Radiology: PET could serve as surrogate marker for head, neck cancer outcomes

Planar images of 186Re–liposomal doxorubicin accumulation in tumor with and without RF ablation. Source: Radiology 2011;261(3):813-823.

FDG PET could be used as a noninvasive surrogate marker for tumor growth and viability in treatment of head and neck cancer, based on a rodent model study published in the December issue of Radiology.

The management of advanced disease may be improved by using liposomes to deliver a high concentration of a drug to the tumor to prevent local recurrence, according to the study authors, who hypothesized that concordant benefits for solid tumor therapy would be obtained by combining radiofrequency (RF) ablation with liposomes encapsulating both doxorubicin and rhenium 186 (¹⁸⁶Re).

Thus, Anuradha Soundararajan, PhD, from the department of radiology at the University of Texas Health Science Center at San Antonio, and colleagues sought to determine the therapeutic efficacy of ¹⁸⁶Re–labeled PEGylated liposomal doxorubicin (¹⁸⁶Re–liposomal doxorubicin) in combination with RF ablation of human head and neck squamous cell carcinoma (HNSCC) xenograft in nude rats.

In the study, 60 nude rats with subcutaneously implanted HNSCC xenografts (six per group) were treated with RF ablation (70°C for five minutes); PEGylated liposomes; liposomal doxorubicin; ¹⁸⁶Re–PEGylated liposomes (1295 MBq/kg); ¹⁸⁶Re–liposomal doxorubicin (555 MBq/kg); PEGylated liposomes plus RF ablation; liposomal doxorubicin plus RF ablation; ¹⁸⁶Re–PEGylated liposomes plus RF ablation; or ¹⁸⁶Re–liposomal doxorubicin plus RF ablation. Six rats served as the control group, and did not receive any treatment.

The researchers monitored tumor uptake in ¹⁸⁶Re therapy groups with small-animal SPECT for five days; and monitored the therapeutic efficacy for six weeks with measurement of tumor volume, calculation of the percentage injected dose of fluorine 18-FDG in tumor from small-animal PET images. They determined significant differences between groups with analysis of variance.

The average tumor volume on the day of therapy was 1.32 cm³. At six weeks after therapy, control of tumor growth was better with ¹⁸⁶Re–liposomal doxorubicin than with liposomal doxorubicin alone (tumor volume, 2.26 cm³ vs. 5.43 cm³, respectively), according to the authors. The use of RF ablation with liposomal doxorubicin and ¹⁸⁶Re–liposomal doxorubicin further improved tumor control (tumor volume, 2.05 cm³ and 1.49 cm³, respectively).

Also, they wrote that the tumor growth trend correlated with change in percentage of injected dose of FDG in tumor for all groups. Finally, viable tumor volume was “significantly decreased” in the group treated with ¹⁸⁶Re–liposomal doxorubicin plus RF ablation (0.54 cm³ ± 0.38).

Based on their findings, Soundararajan and colleagues concluded that triple and dual therapies had an observable trend (¹⁸⁶Re–liposomal doxorubicin plus RF ablation > ¹⁸⁶Re–liposomal doxorubicin > liposomal doxorubicin plus RF ablation > liposomal doxorubicin) of improved tumor growth control and decreased viable tumor compared with other therapies.