Breathing during Radiotherapy
(Ivanhoe Newswire) — Respiratory movement during radiotherapy makes it difficult to hit the right treatment target and this in turn can lead to an under-dose of radiation to the tumor, or a potentially toxic over-dose to the surrounding healthy tissue. Getting this right is a real challenge for the radiotherapist, but new techniques are helping to deliver the correct dose to the right place
Deep Inspiration Breath Hold (DIBH) can spare the heart when irradiating left-side breast cancer tumors.
“Unlike treatment under free breathing (FB), where the patient breathes normally, DIBH spares the heart by reducing its volume and movement in the field to be irradiated, and the lung expansion involved in holding breath leads to a decrease of relative lung volume which is irradiated,” Dr. Amira ZiouÃ¨che, a radiotherapy specialist from the Centre LÃ©on BÃ©rard, Lyon, France, was quoted as saying. “In effect, we can largely eliminate the problem of respiratory movement by using this technique, which allows us to reduce the volume of the healthy organ irradiated around the target volume while improving treatment precision. This is particularly important in breast cancer cases, where the life expectancy of most patients is long.”
In a prospective study, undertaken while she was working with Dr. Alice Mege at the Institut Sainte Catherine, Avignon, France, she showed that treating patients during DIBH, while they were holding their breath at between 60% to 80% of their maximum inspiratory (breathing-in) capacity, could spare their hearts and lungs from radiation without compromising the quality of their treatment.
They collected data on 31 patients treated with DIBH between October 2007 and June 2010 at the Institut Sainte Catherine. Each patient was her own case-control and underwent two CT scans, one in FB and the other in DIBH. The dose to healthy organs and targets was calculated based on these scans. Analysis showed that the heart mean dose decreased from 9 Gy in FB to 3.7 Gy in DIBH, and the maximum heart dose from 44.9 Gy to 24.7 Gy. The amount of radiation to the lung was also decreased with DIBH.
“This is the largest study to date of the use of DIBH in patients undergoing radiotherapy for breast cancer,” Dr ZiouÃ¨che was quoted saying. “It is an important result for breast cancer patients, where it can spare the volume of heart and lungs that are irradiated. Commonly, the margins around the tumor to be treated are increased in order to take movement into account. But this involves treating a larger area, some of it unnecessarily. The use of DIBH avoids this problem.
In an earlier presentation, researchers compared results from two different kinds of CT scan to see which could more accurately estimate safety margins for radiotherapy treatment where breathing motion was involved. They compared the results from 3D and 4D treatment-planning CT scans of 50 patients with lung tumors and found that the more recent 4D scans provided better results in cases where large tumor motion was involved.
“The results from this study have shown that we can safely apply the ‘mid-ventilation’ concept, where we only irradiate part of the tumor trajectory instead of the entire volume in which the tumor resides during a breathing cycle. Thus we can reduce treatment volumes, with the result that patients have fewer complications,” Ms Fanneke van den Boomen, from the Catharina Hospital, Eindhoven, The Netherlands, was quoted as saying.
4D scanning equipment has only become available recently, and therefore the number of institutes using it is still limited. However, the researchers say, the results are so impressive that their hospital is now performing it routinely in cases where there is large tumor movement.
Source: 31st conference of the European Society for Radiotherapy and Oncology, May 2012