Do you use specific scalp dosimetry constraints to prevent chronic alopecia when treating partial brain volumes with VMAT?

I have been using VMAT for 8 years to treat brain tumors, and permanent alopecia is rarely a complication in patients treated with doses of >50 Gy. For that reason, I personally do not use a scalp OAR constraint when planning a course of partial brain radiation. Prior to the adoption of VMAT, the occurrence of chronic alopecia was much more common although this is an anecdotal observation, A recent paper analyzed dosimetric factors associated with chronic alopecia (defined as lasting longer than 9 months, and found that only V40 Gy > 5.4 cc and D0.1 cc > 47.6 Gy were found to be independent predictors of chronic G2-alopecia according to correlation coefficient r. On multivariate analysis, age (p = 0.0002) and V40 Gy (p = 0.02) were found to...

I do try to be mindful of scalp dose for partial brain VMAT, mainly to reduce the risk of alopecia. If feasible, I generally try to keep the scalp/skin max dose around 39 Gy to D0.03 cc or lower. That said, I would prioritize target coverage and overall plan quality if there is a tradeoff. In my practice, this is more of a planning goal than a hard constraint, especially when the target is close to the calvarium or skin surface.

In addition to Dr. @Dr. First Last's planning guidance, another helpful resource to inform planning is this detailed study from MSKCC, which attempts to model the dose dependence of alopecia grade based on radiation exposure (Phillips et al., PMID 32756880). Based on their data, they estimate a 50% risk of G2 alopecia (hair loss > 50% of normal / altering QoL / requiring concealment) at ~36 Gy. As noted, avoidance of this side effect is rarely appropriate if it requires compromising the delivery of the therapeutic dose, so the data contained in this study is really more helpful to guide plan evaluation only when tumor coverage measures are well met. Of interest, they also report a response rate of ~80% by blinded review for the use of minox...

This may be an interesting or even controversial aside. My personal observation of brain tumors treated with protons is that geographic alopecia is more significant because the skin sparing is less, regardless of the radiation type, when you treat with only a small number of static fields. Same with skin doses, treating post-mastectomy chest walls with protons showing more desquamation than we would expect with well-planned photons. Proton planning reminds me of what we did with photons in the 90s when IMRT first appeared—planning/delivery has a lot of room to grow.

But I'm less concerned with looking at proton plans with the increased skin dose than I am with the implications of dose to the cortex when treating through a small number of po...