Ganglioglioma

Abstract

Ganglioglioma is a mixed tumor of glial and neuronal cells that occurs predominantly in the pediatric and young adult population. These tumors classically occur in the temporal lobes and present with seizures. They are commonly low grade and often managed successfully with surgery alone. Indications for radiotherapy include higher-grade tumor (grade 3) or lower-grade tumor (grade 1 or 2) with multiple recurrences. Treatment planning is similar to that of other low-grade gliomas, and stereotactic techniques are generally used to minimize the setup error given the intention of minimizing brain exposure to radiation in this population that generally has a long survival.

10.1 General Principles of Simulation and Target Delineation (Table 10.1)

• Information on simulation

  • Recommended imaging

    • Preoperative as well as postoperative imaging should be obtained.

    • Imaging sequences should include at least T1, T1 with contrast, T2, and FLAIR. Consideration to obtaining either susceptibility-weighted imaging, T2 gradient recalled echo, or T2 star as these sequences can be helpful in delineating the operative bed and distinguishing blood products from residual disease.

  • Patient positioning

    • Supine positioning and immobilization with a short aquaplast mask is recommended. The use of photon vs. proton radiotherapy may dictate head position or the need for other special setup devices like table-associated range shifter, etc.

• Recommendations for target delineation (Figs. 10.1 and 10.2)

  • Imaging sequences and special circumstances

    • The T1 and T1 contrast-enhanced studies are most useful for delineation of the operative bed and determining if residual disease is present. Most high-grade gangliogliomas will enhance with contrast on T1, while low-grade gangliogliomas may only partially enhance or not enhance at all. T2 imaging is useful for delineating the operative bed as it highlights the presence of cerebrospinal fluid within the cavity, while susceptibility-weighted imaging may illustrate regions that the surgeon explored intraoperatively which are not apparent after review of the operative report or the T1 contrast-enhanced study.

  • On treatment imaging

    • Most gliomas can exhibit pseudo-progression which may occur during therapy. Interval imaging at 1–2 week intervals may be useful when smaller disease volumes are utilized to ensure that a marginal miss or insufficient coverage does not occur during the course of therapy from volumetric changes in the tumor.

Table 10.1 Target volume guidelines

Fig. 10.1

Preoperative tumor volume. Top row: T1 stealth. Bottom row: T1 stealth + contrast. Blue = preoperative tumor volume segmentation

Fig. 10.2

Postoperative treatment volumes. Top row, from right to left: T1 post-contrast, T2, T1 subtraction. Bottom row, from right to left: T2 flair, T2 fast spin echo, CT planning scan. Pink, gross tumor volume; yellow, clinical target volume

10.2 Dose Prescriptions

• Recommended doses for ganglioglioma range from 54 to 59.4 Gy depending on tumor grade and presence of residual disease. Most would favor 59.4 Gy for anaplastic ganglioglioma, while 54 Gy would be considered standard for treatment of low-grade ganglioglioma cases after progression on chemotherapy following resection.

10.3 Treatment Planning Techniques (Table 10.2 and Fig. 10.3)

• Modality

  • Protons or 4–6 MV photons are typically utilized for treatment.

• Treatment technique

  • Treatment technique with photons is highly location-dependent although IMRT is increasingly utilized. 3DCRT may be more favorable in situations where integral dose to the brain is of concern. VMAT may offer improved conformality and reduced treatment delivery times over IMRT; however, this may limit certain noncoplanar beam angles. Stereotactic radiosurgery (SRS) may be appropriate at the time of salvage for small focal recurrences or as a boost for residual disease, where further surgery was not possible. Proton therapy is increasingly favored for its dose fall off at depth and reduced integral dose. There are a wide variety of proton delivery methods (passive scatter, pencil beam scanning—single or multiple field optimization, etc.). Concerns over end of range biologic effects may be less pronounced with pencil beam scanning approaches.

• Representative DVH

Table 10.2 Recommended coverage guidelines and dose constraints

Fig. 10.3

Treatment plan. Isodose lines shown in red, yellow, turquoise, blue, and purple for 100%, 95%, 80%, 50%, and 20%, respectively. Pink, gross tumor volume; yellow, clinical target volume

10.4 Side Effects

• Acute side effects to evaluate during weekly on-treatment visits

  • Hair loss, fatigue, radiation dermatitis, headaches, nausea, seizures

• Late side effects and complications

  • The late effects of focal cranial radiotherapy are highly location-dependent but may include bony hypoplasia, increased soft tissue fibrosis, overlying subcutaneous hypoplasia, endocrine deficits, decline in hearing, neurocognitive and psychological sequelae, vasculopathy, second cancers, necrosis, and decline in vision or cataracts.

• Clinical pearls for addressing those side effects

  • If patients are on steroids at the time of radiotherapy, utilization of gastric prophylaxis (e.g., ranitidine) and evaluation for oral thrush are recommended.

  • Topical water-based lotions are recommended for local application over the treated region following (but not before) treatment, three to four times per day depending on the topical lotion utilized.

  • As gangliogliomas can be epileptogenic, patients generally are on seizure prophylaxis with levetiracetam during radiotherapy. Exacerbation of seizures during radiotherapy may require increase in anti-epileptic doses, additional anti-epileptic, and/or use of steroids.