[Lung dose depending on exact patient positioning during total body irradiation (TBI). Isoeffectiveness considerations to assess the risk of interstitial pneumonia after TBI].
OBJECTIVE
In this case report, we studied the effect of patient's movements on total lung dose during total body irradiation (TBI). The dose-effect relationship regarding the development of interstitial pneumonitis and the problem of defining a threshold value are discussed. Based on considerations about the isoeffects we calculated the pneumonitis risk in dependence of increasing lung dose.


METHODS
We calculated dose-volume histograms of the lung for defined lateral deviations (0-3 cm) from the isocenter. Total dose was 12 Gy, given in six fractions over 3 days. Lung shields were used after a total dose of 9 Gy. Lung shields were transferred into the Helax-TMS planning system to quantify the influence of lateral deviation to lung dose.


RESULTS
The child's lateral deviation amounted up to 3 cm. Median dose of the whole lung amounted up to 11.64 Gy depending on lateral deviation.


CONCLUSIONS
In TBI, the lung limits the total dose. To estimate the risk of radiation pneumonitis, we calculated the isoeffective lung dose of our TBI regime for a fractionation scheme of 2 Gy daily using a formalism of van Dyk. The increase of median lung dose from 9.76 to 11.64 Gy would isoeffectively correspond to the increase from 19 Gy (no deviation) to 20.9 Gy (3 cm lateral deviation) with conventional fractionation. According to Burman, a pneumonitis risk of approximately 20% could be expected.


CONCLUSIONS
With an estimated pneumonitis risk of approximately 20%, in indication for irradiation in general anesthesia seems to be reasonable. This is practicable in cooperation with radiation oncologists, anesthesists and pediatricians and should be included into therapeutic concepts.
Piroth
Marc D
MD
Abteilung für Klinische Radiologie, Radiologische Klinik, Universität Heidelberg. marc_piroth@med.uni-heidelberg.de
Zierhut
Dietmar
D
van Kampen
Michael
M
Sroka-Perez
Gabriele
G
Wannenmacher
Michael
M
D000768:Anesthesia, General; D016026:Bone Marrow Transplantation; D002675:Child, Preschool; D005260:Female; D006801:Humans; D008168:Lung / Q000528:radiation effects*; D017563:Lung Diseases, Interstitial / Q000209:etiology* / Q000517:prevention & control; D008962:Models, Theoretical; D011187:Posture; D011300:Preoperative Care; D011829:Radiation Dosage; D017564:Radiation Pneumonitis / Q000209:etiology / Q000517:prevention & control*; D012307:Risk Factors; D013997:Time Factors; D014916:Whole-Body Irradiation