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 feasibility of a deep inspiration breath-hold (DIBH) technique in the treatment of lung tumors. The technique has two distinct features--deep inspiration, which reduces lung density, and breath-hold, which immobilizes lung tumors, thereby allowing for reduced margins. Both of these properties can potentially reduce the amount of normal lung tissue in the high-dose region, thus reducing morbidity and improving the possibility of dose escalation. METHODS AND MATERIALS: Five patients treated for non-small cell lung carcinoma (Stage IIA-IIIB) received computed tomography (CT) scans under 4 respiration conditions: free-breathing, DIBH, shallow inspiration breath-hold, and shallow expiration breath-hold. The free-breathing and DIBH scans were used to generate 3-dimensional conformal treatment plans for comparison, while the shallow inspiration and expiration scans determined the extent of tumor motion under free-breathing conditions. To acquire the breath-hold scans, the patients are brought to reproducible respiration levels using spirometry, 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 respiration (1-2 cm). Planning target volumes for DIBH plans included the same margin for setup error, with a reduced margin for residual uncertainty in tumor position (0.2-0.5 cm) as determined from repeat fluoroscopic movies. To simulate the effects of respiration-gated treatments and estimate the role of target immobilization alone (i.e., without the benefit of reduced lung density), a third plan is generated from the free-breathing scan using a PTV with 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% compared to free-breathing plans, while respiration gating can reduce the volume by 18%. The DIBH maneuver was found to be highly reproducible, with intra breath-hold reproducibility of 1.0 (+/- 0.9) mm and inter breath-hold reproducibility of 2.5 (+/- 1.6) mm, as determined from diaphragm position. Patients were able to perform 10-13 breath-holds in one session, with a comfortable 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 treatment, the DIBH technique benefits from reduced margins, as a result of the suppressed target motion, as well as a decreased lung density; both contribute 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 escalation is significantly improved.

Background ventilatory stimulus as a determinant of load compensation.

Compensation for inspiratory flow-resistive loading was compared during progressive hypercapnia and incremental exercise to determine the effect of changing the background ventilatory stimulus and to assess the influence of the interindividual variability of the unloaded CO2 response on evaluation of load compensation in normal subjects. During progressive hypercapnia, ventilatory response was incompletely defended with loading (mean unloaded delta VE/delta PCO2 = 3.02 +/- 2.29, loaded = 1.60 +/- 0.67 1.min-1.Torr-1 CO2, where VE is minute ventilation and PCO2 is CO2 partial pressure; P less than 0.01). Furthermore the degree of defense of ventilation with loading was inversely correlated with the magnitude of the unloaded CO2 response. During exercise, loading produced no depression in ventilatory response (mean delta VE/delta VCO2 unloaded = 20.5 +/- 1.9, loaded = 19.2 +/- 2.5 l.min-1.l-1.min-1 CO2 where VCO is CO2 production; P = NS), and no relationship was demonstrated between degree of defense of the exercise ventilatory response and the unloaded CO2 response. Differences in load compensation during CO2 rebreathing and exercise suggest the presence of independent ventilatory control mechanisms in these states. The type of background ventilatory stimulus should therefore be considered in load compensation assessment.

Pulmonary function changes during interscalene brachial plexus block: effects of decreasing local anesthetic injection volume.

BACKGROUND AND OBJECTIVES: During interscalene block, ipsilateral hemidiaphragmatic paresis occurred in all patients who received > 34 ml of local anesthetic in the authors' previous studies. This study was done to determine whether diaphragmatic function could be spared by a smaller local anesthetic volume. METHODS: Twenty patients were randomly assigned to receive either a 45 ml or 20 ml interscalene brachial plexus block. For all blocks, 1.5% mepivacaine with added epinephrine and bicarbonate was used. Baseline serial measurements and those over a 30-minute test period before surgery were analyzed for significant differences between groups in onset or final change in any of the following measured variables: cephalad dermatomal extent of sensory anesthesia, clinically assessed upper extremity motor function, ipsilateral hemidiaphragmatic excursion during maximal sniff (inspiratory), and pulmonary function. RESULTS: There were no clinically significant differences between groups in any of the measured variables. Large reductions in routine pulmonary function tests were measured in all patients in both groups at 2 minutes after injection. At 30 minutes, baseline forced vital capacity (FVC) had diminished by 40.9 +/- 11.7% in the 45 ml group and 32.0 +/- 8.9% in the 20 ml group. One patient with pre-existing chronic obstructive pulmonary disease had a decrease in FVC from 1.83 l to 0.59 l, a 68% decrement from the baseline measurement, both measured in the supine position. CONCLUSION: Reducing the volume of local anesthetic to 20 ml did not prevent the 100% incidence of diaphragmatic paresis or significantly lessen the compromise in pulmonary function that had been reported to occur during interscalene brachial plexus anesthesia.

Digital pressure during interscalene block is clinically ineffective in preventing anesthetic spread to the cervical plexus.

The application of digital pressure above the injection site during interscalene block has been advocated to prevent cephalad spread of local anesthetic. In prior studies, radiographs taken immediately after interscalene injection of radiographic contrast have supported this concept. However, the clinical efficacy of digital pressure has not been previously tested. If digital pressure were effective in inhibiting cephalad spread of local anesthetic, attenuation of both hemidiaphragmatic paresis and the resulting compromise in pulmonary function would be expected. Sensory, motor, and pulmonary effects were prospectively evaluated in 20 patients presenting for elective shoulder surgery. Patients were randomly assigned to receive interscalene block with or without digital pressure. No clinical differences were seen between groups. All 20 patients had ipsilateral hemidiaphragmatic paresis by ultrasonographic evaluation and large mean decreases in forced vital capacity, 31.2% +/- 7.8% (with digital pressure), 33.7% +/- 12.8% (without digital pressure), and forced expiratory volume at one second, 27.9% +/- 9.3% (with digital pressure), 33.7 +/- 12.8% (without digital pressure). Peak sensory level of anesthesia to pinprick was not significantly different between groups, each group having mean levels of C-2 to C-3. Digital pressure was ineffective in limiting the flow of local anesthetic into the cervical plexus. Digital pressure influenced neither the incidence of diaphragmatic paresis nor the resulting large decreases in pulmonary function that result from interscalene block.