Limited field adaptive radiotherapy for glioblastoma: changes in target volume and organ at risk doses

Abstract

Objective: This study aimed to investigate the tumor volume changes occurring during limited-field radiotherapy (RT) for glioblastoma patients and whether a volume-adapted boost planning approach provided any benefit on tumor coverage and normal tissue sparing. Meterials and Methods: Twenty-four patients underwent simulation with magnetic resonance (MR) and computed tomography (CT) scans prior to RT (MR_initial, CT_initial) and boost treatment (MR_adapt, CT_adapt). For the boost phase, MR_initial and MR_adapt images were used to delineate GTV2 and GTV2_adapt, respectively. An initial boost plan (Plan_initial) created on CT_initial for PTV2 was then reoptimized on CT_adapt by keeping the same optimization and normalization values. Plan_adapt was generated on CT_adapt for PTV2_adapt volume. Dose volume histogram parameters for target volumes and organs-at-risk were compared using these boost plans generated on CT_adapt. Plan_initial and Plan_adaptive boost plans were summed with the first phase plan and the effect on the total dose was investigated. Results: Target volume expansion was noted in 21% of patients while 79% had shrinkage. The average difference for the initial and adaptive gross tumor volume (GTV), clinical target volume (CTV), and planning target volume (PTV) volumes were statistically significant. Maximum dose differences for brainstem and optic chiasm were significant. Healthy brain tissue V10 and ipsilateral optic nerve maximum doses were found to decrease significantly in Plan_adaptive.Conclusion: Results of this study confirm occurrence of target volume changes during RT for glioblastoma patients. An adaptive plan can provide better normal tissue sparing for patients with lesion shrinkage and avoid undercoverage of treatment volumes in case of target volume expansion especially when limited-fields are used.

Adoption of Hybrid MRI-Linac Systems for the Treatment of Brain Tumors: A Systematic Review of the Current Literature Regarding Clinical and Technical Features

“… 93 Indeed, several studies performed in patients that underwent adjuvant RT on conventional linacs demonstrated relevant changes of target volume between post-operative MRIs and planning MRIs 94 , 95 or MRIs performed at the first day of RT 96 – 98 and this could affect CTV definition. 94 Moreover, repeated MRIs performed during RT course invariably resulted in volumetric and/or geometric variations of disease and target volumes 98 – 102 and allowed to improve doses to the OARs 99 , 100 , 102 or to improve target coverage. 99 , 102 Volumetric variation of target volumes was heterogeneous, but in most series the majority of lesions progressively shrinked during radiotherapy 98 – 100 although expansion was consistently reported in a fraction of the cases.…”

“… 94 Moreover, repeated MRIs performed during RT course invariably resulted in volumetric and/or geometric variations of disease and target volumes 98 – 102 and allowed to improve doses to the OARs 99 , 100 , 102 or to improve target coverage. 99 , 102 Volumetric variation of target volumes was heterogeneous, but in most series the majority of lesions progressively shrinked during radiotherapy 98 – 100 although expansion was consistently reported in a fraction of the cases. 98 , 99 , 101 , 102 Adaptive radiotherapy based on serial MRI findings could improve doses to the OARs particularly in case of volume reduction 99 , 101 , 103 and guarantee adequate coverage in case of volumetric increase.…”

“…99,102 Volumetric variation of target volumes was heterogeneous, but in most series the majority of lesions progressively shrinked during radiotherapy [98][99][100] although expansion was consistently reported in a fraction of the cases. 98,99,101,102 Adaptive radiotherapy based on serial MRI findings could improve doses to the OARs particularly in case of volume reduction 99,101,103 and guarantee adequate coverage in case of volumetric increase. 103 An example of volumetric changes during radiotherapy in a glioblastoma patient are represented in Figure 2.…”

Impact of Postoperative Changes in Brain Anatomy on Target Volume Delineation for High-Grade Glioma

“…Yang et al observed better sparing of the OARs if IMRT was replanned with an MRI performed at the end of radiation treatment, mainly due to shrinkage of the resection cavity [31]. Şenkesen et al came to the same conclusions after MRI-based replanning of the boost volume [32]. The subsequent clinical impact and relevance (e.g., regarding treatment-related side effects, local control, and survival) are, however, still unclear.…”