Impact of fraction size on lung radiation toxicity: hypofractionation may be beneficial in dose escalation of radiotherapy for lung cancers.
OBJECTIVE
To assess how fraction size impacts lung radiation toxicity and therapeutic ratio in treatment of lung cancers.


METHODS
The relative damaged volume (RDV) of lung was used as the endpoint in the comparison of various fractionation schemes with the same normalized total dose (NTD) to the tumor. The RDV was computed from the biologically corrected lung dose-volume histogram (DVH), with an alpha/beta ratio of 3 and 10 for lung and tumor, respectively. Two different (linear and S-shaped) local dose-effect models that incorporated the concept of a threshold dose effect with a single parameter D(L50) (dose at 50% local dose effect) were used to convert the DVH into the RDV. The comparison was conducted using four representative DVHs at different NTD and D(L50) values.


RESULTS
The RDV decreased with increasing dose/fraction when the NTD was larger than a critical dose (D(CR)) and increased when the NTD was less than D(CR). The D(CR) was 32-50 Gy and 58-87 Gy for a small tumor (11 cm(3)) for the linear and S-shaped local dose-effect models, respectively, when D(L50) was 20-30 Gy. The D(CR) was 66-97 Gy and 66-99 Gy, respectively, for a large tumor (266 cm(3)). Hypofractionation was preferred for small tumors and higher NTDs, and conventional fractionation was better for large tumors and lower NTDs. Hypofractionation might be beneficial for intermediate-sized tumors when NTD = 80-90 Gy, especially if the D(L50) is small (20 Gy).


CONCLUSIONS
This computational study demonstrated that hypofractionated stereotactic body radiotherapy is a better regimen than conventional fractionation in lung cancer patients with small tumors and high doses, because it generates lower RDV when the tumor NTD is kept unchanged.
Jin
Jin-Yue
JY
Department of Radiation Oncology, Henry Ford Hospital, Detroit, MI 48202, USA. jjin1@hfhs.org
Kong
Feng-Ming
FM
Chetty
Indrin J
IJ
Ajlouni
Munther
M
Ryu
Samuel
S
Ten Haken
Randall
R
Movsas
Benjamin
B
D019583:Dose Fractionation, Radiation; D006801:Humans; D008168:Lung / Q000528:radiation effects*; D008175:Lung Neoplasms / Q000473:pathology / Q000532:radiotherapy* / Q000601:surgery*; D008297:Male; D008954:Models, Biological; D011832:Radiation Injuries / Q000473:pathology* / Q000517:prevention & control; D016634:Radiosurgery; D047368:Tumor Burden