Renal shielding and dosimetry for patients with severe systemic sclerosis receiving immunoablation with total body irradiation in the scleroderma: cyclophosphamide or transplantation trial

Abstract

Purpose: To describe renal shielding techniques and dosimetry in delivering total body irradiation (TBI) to patients with severe systemic sclerosis (SSc) enrolled in a hematopoietic stem cell transplant protocol.

Methods and materials: The Scleroderma: Cyclophosphamide or Transplantation (SCOT) protocol uses a lymphoablative preparative regimen including 800 cGy TBI delivered in two 200-cGy fractions twice a day before CD34(+) selected autologous hematopoietic stem cell transplantation. Lung and kidney doses are limited to 200 cGy to protect organs damaged by SSc. Kidney block proximity to the spinal cord was investigated, and guidelines were developed for acceptable lumbar area TBI dosing. Information about kidney size and the organ shifts from supine to standing positions were recorded using diagnostic ultrasound (US). Minimum distance between the kidney blocks (dkB) and the lumbar spine region dose was recorded, and in vivo dosimetry was performed at several locations to determine the radiation doses delivered.

Results: Eleven patients were treated at our center with an anteroposterior (AP)/posteroanterior (PA) TBI technique. A 10% to 20% dose inhomogeneity in the lumbar spine region was achieved with a minimum kidney block separation of 4 to 5 cm. The average lumbar spine dose was 179.6 ± 18.1 cGy, with an average dkB of 5.0 ± 1.0 cm. Kidney block shield design was accomplished using a combination of US and noncontrast computerized tomography (CT) or CT imaging alone. The renal US revealed a wide range of kidney displacement from upright to supine positions. Overall, the average in vivo dose for the kidney prescription point was 193.4 ± 5.1 cGy.

Conclusions: The dose to the kidneys can be attenuated while maintaining a 10% to 20% dose inhomogeneity in the lumbar spine area. Kidneys were localized more accurately using both US and CT imaging. With this technique, renal function has been preserved, and the study continues to enroll patients.

Copyright © 2011 Elsevier Inc. All rights reserved.

Figures

Figure 1

a) Patient in treatment position on the TBI stand with lung and kidney blocks in place. Spoiler is also visible, as well as the positioning of the in vivo dosimeters; b) Detail of patient's torso and abdomen with skin marks for the lung and kidney block placement and the location of the anterior surface positioning BBs.

Figure 2

a) AP DRR with kidney contours; b) Marks on posterior skin surface that reflect the kidney shifts, as measured by US, from supine position (blue marks) to standing position (red marks); c) AP DRR with kidney blocks drawn per current protocol guidelines when ultrasound (US) is available. In this case, 1.5 cm superior, inferior and lateral margin, no medial margin; d) AP DRR with kidney blocks shifted per US findings.

Figure 3

Kidney displacement from supine to standing position assuming the computerized tomography (CT) kidney position as reference for the a) left (LT) kidney and b) right (RT) kidney. High variability is noticed in the kidney travel for the 11 patients treated so far. Kidneys compressed, shifted inferiorly, and even shifted superiorly (see RT kidney, patient Pt5).

Figure 4

Computerized tomography (CT)-based kidney contours showing the possibility to use standardized kidney blocks. The red dotted contours represent an envelope of all the kidney contours for right (RT) and left (LT) kidneys, respectively. The blue dotted contours represent hypothetical kidney blocks defined per current protocol.

Figure 5

Single dose average for 11 patients measured at selected anatomical points. The error bars represent the standard deviation.

Figure 6

Total dose to the lumbar spine area for 11 subjects binned as a function of the distance between the kidney blocks (dkB). With dkB > 4 cm, a 10–20 % inhomogeneity in the lumbar spine area is achievable.