Metachronous medulloblastoma and glioblastoma: Implications for clinical and technical aspects of re-irradiation

Abstract

Glioblastoma Re-irradiation Brainstem tolerance Toxicity a b s t r a c tA seven-year-old male underwent surgical resection and chemoradiation for average risk medulloblastoma; twelve years later, the presence of a necrotic and infiltrative mass in the same area and invading the brainstem prompted a subtotal resection. Pathology was indicative of glioblastoma. He was then treated with concurrent temozolomide and using biologically effective dose calculations for gross residual tumor tissue in the brainstem as well as brainstem tolerance, a radiotherapy dose of 3750 cGy was chosen, fractionated in twice-daily fractions of 125 cGy each. The gross tumor volume was expanded with a 5 mm margin to the planning target volume, which was also judiciously subtracted from the normal brainstem. He completed his radiotherapy course with subsequent imaging free of residual tumor and continued adjuvant temozolomide and remains under followup surveillance. This case underscores the rarity of metachronous medulloblastoma and glioblastoma, of which only five known cases heretofore have been described. We discuss the technicalities of radiotherapy planning in this patient, including common hurdles for radiation oncologists in similar patients. BackgroundMetachronous brain tumors are defined as the development of at least two histologically distinct primary intracranial neoplasms, not related to local recurrence of the initial tumor. novo tumor. 1 Sometimes, the development of a second primary brain tumor is a result of previous radiation, especially in pediatric patients. 2,3 The presence of certain risk factors, such as familial cancer syndromes, may increase the chance of developing secondary neoplasms after radiotherapy. 4 While many radiation-induced intracranial neoplasms have been reported within fifteen years of radiotherapy, 2,3 http://dx

Circulating tumour DNA from the cerebrospinal fluid allows the characterisation and monitoring of medulloblastoma

“…Biopsies are rarely performed at relapse and the absence of data about the tumour characteristics may challenge the selection of effective second-line therapeutic strategies. In addition, studies comparing primary versus relapse tumours have shown that other mutations can arise in the recurrent tumour and that secondary tumours can be completely different from the primary tumour [11][12][13][14] . In this study, we have shown that WES of CSF ctDNA can characterise the disease at relapse, including the detection of CSF-private mutations that reveal the intratumour/interlesion heterogeneity.…”

“…The comparison of primary and relapsed tumours has shown that specific molecular alterations can appear in the relapse setting 10 , 11 . In addition, secondary radiotherapy-induced tumours can emerge in some patients 12 – 14 . To assess metastatic dissemination, cerebrospinal fluid (CSF) cytology together with brain and spinal MRI are performed and patients are classified according to Chang M-staging system 15 .…”

The Role of CyberKnife Stereotactic Radiosurgery in Recurrent Cranial Medulloblastomas across Pediatric and Adult Populations

“…The biologically effective dose (BED) was calculated using the linear-quadratic (LQ) model with a α/β ratio of 3 Gy, following established methods outlined in previous studies [11,12]. BED values were subsequently converted to SFED and equivalent total doses in 2-Gy fractions (EQD2) using LQ model [13].…”

The Role of CyberKnife Stereotactic Radiosurgery in Recurrent Cranial Medulloblastomas across Pediatric and Adult Populations

“…The biologically effective dose (BED) was calculated using the linear-quadratic (LQ) model with a α/β ratio of 3 Gy [11,12]. The BED was converted to SFED and the equivalent total doses in 2-Gy fractions (EQD2) using LQ model [13].…”