Radiation-induced pulmonary injury: symptomatic versus subclinical endpoints

Systemic polyethylene glycol-modified (PEGylated) superoxide dismutase and catalase mixture attenuates radiation pulmonary fibrosis in the C57/bl6 mouse

PURPOSE

Since oxidative injury is implicated in radiation-induced tissue damage to the lung, we studied systemically administered polyethylene glycol (PEGylated) antioxidant enzymes (AOEs) as pulmonary radioprotectors in mice.

METHODS AND MATERIALS

C57/bl6 Mice received 13.5 Gy single-dose irradiation to the thorax. One cohort also received 100 microg of a 1:1 mixture of PEG-AOEs {PEG-catalase and PEG-superoxide dismutase (SOD)} intravenously, pre-irradiation and subgroups were evaluated at variable time-points for inflammation and fibrosis. Potential for AOE tumor protection was studied by thoracic irradiation of mice with Lewis lung carcinoma.

RESULTS

At 48 h post-irradiation, control irradiated mice had marked elevations of tissue p21, Bax and TGF-beta1 in lungs, not seen in irradiated, PEG-AOE-treated mice. TUNEL staining of lung sections was performed at just one time-point (24 h post-irradiation) and revealed a decrease in apoptotic cells with AOE treatment. At four months post-irradiation, these mice had significantly increased pulmonary fibrosis as measured by hydroxyproline content. Mice treated with PEG-AOE prior to irradiation had 4-month hydroxyproline levels that were similar to that of unirradiated controls (p = 0.28). This corresponded to less pulmonary fibrosis as visualized histologically when compared with mice irradiated without AOEs. PEG-AOEs did not prevent post-irradiation pulmonary inflammation or lung cancer response to irradiation.

CONCLUSIONS

A mixture of PEG-SOD and PEG-CAT successfully diminished radiation pulmonary fibrosis in mice. There was also a corresponding effect on several early biomarkers of lung injury and decreased apoptosis. There were no significant effects on acute pneumonitis or tumor protection.

Does transforming growth factor-beta1 predict for radiation-induced pneumonitis in patients treated for lung cancer?

The purpose of the study was to reassess the utility of transforming growth factor-beta-1 (TGF-beta1) together with dosimetric and tumor parameters as a predictor for radiation pneumonitis (RP). Of the 121 patients studied, 32 (26.4%) developed grade > or =1 RP, and 27 (22.3%) developed grade > or =2 RP. For the endpoint of grade > or =1 RP, those with V30>30% and an end-RT/baseline TGF-beta1 ratio> or =1 had a significantly higher incidence of RP than did those with V30>30% and an end-RT/baseline TGF-beta1 ratio<1. For most other patient groups, there were no clear associations between TGF-beta1 values and rates of RP. These findings suggest that TGF-beta1 is generally not predictive for RP except for the group of patients with a high V30.

Relation between radiation-induced whole lung functional loss and regional structural changes in partial irradiated rat lung

PURPOSE

Radiation-induced pulmonary toxicity is characterized by dose, region, and time-dependent severe changes in lung morphology and function. This study sought to determine the relation between the structural and functional changes in the irradiated rat lung at three different phases after irradiation.

MATERIALS AND METHODS

Six groups of animals were irradiated to 16-22 Gy to six different lung regions, each containing 50% of the total lung volume. Before and every 2 weeks after irradiation, the breathing rate (BR) was measured, and at Weeks 8, 26, and 38 CT was performed. From the computed tomography scans, the irradiated lung tissue was delineated using a computerized algorithm. A single quantitative measure for structural change was derived from changes of the mean and standard deviation of the density within the delineated lung. Subsequently, this was correlated with the BR in the corresponding phase.

RESULTS

In the mediastinal and apex region, the BR and computed tomography density changes did not correlate in any phase. After lateral irradiation, the density changes always correlated with the BR; however, in all other regions, the density changes only correlated significantly (r(2) = 0.46-0.85, p < 0.05) with the BR in Week 26.

CONCLUSION

Changes in pulmonary function correlated with the structural changes in the absence of confounding heart irradiation.

Pulmonary radiation injury: identification of risk factors associated with regional hypersensitivity

Effective radiation treatment of thoracic tumors is often limited by radiosensitivity of surrounding tissues. Several experimental studies have suggested variations in radiosensitivity of different pulmonary regions. Mice and rat studies in part contradict each other and urge for a more detailed analysis. This study was designed to obtain a more comprehensive insight in radiation injury development, expression, and its regional heterogeneity in lung. The latter is obviously highly critical for optimization of radiotherapy treatment plans and may shed light on the mechanisms of lung dysfunction after irradiation. Six different but volume-equal regions in rat lung were irradiated. Whereas the severity of damage, as seen in histologic analysis, was comparable in all regions, the degree of lung dysfunction, measured as breathing rates, largely varied. During the pneumonitic phase (early: 6-12 weeks), the most sensitive regions contained a substantial part of alveolar lung parenchyma. Also, a trend for hypersensitivity was observed when the heart lay in the irradiation field. In the fibrotic phase (late: 34-38 weeks), lung parenchyma and heart-encompassing regions were the most sensitive. No impact of the heart was observed during the intermediate phase (16-28 weeks). The severity of respiratory dysfunction after partial thoracic irradiation is likely governed by an interaction between pulmonary and cardiac functional deficits. As a repercussion, more severe acute and delayed toxicity should be expected after combined lung and heart irradiation. This should be considered in the process of radiotherapy treatment planning of thoracic malignancies.

Post-operative radiotherapy (PORT) or chemoradiotherapy (CPORT) following resection of stages II and IIIA non-small cell lung cancer (NSCLC) does not increase the expected risk of death from intercurrent disease (DID) in Eastern Cooperative Oncology Group (ECOG) trial E3590

To determine the influence of adjuvant therapy on the risk of DID following resection of NSCLC, we compared the actuarial rate of non-cancer related deaths of patients who had been entered in Eastern Cooperative Oncology Group E3590 (a phase III trial of adjuvant therapy in patients with completely resected stages II and IIIA NSCLC) to the actuarial death rate of age and gender matched controls. Following surgery, patients were randomized to receive either PORT (5040 cGy in 28 daily fractions) or CPORT (PORT plus four cycles of cisplatin (60 mg/m2, day 1) and etoposide (120 mg/m2, days 1-3) administered concurrently). The study accrued 488 patients, 242 to the PORT only arm and 246 to the CPORT arm. The overall 4 years actuarial rate of DID for the two arms combined, with a median follow-up of 82 months, was 12.9%, not significantly different from the 10.1% expected rate of DID, based on mortality rates for age and gender matched controls derived from US vital statistics and corrected for smoking status (p=0.16). Survival distributions with regard to DID did not differ between the two treatment arms (p=0.96). DID increased with age (treated as a continuous variable, p<0.01), but was not affected by histology, side of chest irradiated, type of surgery, FEV1 or weight loss in the previous 6 months. The risk of DID following resection of stages II and IIIA NSCLC is not increased in patients who received PORT or CPORT.

Sequential pulmonary effects of radiotherapy detected by functional and radiological end points in women with breast cancer

AIMS

To determine the pulmonary effects of locoregional irradiation on clinical and sub-clinical radiographic and functional end points in women with breast cancer, and whether the course of these end points is affected by laterality.

MATERIALS AND METHODS

Twenty patients (10 irradiated on the left side and 10 irradiated on the right side) were prospectively evaluated for changes in pulmonary function tests, Tc-99m DTPA (diethylenetriamine pentaacetic acid) lung clearance scintigraphy and high-resolution computed tomography (HRCT) at 6, 16 and 52 weeks after radiotherapy. Tc-99m DTPA clearance, expressed as the biological half-time, T(1/2), was computed from the time-activity curves for 10 min for each lung. The irradiated lung volume was calculated for each patient.

RESULTS

The mean irradiated lung volume was 6.4% +/- 2 (range 3-11%) for the entire population. In the whole study population, two (10%) patients, who were irradiated on the left side, had mild symptomatic radiation pneumonitis in the follow-up period. There was a statistically significant gradual reduction in all pulmonary function test values during the follow-up period. For patients irradiated on the left side, Tc-99m DTPA clearance T(1/2) values were statistically significantly decreased during the follow-up period (P = 0.03), but the decrease was not statistically significant for patients irradiated on the right side (P = 0.62). Tc-99m DTPA clearance T(1/2) values were statistically significantly decreased in the irradiated lung compared with the opposite lung, and no improvement was seen at week 52 after radiotherapy. The number of patients with changes on HRCT scans increased after radiotherapy, reaching a maximum at 16 weeks, when 80% of patients had changes. There was subsequent partial recovery 52 weeks after radiotherapy.

CONCLUSION

Locoregional irradiation for breast cancer may cause sub-clinical irreversible impairment of radiological and functional pulmonary parameters. The increase in clearance rate of Tc-99m DTPA may be more prominent for patients with left-sided breast cancer.

Carboplatin/Paclitaxel or Carboplatin/Vinorelbine Followed by Accelerated Hyperfractionated Conformal Radiation Therapy: Report of a Prospective Phase I Dose Escalation Trial From the Carolina Conformal Therapy Consortium

Purpose

To prospectively determine the maximum-tolerated dose of accelerated hyperfractionated conformal radiotherapy (RT; 1.6 Gy bid) for unresectable locally advanced lung cancer (IIB to IIIA/B) following induction carboplatin/paclitaxel (C/T) or carboplatin/vinorelbine (C/N).

Methods

Induction chemotherapy, C/T or C/N, was followed by escalating doses of conformally-planned RT (73.6 to 86.4 Gy in 6.4-Gy increments). Concurrent boost methods delivered 1.6 and 1.25 Gy bid to the gross and clinical target volumes, respectively.

Results

Between November 1997 and February 2002, 44 patients were enrolled (median age, 59 years; 59% male; stage III, 98%; median tumor size, 4 cm). Thirty-nine patients completed induction chemotherapy: 19 had a partial response, seven progressed, 15 had no response, and three were not assessable. Chemotherapy-associated toxicities were similar in the two chemotherapy groups. The incidence of grade ≥ 3 RT-induced toxicity was 1/13, 2/14, and 4/12 at 73.6, 80, and 86.4 Gy, respectively, thus defining the maximum tolerated dose at ≈80 Gy. Toxicities were in both lung and esophagus and were similar in the two chemotherapy arms. With a median followup of 34 months in the survivors, the actuarial 2-year survival was 47%, the median survival was 18 months. Fifteen patients had tumor relapse: 5 local failures in the high-dose volume, 2 regional failures outside of the high-dose volume, and 8 distant metastases.

Conclusion

High-dose conformal twice-daily radiation therapy to approximately 80 Gy appears tolerable in well-selected patients with unresectable lung cancer following either C/T or C/N. Dose-limiting toxicities are mainly pulmonary and esophageal.

Transforming growth factor-beta plasma dynamics and post-irradiation lung injury in lung cancer patients

PURPOSE

To investigate the relevance of transforming growth factor-beta (TGF-beta) dynamics in plasma for identification of patients at low risk for developing pneumonitis as a complication of thoracic radiotherapy (RT).

PATIENTS AND METHODS

Non-small cell lung cancer patients undergoing conventional RT were included in the prospective study. Concentrations of TGF-beta were measured in the patients' plasma prior to and weekly during 6 weeks of RT. The incidence of symptoms of early post-irradiation lung injury, i.e. symptomatic radiation pneumonitis, was correlated with TGF-beta parameters.

RESULTS

Forty-six patients were included in the study. Eleven patients (24%) developed symptomatic radiation pneumonitis. Absolute TGF-beta plasma levels did not differ between the groups of patients without or with pneumonitis. However, patients who developed pneumonitis tended to show increases in TGF-beta levels in the middle of the RT course relative to their pre-treatment levels while TGF-beta plasma levels of patients who did not develop pneumonitis tended to decrease over the RT treatment. The difference in the relative TGF-beta dynamics between the groups reached marginal significance in the third week of the treatment (P = 0.055) but weakened towards the end of the RT course. The utility of TGF-beta testing was evaluated at each RT week based on the test's ability to yield more accurate estimate of complication probability in an individual patient compared to empirically expected probability in similar group of patients. The ratio of TGF-beta level at week 3/week 0 being <1 showed an ability to improve the prediction of freedom from pneumonitis, yet with a large degree of uncertainty (wide confidence intervals). The accuracy of prediction deteriorated at later time points (weeks 4, 5 and 6) rendering the end-RT ratios without predictive power.

CONCLUSIONS

We observed a trend of plasma TGF-beta concentration to decrease below the pre-treatment value during the RT treatment in patients who did not develop pulmonary complications after the RT treatment. However, this trend was not consistent enough to warrant safe decision-making in clinical setting.

Pulmonary complications of radiation therapy

There have been important developments in understanding the difference in pathogenesis and clinical significance between acute or sporadic pneumonitis and late radiation fibrosis. Corticosteroid therapy and other forms of therapy are useful in the treatment of acute pneumonitis. Late radiation fibrosis is refractory to treatment; therefore, minimizing the likelihood of developing it is particularly important. Baseline lung assessments are appropriate in patients who are clinically at risk. A new development is the use of the DVH to compare radiation treatment plans to minimize the volume of normal lung irradiated in patients who are at risk. It is hoped that the study of mechanisms that lead to the development of radiation fibrosis will point the way to possible future therapies. Patients who are included in studies of novel irradiation treatments for lung cancer need, in particular, to be monitored for late radiation lung toxicity.

Pulmonary function following high-dose radiotherapy of non-small-cell lung cancer

PURPOSE

To study changes of pulmonary function tests (PFTs) after radiotherapy (RT) of non-small-cell lung cancer (NSCLC) in relation to radiation dose, tumor regression, and changes in lung perfusion.

METHODS AND MATERIALS

Eighty-two patients with inoperable NSCLC were evaluated with PFTs (forced expiratory volume in 1 s [FEV(1)] and diffusion capacity [T(L,COc)]), a computed tomography (CT) scan of the chest, and a single photon emission CT (SPECT) lung perfusion scan, before and 3-4 months after RT. The reductions of PFTs and tumor volume were calculated. The lung perfusion was measured from pre- and post-RT SPECT scans, and the difference was defined as the measured perfusion reduction (MPR). In addition, the perfusion post-RT was estimated from the dose distribution using a dose-effect relation for regional lung perfusion, and compared with the pre-RT lung perfusion to obtain the predicted perfusion reduction (PPR). The difference between the actually measured and the PPR was defined as reperfusion. The mean lung dose (MLD) was computed and weighted with the pre-RT perfusion, resulting in the mean perfusion-weighted lung dose (MpLD). Changes of PFTs were evaluated in relation to tumor dose, MLD, MpLD, tumor regression, and parameters related to perfusion changes.

RESULTS

In a multivariate analysis, the total tumor dose and MLD were not associated with reductions of PFTs. Tumor regression resulted in a significant improvement of FEV(1) (p = 0.02), but was associated with a reduction of T(L,COc) (p = 0.05). The MpLD and the PPR showed a significant (p = 0.01 to 0.04) but low correlation (r = 0.24 to 0.31) with the reduction of both PFTs. The other parameters for perfusion changes, the MPR and reperfusion were not correlated with changes in PFTs.

CONCLUSION

The perfusion-related dose variables, the MpLD or the PPR, are the best parameters to estimate PFTs after RT. Tumor regression is associated with an improvement of FEV(1) and a decline of T(L,COc). Reperfusion was not associated with an improvement of global pulmonary function.

Effect of concurrent radiation therapy and chemotherapy on pulmonary function in patients with esophageal cancer: dose-volume histogram analysis

PURPOSE

The pulmonary effects of concurrent radiation therapy and chemotherapy were studied in patients enrolled in a phase I trial for esophageal cancer.

MATERIALS AND METHODS

Pulmonary function tests were performed prospectively before and after combined-modality therapy (oxaliplatin, 5-fluorouracil, and radiation therapy) in 20 patients with esophageal cancer. Cumulative and differential lung DVH analysis from 0 to 5400 cGy in 25-cGy intervals was performed for the last 15 patients. Correlation between radiation exposure in various dose ranges and percent reduction in pulmonary function tests was calculated as an exploratory analysis.

RESULTS

Significant reductions in carbon monoxide diffusion capacity corrected for hemoglobin (12.3%) and total lung capacity (2.5%) were evident at a median of 15.5 days after radiation therapy. DVH analysis revealed that the single dose of maximum correlation between lung volume radiation exposure and lung function reduction was less than 1000 cGy for all pulmonary functions. The percent lung volume that received a total dose between 700 and 1000 cGy maximally correlated with the percent reductions in total lung capacity and vital capacity, and the absolute lung volume that received a total dose between 700 and 1000 cGy maximally correlated with the percent reductions in total lung capacity, vital capacity, and carbon monoxide diffusion capacity.

DISCUSSION

Significant declines in carbon monoxide diffusion capacity and total lung capacity are evident immediately after the administration of conformal radiation therapy, oxaliplatin, and 5-fluorouracil for esophageal cancer. Other lung functions remain statistically unchanged. The percent or absolute lung volume that received a total dose between 700 and 1000 cGy may be significantly correlated with the percent decline of carbon monoxide diffusion capacity, total lung capacity, and vital capacity. These associations will be evaluated further in a follow-up study.

Methodological issues in radiation dose-volume outcome analyses: summary of a joint AAPM/NIH workshop

This report represents a summary of presentations at a joint workshop of the National Institutes of Health and the American Association of Physicists in Medicine (AAPM). Current methodological issues in dose-volume modeling are addressed here from several different perspectives. Areas of emphasis include (a) basic modeling issues including the equivalent uniform dose framework and the bootstrap method, (b) issues in the valid use of statistics, including the need for meta-analysis, (c) issues in dealing with organ deformation and its effects on treatment response, (d) evidence for volume effects for rectal complications, (e) the use of volume effect data in liver and lung as a basis for dose escalation studies, and (f) implications of uncertainties in volume effect knowledge on optimized treatment planning. Taken together, these approaches to studying volume effects describe many implications for the development and use of this information in radiation oncology practice. Areas of significant interest for further research include the meta-analysis of clinical data; interinstitutional pooled data analyses of volume effects; analyses of the uncertainties in outcome prediction models, minimal parameter number outcome models for ranking treatment plans (e.g., equivalent uniform dose); incorporation of the effect of motion in the outcome prediction; dose-escalation/isorisk protocols based on outcome models; the use of functional imaging to study radioresponse; and the need for further small animal tumor control probability/normal tissue complication probability studies.

Lung toxicity following chest irradiation in patients with lung cancer

Classical radiation pneumonitis has been described after single dose whole lung irradiation in experimental animals where above a threshold dose of irradiation, there is a sigmoid dose response curve with increasing morbidity and mortality. After clinical fractionated irradiation, however, acute radiation pneumonitis consisting of cough shortness of breath and patchy radiological changes, occurs in <10% of patients, has dyspnoea out of proportion to the volume of lung irradiated and usually resolves completely without long-term effects. There is increasing evidence that this represents a bilateral lymphocytic alveolitis or hypersensitivity pneumonitis and has been termed sporadic pneumonitis. Late radiation toxicity results in pulmonary fibrosis. This is a consequence of repair, which is initiated by tissue injury within the radiation portal. It follows release of chemotactic factors for fibroblasts including transforming growth factor-beta, fibronectin and platelet derived growth factor. Radiation fibrosis is the clinically more significant syndrome for patients. It may result in progressive dyspnoea and mortality in patients. The most predictable change in laboratory lung function tests is a decrease in transfer factor due to damage at the capillary-alveolar level. It also results in decreased lung compliance, which will affect the total lung capacity and the forced vital capacity. The forced expiratory volume in 1 s is less affected, although this seems to depend on the volume of lung irradiated. There is also a decrease in perfusion in the irradiated lung. Radiation fibrosis seems to depend, amongst other factors, on the volume of lung, which is irradiated above a threshold of 20-30 Gy. The morbidity of radiation fibrosis may therefore be minimized by the use of dose volume histogram to minimize the volume of normal lung irradiated in patients at high risk, e.g., patients with who present with poor lung function. The importance of the baseline perfusion in the irradiated areas continues to be studied.

The time course of radiation therapy-induced reductions in regional perfusion: a prospective study with >5 years of follow-up

PURPOSE

To assess the time-dependence of radiation therapy (RT)-induced reductions in regional lung perfusion, as measured by single photon emission computed tomography (SPECT) lung perfusion scans.

METHODS AND MATERIALS

Between 1991 and 1999, 79 patients had SPECT lung perfusion scans before and serially after RT. Changes in regional perfusion were correlated with regional dose using 3D planning tools and image fusion (PLUNC-Plan UNC). Multiple post-RT follow-up scans were evaluated to determine the temporal nature of RT-induced regional perfusion changes. To facilitate the comparison of dose-response curves (DRCs) at different post-RT intervals, each DRC was fit to a linear model and thus described by its slope.

RESULTS

There was a dose-dependent reduction in regional perfusion at nearly all time points post-RT (p = 0.0001). The slope of the DRCs for RT-induced reductions in regional perfusion became steeper at essentially each successive follow-up interval (p = 0.0001). However, the increases in slope became progressively smaller at later follow-up intervals. Overall, about 80% of the long-term RT-induced regional perfusion injury was manifest within 12 months post-RT.

CONCLUSION

There is a progression of RT-induced reductions in regional perfusion, with most of this injury manifest within 12 months post-RT. Additional regional injury appears to evolve for years.

Radiation-induced pulmonary toxicity: a dose-volume histogram analysis in 201 patients with lung cancer

PURPOSE

To relate lung dose-volume histogram-based factors to symptomatic radiation pneumonitis (RP) in patients with lung cancer undergoing 3-dimensional (3D) radiotherapy planning.

METHODS AND MATERIALS

Between 1991 and 1999, 318 patients with lung cancer received external beam radiotherapy (RT) with 3D planning tools at Duke University Medical Center. One hundred seventeen patients were not evaluated for RP because of <6 months of follow-up, development of progressive intrathoracic disease making scoring of pulmonary symptoms difficult, or unretrievable 3D dosimetry data. Thus, 201 patients were analyzed for RP. Univariate and multivariate analyses were performed to test the association between RP and dosimetric factors (i.e., mean lung dose, volume of lung receiving >or=30 Gy, and normal tissue complication probability derived from the Lyman and Kutcher models) and clinical factors, including tobacco use, age, sex, chemotherapy exposure, tumor site, pre-RT forced expiratory volume in 1 s, weight loss, and performance status.

RESULTS

Thirty-nine patients (19%) developed RP. In the univariate analysis, all dosimetric factors (i.e., mean lung dose, volume of lung receiving >or=30 Gy, and normal tissue complication probability) were associated with RP (p range 0.006-0.003). Of the clinical factors, ongoing tobacco use at the time of referral for RT was associated with fewer cases of RP (p = 0.05). These factors were also independently associated with RP according to the multivariate analysis (p = 0.001). Models predictive for RP based on dosimetric factors only, or on a combination with the influence of tobacco use, had a concordance of 64% and 68%, respectively.

CONCLUSIONS

Dosimetric factors were the best predictors of symptomatic RP after external beam RT for lung cancer. Multivariate models that also include clinical variables were slightly more predictive.

Keratinocyte growth factors radioprotect bowel and bone marrow but not KHT sarcoma

Various members of the fibroblast growth factor (FGF) family of proteins have been shown to protect against acute and late radiation damage of normal tissues. Protection of the small bowel, for example, occurs via both increased proliferation and reduced apoptosis. Other beneficial effects of FGFs include promotion of bone growth, pneumonitis prevention, and apoptosis suppression of endothelium in vivo and in vitro after irradiation. This protection against radiation requires only low and infrequent doses of FGFs. Two newly identified members of the FGF family, FGF7 and FGF10, have effects similar to many of the other FGF family proteins, but with more specificity for normal epithelial structures. For this reason, they have also been named keratinocyte growth factors one and two (KGF1 and KGF2, respectively). We therefore examined the potential utility of KGFs for radioprotection of the bone marrow and small bowel and examined safety issues concerning their adverse effects on KHT sarcoma. The results suggest that KGFs could be safely used to prevent radiation toxicity of the abdomen or pelvis and may in fact improve tumor response to radiation.

Relating radiation-induced regional lung injury to changes in pulmonary function tests

PURPOSE

To determine whether the sum of radiotherapy (RT)-induced reductions in regional lung perfusion is quantitatively related to changes in global lung function as assessed by reductions in pulmonary function tests (PFTs).

METHODS AND MATERIALS

Two hundred seven patients (70% with lung cancer) who received incidental partial lung irradiation underwent PFTs (forced expiratory volume in 1 s and diffusion capacity for carbon monoxide) before and repeatedly after RT as part of a prospective clinical study. Regional lung function was serially assessed before and after RT by single photon emission computed tomography perfusion scans. Of these, 53 patients had 105 post-RT evaluations of changes in both regional perfusion and PFTs, were without evidence of intrathoracic disease recurrence that might influence regional perfusion and PFT findings, and were not taking steroids. The summation of the regional functional perfusion changes were compared with changes in PFTs using linear regression analysis.

RESULTS

Follow-up ranged from 3 to 86 months (median 19). Overall, a significant correlation was found between the sum of changes in regional perfusion and the changes in the PFTs (p = 0.002-0.24, depending on the particular PFT index). However, the correlation coefficients were small (r = 0.16-0.41).

CONCLUSIONS

A statistically significant correlation was found between RT-induced changes in regional function (i.e., perfusion) and global function (i.e., PFTs). However, the correlation coefficients are low, making it difficult to relate changes in perfusion to changes in the PFT results. Thus, with our current techniques, the prediction of changes in perfusion alone does not appear to be sufficient to predict the changes in PFTs accurately. Additional studies to clarify the relationship between regional and global lung injury are needed.

Radiation-induced and chemotherapy-induced pulmonary injury

The management of cancer has continued to advance with the development of new chemotherapeutic agents and improved techniques of radiation therapy. Although new therapeutic approaches have improved survival in cancer patients, each form of intervention has the potential to produce adverse effects on normal host tissues. Some of these toxicities may be accentuated with combined modality therapy. The use of chemotherapy and radiation therapy, alone or combined, can be associated with clinically significant pulmonary toxicity. The pulmonary toxic effects of chemotherapy can be divided into (1) early onset, resulting in interstitial lung injury, and (2) late onset, with pulmonary fibrosis as a sequela. These toxic effects are frequently dose related but may be enhanced by radiation therapy. Similar to chemotherapy, radiation can produce acute or chronic lung injury depending on dose rate, duration, preexisting lung disease, and concomitant steroid use. Acute radiation injury typically occurs 2 weeks to 3 months after treatment and is usually limited to the irradiated field. Mild injury often resolves without treatment, whereas more serious injury results in fibrosis 6 to 12 months after treatment. Histopathologic evaluation of acute lung injury is no different from drug-induced injury, and damage to vascular endothelial cells and alveolar lining cells is seen. This article reviews and provides an update on the clinically important chemotherapy and radiation-induced pulmonary injuries, the pathologic mechanisms, where known, and the treatment advances that have occurred in this field.

Can we predict radiation-induced changes in pulmonary function based on the sum of predicted regional dysfunction?

PURPOSE

To determine whether changes in whole-lung pulmonary function test (PFT) values are related to the sum of predicted radiation therapy (RT)-induced changes in regional lung perfusion.

PATIENTS AND METHODS

Between 1991 and 1998, 96 patients (61% with lung cancer) who were receiving incidental partial lung irradiation were studied prospectively. The patients were assessed with pre- and post-RT PFTs (forced expiratory volume in one second [FEV1] and diffusion capacity for carbon monoxide [DLCO]) for at least a 6-month follow-up period, and patients were excluded if it was determined that intrathoracic recurrence had an impact on lung function. The maximal declines in PFT values were noted. A dose-response model based on RT-induced reduction in regional perfusion (function) was used to predict regional dysfunction. The predicted decline in pulmonary function was calculated as the weighted sum of the predicted regional injuries: equation [see text] where Vd is the volume of lung irradiated to dose d, and Rd is the reduction in regional perfusion anticipated at dose d.

RESULTS

The relationship between the predicted and measured reduction in PFT values was significant for uncorrected DLCO (P = .005) and borderline significant for DLCO (P = .06) and FEV1 (P = .08). However, the correlation coefficients were small (range,.18 to.30). In patients with lung cancer, the correlation coefficients improved as the number of follow-up evaluations increased (range,.43 to.60), especially when patients with hypoperfusion in the lung adjacent to a central mediastinal/hilar thoracic mass were excluded (range,.59 to.91).

CONCLUSION

The sum of predicted RT-induced changes in regional perfusion is related to RT-induced changes in pulmonary function. In many patients, however, the percentage of variation explained is small, which renders accurate predictions difficult.