Would you use SBRT, hypofractionated or standard fractionated boost?
The question posed is clinically relevant and asks us to weigh the optimal treatment for a high risk patient in the current pandemic setting. I presume the initial course of radiotherapy was standard fractionation of 45 Gy in 25 fractions. Boosting the primary would be standard of care and supported by multiple RCTs that uniformly demonstrated improved tumor control with dose escalation.
Could you simply delay the boost a few months while the patient continues to receive ADT? Retrospective data indicate that treatment delays / prolonged treatment duration increases risk of biochemical failure (PMID 20400191, PMID 18472368). A randomized trial that compared split course to continuous treatment for pelvic malignancies (cervix, bladder, prostate) saw no difference in local control between the two approaches (n=65 for prostate), though it predated the PSA era and the assessment of local failure is crude by today's standards (Parsons et al., Int J Radiat Oncol Biol Phys. 1980).
Removing LDR for consideration, current options for boosting high risk patients include standard fractionation EBRT, hypofractionated EBRT, SBRT, or HDR. Using HDR requires some PPE utilization, so avoiding anything procedural during COVID-19 seems prudent. To avoid fiducials / hydrogel spacer, I would not advocate for SBRT. If your center is comfortable treating without, then a boost of 6-7 Gy X 3 has been reported though this series used CK with fiducials (PMID: 24382205).
In the current setting, I would specifically look to the recently published study from Zaorsky et al in Advances in Radiation Oncology for guidance. As those authors conclude, what makes sense right now is to delay when possible, then simplify and shorten treatment schedules. Since treatment is started, I wouldn't break treatment but would shorten as efficiently as possible. I would use a hypofractionated boost regimen of something like 3 Gy x 8. Such a regimen has a similar BED to the traditional 1.8 Gy x 19 EBRT boost.
As long as the patient is on androgen deprivation, treatment relay is less impactful.
However, it has been well established (with solid evidence) that removing LDR will result in doubling the recurrence rate.
I believe patients must be informed about these facts and it is important to have them involved in the decision-making process.
We are currently going through extraordinary circumstances which would require unique interventions and approaches.
Most high risk patients prostate cancer patients should already be on androgen deprivation. Hence, delaying the seed implant a few weeks or even months until we address our PPE shortage and COVID-19 is a reasonable approach and unlikely to be detrimental.
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I will assume for the sake of argument that he is also getting ADT as part of his treatment.
If he has responded well to ADT (I like to see about a 90% drop in the PSA within 3 months), my preference would be to try to delay until it's reasonable from an infectious disease perspective to proceed with brachytherapy. Although there are no great data to call upon here, I think the potential benefit from brachytherapy outweighs the risk from a delay of a few months, although admittedly we can't be sure yet exactly how long that delay may be.
If the patient is not comfortable with that approach, or he has had a poor response to ADT, I would pick an option that would minimize the number of trips he has to make to the radiation center for treatment. Every trip presents a potential health risk to everyone involved, both patient and providers. The options will depend on the dose-fractionation schedule used this point, and how well it has been tolerated, but I would favor hypofractionation. An SBRT boost falls more in the realm of research, but if you have experience with prostate SBRT, this might be a reasonable approach, too, given these exceptional times.