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Radiation-induced alopecia occurs in a dose-dependent manner and has distinctive clinical and trichoscopic features, according to a retrospective study of patients with brain tumors or head and neck sarcomas.

Alopecia severity increased with radiation dose and with use of proton (versus photon) irradiation. Principal trichoscopic features included white patches and a negative correlation between hair-shaft caliber and radiation dose to the scalp. Hair density and scalp radiation dose were not significantly associated, Mario E. Lacouture, MD, of Memorial Sloan Kettering Cancer Center (MSKCC) in New York City, and coauthors reported in .

In a subgroup of patients treated with topical minoxidil, however, the vast majority responded to the hair-growth stimulant.

"Persistent radiation-induced alopecia (pRIA) among patients with primary CNS [central nervous system] or head and neck sarcomas represents a dose-dependent phenomenon that is tractable in clinical severity evaluation, clinical photographs, and trichoscopic images," the authors wrote in conclusion. "In this study, we present evidence for the potential utility of topical minoxidil, hair transplantation, and plastic surgical reconstruction for pRIA.

"These findings may inform pretherapy counseling and efforts to identify preventive and therapeutic strategies, including randomized clinical trials in cancer survivors, for this burdensome sequela of a principal axis of cancer therapy."

Paucity of Information

Perhaps less publicized as compared with chemotherapy-induced alopecia, hair loss is a well recognized side effect of cranial radiation therapy, particularly for patients with CNS or head and neck tumors. From 75% to 100% of patients who undergo cranial radiotherapy have noticeable hair loss with single-fraction radiation doses >2 Gy, the authors noted.

In many cases hair regrowth occurs within 2 to 4 months. However, persistent radiation-induced alopecia, defined as incomplete hair regrowth within 6 months after completing radiotherapy, occurs in approximately 60% of recipients of cranial irradiation, Lacouture and colleagues continued.

Despite the high frequency of hair loss with cranial irradiation, the medical literature has limited information about the clinical course of pRIA and its treatment, providing a rationale for the retrospective cohort study. Data analysis included 71 adult and pediatric patients treated from Jan. 1, 2011, to Jan. 30, 2019, at MSKCC and St. Jude Children's Research Hospital in Memphis, Tennessee. All the patients developed pRIA following cranial irradiation for primary CNS tumors or head and neck sarcomas.

The primary outcomes were clinical and trichoscopic features of pRIA, scalp radiation dose-response relationship, and response to topical minoxidil. Assessments included standard clinical photographs of the scalp, trichoscopic images, and radiotherapy treatment plans.

The 71 patients had a median age of 27 and range of 4 to 75, and a majority (52 of 71) of the patients were women. Primary CNS tumors accounted for all but seven of the cancers treated with radiation therapy.

Most (N=40) of the patients had grade 1 alopecia. In a subgroup of 54 patients with data on pattern of hair loss, the alopecia was localized in 29 (54%) patients, diffuse in 13 (24%), and mixed in 12 (22%).

The median estimated scalp radiation dose was 39.6 Gy, and total dose ranged from 15.1 to 50.0 Gy. Two factors were significantly associated (P<0.001) with greater alopecia severity: higher radiation dose (OR 1.15, 95% CI 1.04-1.28) and use of proton therapy (OR 5.7, 95% CI 1.05 to 30.8). The estimated radiation dose necessary to cause severe (grade 2) alopecia in 50% of patients was 36.1 Gy.

In a subgroup of 28 patients, 16 had white patches as the predominant trichoscopic feature. Hair-shaft caliber had a negative correlation with radiation dose to the scalp (P=0.01) in an analysis involving 15 patients.

Among 34 patients treated with topical 5% minoxidil, 28 (72%) met criteria for clinical response after a median follow-up of 61 weeks. Analysis of clinical images in 25 minoxidil patients showed four complete responses and 13 partial responses. Two patients responded to hair transplantation and one responded to reconstructive plastic surgery.

Informative Study

The study provided useful information about several key issues surrounding radiation-induced alopecia, said Stephanie Weiss, MD, of Fox Chase Cancer Center in Philadelphia.

"It's a little more difficult than you'd imagine to tease out radiation-related factors, such as dose," she told 名媛直播. "The reason for that is that there are strict standard doses that people will receive, a pre-prescribed dose per day and some total dose. Basically, anytime you're going to have some dose to the scalp. What's interesting is that this paper showed that it's not just total dose but dose per day."

"I've had patients, for instance, who have received only a fraction or two of the prescribed dose and then had to stop for whatever reason," Weiss added. "Then several weeks down the road, they will develop alopecia. The condition doesn't manifest until several weeks later."

The timing of hair loss varies from patient to patient and depends on the frequency and size of radiation fractions, she continued. Hair loss often begins subtly, and patients will notice strands coming out during a shower or left on a pillow after sleep.

"I tell my patients right up front that they are going to lose their hair," said Weiss. "Just when you think you're not going to lose your hair, that's probably when you're going to start losing it."

The observation that proton therapy increased the likelihood of hair loss might be an eye opener for some radiation oncologists who have become accustomed to hearing that proton therapy has a more favorable safety profile as compared with photons. By focusing more specifically on the tumor, proton therapy does spare more surrounding normal tissue. However, the delivery process results in a higher dose to superficial areas, such as the scalp, said Weiss.

Whether the hair loss becomes chronic or permanent depends on the extent of radiation damage to hair follicles. Patients treated with both chemotherapy and radiation therapy may have particularly fragile follicles.

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