International Journal of Radiation Oncology*Biology*Physics
Physics contributionTechnical aspects of the deep inspiration breath-hold technique in the treatment of thoracic cancer
Introduction
Conformal therapy may improve local control and long-term survival by facilitating dose escalation (1). By tailoring the radiation dose distribution, a higher dose is delivered to the tumor while maintaining the dose to nearby healthy tissue below tolerance. One promising site for conformal therapy is lung (2). Lungs show a strong volume effect for radiation pneumonitis 3, 4, 5; i.e., as a greater percentage of lung is irradiated to a particular dose, the normal tissue complication probability (NTCP) increases. If the fractional lung volume within the field could be reduced, higher dose could be delivered to the tumor, thus increasing the probability of local control while maintaining the same NTCP.
Recent approaches to reducing the fraction of lung irradiated have focused on reducing the margin added around the clinical target volume (CTV) (6). This margin accounts for both respiratory motion and setup error. Because setup errors are typically a few mm (7) and organ motion in the thorax is up to 3 cm during normal quiet breathing 8, 9, 10, the size of the margin for the thorax is dominated by respiratory motion. Hence, approaches to reduce safely this margin, using methods such as conformal therapy, respiratory gating of the accelerator 11, 12, 13, 14, and controlled breathing, either voluntary (15) or assisted by means of an occlusion valve (16), have been investigated.
Recently, we have described a deep inspiration breath-hold (DIBH) technique (17), which has two advantages. First, like the other approaches, the breath hold minimizes tumor motion due to breathing. Furthermore, deep inspiration expands the patient’s lungs to maximum volume thus driving healthy lung tissue out of the primary radiation beam, thereby reducing the fraction of the lung in the treatment field. Our initial implementation has capitalized on the benefit of maximum lung inflation without margin reduction (18). Here, we describe technical aspects of the implementation of DIBH including quality assurance and tumor motion studies.
Section snippets
Methods and materials
Because the details of the DIBH procedure have been described previously 17, 18, we briefly summarize the approach here while emphasizing features that have not been provided in earlier reports. In DIBH, a patient is coached through a modified slow vital capacity breathing maneuver (19) to reach a reproducible deep inspiration point. The patient then holds her breath during the (approximate) 10-s treatment at high-dose rate (e.g., 500 monitor units/min). There are three distinct steps in the
Results
At the time of manuscript preparation (June 22, 2000), 16 patients have been treated with the DIBH technique encompassing over 400 fractions. Here we report on the results for the first 7 patients encompassing over 250 fractions. The 1st patient was planned and treated with the DIBH technique for the last 10 fractions, the next 2 patients for the last 20 fractions, and so on until the 8th, and all subsequent patients were either treated fully with the technique (6 patients) or were switched to
Discussion
As shown in Fig. 2a for some patients, there is a pronounced change in diaphragm position immediately as the breath hold begins. We interpreted this to be an initial relaxation of the diaphragm after reaching the maximum breath hold. The subsequent small variation in diaphragm position during breath hold likely reflects both voluntary and involuntary muscle movements as the patient maintains his breath hold. Because there is a width to the distribution in Fig. 2c, a given spirometer reading
Conclusions
We have shown that DIBH can be performed in the clinic on a routine basis. This paper has indicated some of the technical details of this approach and has established that the technique is robust and readily implemented. We have shown that DIBH can reduce lung and presumably tumor motion. Margin reduction was not performed at this stage and will not be performed until a careful dosimetric study has been completed. We have shown elsewhere 17, 18 that deep inspiration can allow substantial dose
Acknowledgements
Funded in part by National Cancer Institute Grant 5PO1CA59017, U.S. National Institutes of Health. We are very grateful to David Lynn of Burdick Inc. for numerous conversations and advice about the software and hardware.
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