain areas evaluated (P<0.05). No participants reported any neurologic adverse event (e.g., seizures, tingling, convulsions) during the intervention.
Answer: Supplemental GAA led to a region-dependent increase of the creatine pool in the human brain. This might be relevant for restoring cellular bioenergetics in disorders characterized by low brain creatine and functional enzymatic machinery for creatine synthesis, including neurodegenerative diseases, brain tumors, or cerebrovascular disease.
Does dietary guanidinoacetic acid increase brain creatine levels in healthy men?

Context: Among factors that may affect the potency of botulinum toxin A (Botox), it is said that foam, together with bubbles, may cause surface denaturation of the toxin.', 'To determine whether the muscle relaxation effect of Botox is preserved and has the same duration when it is reconstituted in the presence of foam.', 'Six female volunteers, aged 42 to 56 years old, were treated for glabellar and periocular wrinkles. Each half of the face was treated with 16 U of Botox divided in four sites: three at the lateral orbital area and one at the medial brow, in the glabellar region. The right side received Botox gently reconstituted with saline to avoid foaming formation. The left side of the face was treated with Botox that was rapidly reconstituted in order to achieve as many bubbles as possible, even with shaking. Blinded observers compared pretreatment and posttreatment photographs and answered assessment-related questions. The results were analyzed clinically and statistically.', 'There was no difference in muscle paralysis between treated sides in all patients, neither in early (15 days) nor late (4 months) follow-up evaluations.
Answer: Botox maintains its potency even in the presence of foaming during the reconstitution process.
Does foam during reconstitution affect the potency of botulinum toxin type A?