Gross Tumor Volume and Metastases Evaluations
Prior to course 1, imaging examinations by magnetic resonance imaging
(MRI) and/or computed tomography (CT) were performed to quantify the
gross tumor volume (GTV, in cm3) of the primary NB
tumor. Imaging examinations were repeated after course 2 of antibody
infusions to obtain a new GTV following induction chemotherapy. These
volumes were available from the institutional NB study database. A
“tumor volume ratio” was calculated by dividing the GTV prior to
course 1 by the GTV following course 2. A greater treatment response led
to smaller GTV following course 2 (smaller denominator) and therefore a
higher tumor volume ratio. In the absence of response, both the
numerator and denominator of the tumor volume ratio are the initial GTV,
which led to a tumor volume ratio of 1. For patients with acomplete response to treatment (2nd GTV
essentially 0 cm3), the denominator of the tumor
volume ratio was credited as “1 cm3” to prevent an
undefined fraction. To summarize, a higher tumor volume ratio equated to
a greater response to treatment. A tumor volume ratio of 1 equated to a
complete lack of response to treatment.
Additionally, tumor burden outside of the primary tumor was
evaluated using Curie scores obtained by meta-iodobenzylguanidine (MIBG)
scans.21 A Curie score ratio (Curie score prior to
course 1 divided by Curie score following course 2) was calculated and
used for analysis rather than raw Curie scores.