Here is Daniel Hamstra's response to the section where I wrote:
Keeping in mind that LDRBT patients were a median of 5 years younger than the other two groups, the increase in erectile dysfunction among LDRBT patients is troubling. As we saw in a recent study, the deterioration occurs earlier than was previously thought. For SBRT, in contrast, there was only a +5 percent increase in erectile dysfunction severity at 2 months after treatment, but that increased to +11 percent by 2 years. Nevertheless, that was still lower than the other two therapies.
Dr. Hamstra said...
But I don’t think it is a good idea to put out there that SBRT is better for sexual function and LDR is worse. I really don’t think we have that good of a handle on it.
I don’t think the conclusion or concern that LDR leads to worse sexual decline is an accurate one. The main reason SBRT looks better for sexual function is that they were the oldest group and had the worst sexual function to begin with. Fundamentally, if sexual function is bad, the EPIC instrument does a poor job of documenting it getting much worse. So, the multivariate analysis of sexual function at 2 years indicated that the only variables significant for decline in sexual function were:
• Baseline sexual function (with a large effect size)
• Baseline physical function (with a somewhat smaller effect size)
• With borderline associations with baseline mental health and age.
Age and baseline function are highly inter-related which is likely why age was less prognostic.
I would not conclude that LDR was worse. In fact, the analysis previously reported using the PROSTQA data (below) found that age was very important as was baseline function. It then built prognostic models based upon differing treatment techniques etc. and found not huge differences between IMRT and LDR.
“Prediction of erectile function following treatment for prostate cancer.”
Alemozaffar M, Regan MM, Cooperberg MR, Wei JT, Michalski JM, Sandler HM, Hembroff L, Sadetsky N, Saigal CS, Litwin MS, Klein E, Kibel AS, Hamstra DA, Pisters LL, Kuban DA, Kaplan ID, Wood DP, Ciezki J, Dunn RL, Carroll PR, Sanda MG.
JAMA. 2011 Sep 21;306(11):1205-14. doi: 10.1001/jama.2011.1333.
Thank you for explaining that. You are quite right that age only seemed to be less prognostic in multivariate analysis because it’s interrelated with baseline function. My guess is that the problem of covariance also affects changes over time. Age-adjusted baseline sexual function and age-adjusted EPIC scores over time might obviate the problem. My guess is that treatment effects might turn out to be independently significant in the age-adjusted changes.
I don’t know if you saw the analysis from BC:
Half of long-term erectile function (EF) loss after brachytherapy (BT) is due to aging
I hear what you’re saying that the older men in the external beam cohorts had less relative deterioration because they were already so low. Yet the Massachusetts Male Aging Study (used in their analysis) seems to show the opposite — the relative deterioration in sexual function in 70-year-old men is actually much greater than for 65-year-old men.
In the BC study, they noticed the same temporal pattern that you did — the deterioration in sexual function after BT occurred quite early. I don’t know why the temporal pattern should differ from external beam, but it certainly seems to. Perhaps future follow-up studies will elucidate this phenomenon.”