CT-based analysis of dose homogeneity in total body irradiation using lateral beam

Abstract

A computed tomography (CT) based treatment planning system for total body irradiation (TBI) is presented and compared with the commonly practiced lateral treatment delivery. The TBI regimen has been proved to be an essential conditional regimen for patients undergoing bone marrow transplantation. The advantage of the TBI regimen with bone marrow transplantation (BMT) in hematological malignancies can be offset by toxicities arising from TBI in posttransplant complications. With the increasing survival rates, the evaluation of long-term side effects and quality of life has become an important area of research interest. There have been several treatment techniques developed over the decades designed to achieve accurate dose delivery and dose homogeneity. This paper reports on the verification of the dose delivery for a basic lateral technique using thermoluminescent dosimeters (TLDs) placed in an anthropomorphic phantom and its correlation with CT-based treatment planning. CT-based treatment plans on several patients were used to evaluate the doses delivered to the whole body and critical organs. A large variation in doses delivered to the whole body was demonstrated, with some parts of the bone marrow failing to receive the prescribed dose and some critical organs, such as the lungs, receiving excessive doses. Placing the arms at the sides only partially compensates for the increased transmission of the lungs because the arms only shadow part of the lung. This study shows that CT-based treatment planning for TBI provides precise and accurate dose calculations and allows for the correlation of clinical outcomes with the doses actually delivered to various organs.

Figure 1

Doses measured with TLD compared with prescribed doses at the selected points in the Rando phantom irradiated with parallel‐opposed lateral beams. The error bars indicate the 5% uncertainty in TLD measurements.

Figure 2

Doses in phantom measured with TLD and calculation based on CT treatment plan.

Figure 3

Isodose distribution shown on a patient CT, as calculated by treatment‐planning system for lateral‐opposed beam. The horizontal white lines show the levels of the transverse images (manubrium and midlung) to the left of the sagittal images. (a) coronal; (b) sagittal; (c) transverse manubrium; (d) transverse midlung image.

Figure 4

Midline dose profile in the anterior‐posterior direction at the level of the manubrium.

Figure 5

Midline dose profile in the lateral direction at the transverse level of the midlung, along line I in (Fig. 3d).

Figure 6

Midline dose profile in the lateral direction at the transverse level of the midlung, along line II in (Fig. 3d).

Figure 7

Beam's‐eye view of one of the lateral fields. Body skin is a gray transparent color, the lung is in the pink wire frame, and the arm is in the blue wire frame.