TITLE:
Dosimetric Improvements Utilising Intensity Modulated Radiation Therapy for Patients with Glioblastoma Multiforme
AUTHORS:
Michael Back, Shaun Clifford, Helen Wheeler, Thomas Eade
KEYWORDS:
Intensity Modulated Radiation Therapy; Glioblastoma; Dosimetry
JOURNAL NAME:
Journal of Cancer Therapy,
Vol.4 No.11A,
December
2,
2013
ABSTRACT: Aims: The EORTC-NCI study investigating the addition
of temozolomide trial to standard radiation therapy has demonstrated improved
duration of survival in patients with Glioblastoma multiforme (GBM). With
longer survival duration, there is the potential for latent RT morbidity, not
previously seen in historical patients. This study evaluates the potential
dosimetric advantages of utilising IMRT over 3D-conformal RT in such patients.
Methods: 10 consecutive patients with GBM formally screened for a clinical
study over a two-month
period were planned and treated with IMRT utilising daily on-board imaging
(OBI). The EORTC protocol dosimetric criteria and constraints were used in
target delineation and planning. For each patient, a 3DCRT plan was also produced.
Endpoints for dosimetric evaluation analysed related to
tumour dose: mean PTV60 dose (mPTV60Dose), Conformity Index (CI); and normal
tissue dose: mean normal brain dose (mBrainDose) and V40 Brain (Brainv40). IGRT
endpoints were the median isocentre shifts required in 3 axes measured in one
direction. The variation between the IMRT and 3DCRT dosimetric endpoints was
examined using Wilcoxon analysis. Results: The 10 patients had tumours located in temporal (3), parietal
(3), occipital (2) and callosal (2) regions. The median PTV and normal brain
volumes were 308.1 cm3 and 1077.5 cm3 respectively. The IMRT dosimetry was significantly improved in all endpoints
specifically CI (p = 0.002), mPTV60Dose (p = 0.004), mBrainDose (p = 0.002) and Brainv40 (p = 0.019). OBI directed isocentre
measurements in the patient group were available for 230 treatments. The median
shifts (and 95% C.I.s)
were 0.1 cm vertical (0.1 - 0.2), 0.1 cm longitudinal (0.1 - 0.2) and 0.2 cm lateral (0.2 - 0.2). At a minimum follow-up of 2 years’ post diagnosis, the median survival
of the group is 18.0 months (95% CI: 13.4 - 22.6 months). Conclusion: IMRT for GBM produces significant dosimetric advantages
in relation to planning target volume and normal tissue dose compared with 3D
conformal plans. The data also confirm the accuracy of IMRT technique for CNS
with IGRT delivery utilising OBI demonstrating minimal deviation from planned
to treated isocentre.