Deep inspiration breath-hold technique for lung tumors: The potential value of target immobilization and reduced lung density in dose escalation

Purpose/Objective: This study evaluates the dosimetric benefits and feasibi lity of a deep inspiration breath-hold (DIBH) technique in the treatment of lung tumors. The technique has two distinct features-deep inspiration, whi ch reduces lung density, and breath-hold, which immobilizes lung tumors, th ereby allowing for reduced margins. Both of these properties can potentiall y reduce the amount of normal lung tissue in the high-dose region, thus red ucing morbidity and improving the possibility of dose escalation. Methods and Materials: Five patients treated for non-small cell lung carcin oma (Stage IIA-IIIB) received computed tomography (CT) scans under 4 respir ation conditions: free-breathing, DIBH, shallow inspiration breath-hold, an d shallow expiration breath-hold. The free-breathing and DIBH scans were us ed to generate 3-dimensional conformal treatment plans for comparison, whil e the shallow inspiration and expiration scans determined the extent of tum or motion under free-breathing conditions. To acquire the breath-hold scans , the patients are brought to reproducible respiration levels using spirome try, and for DIBH, modified slow vital capacity maneuvers. Planning target volumes (PTVs) for free-breathing plans included a margin for setup error ( 0.75 cm) plus a margin equal to the extent of tumor motion due to respirati on (1-2 cm). Planning target volumes for DIBH plans included the same margi n for setup error, with a reduced margin for residual uncertainty in tumor position (0.20.5 cm) as determined from repeat fluoroscopic movies. To simu late the effects of respiration-gated treatments and estimate the role of t arget immobilization alone (i.e., without the benefit of reduced lung densi ty), a third plan is generated from the free-breathing scan using a PTV wit h the same margins as for DIBH plans. Results: The treatment plan comparison suggests that, on average, the DIBH technique can reduce the volume of lung receiving more than 25 Gy by 30% co mpared to free-breathing plans, while respiration gating can reduce the vol ume by 18%. The DIBH maneuver was found to be highly reproducible, with int ra breath-hold reproducibility of 1.0 (+/- 0.9) mm and inter breath-hold re producibility of 2.5 (+/- 1.6) mm, as determined from diaphragm position. P atients were able to perform 10-13 breath-holds in one session, with a comf ortable breath-hold duration of 12-16 s. Conclusion: Patients tolerate DIBH maneuvers well and can perform them in a highly reproducible fashion. Compared to conventional free-breathing treat ment, the DIBH technique benefits from reduced margins, as a result of the suppressed target motion, as well as a decreased lung density; both contrib ute to moving normal lung tissue out of the high-dose region. Because less normal lung tissue is irradiated to high dose, the possibility for dose esc alation is significantly improved. (C) 1999 Elsevier Science Inc.