What is the appropriate dosage of radiotherapy for early breast cancer?

This paper studied the dosage of radiotherapy in women who have had surgery for early breast cancer. 

After surgical removal of tumour, radiation is often given to prevent relapse (return of cancer). Radiation therapy can be fractionated (dividing the total radiation into smaller doses over time). Fractionation is less harmful to healthy cells. However, a balance needs to be found between killing cancer cells and protecting healthy cells.

The standard regimen is a total of 50 Gy (Gray, measurement of radiation) delivered in 25 fractions (25 times) of 2 Gy over 5 weeks. However, if delivering less radiation overall (via fewer, larger doses) is as effective as this standard regimen, this would be preferred due to the reduced effect on healthy cells. 

The authors evaluated two trials which studied whether delivering less radiation in fewer larger doses are as safe as the standard regimen. 

Trial A

2,236 women were randomly assigned to receive 50 Gy in 25 fractions, 41·6 Gy in 13 fractions or 39 Gy in 13 fractions over 5 weeks. After an average of 9.3 years, 76% of patients were alive and without relapse. 2.5% were alive with local relapse (return of cancer to original site). 3.5% were alive with distant relapse (return of cancer to other part of body). 17.5% had died.

Patients receiving 41·6 Gy were 9% less at risk of local relapse compared to patients receiving 50 Gy. Patients receiving 39 Gy were 1.18 times more at risk of a local relapse than patients receiving 50 Gy. However, these differences were not deemed to be significant. Breast hardening, swelling, and widening of blood vessels of the skin were less common in patients receiving 39 Gy than 50 Gy.

Trial B

2,215 female patients were randomly assigned to receive either 50 Gy in 25 fractions over 5 weeks or 40 Gy in 15 fractions over 3 weeks. After an average of 9.9 years, 78.2% of patients were alive and without relapse. 2.3% were alive with local relapse while 2.8% were alive with distant relapse. 15.8% had died.

Patients receiving the 40 Gy radiation were 23% less at risk of a local relapse compared to patients receiving 50 Gy radiation. Again, these resuts were not deemed to be significant. Breast shrinkage, swelling and widening of blood vessels of the skin were less common in patients receiving 40 Gy than 50 Gy. 

The authors concluded that appropriately dosed fractionated radiotherapy (such as 40 Gy in 15 fractions) for women with early breast cancer is as safe and effective.