Radiotherapists are constantly battling in order to administer the correct dose of radiotherapy, as respiratory movement during radiotherapy poses a certain risk that a tumor receives either a dose that is insufficient, or the surrounding healthy tissue is being subjected to a potentially toxic over-dose.

Dr. Amira Ziouèche presented a study at the 31st conference of the European Society for Radiotherapy and Oncology (ESTRO 31), which reveals a novel technique of how Deep Inspiration Breath Hold (DIBH) protects the heart during irradiation of left-side breast cancer tumors. The technique can assist radiologists in administering the correct dose to the precise location.

Dr. Ziouèche and Dr. Alice Mege conducted a prospective study at the Institut Sainte Catherine in Avignon, France, which demonstrated that patients who were treated whilst holding their breath at between 60 to 80% of their maximum inspiratory capacity, managed to protect their hearts and lungs from being subjected to radiation without compromising their treatment quality.

Dr. Ziouèche explains:

“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. 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.”

Between October 2007 and June 2010, Dr. Ziouèche and her team collected data on 31 patients who were treated with DIBH at the Institut Sainte Catherine. All patients were also their own control case, given that they all received two CT scans of which one was performed under FB, and the other under DIBH. The dose that was administered to targets and healthy organs was calculated based on these scans.

The evaluation demonstrated that under DIBH, the average dose to the heart decreased from 9 Gy under FB to 3.7 Gy, with the maximum heart dose being reduced from 44.9 Gy to 24.7 Gy. DIBH was also noted to reduce the amount of radiation to the lung.

Dr Ziouèche comments:

“This is the largest study to date of the use of DIBH in patients undergoing radiotherapy for breast cancer. 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.”

She concludes:

“Although the DIBH procedure initially involves additional time and therefore cost, if this technique results as we believe it will, in a clinical benefit in terms of reducing cardiac and pulmonary sequelae in specific cases it could result in lower healthcare costs in the longer term. Currently the DIBH technique is little used in breast cancer, and we need further studies of its clinical and economic benefits to demonstrate its value in breast radiation treatment. Once these studies are completed we would hope to see it in widespread use in the future, to the benefit of patients and healthcare systems alike.”

An earlier presentation of a study by Ms Fanneke van den Boomen, from Eindhoven’s Catharina Hospital in The Netherlands and her team revealed how to obtain a more accurate estimate of safety margins for radiotherapy treatments under respiratory movement by comparing results from two different types of CT scans. The study involved 50 patients with lung tumors who underwent 3D and 4D treatment planning CT scans. They discovered that 4D scans provided superior results in cases that involved a large tumor motion.

According to Ms van den Boomen:

“In a conventional 3D scan the scan is taken with the patient in the treatment position, but not taking breathing motion into account. Due to the fact that it takes around two minutes to perform the scan, the result is blurred due to the motion of the tumor. With 4D scanning you can account for breathing because the software creates a number of datasets at different phases of the breathing cycle, thus freezing the tumor in a certain position.”

Due to the fact that 4D scanning equipment has only fairly recently become available, the numbers of institutes using this technology is still limited. The team announces that their study results have been so convincing that their hospital now routinely performs 4D scans in cases where there is large tumor movement.

Ms van den Boomen says:

“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.”

Gauthier Bouilhol, M.Sc, from the Centre Léon Bérard, Lyon presented a newly developed model at the conference, which adjusts the currently used method for calculating safety margins to account for respiratory motion asymmetry during radiotherapy.

Bouilhol explains:

“When a patient breathes during radiotherapy treatment the tumor may also move. The normal way of calculating the treatment margins to compensate for potential errors is based on a symmetrical model. But if tumor motion is asymmetric the model is wrong.”

Bouilhol and his team from CREATIS (CNRS UMR5220, Inserm U1044) suggest a new model that takes the differences between the two margins during inhalation and exhalation into account, saying:

“We believe that our model, once clinically validated, will provide a more accurate assessment of the area which is required to be treated with radiation, and this will improve both safety and efficacy for patients.”

Chair of the ESTRO-31 scientific program committee, Dr. Núria Jornet, a medical physicist from the Hospital de la Santa Creu i Sant Pau in Barcelona declares:

“Organ motion due to physiological processes such as breathing poses a challenge in highly accurate radiation therapy. With the advent of technological advances such as 4D imagers, which allow making ‘cine’ images of internal organ motion, and treatment units that can synchronize radiation with the organ movement this motion can be monitored and accounted for.

Nowadays, we are not only able to know where the tumor is in each moment but also have methods to hit it with a millimetric accuracy. These three abstracts are a good example of how breathing motion is managed using different approaches either by reducing motion by irradiating in deep inspiration breath hold which also exploits lung inflation to spare normal tissues, or by personalizing safety margins around the tumor so that we are sure that the tumor will be correctly irradiated in all breathing phases.

Regardless of the method used to manage motion, image guidance during treatment is needed, as is shown in the study by Mrs. van den Boomen. Other abstracts in this meeting present novel motion management methods such as real time motion tracking in which the radiation beam follows the tumor movement.”

Written By Petra Rattue