Prone Position During Breast Irradiation Lessens Lung Cancer Risk

[Hopeful]

Elsevier Global Medical News. 2011 Oct 3, N Osterweil

MIAMI BEACH (EGMN) - Placing breast cancer patients in a prone rather than supine position during whole breast irradiation may significantly reduce their risk for secondary lung cancers, investigators reported at the annual meeting of the American Society for Radiation Oncology.

The total radiation dose that would be delivered to the corresponding (ipsilateral) lung of patients treated while they were lying face down was less than one-tenth of the dose delivered to that of patients treated while lying on their backs, said Dr. John Ng, senior radiation oncology resident at Columbia University Medical Center in New York.

The mean expected lifetime risk for radiation-associated secondary lung cancer is 1.99% in patients given whole breast irradiation with a prone technique, compared with 4.86% for patients treated with a supine technique, he reported. It was 3.87% for patients treated with a 3-D conformal partial breast irradiation technique, and 2.92% for patients treated with balloon brachytherapy (P less than .001 for all comparisons).

By way of comparison, the estimated expected background risk for lung cancer is about 1.5%, Dr. Ng and his colleagues wrote in a poster presentation.

"It's documented that there is some excess relative risk of lung cancers after breast radiation treatment - I think everybody agrees with that. What people will disagree on is how significant this risk is, and that's what motivates us to do this study," Dr. Ng said in an interview.

The prone technique is, however, considerably more time consuming in terms of treatment planning and positioning of the patient, resulting in treatment sessions that are about twice as long as those for patients treated supinely (about 45 vs. 20 minutes, Dr. Ng said).

The investigators used a mathematical model to estimate the risk of both spontaneous and radiation-induced lung cancer risk in 25 women with early-stage breast cancer undergoing treatment planning with CT simulation for post-lumpectomy radiation therapy. Patients scheduled for whole breast irradiation were simulated in both the prone and the supine positions; those scheduled for partial breast irradiation were simulated in the supine position only.

The model encompassed standard dosing (50 Gy, delivered in 25 fractions), hypofractionation (42 Gy in 16 fractions), or standard external-beam accelerated partial breast irradiation (38.5 Gy in 10 fractions).

For each of the 15 patients treated in the prone technique, there would be significantly less radiation (54.2 cGy, on average) delivered to the lung than with the supine technique (646.5 cGy), balloon brachytherapy (291.0 cGy), or partial-breast irradiation (275.2 cGy; P less than .001 for all comparisons).

The relative risks for each technique and dosing schedule, compared with background risk, were 4.04 for supine standard fractionation, 3.98 for supine hypofractionation, 2.54 for balloon brachytherapy, 2.36 for 3D conformal accelerated partial-breast irradiation, and 1.56 for standard fractionation.

"The take-home point is that there is substantial risk of secondary lung malignancy from our standard technique. You can improve it with partial breast irradiation, but our study shows that the best results come from the prone technique," Dr. Ng said.

Dr. Phillip M. Devlin, chief of the division of brachytherapy at Dana-Farber Cancer Institute, Boston, commented that the study was interesting but complex, with the issue of prone vs. supine muddied by the inclusion of brachytherapy into the mix.

"In this small study, the hypothesis is generated that there would be less cancer caused by prone technique than by supine technique, and therefore a prospective analysis of this may be warranted. However, with these findings one might even ask whether it would be ethical to do the prospective study," said Dr. Devlin, who was not involved in the study.

He noted that the prone technique was originally developed to help women with more pendulous breasts tolerate whole breast irradiation better, with fewer side effects and improved cosmesis.

"Given the fact that we chose this technique for other end points, isn't it interesting that if we also look at reasonable modeling done on a reasonably small data set, in the model the risk is lower with the prone technique, further endorsing what we've already found for a bigger and different reason. The cost to achieve this in terms of patient throughput is in play, but it is counterbalanced against the potential extra cost of treating either a local recurrence or a second malignant neoplasm," Dr. Devlin said.

The study was internally funded. Neither Dr. Ng nor Dr. Devlin had conflicts of interest to disclose.

Hopeful