Abstract
PURPOSE: To investigate the appropriate timing of adaptive radiotherapy (ART) for high-grade glioma. METHODS: Ten patients with high-grade gliomas were selected and underwent CT/MRI (CT(1)/MRI(1), CT(2)/MRI(2), CT(3)/MRI(3), and CT(4)/MRI(4)) scans before RT and during 10-, 20- and 30-fraction RT, and the corresponding RT plans (plan(1), plan(2), plan(3) and plan(4)) were made. The dose of the initial plan (plan(1)) was projected to CT2 and CT3 using the image registration technique to obtain the projection plans (plan(1-2) and plan(1-3)) and by superimposing the doses to obtain the ART plans (plan(10+20) and plan(20+10)), respectively. The dosimetric differences in the target volume and organs at risk (OARs) were compared between the projection and adaptive plans. The tumor control probability (TCP) for the planning target volume (PTV) and normal tissue complication probability (NTCP) for the OARs were compared between the two adaptive plans. RESULTS: Compared with the projection plan, the D(2) to the PTV of ART decreased, the conformity index (CI) to the PTV increased, and the D(2)/D(mean) to the brainstem, optic chiasm and pituitary, as well as the V(20), V(30), V(40) and V(50) to the normal brain decreased. The D(2) to the pituitary and optic chiasm as well as the V(20), V(30), V(40) and V(50) to the normal brain in plan(10+20) were lower than those in plan(20+10), while the CI to the PTV was higher than that in plan(20+10). The TCP of the PTV in plan(10+20) was higher than that in plan(20+10). CONCLUSION: ART can improve the precision of target volume irradiation and reduce the irradiation dose to the OARs in high-grade glioma. The time point after 10 fractions of RT is appropriate for ART.