Effect of respiratory gating on reducing lung motion artifacts in PET imaging of lung cancer

Positron emission tomography (PET) has shown an increase in both sensitivity and specificity over computed tomography (CT) in lung cancer. However, motion artifacts in the 18F fluorodioxydoglucose (FDG) PET images caused by respiration persists to be an important factor in degrading PET image quality and quantification. Motion artifacts lead to two major effects: First, it affects the accuracy of quantitation, producing a reduction of the measured standard uptake value (SUV). Second, the apparent lesion volume is overestimated. Both impact upon the usage of PET images for radiation treatment planning. The first affects the visibility, or contrast, of the lesion. The second results in an increase in the planning target volume, and consequently a greater radiation dose to the normal tissues. One way to compensate for this effect is by applying a multiple-frame capture technique. The PET data are then acquired in synchronization with the respiratory motion. Reduction in smearing due to gating was investigated in both phantoms and patient studies. Phantom studies showed a dependence of the reduction in smearing on the lesion size, the motion amplitude, and the number of bins used for data acquisition. These studies also showed an improvement in the target-to-background ratio, and a more accurate measurement of the SUV. When applied to one patient, respiratory gating showed a 28% reduction in the total lesion volume, and a 56.5% increase in the SUV. This study was conducted as a proof of principle that a gating technique can effectively reduce motion artifacts in PET image acquisition.

Three-Dimensional Conformal Radiation Therapy (3D-CRT) for Early-Stage Non–Small-Cell Lung Cancer

The standard treatment for early-stage non-small-cell lung cancer is surgical resection. However, many patients are inoperable due to medical comorbidities. Thirty-two medically inoperable patients with early-stage non-small-cell lung cancer were treated with 3-dimensional conformal radiation therapy between January 1991 and December 2000. The median dose was 70.2 Gy, and the median follow-up time in survivors was 30 months. The 2-year actuarial local control, overall survival, and cancer-specific survival rates were 43%, 54%, and 57%, respectively. The 5-year actuarial local control, overall survival, and cancer-specific survival rates were 43%, 33%, and 39%, respectively. This report suggests that local control is improved with high-dose conformal radiation therapy when compared to other institutions' retrospective experiences.

Elective nodal irradiation in the treatment of non-small-cell lung cancer with three-dimensional conformal radiation therapy

PURPOSE

Dose escalation using three-dimensional conformal radiation therapy (3D-CRT) has been investigated as a means to improve local control. However, with higher doses, the risk of toxicity increases. Early in our experience, we ceased treating elective nodal areas (lymph node stations without evidence of tumor involvement) in an effort to decrease toxicity while treating the gross tumor to higher doses. This report measures the rate of regional failure without elective radiation therapy to uninvolved lymph nodes.

METHODS AND MATERIALS

A total of 171 patients with non-small-cell lung cancer treated with 3D-CRT at Memorial Sloan-Kettering Cancer Center between 1991 and 1998 were reviewed. Only lymph node regions initially involved with tumor either by biopsy (55%) or radiographic criteria (node > or =15 mm in the short axis on CT) were included in the clinical target volume. Elective nodal failure was defined as a recurrence in an initially uninvolved lymph node in the absence of local failure.

RESULTS

Only 11 patients (6.4%) with elective nodal failure were identified. With a median follow-up of 21 months in survivors, the 2-year actuarial rates of elective nodal control and primary tumor control were 91% and 38%, respectively. In patients who were locally controlled, the 2-year rate of elective nodal control was 85%. The median time to elective nodal failure was 4 months (range, 1-19 months). Most patients failed in multiple lymph node regions simultaneously.

CONCLUSION

Local control remains one of the biggest challenges in the treatment of non-small-cell lung cancer. Most patients in our series developed local failure within 2 years of radiation therapy. The omission of elective nodal treatment did not cause a significant amount of failure in lymph node regions not included in the clinical target volume. Therefore, we will continue our policy of treating mediastinal lymph node regions only if they are clinically involved with tumor.

Quantitative effect of combined chemotherapy and fractionated radiotherapy on the incidence of radiation-induced lung damage: a prospective clinical study

PURPOSE

The objective of this work was to assess the incidence of radiological changes compatible with radiation-induced lung damage as determined by computed tomography (CT), and subsequently calculate the dose effect factors (DEF) for specified chemotherapeutic regimens.

METHODS AND MATERIALS

A prospective, clinical study was conducted to determine the response of normal lung tissue to combined chemotherapy and radiotherapy. Radiation treatments were administered once daily, 5 days-per-week. Six clinical protocols were evaluated: ABVD (adriamycin, bleomycin, vincristine, and DTIC) followed by 35 Gy in 20 fractions; MOPP (nitrogen mustard, vincristine, procarbazine, and prednisone) followed by 35 Gy in 20; MOPP/ABVD followed by 35 Gy in 20; CAV (cyclophosphamide, adriamycin, and vincristine) followed by 25 Gy in 10; and 5-FU (5-fluorouracil) concurrent with either 50-52 Gy in 20-21 or 30-36 Gy in 10-15 fractions. CT examinations were taken before and at predetermined intervals following radiotherapy. CT evidence for the development of radiation-induced damage was defined as an increase in lung density within the irradiated volume. The radiation dose to lung was calculated using a CT-based algorithm to account for tissue inhomogeneities. Different fractionation schedules were converted using two isoeffect models, the estimated single dose (ED) and the normalized total dose (NTD).

RESULTS

A total of 102 patients were entered and 70 completed the study. Forty-two patients developed CT changes compatible with lung damage. The actuarial incidence of radiological pneumonitis was 71% for the ABVD, 49% for MOPP, 52% for MOPP/ABVD, 67% for CAV, 73% for 5-FU radical, and 58% for 5-FU palliative protocols. Depending on the isoeffect model selected and the method of analysis, the DEF was 1.11-1.14 for the ABVD, 0.96-0.97 for the MOPP, 0.96-1.02 for the MOPP/ABVD, 1.03-1.10 for the CAV, 0.74-0.79 for the 5-FU radical, and 0.94 for the 5-FU palliative protocols.

CONCLUSION

Quantitative dose effect factors (DEF) were measured by comparing the incidences of CT-observed lung damage in patients receiving chemotherapy and radiotherapy to those receiving radiotherapy alone. The addition of ABVD or CAV appeared to reduce the tolerance of lung to radiation.