Reirradiation of Recurrent Pediatric Brain Tumors after Initial Proton Therapy

The use of reirradiation for recurrent pediatric brain tumors has been increasing, but the effect of repeat radiation on critical cranial structures is unknown.

Between July 2009 and May 2013, the records of 12 pediatric patients initially treated with proton therapy and then with reirradiation for recurrent brain tumors were retrospectively reviewed for toxicity and outcomes. Initial and repeat radiation dose distributions were deformed and merged to determine the maximum dose to 0.03 cm³ of the optic chiasm, optic nerves, spinal cord, brainstem, cochleae, pituitary, and uninvolved brain, and to 1 cm³ of the brainstem and brain on individual and composite plans. These dosimetric results were compared with auditory, neurocognitive, ophthalmologic, and endocrine outcomes to identify radiation-associated toxicities.

Median follow-up was 3.5 years from diagnosis. Median ages at initial and repeat radiation were 4.6 and 6.7 years, respectively. All patients initially received proton radiotherapy to a median tumor dose of 55.8 Gy relative biological effectiveness (RBE) (range, 45 to 60 Gy [RBE]). At progression, patients completed a second course of radiation to local fields (n = 7) or the craniospinal axis (n = 5) with a median tumor dose of 40 Gy (RBE) (range, 20 to 54 Gy [RBE]). Median progression-free survival was 22.7 months from the last day of the second radiation course. No patient developed central nervous system necrosis requiring treatment. Of evaluable patients, none developed radiation-related high-grade hearing loss (n = 11), visual pathway deficit (n = 10), or significant change in pre- and post-reirradiation full-scale intelligence quotient (n = 4). Of 11 evaluable patients, 4 (36.4%) developed secondary hypothyroidism and 1 (9.1%) developed growth hormone deficiency.

Repeat radiation for recurrent brain tumors after proton therapy may be performed in the pediatric population with acceptable short- and long-term toxicity.