Retreatment tolerance of the spinal cord

Re-irradiation for recurrent/progressive pediatric brain tumors: from radiobiology to clinical outcomes

INTRODUCTION

Brain tumors are the most common solid tumors in children. Neurosurgical excision, radiotherapy, and/or chemotherapy represent the standard of care in most histopathological types of pediatric central nervous system (CNS) tumors. Even though the successful cure rate is reasonable, some patients may develop recurrence locally or within the neuroaxis.

AREA COVERED

The management of these recurrences is not easy; however, significant advances in neurosurgery, radiation techniques, radiobiology, and the introduction of newer biological therapies, have improved the results of their salvage treatment. In many cases, salvage re-irradiation is feasible and has achieved encouraging results. The results of re-irradiation depend upon several factors. These factors include tumor type, extent of the second surgery, tumor volume, location of the recurrence, time that elapses between the initial treatment, the combination with other treatment agents, relapse, and the initial response to radiotherapy.

EXPERT OPINION

Reviewing the radiobiological basis and clinical outcome of pediatric brain re-irradiation revealed that re-irradiation is safe, feasible, and indicated for recurrent/progressive different tumor types such as; ependymoma, medulloblastoma, diffuse intrinsic pontine glioma (DIPG) and glioblastoma. It is now considered part of the treatment armamentarium for these patients. The challenges and clinical results in treating recurrent pediatric brain tumors were highly documented.

Management of locally recurrent nasopharyngeal carcinoma

As a consequence of the current excellent loco-regional control rates attained using the generally accepted treatment paradigms involving intensity-modulated radiotherapy for nasopharyngeal carcinoma (NPC), only 10-20% of patients will suffer from local and/or nodal recurrence after primary treatment. Early detection of recurrence is important as localized recurrent disease is still potentially salvageable, but this treatment often incurs a high risk of major toxicities. Due to the possibility of radio-resistance of tumors which persist or recur despite adequate prior irradiation and the limited tolerance of adjacent normal tissues to sustain further additional treatment, the management of local failures remains one of the greatest challenges in this disease. Both surgical approaches for radical resection and specialized re-irradiation modalities have been explored. Unfortunately, available data are based on retrospective studies, and the majority of them are based on a small number of patients or relatively short follow-up. In this article, we will review the different salvage treatment options and associated prognostic factors for each of them. We will also propose a treatment algorithm based on the latest available evidence and discuss the future directions of treatment for locally recurrent NPC.

Reirradiation of Recurrent Pediatric Brain Tumors after Initial Proton Therapy

PURPOSE

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

METHODS AND MATERIALS

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.

RESULTS

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.

CONCLUSION

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

Adjuvant radiotherapy delays recurrence following subtotal resection of spinal cord ependymomas

BACKGROUND

Ependymoma is the most common glial tumor of the adult spinal cord. Current consensus recommends surgical resection with gross total resection (GTR) whenever possible. We performed a comprehensive review of the literature to evaluate whether adjuvant radiotherapy after subtotal resection (STR) has any benefit.

METHODS

A PubMed search was performed to identify adult patients with spinal cord ependymoma who underwent surgical resection. Only patients who had clearly defined extent of resection with or without adjuvant radiotherapy were included for analysis. Kaplan-Meier and multivariate Cox regression survival analyses were performed to determine the effects of adjuvant radiotherapy on progression-free survival (PFS) and overall survival (OS).

RESULTS

A total of 348 patients underwent surgical resection of spinal cord ependymomas, where GTR was obtained in 77.0% (268/348) of patients. Among those who received STR, 58.8% (47/80) received adjuvant radiotherapy. PFS was significantly prolonged among those who received adjuvant radiotherapy after STR (log rank; P < .001). This prolonged PFS with adjuvant radiotherapy remained significant in multivariate Cox regression analysis (STR versus STR + RT group; hazard ratio (HR) = 2.26, P = .047). By contrast, improved OS was only associated with GTR (GTR versus STR + RT group; HR = 0.07, P = .001) and benign ependymomas (HR = 0.16, P = .001).

CONCLUSIONS

Surgery remains the mainstay treatment for spinal cord ependymomas, where GTR provides optimal outcomes with longest PFS and OS. Adjuvant radiotherapy prolongs PFS after STR significantly, and OS is improved by GTR and benign tumor grade only.

Nasopharyngeal carcinoma: salvage of local recurrence

Local control of nasopharyngeal carcinoma has substantially improved with advancing radiotherapy technology and appropriate combination with chemotherapy. However, when local recurrence occurs, this is one of the most difficult challenges. Aggressive treatment is indicated because long term salvage is achievable particularly for early recurrence, but high risk of complications is a serious concern. Treatment options include different methods of surgery and/or re-irradiation with/without chemotherapy. Available information in the literature is grossly inadequate; most reports compose of small series of highly selected patients with heterogeneous characteristics and treatment. No randomized trials have been performed to evaluate the therapeutic ratio of different treatment methods. This article reviews available treatment options, their therapeutic benefits and risks of complications; the objective is to provide information for developing treatment recommendations and suggestions for future improvement.

Ependymomas of the adult: molecular biology and treatment

PURPOSE OF REVIEW

To review state of art and relevant advances in the molecular biology and management of ependymomas of the adult.

RECENT FINDINGS

Ependymomas of the adult are uncommon neoplasms of the central nervous system, and may occur either in the brain or the spinal cord. Compared with intracranial ependymomas, spinal ependymomas are less frequent and exhibit a better prognosis. Studies performed on genetic changes in ependymoma provide some insight into the pathogenesis and prognostic markers and yield new therapeutic targets, particularly focused on signal transduction modulators. The majority of studies have shown a major impact of extent of resection; thus, a complete resection must be performed, whenever possible, at first surgery or at reoperation. Involved field radiotherapy is recommended for anaplastic or incompletely resected grade II tumors. Craniospinal irradiation is reserved for metastatic disease. Chemotherapy is not advocated as primary treatment, and is best utilized as salvage treatment for patients failing surgery and radiotherapy.

SUMMARY

Owing to the rarity of the disease, the literature regarding ependymomas in adults is scarce and limited to retrospective series. Thus, the level of evidence regarding therapeutic strategies is low and universally accepted guidelines are lacking. Molecular biology studies suggest some potential new therapeutic targets.

Long term outcome with post-operative radiation therapy for spinal canal ependymoma

PURPOSE

A retrospective study was performed to evaluate the long term efficacy and safety of post-operative radiation therapy in the management of spinal canal ependymoma at our institution.

METHODS AND MATERIALS

Between 1954 and 1997, 22 patients with spinal canal ependymoma were treated with post-operative radiotherapy at our institution. The median age at diagnosis was 34.7 years (range 9.8-56.1 years). All patients underwent open biopsy with histologic diagnosis: 13 patients (59%) had ependymoma (WHO Grade II) and 9 patients (41%) had myxopapillary ependymoma (WHO Grade I). The median tumor size was 4.0 cm (range 1.5-15.0 cm). Twenty patients received subtotal resection and 2 patients received gross-total resection. Median radiation dose was 45.0 Gy.

RESULTS

The median follow up for surviving patients was 11.4 years (range 0.6-37.0 years). An 80% progression-free-survival (PFS) was observed for all patients at 5-, 10- and 15-year endpoints. All recurrences were within 3 years of treatment. The 5-, 10- and 15-year overall-survivals (OS) for all patients were 85%, 78% and 64%, respectively. Patients with tumors larger than 6.0 cm at time of presentation demonstrated 5- and 10-year PFS of 58.3% compared to 92.3% for patients with tumors 6.0 cm or smaller (P = 0.047). There was no significant correlation between tumor size and OS.

CONCLUSIONS

Post-operative radiation after subtotal resection is safe and offers durable tumor control and long term patient survival.

Postoperative Radiosurgery for Malignant Spinal Tumors

OBJECTIVE:

Although, as a primary therapy, radiosurgery for spinal tumors is becoming more common in clinical practice and is associated with encouraging clinical results, we wanted to evaluate outcomes after radiosurgery in a series of postoperative patients.

METHODS:

We examined the medical records of 18 postoperative patients who received radiosurgical treatment to their residual spinal tumors: metastatic carcinoma (10), sarcoma (3), multiple myeloma/plasmacytoma (4), and giant cell tumor (1). Marginal radiosurgical doses ranged from 6 to 16 Gy (mean, 11.4 Gy) prescribed to the 90% isodose line. All regions of the spine received treatment: 2 cervical, 15 thoracic, and 1 lumbosacral. The volume of irradiated spinal elements receiving 30, 50, and 80% of the total dose ranged from 0.51 to 11.05, 0.19 to 6.34, and 0.06 to 1.73 cm3, respectively. Treatment sessions (i.e., patient in to patient out of the room) varied between 20 and 40 minutes. Follow-up ranged from 4 to 36 months (median, 7 mo).

RESULTS:

Even though significant doses of radiation were delivered to all regions of the spinal cord and nerve roots coincidentally involved in the treatments, only one patient in this series developed progressive symptoms possibly attributable to a toxic effect of the radiosurgery. Of those patients initially presenting with neurological deficits, 92% either remained neurologically stable or improved.

CONCLUSION:

Our observations suggest that radiosurgery as prescribed in this series of postoperative patients with residual spinal tumor is well-tolerated and associated with little to no significant morbidity.

Prophylactic hyperbaric oxygen treatment and rat spinal cord re-irradiation

Normal tissue injury may lead to severe, life threatening, late side effects after therapeutic use of irradiation. Neurological complications caused by radiation of the spinal cord are ascribed to progressive, irreversible damage to the vasculature. Hyperbaric oxygen (HBO) is known to induce angiogenesis in irradiated tissue and has been proven to reduce late radiation injury in several normal tissues when applied during the latent period before complications become manifest. In the present study: (1). the prophylactic potential of HBO; (2). optimal timing of HBO therapy after spinal cord irradiation, i.e. during the latent period; and (3). effect of HBO on the re-irradiation tolerance of the spinal cord were investigated. The rat cervical spinal cord was locally X-ray irradiated with ten fractions of 6.5 Gy in 11 days. Five treatment groups (n=10) included: irradiation alone and irradiation followed by 30 HBO treatments (100% oxygen at 240 kPa for 90 min) during latency, with HBO starting either immediately, 5, 10 or 15 weeks after the primary irradiation course. One year after the primary treatment, the same spinal cord volume was re-irradiated with 20 Gy single dose. During life span, the animals were observed on the incidence of myelitis and the duration of the latent period. The actuarial analysis revealed no significant difference in neurological complications free survival between the irradiation alone and the irradiation+HBO treatment groups. A tendency towards radiosensitization was found in the group in which the primary irradiation course was immediately followed by the HBO treatment course. The data show that HBO applied during the latent period of progressively developing irradiation damage to the spinal cord does not increase the re-irradiation tolerance of this tissue.

Radiation myelitis following allogeneic stem cell transplantation and consolidation radiotherapy for non-Hodgkin's lymphoma

Myelitis is a rare but well documented complication of therapeutic radiation exposure to the spinal cord and is characterized by delayed development of paresthesias, sensory changes and, in severe cases, progressive paresis and paralysis. Although accepted radiation tolerance limits for the spinal cord have successfully limited the incidence of this problem (45-50 Gy, in daily 1.8-2 Gy fractions), aggressive systemic therapy may render patients more susceptible to radiation-related neurotoxicity. We describe the case of a 38-year-old man with refractory non-Hodgkin's lymphoma who underwent matched sibling peripheral blood stem cell transplant following a conditioning regimen of cyclophosphamide (60 mg/kg x 2) and total body irradiation (120 cGy x 11). This was followed by delivery of 30.6 Gy involved-field radiation at 1.8 Gy/day to the mediastinum and left supraclavicular fossa for bulky residual tumor. Although maximum cumulative radiation dose to the spinal cord was less than 45 Gy, the patient subsequently developed progressive lower extremity weakness and MRI abnormalities of the spinal cord limited to the radiation field. This represents the second report in the literature of this unexpected complication, prompting a need to re-examine current guidelines for radiotherapy in the context of high-dose systemic treatment.

Radiation therapy and the management of intramedullary spinal cord tumors

The use of radiation therapy in the management of intramedullary spinal cord tumors remains controversial. Several studies indicate that the use of postoperative radiation therapy modestly improves both local control and survival in spinal cord ependymomas and astrocytomas. Modern treatment planning and imaging allow more accurate target definition and respect for related normal tissue tolerances.

Total biological effect on late reactive tissues following reirradiation for recurrent nasopharyngeal carcinoma

PURPOSE

To assess the additional damage of normal tissues attributable to reirradiation and the magnitude of partial recovery following the initial course.

METHODS AND MATERIALS

Symptomatic late complication rates (excluding xerostomia) in 3635 patients receiving one course (Group 1) and 487 patients receiving two courses of external radiotherapy (Group 2) for nasopharyngeal carcinoma were retrospectively analyzed and compared.

RESULTS

Group 2 had significantly lower actuarial complication-free survival rates than Group 1: 48% versus 81% at 5 years. The post-retreatment incidence was significantly affected by biologically effective dose (BED) (assuming an alpha/beta ratio of 3 Gy) of the first course: hazard ratio (HR) = 1.04 per Gy(3) (p = 0.01), but only marginally by that of the second course: HR = 1.01 per Gy(3) (p = 0.06). If the summated BED was taken as the dose unit, it was estimated that a total BED of 143 Gy(3) would induce a 20% incidence at 5 years, while the corresponding dose projected from Group 1 was 111 Gy(3). The gap effect was insignificant in the overall analyses, but a trend of decreasing risk with increasing interval was observed in patients with gap > or = 2 years: HR = 0.86 per year (p = 0.07).

CONCLUSION

The major determinant of post-retreatment complication is the severity of damage during the initial course. The sum of total doses tolerated is higher than that expected with a single-course treatment, suggesting occurrence of partial recovery (particularly in those reirradiated after an interval of 2 years or more).