International Journal of Radiation Oncology*Biology*Physics
Clinical InvestigationPossible Misinterpretation of Demarcated Solid Patterns of Radiation Fibrosis on CT Scans as Tumor Recurrence in Patients Receiving Hypofractionated Stereotactic Radiotherapy for Lung Cancer
Introduction
Delivery of a high dose of radiation by using hypofractionated stereotactic radiotherapy (HSRT) often results in radiopacity within the boundaries of a tumor, which would be considered tumor progression. To our knowledge, no study to date evaluated morphologic changes in tumors after HSRT, and only a few reports focused on HSRT-induced lung injuries 1, 2, 3.
Complete disappearance of the tumor is rarely seen during follow-up of patients with lung cancer with HSRT. As in many cases, after conventional radiotherapy, the primary tumor may be obscured by postradiation change. A degree of tumor shrinkage usually is observed, and a variety of radiologic patterns that may reflect modifications caused by irradiation also is seen 1, 3. In patients with a good response, tumor opacities usually shrink and thereafter appear as scar-like or linear patterns that persist on radiologic follow-up images. We generally consider these radiologic patterns to reflect tumor control. However, there are cases in which opacities are only minimally reduced in size. Moreover, diagnostic difficulty is often encountered when trying to determine whether the patterns reflect tumor recurrence or mass-like fibrosis after radiotherapy 4, 5. In patients who are candidates for such salvage treatments as surgery, cryoablation (6), and radiofrequency ablation (7), it is essential to diagnose recurrence as early as possible because the smaller the tumor, the easier it is to treat. For example, an adequate size for cryoablation of lung tumors is less than 3 cm in diameter (6). Needless to say, it is important to establish standards for determining tumor recurrence after HSRT to appropriately assess its treatment outcome.
In this study, we retrospectively reviewed follow-up computed tomography (CT) studies of 50 patients obtained during a period of at least 1 year after HSRT for localized peripheral primary lung cancer. Our goal was to analyze opacity changes in the vicinity of irradiated tumors to determine whether there was tumor recurrence.
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Patients
Our institutional review boards approved this study and waived the need for informed consent based on the retrospective design. The study group was composed of 50 patients who underwent HSRT with curative intent for proven or highly suspected localized primary lung cancer located in the periphery of the lung. One case was located in segment 1 + 2 of the left lung and invasion to the aortic arch was noted; however, no patient with thoracic wall invasion was included. All were treated at
Results
Median follow-up was 30.4 months (range, 12.0–73.8 months). Excluding radiologic patterns typical of radiation pneumonitis that occurred 2 to 7 months after radiotherapy, abnormal opacities suspected of being recurrent tumors appeared in 20 patients (Fig. 1). Median time between completion of HSRT and a radiologically recognizable increase in tumor opacity was 20.7 months (range, 5.9–61.4 months). The remaining 30 patients were judged to have achieved tumor control because tumor opacities
Discussion
Careful follow-up reading of radiologic images from patients treated with HSRT showed that radiologic patterns seen after HSRT are likely to differ from those appearing after conventional radiotherapy. An earlier report found that radiation-induced lung injury occurred during the first year after HSRT (2). The conduction of longer term follow-up of radiologic patterns after HSRT is showing many cases in which it is difficult to determine whether residual opacities reflect viable malignant
Conclusion
In conclusion, it should be noted that radiation fibrosis, which may occur 1 year or more after completion of HSRT, is difficult to distinguish from tumor recurrence. Even when opacities increase on follow-up radiologic scans and high uptake is noted on FDG-PET scans, recurrence cannot be conclusively diagnosed based on image findings of increased opacities and high metabolism on PET scans. Biopsy occasionally is still warranted.
References (21)
- et al.
CT appearance of radiation injury of the lung and clinical symptoms after stereotactic body radiation therapy (SBRT) for lung cancers: Are patients with pulmonary emphysema also candidates for SBRT for lung cancers?
Int J Radiat Oncol Biol Phys
(2006) - et al.
Percutaneous cryoablation of small pulmonary malignant tumors under computed tomographic guidance with local anesthesia for nonsurgical candidates
J Thorac Cardiovasc Surg
(2006) - et al.
Radiofrequency ablation for the treatment of non-small cell lung cancer in marginal surgical candidates
J Thorac Cardiovasc Surg
(2005) - et al.
Complications of radiation therapy: The thorax
Semin Roentgenol
(1974) - et al.
Extracranial radiosurgery (stereotactic body radiation therapy) for oligometastases
Semin Radiat Oncol
(2006) - et al.
A prospective trial of serial FDG-PET in patients with medically inoperable stage 1 non-small lung cancer treated with Hypofractionated stereotactic body radiotherapy (SBRT)
Int J Radiat Oncol Biol Phys
(2006) - et al.
Evaluation of lung injury after three-dimensional conformal stereotactic radiation therapy for solitary lung tumors: CT appearance
Radiology
(2004) - et al.
Radiation injury after hypofractionated stereotactic radiotherapy for peripheral small lung tumors: Serial changes on CT
AJR Am J Roentgenol
(2004) - et al.
Radiation injury of the lung after three-dimensional conformal radiation therapy
AJR Am J Roentgenol
(2002) - et al.
Stereotactic radiotherapy of targets in the lung and liver
Strahlenther Onkol
(2001)
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Conflict of interest: none.