Glasses for Radiotherapy - Bio-Glasses: An Introduction - page 210

The advantages of irradiating hepatic tumors with an in situ radiation
source so as to avoid damaging nearby healthy tissue and thereby
deliver larger doses ( 100Gy) was recognized in the early 1960s when

patients were treated with ceramic microspheres, 40-60

>

m in diameter,
which contained the beta emitter 90 Y [22-24]. These early studies were
not without problems, such as leakage of the radioisotope from the
tumor site and the migration of radioactive particles to other organs.
Nevertheless, the procedure of infusing radioactive particles into the
liver via the hepatic artery was deemed to be simple and reasonably
safe, reductions in tumor size were noted, complications were minimal,
and clinical and subjective improvements were noted in some patients.
The remainder of this section will focus on the use of radioactive 90 YAS
glass microspheres to treat patients with primary liver tumors, HCC,
that started in the mid-1980s. In 2000, YAS glass microspheres were
approved by the US Food and Drug Administration (FDA) for treating
patients with inoperable primary liver cancer (HCC).
Patients were first treated with 90 YAS glass microspheres at the
University of Michigan [15, 21] and later at Toronto General Hospital
in Canada [3] in dose escalation studies. The microspheres were made
from YAS glass, which had been selected for its outstanding chemical
durability and high yttria content. Yttrium was the element of choice,
since 90 Y emits beta radiation, which has an average range of 2.5mm
in soft tissue, has an acceptable half-life, and can be formed by neutron
activation of the naturally occurring 89 Y, which is 100% abundant.
The technique employed to deliver the radioactive microspheres to the
liver via the hepatic artery is depicted schematically in Figure 13.7. A
catheter is inserted into the patient and manipulated to the desired loca-
tion. The desired amount (typically

μ

m radioactive
90 YAS microspheres (Figure 13.1) is flushed from the dose vial with a
saline solution into the catheter, where the microspheres enter the blood
stream and are eventually deposited in the capillary bed of the targeted
tumor(s). The infusion of radioactive microspheres to either a single or
multiple tumors is complete in a few minutes.
The results of the early studies were promising, and doses up to 150Gy,
calculated as whole liver dose, were deemed safe. Since the 90 YAS
glass microspheres tend to follow the blood flow, the microspheres
preferentially concentrate in the tumor mass at ratios from 10 to 40
times higher than in the healthy tissue. Because of the outstanding
chemical durability of the YAS glass, no leakage of the 90 Yfromthe
target site was detected, and no serious side effects were observed. Over
time, the infusion techniques have improved, especially the positioning of

< 100mg) of 20-30 μ