Assessment of lung cancer response after nonoperative therapy: tumor diameter, bidimensional product, and volume. A serial CT scan-based study.

PURPOSE: Tumor response after nonoperative lung cancer therapy is traditionally evaluated by bidimensional measurement of maximum tumor diameters. The purpose of this analysis is to investigate whether tumor largest dimension (based on RECIST [Response Evaluation Criteria In Solid Tumors]), bidimensional tumor product, and volume correlate with each other in evaluating tumors of patients with locally advanced non-small-cell lung cancer (NSCLC). In addition, the pace of locally advanced NSCLC volumetric response over time, as well as the prognostic value of tumor size, was assessed in this report with software-assisted evaluation of sequential tumor measurement.

METHODS AND MATERIALS: Patients with locally advanced NSCLC treated with thoracic radiotherapy (RT) with or without chemotherapy were included, if the following were available: a pretreatment computed tomography (CT) simulation and at least two follow-up diagnostic thoracic CT scans taken at our institution after 1996 that were available in Dicom format for electronic transfer of images from diagnostic radiology to a computer terminal with commercial statistics software (AcQsim/CMS Focus). Primary lung tumor and grossly involved lymph nodes were contoured manually on pre-RT axial images and on all follow-up CT scans. Tumor/lymph node largest dimensions, bidimensional products (BP), and volumes were measured using the same software. Data were presented as percent change in volume or unidimensional and bidimensional measurements, with the CT simulation measurements serving as baseline.

RESULTS: A total of 22 patients were evaluated. The median thoracic RT dose was 62.4 Gy (range: 50.0-69.6), and all patients had a Karnofsky performance status > or =80. Chemotherapy (mostly carboplatin/paclitaxel) was given to 17 patients. Nineteen patients had Stage III NSCLC; 1 patient was in Stage I, 1 was in Stage IV, and 1 was recurrent. A total of 107 thoracic CT scans (22 pretreatment and 85 follow-up), averaging 4.9 scans per patient, were analyzed. Tumors reached the smallest volume at a median of 11.0 months from RT completion in all patients, 8.5 months in patients who subsequently failed locally (n = 8), and 11.9 months in those who did not fail locally. Failure rates were as follows: in-field, 36% (8/22); intrathoracic (lung nodules, effusion, pleura), 55% (12/22); and distant, 50% (11/22). Eleven patients are still alive, 4 free of disease. Overall median survival time (MST) is 27.3 months. The median initial tumor volume was 88.0 cc (range: 3.8-218) for all patients; median BP was 33.0 cm(2) (range: 3.1-112.1), and median tumor largest dimension was 7.6 cm (range: 2.2-13.5). The MST of patients with initial tumor volume < or =63.0 cc (n = 9) was >53.0 months and of those with tumor volume > 63.0 cc was 17.3 months. The MST of patients (n = 6) with initial bidimensional tumor product < or =16 cm(2) was >53.0 months and of those with tumor product >16 cm(2) was 17.3 months. The MST of patients with largest initial dimension < or =4 cm was >53.1 months and of those with largest dimension > 4 cm was 25.0 months. At 24 months, 79% of patients with a tumor volume < or =124.0 cc (n = 18) had locally controlled tumors, vs. 0% of patients with tumor volumes >124.0 cc. At the same time point, 93% of patients with BP < or =40 cm(2) were locally controlled, vs. 0% of those with BP > 40 cm(2); 100% of patients with tumor dimensions < or =7.5 cm were locally controlled, vs. 40% of those with dimensions >7.5 cm. The partial responses in our series (assessed as the best response obtained during observation period) were as follows: 4 patients assessed based on either dimension only, product only, or volume only; 15 partial responses based on dimension or product; 16 partial responses based on volume alone; 3 cases of no tumor response, based on dimension or product; and 2 cases based on tumor volume alone. That represents good to excellent agreement among all three methods of measurement.

CONCLUSIONS: (1) The response of locally advanced NSCLC to nonoperative therapy is a slow process, with tumor volumes reaching their nadir several months after treatment. (2) Smaller initial tumor size, as measured by largest tumor dimension, bidimensional product, or tumor volume, is associated with better local control and survival than larger initial measurements. (3) Any of the three tumor measurements (largest dimension, bidimensional product, or volume) can be used as a reliable tool in assessing lung cancer response to nonoperative therapy. This confirms further the validity of RECIST and does not suggest that tumor volume is significantly superior for response evaluation.