Hippocampal avoidance with volumetric modulated arc therapy in melanoma brain metastases – the first Australian experience

Abstract

PurposeVolumetric modulated arc therapy (VMAT) can deliver intensity modulated radiotherapy (IMRT) like dose distributions in a short time; this allows the expansion of IMRT treatments to palliative situations like brain metastases (BMs). VMAT can deliver whole brain radiotherapy (WBRT) with hippocampal avoidance and a simultaneous integrated boost (SIB) to achieve stereotactic radiotherapy (SRT) for BMs. This study is an audit of our experience in the treatment of brain metastases with VMAT in our institution.Methods and materialsMetastases were volumetrically contoured on fused diagnostic gadolinium enhanced T1 weighted MRI/planning CT images. Risk organs included hippocampus, optic nerve, optic chiasm, eye, and brain stem. The hippocampi were contoured manually as one paired organ with assistance from a neuroradiologist. WBRT and SIB were integrated into a single plan.ResultsThirty patients with 73 BMs were treated between March 2010 and February 2012 with VMAT. Mean follow up time was 3.5 months. For 26 patients, BMs arose from primary melanoma and for the remaining four patients from non-small cell lung cancer (n= 2), primary breast cancer, and sarcoma. Mean age was 60 years. The male to female ratio was 2:1. Five patients were treated without hippocampal avoidance (HA) intent. The median WBRT dose was 31 Gy with a median SIB dose for BMs of 50 Gy, given over a median of 15 fractions. Mean values for BMs were as follows: GTV = 6.9 cc, PTV = 13.3 cc, conformity index = 8.6, homogeneity index = 1.06. Mean and maximum hippocampus dose was 20.4 Gy, and 32.4 Gy, respectively, in patients treated with HA intent. Mean VMAT treatment time from beam on to beam off for one fraction was 3.43 minutes, which compared to WBRT time of 1.3 minutes. Twenty out of 25 assessable lesions at the time of analysis were controlled. Treatment was well tolerated; grade 4 toxicity was reported in one patient. The median overall survival was 9.40 monthsConclusionsVMAT for BMs is feasible, safe and associated with a similar survival times and toxicities to conventional SRT+/−WBRT. The advantage of VMAT is that WBRT and SRT can be delivered at the same time on one machine.

Potential for reduced radiation‐induced toxicity using intensity‐modulated arc therapy for whole‐brain radiotherapy with hippocampal sparing

“…Both planning techniques were able to achieve adequate whole‐brain coverage and radiosurgical quality of dose distributions to each of the brain metastases and spared hippocampi. A study by Awad et al (26) presented clinical data on hippocampus sparing for WBRT patients using VMAT with SIB for brain metastases from primarily melanoma origin. In their institution, 30 patients with 73 brain tumors were treated with VMAT.…”

Tomotherapy and Brain Metastases: Towards the Neuroanatomical Target Theory

“…The dose to the region of the hippocampus may delay or reduce neurocognitive deterioration [16,18], giving higher doses to the macroscopic metastases should progression of intracranial disease. We think this goal is achievable adopting Tomo-Therapy with WBRT-HS/SIB (our proposed schedule).We started a Phase II randomized trial of comparison between WBRT and WBRT-HS/SIB in oligometastatic patients to elucidate the real benefit of the new technique in this setting.…”

“…This hypothesis has therefore prompted several researchers to investigate the selective avoidance of certain brain areas. The impairment of learning, memory, and motor coordination seem to be linked to irradiation of the hippocampus [16][17][18][19][20]. Despite the fact that these functions are located in different brain areas, the pathogenetic hypothesis of these changes can be attributed to radiation damage suffered by the progenitor cells that are in the sub-granular zone of the hippocampus.…”

Left hippocampus sparing whole brain radiotherapy (WBRT): A planning study

“…Many planning studies have shown the dosimetric feasibility of hippocampus avoiding (HA) WBRT in different clinical situations using many different radiotherapy systems and techniques [2][3][4][5] . However, these studies must be considered as experimental until well designed clinical trials with appropriate endpoints definitely reveal the significant clinical benefit of these novel approaches 2,6 .…”