Initial tumor size and local control in stage III non-small cell lung cancer treated by radio-chemotherapy

A pharmacokinetic model for radioimmunotherapy delivered through cerebrospinal fluid for the treatment of leptomeningeal metastases

Radioimmunotherapy can effectively treat leptomeningeal metastases when radiolabeled antibodies are administered into the cerebrospinal fluid (CSF). We developed a pharmacokinetic model to evaluate the role of kinetic and transport parameters of radioimmunotherapy in maximizing the therapeutic ratio, the ratio of the area under the curve for the concentration of the bound antibodies versus time (AUC[C(IAR)]), to that for unbound antibodies (AUC[C(IA)]).

METHODS

We simplified the CSF space as a single compartment and considered the binding of antibodies to antigens on tumor cells lining the surface of the CSF space. Mass conservation was applied to set up the equations for C(IAR), C(IA), and other pharmacokinetic variables. A Runge-Kutta method was used to solve the equations.

RESULTS

This model agreed with the measured data in 10 of 14 patients in the phase I trial of intra-Ommaya radioimmunotherapy using (131)I-3F8. Using this model, we predicted that increasing the affinity of antibodies to antigens greatly increases AUC(C(IAR)) but not AUC(C(IA)); for the same amount of isotope administered, the smaller antibody dose and the higher specific activity improves therapeutic ratio. When the isotope half-life (t(1/2-I)) was 0.77 h, increasing the antibody association constant enhanced AUC(C(IAR)) much more than did decreasing the dissociation constant, even if overall affinity was unchanged. When t(1/2-I) reached 240 h, decreasing the dissociation constant would slightly enhance AUC(C(IAR)). Other predictions were that decreasing the CSF bulk flow rate would increase AUC(C(IAR)), with 3 mL/h being optimal; at the same amount of antibody administered by continuous infusion and by split administrations, compared with that by the single bolus administration, one could improve AUC(C(IAR)) by up to 1.8- and 1.7-fold, respectively; and for an antibody affinity of 10(-8) M, increasing t(1/2-I) from 0.77 up to 64 h could greatly enhance the therapeutic ratio.

CONCLUSION

The strong agreement between model predictions and patient data supports the validity of the assumptions and simplifications in our model. The predictions using this model are not intuitive and need to be validated in future clinical trials. The improved therapeutic ratio by optimized kinetic and transport parameters may enhance the clinical efficacy of this new treatment modality.

Dose, volume, and tumor control prediction in primary radiotherapy of non-small-cell lung cancer

BACKGROUND

To evaluate the influence of total dose and tumor volume on local control and survival in primary radiotherapy of non-small-cell lung cancer (NSCLC).

METHODS AND MATERIALS

We retrospectively analyzed the clinical course and CT-derived pre- and post-therapeutic tumor volume data of 135 patients with NSCLC undergoing primary radiotherapy at our department between 1989 and 1996. Among these, a total of 192 spatially separated tumor volumes (135 primary tumors, 1 additional intrapulmonary tumor, and 56 involved lymph nodes) were available for analysis. In all patients, treatment was planned using CT-based three-dimensional treatment planning. The dose to each tumor volume was derived from the individual dose plans. Mean total dose was 59.9 Gy (range: 30-80 Gy). All but 3 patients were followed until death. For local control analysis, each tumor was analyzed separately, and its remission status was determined in serial follow-up CT scans. A total of 784 CT scans were analyzed. Actuarial local control analysis was performed for the 192 separated tumor volumes, and survival analysis was performed for the 135 patients. Tumor control probability was calculated using a Poisson statistical model.

RESULTS

Overall 1- and 2-year local control rate was 50% and 37%, respectively. The 2-year local control rate for tumors <50 ccm, 50-200 ccm, and >200 ccm was 51%, 22%, and 10%, respectively (p = 0.02). The 2-year local control rate for dose levels < or = 60 Gy and >60 Gy was 28% and 43% (p < 0.001). For the subgroup of 147 tumors smaller than 100 ccm, the local control rate increased up to 70% (1 year) and 51% (2 years) with doses of more than 60 Gy. For tumors larger than 100 ccm, no dose effect was seen. Only 2 of 45 tumors >100 ccm were controlled more than 2 years. Multivariate analysis revealed tumor volume, total dose, histopathologic type, and grading as significant and independent prognostic factors for local control. The number of delay days by split course (if used) and application of chemotherapy was not found to influence local control. Overall 1- and 2-year survival rate was 42% and 13%. Total radiation dose, chemotherapy, and T and N stage---but not tumor volume---were found to be independent and significant prognostic factors for survival in multivariate analysis.

CONCLUSION

Tumor volume is an important predictor of local control in NSCLC. We found a clear dose effect for local control and survival in NSCLC. Long-term local control for a significant proportion of patients seems possible for small tumors only (<100 ccm, i.e., maximum diameter 6 cm) with doses of 70 Gy and more. Tumors of > or = 100 ccm are unlikely to be controlled long term by conventional doses up to 70 Gy. These results support dose escalation in patients with NSCLC.