Drh. Christie et al., THE DOSES RECEIVED BY THE BREAST DURING MANTLE RADIOTHERAPY, International journal of radiation oncology, biology, physics, 41(1), 1998, pp. 223-226
Citations number
18
Categorie Soggetti
Oncology,"Radiology,Nuclear Medicine & Medical Imaging
Purpose: To accurately measure the dose received by the breast during
mantle radiotherapy. Methods and Materials: A phantom containing lung-
equivalent material was used to measure the doses received by the brea
st during mantle radiotherapy given by anterior and posterior opposing
fields. These were measured using thermoluminescent dosimeters and co
mpared with point dose calculations obtained by computer planning. Res
ults: Most of the breast lies under the lung shields or inferior to th
e mantle field, but the upper outer quadrant of the breast remains uns
hielded. In the unshielded areas of the breast, the average dose measu
red was nearly 13% higher than the dose prescribed at the central axis
, In the shielded parts of the breast, the average measured dose was n
early 10% of the dose prescribed at the central axes, decreasing from
18% superiorly to 4% inferiorly. The posterior field contributed 45% t
o the dose in the breast, even though doses were prescribed at the mid
plane. The computer calculations systematically varied from measured d
oses by up to 35%, becoming less accurate towards the inferior edge of
the field. Conclusions: In a conventional course of mantle radiothera
py (for example, 36 Gy in 20 fractions), most of the breast is shielde
d but will receive a dose of 3-4 Gy, higher than expected largely due
to internally scattered radiation passing through the lungs from the p
osterior field. Computer dose calculations may poorly reflect actual o
ff-axis doses in large fields with complex shielding, containing inhom
ogeneous tissue. (C) 1998 Elsevier Science Inc.