Radiation- Induced Alopecia in Patients Undergoing Radiation Therapy to the Brain: A Prospective Clinical and Dosimetric Study of Primary and Metastatic Brain Tumour Patients

Patients with primary or metastatic cancers to the brain need to undergo partial or whole brain radiotherapy. Alopecia is an inadvertent side effect of Radiation therapy to the brain. Much of this alopecia occurs in patches and is often associated with permanent loss of hair. Irradiation-induced epilation is due to high susceptibility of anagen follicles to radiation. Loss of hair can be stressful and distressing for cancer patients.

Various studies have tried to address the issue of threshold dose for radiotherapy induced alopecia. The severity and type of skin response and consequent alopecia to radiation is decided by multitude of factors - total dose and dose fractionation, quality of radiation, area or volume of tissue irradiated, anatomic site and vascular response. Studies have shown that 3Gy produces complete, reversible anagen alopecia and permanent alopecia begins to occur at 5Gy.

At higher dose rates the susceptibility of hair melanocytes is much more than epidermal melanocytes. Freysz et al in a retrospective analysis of 18 patients deduced that a cumulative dose as high as 12Gy results in alopecia that is reversible.Temporary alopecia is seen in most patients receiving WBRT with conventional fractionation. Most of these studies are either small reports or were done before the advent of modern technology. The advent of precision radiotherapy techniques has made it possible to utilize techniques that reduce the dose to the scalp in an attempt to minimize the chances of radiation- induced alopecia.

In a first, a phase II dosimetric and clinical study by De Puysseleyr et al concluded that Volumetric Modulated Arc Therapy (VMAT)- WBRT delivers lower scalp doses as compared to conventional parallel opposed fields but the study was closed prematurely as it failed to show any clinical benefit in terms of preventing alopecia. They however, concluded that the threshold Treatment Planning System (TPS) dose for temporary alopecia is around 10Gy in 5 fractions.

In a study by Ting et al alopecia was observed in half of the patients undergoing Whole Brain Radiotherapy (WBRT) to a dose of 30Gy/10 fractions did not have significant alopecia. The remaining half had mild alopecia. In the study by Mahadevan A et al, hippocampus sparing WBRT also spares hair follicle bearing regions of the scalp while maintaining strict compliance to hippocampus avoidance zone. There is no consensus regarding the threshold TPS dose for alopecia as the study of dose received by hair follicles during intensity modulated radiotherapy for whole brain is limited by lack of knowledge of dose-effect relation of temporary alopecia.