paediatrics Brussels 17

I. J. Radiation Oncology d Biology d Physics

88

Volume 71, Number 1, 2008

additional 3–5 mm to form the planning target volume. All patients were treated with 4- or 6-MV photons. An example of FFRT for lo- cal failure is shown in Fig. 1 , and an example of CSI after metastatic failure and metastasectomy is shown in Fig. 2 . With reference to Table 1 , treatment details for the 6 patients treated with radiosurgery at the time of failure include the following: Patient 1, Gamma Knife, 20 Gy to 50% using 8-mm collimator and one shot; Patient 2, stereo- tactic radiosurgery (SRS), 17.5 Gy to 90% using 25-mm collimator; Patient 3, SRS, 16.5 Gy to 90% using 25-mm collimator; Patient 4, Gamma Knife, 15 Gy to 50% using 8- and 4-mm collimators and six shots; Patient 5, SRS, 18 Gy to 90% using 25-mm collimator; and Patient 6, SRS, 18 Gy to 90% using a 30-mm collimator. Analysis Analysis included descriptive statistics and Kaplan-Meier pro- gression-free survival (PFS) statistics. Results were presented pri- marily with study patients separated into three groups representing those treated at relapse with SRS, FFRT, and CSI, including sequen- tial focal boost treatment of sites of relapse. Definitions Local failure included failure at the primary site with no evidence of metastasis. Metastatic failure included failure at sites not previ- ously involved with tumor with no evidence of recurrence at the pri- mary site. Combined failure included simultaneous local recurrence and metastasis. The RT 1 was defined as the first course of RT, and RT 2 was defined as the second course of RT. Study group Relevant patient information and outcomes are listed in Tables 1, 2, and 3 . The study group included 24 male and 14 female patients with a median age at diagnosis of 2.5 years (range, 0.6–15.0 years), median age at time of RT 1 of 2.7 years (range, 1.1–15.3 years), and median age at time of RT 2 of 4.8 years (range, 2.0–16.9 years). No study patient had evidence of metastatic disease at the time of diagnosis. Eight patients had a supratentorial primary tumor location. Before the initiation of RT 1 , 16 patients underwent chemo- therapy and the extent of resection was recorded as gross total RESULTS

after initial irradiation (the first course of irradiation [RT 1 reirradiation (the second course of irradiation [RT 2 ]), follow-up, and death. Patient sex, extent of resection, tumor grade at initial and subsequent resections, sites of relapse, radiation dose and vol- ume, chemotherapy agents, major toxicities, use of hyperbaric oxy- gen therapy (HBOT), and disease status (no evidence of disease, stable disease, and progressive disease) were recorded. techniques In a nonrandomized manner, patients were offered one of three reirradiation methods: radiosurgery, FFRT, and CSI. Treatment se- lection was driven by treatment era, cumulative experience, and, more recently, patient age. Radiosurgery was considered for some of the earliest patients treated in this series to limit dose to normal tissue. These patients were treated by using conventional irradiation that included substantial normal tissue irradiation. With the ob- served toxicity of radiosurgery, FFRT was explored and found to be tolerable. Considering the very limited volume of normal tissue currently irradiated using three-dimensional treatment techniques and our three-dimensional understanding of the distribution of dose, CSI was explored as a last resort in children with metastatic disease or older patients with local failure, considering their risk of future metastatic failure. The CSI was administered with some modification of the standard technique to patients with metastatic disease and a cohort of patients with local failure. Modifications were limited to patients with a history of previous infratentorial irra- diation, and for the lateral cranial fields, included customized cerro- bend blocking that followed the cranial outline from the temporal bone to the occiput and shielding of the previously irradiated upper cervical spinal that received approximately more than 30% of the previous prescription dose, or about 16.2 Gy. This level of shielding was empirically chosen to limit the combined cord dose to approx- imately 16.2 + 39.6 = 55.8 Gy. All craniospinal treatments were photon based, with dose prescribed at the midplane (cranium) and anterior aspect of the spinal canal (spine). Supplemental treatment of metastatic sites generally included forward-planned conformal RT targeting the tumor and/or tumor bed that was then expanded by a margin of 5 mm to form the planning target volume. Focal frac- tionated irradiation included forward-planned conformal RT in which the gross tumor volume included the tumor and/or tumor bed that was expanded by 5 mm, edited at anatomic boundaries to form a clinical target volume, and then geometrically expanded an ]) and RT 2

Fig. 1. Example of focal reirradiation (second course of radiotherapy [RT 2

]) for ependymoma after prior focal radiation

therapy (RT 1

). The central isodose line (white) represents the prescription dose.