Assuntos
Países em Desenvolvimento , Saúde Global , Acessibilidade aos Serviços de Saúde , Radioterapia (Especialidade) , África Subsaariana , Equipamentos e Provisões/economia , Saúde Global/normas , Acessibilidade aos Serviços de Saúde/organização & administração , Acessibilidade aos Serviços de Saúde/normas , Admissão e Escalonamento de Pessoal , Radioterapia (Especialidade)/educação , Radioterapia (Especialidade)/organização & administração , Radioterapia (Especialidade)/normas , Radioterapia/instrumentação , Radioterapia/normasRESUMO
BACKGROUND: Central nervous system (CNS) injury is a rare complication of radiation therapy for pediatric brain tumors, but its incidence with proton radiation therapy (PRT) is less well defined. Increased linear energy transfer (LET) and relative biological effectiveness (RBE) at the distal end of proton beams may influence this risk. We report the incidence of CNS injury in medulloblastoma patients treated with PRT and investigate correlations with LET and RBE values. METHODS AND MATERIALS: We reviewed 111 consecutive patients treated with PRT for medulloblastoma between 2002 and 2011 and selected patients with clinical symptoms of CNS injury. Magnetic resonance imaging (MRI) findings for all patients were contoured on original planning scans (treatment change areas [TCA]). Dose and LET distributions were calculated for the treated plans using Monte Carlo system. RBE values were estimated based on LET-based published models. RESULTS: At a median follow-up of 4.2 years, the 5-year cumulative incidence of CNS injury was 3.6% for any grade and 2.7% for grade 3+. Three of 4 symptomatic patients were treated with a whole posterior fossa boost. Eight of 10 defined TCAs had higher LET values than the target but statistically nonsignificant differences in RBE values (P=.12). CONCLUSIONS: Central nervous system and brainstem injury incidence for PRT in this series is similar to that reported for photon radiation therapy. The risk of CNS injury was higher for whole posterior fossa boost than for involved field. Although no clear correlation with RBE values was found, numbers were small and additional investigation is warranted to better determine the relationship between injury and LET.
Assuntos
Tronco Encefálico/efeitos da radiação , Neoplasias Cerebelares/radioterapia , Irradiação Craniana/efeitos adversos , Meduloblastoma/radioterapia , Terapia com Prótons/efeitos adversos , Lesões por Radiação/epidemiologia , Medula Espinal/efeitos da radiação , Adolescente , Tronco Encefálico/diagnóstico por imagem , Neoplasias Cerebelares/tratamento farmacológico , Cerebelo/efeitos da radiação , Vértebras Cervicais , Criança , Pré-Escolar , Estudos de Coortes , Irradiação Craniana/métodos , Feminino , Seguimentos , Humanos , Incidência , Transferência Linear de Energia , Espectroscopia de Ressonância Magnética , Masculino , Meduloblastoma/tratamento farmacológico , Método de Monte Carlo , Tratamentos com Preservação do Órgão/efeitos adversos , Tratamentos com Preservação do Órgão/métodos , Terapia com Prótons/métodos , Lesões por Radiação/diagnóstico , Lesões por Radiação/diagnóstico por imagem , Radiografia , Dosagem Radioterapêutica , Eficiência Biológica Relativa , Fatores de Tempo , Adulto JovemRESUMO
PURPOSE: The pattern of failure in medulloblastoma patients treated with proton radiation therapy is unknown. For this increasingly used modality, it is important to ensure that outcomes are comparable to those in modern photon series. It has been suggested this pattern may differ from photons because of variations in linear energy transfer (LET) and relative biological effectiveness (RBE). In addition, the use of matching fields for delivery of craniospinal irradiation (CSI) may influence patterns of relapse. Here we report the patterns of failure after the use of protons, compare it to that in the available photon literature, and determine the LET and RBE values in areas of recurrence. METHODS AND MATERIALS: Retrospective review of patients with medulloblastoma treated with proton radiation therapy at Massachusetts General Hospital (MGH) between 2002 and 2011. We documented the locations of first relapse. Discrete failures were contoured on the original planning computed tomography scan. Monte Carlo calculation methods were used to estimate the proton LET distribution. Models were used to estimate RBE values based on the LET distributions. RESULTS: A total of 109 patients were followed for a median of 38.8 months (range, 1.4-119.2 months). Of the patients, 16 experienced relapse. Relapse involved the supratentorial compartment (n=8), spinal compartment (n=11), and posterior fossa (n=5). Eleven failures were isolated to a single compartment; 6 failures in the spine, 4 failures in the supratentorium, and 1 failure in the posterior fossa. The remaining patients had multiple sites of disease. One isolated spinal failure occurred at the spinal junction of 2 fields. None of the 70 patients treated with an involved-field-only boost failed in the posterior fossa outside of the tumor bed. We found no correlation between Monte Carlo-calculated LET distribution and regions of recurrence. CONCLUSIONS: The most common site of failure in patients treated with protons for medulloblastoma was outside of the posterior fossa. The most common site for isolated local failure was the spine. We recommend consideration of spinal imaging in follow-up and careful attention to dose distribution in the spinal junction regions. Development of techniques that do not require field matching may be of benefit. We did not identify a direct correlation between lower LET values and recurrence in medulloblastoma patients treated with proton therapy. Patterns of failure do not appear to differ from those in patients treated with photon therapy.