Clinical investigation
Brain
Intensity-modulated radiotherapy in high-grade gliomas: Clinical and dosimetric results

Presented at the 40th Annual Meeting of the American Society of Clinical Oncology, New Orleans, Louisiana, June 5–8, 2004.
https://doi.org/10.1016/j.ijrobp.2005.05.067Get rights and content

Purpose: To report preliminary clinical and dosimetric data from intensity-modulated radiotherapy (IMRT) for malignant gliomas.

Methods and Materials: Fifty-eight consecutive high-grade gliomas were treated between January 2001 and December 2003 with dynamic multileaf collimator IMRT, planned with the inverse approach. A dose of 59.4–60 Gy at 1.8–2.0 Gy per fraction was delivered. A total of three to five noncoplanar beams were used to cover at least 95% of the target volume with the prescription isodose line. Glioblastoma accounted for 70% of the cases, and anaplastic oligodendroglioma histology (pure or mixed) was seen in 15% of the cases. Surgery consisted of biopsy only in 26% of the patients, and 80% received adjuvant chemotherapy.

Results: With a median follow-up of 24 months, 85% of the patients have relapsed. The median progression-free survival time for anaplastic astrocytoma and glioblastoma histology was 5.6 and 2.5 months, respectively. The overall survival time for anaplastic glioma and glioblastoma was 36 and 9 months, respectively. Ninety-six percent of the recurrences were local. No Grade IV/V late neurologic toxicities were noted. A comparative dosimetric analysis revealed that regardless of tumor location, IMRT did not significantly improve target coverage compared with three-dimensional planning. However, IMRT resulted in a decreased maximum dose to the spinal cord, optic nerves, and eye by 16%, 7%, and 15%, respectively, owing to its improved dose conformality. The mean brainstem dose also decreased by 7%. Intensity-modulated radiotherapy delivered with a limited number of beams did not result in an increased dose to the normal brain.

Conclusions: It is unlikely that IMRT will improve local control in high-grade gliomas without further dose escalation compared with conventional radiotherapy. However, it might result in decreased late toxicities associated with radiotherapy.

Introduction

The combination of surgery, radiotherapy, and chemotherapy represents the standard approach to the treatment of malignant gliomas. However, survival remains poor. The median survival time with conventional therapy for patients with glioblastoma multiforme is 10–12 months, with a 3-year survival rate of 6–8% (1). The median survival time for patients with anaplastic astrocytoma is 36 months, and the 3-year survival rate is approximately 50%. The pattern of recurrence in high-grade gliomas is almost always local (2). The inability to deliver adequate radiation to the target volume often has been cited as the cause for local failure (3).

Radiation treatment planning for gliomas can be challenging. The goal of treatment planning is to spare the critical structures while delivering the complete prescription dose to the target volume. The tumor often lies in close proximity or surrounds several radiosensitive normal tissues, including the eyes, optic nerves, chiasm, brainstem, and spinal cord. The tolerance of these tissues is less than the desired prescription dose, and the associated morbidity can be severe. Any effort to decrease the treatment toxicity might result in compromised target coverage with conventional therapy, thus increasing the risk of local recurrence.

Intensity-modulated radiotherapy (IMRT) is a more advanced form of three-dimensional conformal radiotherapy (3D-CRT) that relies on advanced accelerator and multileaf collimator technology to deliver nonuniform beam intensities. This approach has been demonstrated to improve tumor coverage while decreasing the dose to critical structures in the head and neck and other sites (4, 5). At present there is very little clinical or dosimetric data regarding the dose distribution and outcomes from IMRT in the treatment of malignant gliomas (6). This retrospective analysis presents the preliminary data on the potential benefits of IMRT in high-grade gliomas.

Section snippets

Methods and materials

Fifty-eight consecutive patients with high-grade gliomas received radiotherapy with IMRT between January 2001 and December 2003 at Memorial Sloan-Kettering Cancer Center (MSKCC). Institutional review board approval was obtained for retrospective review of the data. Patient characteristics are shown in Table 1. Glioblastoma accounted for 70% of the cases. Anaplastic astrocytoma and anaplastic oligodendroglioma histology (pure or mixed) constituted 15% each of the cases. Surgery was limited to

Results

With a median follow-up of 24 months (range, 12–48 months), 49 of the 58 patients (85%) have relapsed. Forty-seven (96%) of the recurrences were local. Of the remaining 2 patients, 1 recurred in a different lobe of the brain outside the radiated region, whereas the other had a leptomeningeal relapse.

Discussion

There has been a dramatic improvement in radiotherapy techniques over the last 2 decades. Improvements in dose distribution and local control have been observed with 3D-CRT as compared with conventional two-dimensional treatment planning for prostate cancer and subsequently for other tumor locations (9, 10). It has also been shown that the morbidity of therapy decreased with the use of 3D-CRT compared with conventional treatment planning (11). Furthermore, IMRT has been shown to improve the

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    Intensity-modulated radiotherapy (IMRT) is an option that has not been validated [84]. Its value in terms of survival has not yet been demonstrated [85,86] but it is used in trials to evaluate the protective effect on healthy tissue without necessarily improving local control rates or as an option to increase the dose within the tumour (hypofractionation, concomitant boost) with or without the use of functional imaging (PET, multimodal MRI) to improve local control [9,15,50–54]. Although quality of life studies must be associated with its use [87].

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