Artificial pneumothorax can be used to prevent lung toxicity in chest wall radiotherapy

Clinical Oncology (1993) 5:257-259 © 1993 The Royal College of Radiologists

Clinical Oncology

Case Report Artificial P n e u m o t h o r a x Can Be Used to Prevent Lung Toxicity in Chest Wall Radiotherapy D. R. H. Christie, N. A. Spry, D. S. Lamb and H. B. Sadler W e l l i n g t o n R e g i o n a l O n c o l o g y U n i t , W e l l i n g t o n Hospital, W e l l i n g t o n , N e w Z e a l a n d

Abstract. We report two patients in whom an artificial pneumothorax was induced to reduce the risk of radiation pneumonitis and fibrosis after treatment for chest wall tumours. The procedure was well tolerated; the only complication observed was a single episode of syncope following overinflation. High doses of radiation were given to large chest wall fields with no clinical or radiological evidence of pneumonitis or fibrosis, either during or after treatment. The available literature on the use of artificial pneumothorax with radiation is reviewed, and the technique of induction is described. Keywords: Artificial pneumothorax; Radiation pneumofibrosis; Radiation pneumonitis; Radiotherapy techniques

INTRODUCTION The chest wall poses some special problems for radiotherapy planning; it has a curved surface, it contains heterogeneous tissue and it overlies a large, sensitive, low density structure. These characteristics influence the selection of a suitable radiotherapy technique. Lung transmission and loss of beam sharpness restrict the use of electron beams [1]. The penetration of megavoltage photon beams necessitates the use of tangential techniques; whilst this often reduces the volume of lung exposed, the treatment of larger chest wall tumours may still result in unacceptable lung irradiation. The lung is highly sensitive to radiation; the toxic effects are well described and have recently been reviewed [2]. For conventionally fractionated courses of radiation treatment an inverse relationship is described between the tolerance of the lung and the proportion of the lung irradiated (Table 1). When the irradiated volume is large, the tolerable dose falls to levels below those required for a radical course of treatment. The two forms of lung toxicity are pneumonitis and fibrosis. Pneumonitis can occasionally be life-threatening when

Correspondence and offprint requests to: Dr. N. A. Spry, Clinical Oncologist, Wellington Regional Oncology Unit, Wellington Hospital, Private Bag, Wellington, New Zealand.

Table 1. The effect of volume on lung tolerance doses [2] Tolerance level (Gy)

TDs/5a TDs0/5a

Irradiated volume (proportion) 1'/3

2/3

3/3

45.00 65.00

30.00 40.00

17.50 24.50

aTolerance doses are those which give a 5% (TDs/5) or 50% (TDs0:5) risk of pneumonitis occurring within 5 years. large lung volumes are involved. Fibrosis can cause a permanent restriction in pulmonary reserve, the degree of restriction relating to the volume irradiated. It is likely that lung fibrosis occurs in all cases in which lung tissue is exposed to radical treatment doses but the effect of small volumes of fibrosed lung remains subclinical. The induction of an artificial pneumothorax (AP) enables the lung to collapse away from the chest wall, reducing the volume of lung exposed to radiation. AP was used previously to treat pulmonary tuberculosis, but is now superseded by multiagent antibiotic therapy. A small number of more recent reports have described the use of AP in association with radiation treatment of cancer, but none has described the technique in detail. In each of the two patients to be reported, the irradiated volume of lung would have been large if an AP had not been induced. In patient two, almost half of the underlying lung would have exceeded the tolerance doses described in Table 1, indicating an unacceptable risk of lung toxicity.

CASE REPORTS Patient 1

Fig. 1. CT scan of patient 1, showing an osteogenic sarcoma of the right scapula.

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Fig. 2. Isodose chart of patient 1, demonstrating the lung sparing effect of AP. logical examination revealed an osteogenic sarcoma. He was treated with high dose melphalan and autologous marrow rescue followed by radical radiotherapy. A multifield radiotherapy technique was designed, irradiating the whole scapula and allowing a margin for subclinical disease and movement during treatment (Fig. 2). A field arrangement, designed to avoid the spinal cord, would have resulted in the irradiation of a significant portion of the right lung. It was therefore decided to induce an AP.

Pneumothorax Technique A 15-year-old boy, AM, presented in September 1986 with a fixed swelling at the medial end of the spine of the left scapula. A C T scan (Fig. 1) demonstrated an 8 cm lesion extending from the spine of the scapula down to the inferior pole, with invasion of the underlying muscle. Excision was attempted but was incomplete. Histo-

A 'Maxwell's Box' (Fig. 3) is used to pump air into the pleural space. The pump consists of a cylinder, a manometer, tubing and needles. Local anaesthetic is injected into the chest wall in the same way as during a chest aspiration. The needle of the pump is then passed through the chest wall; the

258

Fig. 3. Maxwell's Box pump for controlled induction of AP.

manometer records a sudden drop in pressure at the moment the parietal pleura is pierced. The pressure will then be seen to oscillate with respiration within the range - 5 to - 1 5 cm of water. With the inlet valve of the cylinder opened to the atmosphere, the weighted plunger of the cylinder can be raised, drawing air inside. If the valve is then turned to allow air to flow into the pleural space and the plunger allowed to fall, 200 ml of air will flow through the tubing into the pleural space. This process can be repeated several times until the intrapleural pressure rises to between - 5 and 0 cm of water. This will usually require 600-1000 ml. If performed over 20 minutes, and the patient is instructed to rest for 3 hours afterwards, the procedure is easily tolerated. In the case of AM, 600 ml were inserted at the first insufflation, however, a chest radiograph (CXR) taken on the following day revealed complete re-expansion of the lung; 800 ml were then inserted, but with the same result. Finally 1000 ml were inserted, collapsing the lung completely. Over the following 3 days, and intermittently throughout his treatment, CXRs revealed that the AP was persistent. This enabled the use of a medial and lateral wedged pair technique delivered by a 4 MV linear accelerater. A minimum tumour dose of 51 Gy in 30 fractions was prescibed, treating three times per day on three days per week. The interval between treatments was 4 to 6 hours. At 40.80 Gy the field was reduced to include the original sites of disease only. A persisting AP was radiologically confirmed. He tolerated treatment well and CXRs confirmed progressive reinflation of the lung after treatment. The lung remained fully reinflated. During his subsequent follow-up there was no clinical or radiological evidence of either pneumonitis or fibrosis. He unfortunately developed widespread metastatic disease within 3 months of completing treatment, including bilateral pulmonary metastases, and died of disease 6 months later.

N. A. Spry et al. Tangential photon fields were considered to be most appropriate, but would have irradiated almost half of the left lung. He was therefore admitted for induction of an AP, as described above. A CXR taken on the following day confirmed collapse of the lung. He returned for simulation 2 weeks later. It was then found that the lung had partially re-expanded, and a reinduction was arranged. This time the intrapleural pressure was inadvertently raised to 10 cm of water. Shortly afterwards a brief syncopal episode occurred, lasting 30 seconds, with full recovery on lying flat. A CXR revealed a tension pneumothorax, which was relieved by allowing the excess air to escape through a needle. A further CXR confirmed collapse with no mediastinal shift. Simulation films and a planning CT scan were performed. A four-field isocentric plan using a 4 MV linear accelerator was prepared. The isodose pattern confirmed that most of the lung would not receive more than 40% of the total dose (Fig. 5). A tumour absorbed dose of 45 Gy in 25 fractions given over 5 weeks was prescribed. There were no signs of pneumonitis or fibrosis during or after treatment. The lung progressively re-expanded itself after treatment. Post-treatment review was undertaken at 2 monthly intervals with tumour measurements, clinical photographs and CXRs. At each review progressive shrinkage was observed. At 18 months pulmonary function tests were repeated and small reductions in pulmonary reserve were seen (Table 2). In view of his continuing high level of exercise performance, these were considered acceptable. Throughout his follow-up there were no clinical or radiological signs of either pneumonitis or fibrosis.

Fig. 4. CT scan of patient 2, showinghis desmoid turnout of the left anterior chest wall.

Patient 2 A 26-year-old amateur sportsman, LE, presented with a massive desmoid turnout of the left anterior chest wall in June 1990. It extended from the mid-line to the axilla and from the clavicle down to the subcostal margin. It was fixed to the chest wall but not to the overlying skin. A CT scan (Fig. 4) showed deep extension of the tumour causing indentation of the pleural surface. It was considered inoperable and he was referred for radiation treatment.

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Fig. 5. Isodose chart of patient 2.

Table 2. Lung function tests in patient 2

BefureaAfter" Forced expiratory volume (1 min)123 Vital capacity 113 Ratio FEV/VC 107

96 90 100

aFigures are expressed as percentages of values predicted accordingto age and height. Measurements were taken immediately before and 18 months after radiation treatment.

DISCUSSION We have found, in our limited experience, that the induction of an AP appears easily tolerated. In our patients, the only problem encountered during induction was a single episode of syncope due to over-inflation, a reaction not previously recorded in this setting. It was readily reversed and can be avoided by following the guidelines for controlling intrathoracic pressure described in patient 1. The induction does not cause the pain associated with spontaneous pneumothorax, providing the procedure is performed over 20 minutes and the patient rests for 3 hours afterwards. A modification of the induction technique has been described in two previous reports [3,4], in which indwelling catheters facilitated a stepwise induction and allowed reinflation of the lung during weekends. They suggest stepwise induction is probably better than a single large insufflation, however we have found relief at weekends to be unnecessary as the disability is minor. The use of an indwelling catheter may also increase the potential for infection. During the AP, both of our patients were breathing comfortably at rest, but experienced dyspnoea on exertion, a finding consistent with other reports. The first report of AP performed in the context of radiotherapy [5], claimed that a continuous duration of up to 2 months was safe, although after 1 month a small volume of pleural fluid may accumulate and require aspiration. To convince the reader of the safety of the procedure, an illustration of a bilateral AP was included and reported to be well tolerated. It was proposed that adhesions found at induction could be cut using a thoracoscope, enabling complete collapse to occur. In our one surviving patient, no long term complications to AP have been apparent. Lung function tests were recorded and demonstrated a small decrease in lung capacity, however no subjective impairment of breathing has occurred and his vigorous participation in sport continues unaffected. Two other reports have undertaken formal testing of respiratory function before and after AP [3,4]. In each case no changes in lung function were found. The Plymouth Hospital series has been the only series to be reported in which an AP was used routinely for a large number of patients with cancer [6,7]. Fenner induced an AP in 143 patients who were treated with radiation alone for breast cancer. The analysis concentrated on cancer control rates, but also mentioned some of the complications of AP which were encountered. These are summarized in Table 3. The most common delayed complication to AP

P n e u m o t h o r a x to Prevent L u n g Toxicity in Chest Wall Radiotherapy Table 3. Reported number of patients suffering complications of AP [6,7]

Complications

No. (n=143)

During AP Transient mild dyspnoea, cough and pain Majority Brief reactive pleural effusion 11 Transient shoulder tip pain 2a After AP Lung contraction 5 Persistent AP requiring aspiration 3 Persistent pleural effusion 3a Pleural fibrosis ia aReported in [7], in which n = 53. appeared to be lung contraction, occurring in 5 patients. Overall the incidence of long term complications from A P appeared to be very low. In s u m m a r y , we present two patients in which A P s were indt/ced to avoid unnecess-

ary lung irradiation. W e found the procedure to be easy to perform and it could be performed in an outpatient setting with minimal morbidity. Neither of our patients experienced symptomatic pneumonitis or fibrosis; we believe these would have b e e n likely treatment complications in the absence of this technique. A P would appear to be indicated for patients undergoing radiation treatment for large chest wall t u m o u r s for w h o m the probability of cure or long term survival is high, and for w h o m the irradiated lung volume without an A P would be large. T h e A P allows radical treatment doses to be given with minimal risk of tung toxicity, and m a y also permit wider treatment margins.

References 1. Kahn FM. The physics of radiation therapy. Baltimore: Williams and Wilkins, 1984:299353.

259 2. Emami B, Lyman J, Brown A, et al. Tolerance of normal tissue to therapeutic irradiation. Int J Radiat Oncol Biol Phys 1991; 21:109-22. 3. D'Angio GJ, Exelby PR, Ghavimi F, et al. Protection of certain structures from high doses of irradiation. Am J Roentgenol Radium Ther Nucl Med 1974;122:103-8. 4. Ortega JA, Stowe SM, Shore NA, et al. Prevention of radiation pneumonitis by controlled pneumothorax in childhood rhabdomyosarcoma of the chest wall. Int J Radiat Oncol Biol Phys 1985;11:2033-4. 5. Alarcon DGm Zavala E. Intrapleural pneumothorax as a means to protect the lung under roentgenotherapy. Cancer 1969; 23:513-4 6. Benghait A, Tyrell CJ, Davidson HE, et al. Results of treatment of primary breast carcinoma by radical radiotherapy with artificial pneumothorax. Clin Radiol 1986;37:313-5. 7. Fenner M E The treatment of primary breast cancer by radical radiotherapy with artificial pneumothorax. Clin Radiol 1974;25:20310.

Received for publication September 1992 Accepted following revision January 1993