Posterior fossa boost in medulloblastoma: an analysis of dose to surrounding structures using 3-dimensional (conformal) radiotherapy

Relapsed Medulloblastoma in Pre-Irradiated Patients: Current Practice for Diagnostics and Treatment

Relapsed medulloblastoma (rMB) accounts for a considerable, and disproportionate amount of childhood cancer deaths. Recent advances have gone someway to characterising disease biology at relapse including second malignancies that often cannot be distinguished from relapse on imaging alone. Furthermore, there are now multiple international early-phase trials exploring drug-target matches across a range of high-risk/relapsed paediatric tumours. Despite these advances, treatment at relapse in pre-irradiated patients is typically non-curative and focuses on providing life-prolonging and symptom-modifying care that is tailored to the needs and wishes of the individual and their family. Here, we describe the current understanding of prognostic factors at disease relapse such as principal molecular group, adverse molecular biology, and timing of relapse. We provide an overview of the clinical diagnostic process including signs and symptoms, staging investigations, and molecular pathology, followed by a summary of treatment modalities and considerations. Finally, we summarise future directions to progress understanding of treatment resistance and the biological mechanisms underpinning early therapy-refractory and relapsed disease. These initiatives include development of comprehensive and collaborative molecular profiling approaches at relapse, liquid biopsies such as cerebrospinal fluid (CSF) as a biomarker of minimal residual disease (MRD), modelling strategies, and the use of primary tumour material for real-time drug screening approaches.

Toxicity Reduction after Craniospinal Irradiation via Helical Tomotherapy in Patients with Medulloblastoma: A Unicentric Retrospective Analysis

Objectives: Recent trials with craniospinal irradiation (CSI) via helical Tomotherapy (HT) demonstrated encouraging medulloblastoma results. In this study, we assess the toxicity profile of different radiation techniques and estimate survival rates. Materials and Methods: We reviewed the records of 46 patients who underwent irradiation for medulloblastoma between 1999 and 2019 (27 conventional radiotherapy technique (CRT) and 19 HT). Patient, tumor, and treatment characteristics, as well as treatment outcomes-local control rate (LCR), event-free survival (EFS), and overall survival (OS)-were reviewed. Acute and late adverse events (AEs) were evaluated according to the Radiation Therapy Oncology Group and the European Organization for Research and Treatment of Cancer (RTOG/EORTC) criteria. Results: In total, 43 courses of CSI and three local RT were administered to the 46 patients: 30 were male, the median age was 7 years (range 1-56). A median total RT dose of 55 Gy (range 44-68) and a median CSI dose of 35 Gy (range, 23.4-40) was delivered. During follow-up (median, 99 months), six patients (13%) developed recurrence. The EFS rate after 5 years was 84%. The overall OS rates after 5 and 10 years were 95% and 88%, respectively. There were no treatment-related deaths. Following HT, a trend towards lower grade 2/3 acute upper gastrointestinal (p = 0.07) and subacute CNS (p = 0.05) toxicity rates was detected compared to CRT-group. The risk of late CNS toxicities, mainly grade 2/3, was significantly lower following HT technique (p = 0.003). Conclusion: CSI via HT is an efficacious treatment modality in medulloblastoma patients. In all, we detected a reduced rate of several acute, subacute, and chronic toxicities following HT compared to CRT.

Impact of radiation technique, radiation fraction dose, and total cisplatin dose on hearing : Retrospective analysis of 29 medulloblastoma patients

PURPOSE

To analyze the incidence and degree of sensorineural hearing loss (SNHL) resulting from different radiation techniques, fractionation dose, mean cochlear radiation dose (D_mean), and total cisplatin dose.

MATERIAL AND METHODS

In all, 29 children with medulloblastoma (58 ears) with subclinical pretreatment hearing thresholds participated. Radiotherapy (RT) and cisplatin had been applied sequentially according to the HIT MED Guidance. Audiological outcomes up to the latest follow-up (median 2.6 years) were compared.

RESULTS

Bilateral high-frequency SNHL was observed in 26 patients (90%). No significant differences were found in mean hearing threshold between left and right ears at any frequency. A significantly better audiological outcome (p < 0.05) was found after tomotherapy at the 6 kHz bone-conduction threshold (BCT) and left-sided 8 kHz air-conduction threshold (ACT) than after a combined radiotherapy technique (CT). Fraction dose was not found to have any impact on the incidence, degree, and time-to-onset of SNHL. Patients treated with CT had a greater risk of SNHL at high frequencies than tomotherapy patients even though D_mean was similar. Increase in severity of SNHL was seen when the total cisplatin dose reached above 210 mg/m², with the highest abnormal level found 8-12 months after RT regardless of radiation technique or fraction dose.

CONCLUSION

The cochlear radiation dose should be kept as low as possible in patients who receive simultaneous cisplatin-based chemotherapy. The risk of clinically relevant HL was shown when D_mean exceeds 45 Gy independent of radiation technique or radiation regime. Cisplatin ototoxicity was shown to have a dose-dependent effect on bilateral SNHL, which was more pronounced in higher frequencies.

Quantitative Analysis of Three-dimensional Conformal Radiotherapy Techniques for Posterior Fossa Treatment in Children

Numerous beam directions using 3-D conformal techniques can be employed in treating tumors in the posterior fossa, each with characteristic normal tissue exposure along the entrance and exit trajectory. A representative variety of beam configurations were modeled in a modern computer planning system initially with the entire posterior fossa as the target. These beams were quantitatively scored using criteria based on integral doses for both low dose and high dose effects encompassing a variety of critical normal structures, thus identifying strengths and weaknesses of each beam. By blocking portions of a particular beam accounting for unfavorable scores, a map of “zones” within the posterior fossa ideally treated by a certain beam or beams could be constructed. No universally ideal photon beam arrangement for the entire posterior fossa target could be identified. However, using single beam analysis, the strengths and weaknesses of particular strategies could be quantified. For example, vertex beams treating the cerebellar hemispheres allow the greatest sparing of cochlea and hypothalamus but at the cost of increased low to moderate dose to the supratentorial brain. Using the constructed maps identifying “zones” appropriately treated by a given beam or beams, three-dimensional conformal treatment plans with favorable dose-volume statistics can be designed based on previously defined normal tissue tolerance considerations. It is shown how this approach can be individualized based on specific patient characteristics (e.g., age). We conclude that radiotherapy directed to the posterior fossa can be optimized based on systematic assessment of individual beam contributions to normal tissues. This technique allows fast selection of treatment beams based on known normal tissue anatomical and tolerance information. Further studies will be required regarding long term effects of various radiation doses on specific volumes of normal tissue in order to individualize beam selection. When treating children, knowledgeable consideration of these beam characteristics can help avoid late effects.

A comparison of the doses received by normal cranial tissues during different simple model conventional radiotherapeutic approaches to pituitary tumours

This aim of this study was to compare the doses received by critical cranial organs when three different radiation techniques were used to treat pituitary tumours. Cranial computed tomography scans of a RANDO phantom and 30 patients were used for pituitary macroadenoma radiotherapy treatment planning. For each slice, target volumes and other critical organs were contoured and three techniques were applied: (A) two parallel-opposed lateral fields, (B) two oblique fields (45°) in coronal plane and (C) two parallel-opposed lateral and anterior fields while the head was tilted 45° in the sagittal plane. The doses received by the target volume and the critical organs for each technique were calculated for all patients. Irradiation was repeated three times for each technique. Finally, the doses that reached the organs of interest resulting from these techniques were compared. The dose delivered to the temporal lobes was 105, 9 and 72 % of the prescribed dose using techniques A, B and C, respectively. The dose received by the cochlea was the lowest in technique C (27 % of prescribed dose) compared with techniques A (79 %) and B (48 %). All techniques delivered 100 % of the prescribed dose to the chiasma. Technique A increased the dose to temporal lobes and the cochlea to such an extent that they exceeded the tolerance dose. Technique B spared the temporal lobes better than technique C; however, technique C was preferred since the dose received by the cochlea in this case was the lowest of all techniques. None of the techniques spared the chiasma.

Cognitive Sparing during the Administration of Whole Brain Radiotherapy and Prophylactic Cranial Irradiation: Current Concepts and Approaches

Whole brain radiotherapy (WBRT) for the palliation of metastases, or as prophylaxis to prevent intracranial metastases, can be associated with subacute and late decline in memory and other cognitive functions. Moreover, these changes are often increased in both frequency and severity when cranial irradiation is combined with the use of systemic or intrathecal chemotherapy. Approaches to preventing or reducing this toxicity include the use of stereotactic radiosurgery (SRS) instead of WBRT; dose reduction for PCI; exclusion of the limbic circuit, hippocampal formation, and/or neural stem cell regions of the brain during radiotherapy; avoidance of intrathecal and/or systemic chemotherapy during radiotherapy; the use of high-dose, systemic chemotherapy in lieu of WBRT. This review discusses these concepts in detail as well as providing both neuroanatomic and radiobiologic background relevant to these issues.

The potential impact of tumour biology on improved clinical practice for medulloblastoma: progress towards biologically driven clinical trials

Medulloblastoma is the most common malignant brain tumour of childhood and accounts for around 10% of all childhood cancer deaths. Despite recent improvements in survival rates, the delivery of individualised therapies based on disease-risk remains a major goal; intensified treatment for poor-risk disease, whilst reducing therapy for favourable-risk cases, with the overall aim of maximising survival whilst minimising late effects. Current clinical indices for the prediction of disease course are imprecise, however a series of molecular and histopathological biomarkers have been identified recently, which may allow a more accurate prediction of disease outcome (e.g., beta-catenin status as a favourable-risk marker, MYC gene amplification and large-cell histology as high-risk markers). Pan-European clinical trials being planned for medulloblastoma by the SIOP Brain tumour group will assess the stratification of patients using molecular and histological biomarkers, alongside clinical indices, to select favourable, standard and high-risk treatment groups. This selection will underpin two concurrent trials; PNET 5, which will test whether treatment can be reduced for a favourable-risk disease sub-group, with the aim of maintaining survival rates while reducing late-effects, and PNET 6, which will aim to improve survival rates in the standard-risk group. The implementation of these trials presents important new logistical challenges within routine practice, involving (i) the development of quality-controlled sample collection and handling systems across multiple treatment centres, including the mandatory ascertainment of fresh-frozen tumour material, and (ii) the delivery of standardised central biomarker analysis and histopathological review, within the approximately 30-day post-surgical window, prior to the selection and commencement of adjuvant therapy. Feasibility studies to establish these systems are underway across SIOP Europe national groups. Their success will require a coordinated approach by the entire multidisciplinary team, including neurosurgeons, oncologists and neuropathologists, with the common aim of facilitating targeted delivery of individualised risk-adapted therapies for children with medulloblastoma.

Normal tissue tolerance for high-grade gliomas: is it an issue?

In this article, we address the currently accepted dose tolerance parameters for the treatment of high-grade gliomas. The issue of normal tissue tolerance is becoming increasingly important because of the long-term survival of a significant subset of young, good performance status patients and the use of hypofractionated regimens for elderly patients with poor performance status. In addition, we address relevant clinical endpoints including clinical, pathologic, and radiographic changes and highlight the difficulty in discriminating between tumor-related and treatment-related effects. Finally, we review relevant clinical trials addressing issues of dose and/or volume parameters. Future trials for patients with high-grade gliomas should consider the inclusion of a prospective evaluation of neurocognitive function and imaging correlates of the brain to assist in the prediction, prevention, and treatment of radiation-induced damage of normal brain tissue.

Pediatric medulloblastoma: toxicity of current treatment and potential role of protontherapy

Post-operative craniospinal irradiation and systemic chemotherapy are both necessary in the treatment of pediatric medulloblastoma. Late toxicity is a major problem in long term survivors and significantly affects their quality of life. We have systematically reviewed the literature to examine data on late toxicity, specifically focusing on: endocrine function, growth and bone development, neurocognitive development, second cancers, ototoxicity, gynecological toxicity and health of the offspring, cardiac toxicity and pulmonary toxicity. In this paper, we describe qualitatively the kind of detected side effects and, whenever possible, try to assess their incidence and the relative role of craniospinal irradiation (as opposed to other treatments and to the disease itself) in producing them. Subsequently we examine the possible approach to reduce unwanted effects from craniospinal irradiation to target and non-target tissues and we consider briefly the role of hyperfractionation, tomotherapy and IMRT. We describe the characteristics of protontherapy and its potential for non-target tissues toxicity reduction reviewing the existing physical and dosimetric studies and the (still very limited) clinical experiences. Finally we propose intensity modulated spot scanning protontherapy with multiportal simultaneous optimization (IMPT) as a possible tool for dose distribution optimization within different areas of CNS and potential reduction of target tissues toxicity.

Advanced-technology radiation therapy for bone sarcomas

BACKGROUND

Bone sarcomas are rare primary tumors. Radiation therapy (RT) can be useful in securing local control in cases where negative surgical margins cannot be obtained or where tumors are not resected. Recent technical advances in RT offer the opportunity to deliver radiation to these tumors with higher precision, thus allowing higher doses to the tumor target with lower doses to critical normal tissues, which can improve local tumor control and/or reduce treatment-related morbidity.

METHODS

The authors conducted a survey of recent technical developments that have been applied to the RT for bone sarcomas.

RESULTS

RT techniques that show promise include intensity-modulated photon radiation therapy, 3-D conformal proton RT, intensity-modulated proton RT, heavy charged-particle RT, intraoperative RT, and brachytherapy. All of these techniques permit the delivery of higher radiation doses to the target and less dose to normal tissue than had been possible with conventional 3-D conformal radiation techniques. Protons deliver substantially less dose to normal tissues than photons.

CONCLUSIONS

Data from clinical studies using these advanced radiation techniques suggest that they can improve the therapeutic ratio (the ratio of local control efficacy to the risk of complications). This is expected to improve the treatment outcome for these challenging tumors.

What is the best adjuvant treatment for very young patients with medulloblastoma?

The standard treatment for medulloblastoma is surgery followed by adjuvant chemotherapy and external beam radiotherapy to the craniospinal axis and posterior fossa. However, in very young children, craniospinal irradiation has a more significant detrimental effect in terms of neurocognitive function and growth. This article reviews the different strategies used for very young patients with medulloblastoma.

Patterns of failure in children with medulloblastoma treated with 3D conformal radiotherapy

BACKGROUND AND PURPOSE

Craniospinal irradiation for medulloblastoma is one of the most complex techniques employed in radiotherapy. Many reports stress the impact of irradiation quality on survival in these patients. Our report presents the outcome and patterns of failure for 95 patients treated with 3D conformal radiotherapy (3D-CRT).

MATERIALS AND METHODS

From 1998 to 2003, 95 children with medulloblastoma received 3D conformal radiotherapy. All of them were previously treated with surgery and chemotherapy. The brain and upper spinal cord were treated with two lateral 6MV photon fields. In four patients, the cribriform plate was irradiated by the additional field. For primary tumour bed we applied two or three photon beams. Spinal cord was irradiated either with 18-20MeV electron fields or with a mixed beam.

RESULTS

With a median follow-up of 48 months, 32/95 patients suffered a multifocal (21) or isolated (11) recurrence. We evaluated every primary site of failure. In all patients, the recurrence appeared within the isodose level of 95-100%.

CONCLUSIONS

Patterns of failure in medulloblastoma patients treated with 3D conformal radiotherapy indicated that the relapse was mainly associated with poor response to pre-irradiation chemotherapy. We believe that 3D conformal radiotherapy allows avoiding failures, related to radiotherapy uncertainties.

Craniospinal irradiation using a forward planned segmented field technique

Craniospinal irradiation is technically demanding due to the complex shape of the planning target volume (PTV). Radiotherapy treatment techniques have evolved over time as imaging and radiotherapy treatment technology have improved. However, most are variations on a class solution utilizing a prone patient position with two shaped lateral cranial portals and a matched posterior spinal portal with moving junctions. Major areas of difficulty remain with the accurate definition of the PTV and achieving a homogeneous dose within it, especially at the junctions. We describe a three-dimensionally (3D) planned craniospinal radiation technique that permits rapid image acquisition with reduced localization time, simplified spinal PTV definition and standardized cranial PTV definition. Improved dose homogeneity within the PTV is achieved by use of a segmented "field-in-field" technique (forward planned intensity-modulated radiotherapy (IMRT)) in place of customized compensators. This has negated the requirement for constructing physical compensators. Autosequencing for field delivery enables the junction to be "moved" during a single fraction and reduces the overall treatment time, an important consideration when treating very young patients.

Technology insight: Proton beam radiotherapy for treatment in pediatric brain tumors

Tumors of the central nervous system are the most common solid tumor in childhood. Treatment options for childhood brain tumors include radiation therapy, surgery and chemotherapy, often given in combination. Radiation therapy regularly has a pivotal role in treatment, and technological advancements during the past quarter of a century have dramatically improved the ability to deliver radiation in a more focused manner. Improvements in imaging and computing ability led to better targeting of tumor tissue using conventional X-ray therapy. These advances have been harnessed for proton radiation therapy. Proton radiotherapy has special physical characteristics that allow normal tissues to be spared better than even the most conformal photon radiation, and it will reduce the complications from treatment. This review discusses the characteristics of proton radiation, and describes examples of pediatric brain tumor patients who would benefit most from this form of treatment.

White Matter Lesions Detected by Magnetic Resonance Imaging After Radiotherapy and High-Dose Chemotherapy in Children With Medulloblastoma or Primitive Neuroectodermal Tumor

Purpose

White matter lesions (WMLs) have been described as a delayed effect of cranial irradiation in children with brain tumors, or a transient subacute effect characterized by an intralesional or perilesional reaction. We report the occurrence of subacute WMLs detected by magnetic resonance imaging (MRI) in children treated for medulloblastoma or primitive neuroectodermal tumor (PNET) and document the associated clinical, radiologic, and neurocognitive findings.

Patients and Methods

Among 134 patients with medulloblastoma or supratentorial PNET treated prospectively with risk-adjusted craniospinal irradiation and conformal boost to the tumor bed, followed by four high-dose chemotherapy (HDC) cycles with stem-cell rescue, 22 developed WMLs on T1-weighted imaging with and without contrast and/or T2-weighted imaging on MRI. Patients had ≥ 12 months of follow-up. Neurocognitive assessments included intelligence quotient (IQ) tests and tests of academic achievement.

Results

Twenty-two patients developed WMLs at a median of 7.8 months after starting therapy (range, 1.9 to 13.0 months). Lesions were predominantly in the pons (n = 8) and cerebellum (n = 6). Sixteen patients (73%) had WML resolution at a median of 6.2 months (range, 1.68 to 23.5 months) after onset; two patients developed necrosis and atrophy. Three developed persistent neurologic deficits. Cumulative incidence of WMLs at 1 year was 15% ± 3%. Patients with WMLs had a significant decline in estimated IQ (−2.5 per year; P = .03) and math (−4.5 per year; P = .003) scores.

Conclusion

WMLs in medulloblastoma or PNET patients treated with conformal radiotherapy and HDC are typically transient and asymptomatic, and may mimic early tumor recurrence. A minority of patients with WMLs develop permanent neurologic deficits and imaging changes. Overall, the presence of WMLs is associated with greater neurocognitive decline.

A comparison of conventional, conformal and intensity-modulated coplanar radiotherapy plans for posterior fossa treatment

Radiotherapy of the posterior fossa for medulloblastoma treatment can induce ototoxicity, especially when combined with cisplatin chemotherapy. Sensorineural hearing loss can be severe enough to cause permanent disability, which may compromise cognitive development in paediatric patients. This study evaluates the sparing of the cochlea in conventional radiotherapy, three-dimensional conformal radiotherapy (3D-CRT), and intensity-modulated radiotherapy (IMRT). CT scans of three patients were used to plan posterior fossa radiotherapy using coplanar beam arrangements. The posterior fossa and the cochlea were contoured as well as other organs-at-risk (non-posterior fossa brain, lenses, optic nerves, pituitary and cervical spinal cord). Three treatment plans were compared: conventional two-dimensional treatment (parallel-opposed lateral pair); 3D-CRT (two wedged posterior oblique fields); and a four-field coplanar IMRT plan. 3D-CRT and IMRT reduced cochlear doses to less than 70% of the mean target dose. These plans also reduced dose to the non-posterior fossa brain and cervical spinal cord. IMRT showed no advantage over 3D-CRT in sparing the optic nerves and lenses, compared with 3D-CRT. Normal tissue doses were higher in both conformal techniques than in the IMRT plans. Conformal techniques reduced the dose to the cochlea, non-posterior fossa brain and cervical spinal cord. The small size and proximity to the planning target volume (PTV) of the cochlea limited the effectiveness of the IMRT plan. Coplanar 3D-CRT was judged superior to coplanar IMRT, particularly in children, because it achieved adequate sparing of the cochlea and anterior cranial structures, such as the lenses and optic nerves, without compromising the dose to the posterior fossa.

Radiotherapy-induced thyroid disorders

Despite their specific functional consequences, radiotherapy-induced thyroid abnormalities remain under-estimated and underreported. These sequelae may include primary or central hypothyroidism, thyroiditis, Graves' disease, euthyroid Graves' ophthalmopathy, benign adenomas, multinodular goitre and radiation-induced thyroid carcinoma. Primary hypothyroidism, the most common radiation-induced thyroid dysfunction, affects 20-30% of patients administered following curative radiotherapy to the neck region, with approximately half of the events occurring within the first 5 years after therapy. The relative risk of radiation-induced cancer (mainly well-differentiated tumours) is 15-53-fold higher than in non-irradiated population. The aetiology of radiation-induced thyroid injury includes vascular damage, parenchymal cell damage and auto-immune reactions. Total radiotherapy dose, irradiated volume of the thyroid gland, and the extent of prior thyroid resection are among the most important factors associated with the risk of hypothyroidism. The contribution of other treatment modalities (chemotherapy, endocrine therapy) as well as patient- and tumour-related factors is less clear. Reduction in radiation dose to the thyroid gland and hypothalamic/pituitary complex should be attempted whenever possible. New radiotherapy techniques, such as stereotactic radiosurgery, three-dimensional conformal irradiation, intensity modulated radiotherapy and proton therapy allow generally better dose distribution with lower dose to the non-target organs. The diagnostic approach to thyroid radiation injury includes baseline thyroid function assays in all patients undergoing thyroid or parasellar irradiation. Recommended follow-up procedures include at least annual evaluation with a history for symptoms of thyroid dysfunction, clinical examination, and measurement of thyroid hormones and thyrotropin. Management of overt hypothyroidism is based on hormone replacement therapy. Thyroid hormone therapy is also recommended in cases of subclinical hypothyroidism. Treatment of other radiation-induced thyroid disorders (thyroiditis, Graves' disease, thyroid cancer) is similar to that employed in spontaneously occurring conditions. Further improvements in radiotherapy techniques and progress in endocrine diagnostics and therapy may allow better prevention and management of radiation-related thyroid injury.

Advantage of protons compared to conventional X-ray or IMRT in the treatment of a pediatric patient with medulloblastoma

PURPOSE

To compare treatment plans from standard photon therapy to intensity modulated X-rays (IMRT) and protons for craniospinal axis irradiation and posterior fossa boost in a patient with medulloblastoma.

METHODS

Proton planning was accomplished using an in-house 3D planning system. IMRT plans were developed using the KonRad treatment planning system with 6-MV photons.

RESULTS

Substantial normal-tissue dose sparing was realized with IMRT and proton treatment of the posterior fossa and spinal column. For example, the dose to 90% of the cochlea was reduced from 101.2% of the prescribed posterior fossa boost dose from conventional X-rays to 33.4% and 2.4% from IMRT and protons, respectively. Dose to 50% of the heart volume was reduced from 72.2% for conventional X-rays to 29.5% for IMRT and 0.5% for protons. Long-term toxicity with emphasis on hearing and endocrine and cardiac function should be substantially improved secondary to nontarget tissue sparing achieved with protons.

CONCLUSION

The present study clearly demonstrates the advantage of conformal radiation methods for the treatment of posterior fossa and spinal column in children with medulloblastoma, when compared to conventional X-rays. Of the two conformal treatment methods evaluated, protons were found to be superior to IMRT.

Radiotherapy-induced ear toxicity

Despite their particular functional consequences, radiotherapy-induced ear injuries remain under-evaluated and under-reported. These reactions may have acute or late character, may affect all structures of the hearing organ, and result in conductive, sensorineural or mixed hearing loss. Up to 40% of patients have acute middle ear side effects during radical irradiation including acoustic structures and about one-third of patients develop late sensorineural hearing loss (SNHL). Total radiotherapy dose and tumour site seem to be among the most important factors associated with the risk of hearing impairment. Thus, reduction in radiation dose to the auditory structures should be attempted whenever possible. New radiotherapy techniques (3-dimensional conformal irradiation, intensity modulated radiotherapy, proton therapy) allow better dose distribution with lower dose to the non-target organs. Treatment of acute and late external otitis is mainly conservative and includes the anti-inflammatory agents (applied topically and systematically). Post-radiation chronic otitis media and the eustachian tube pathology may be managed with tympanic membrane incision with insertion of a tympanostomy tube (grommet), although the benefit of such approach is controversial and some authors advocate a more conservative approach. In these patients the functional deficit can be alleviated by application of bone conduction hearing aids such as, e.g., the bone anchored hearing aid (BAHA). There is no standard therapy for post-irradiation sudden or progressive SNHL yet corticosteroid therapy, rheologic medications, hyperbaric oxygen or carbogen therapy are usually employed (as for idiopathic SNHL), although controversial data on the efficacy of these treatment modalities have been published. In selected cases with bilateral profound hearing loss or total deafness, cochlear implants may prove effective. Further improvements in radiotherapy techniques and progress in otologic diagnostics and therapy may allow better prevention and management of radiation-related acoustic injury.

Patterns of failure using a conformal radiation therapy tumor bed boost for medulloblastoma

PURPOSE

To assess the patterns of failure for patients with medulloblastoma receiving a conformal tumor bed boost rather than a boost to the entire posterior fossa.

PATIENTS AND METHODS

From 1994 to 2002, 32 consecutive patients with newly diagnosed medulloblastoma treated at Memorial Sloan-Kettering Cancer Center (New York, NY) received a conformal boost to the tumor bed in conjunction with craniospinal radiation therapy. Twenty-eight patients also received chemotherapy. The median age was 9 years (range, 3 to 34 years), and the male to female ratio was 3:1. Twenty-seven patients had standard-risk disease, and five patients had high-risk disease. Craniospinal doses ranged from 23.4 to 39.6 Gy, and total tumor bed doses ranged from 54 to 59.4 Gy.

RESULTS

With a median follow-up of 56 months, six patients have relapsed; five relapsed outside of the posterior fossa, and one failed within the posterior fossa, outside of the high-dose boost volume. Five-year actuarial disease-free and overall survival rates were 84% and 85%, respectively. Freedom from posterior fossa failure was 100% and 86% at 5 and 10 years, respectively. Freedom from distant failure was 84% at 5 years, with a trend for improvement when full-dose craniospinal radiation (36 to 39.6 Gy) was used compared with a reduced dose (23.4 Gy) of radiation (100% v 63%, respectively; P =.06). No other predictive variables were identified.

CONCLUSION

Conformal treatment to the tumor bed allows for significant sparing of critical structures. The posterior fossa failure rate in this series is similar to that reported when the entire posterior fossa is treated. This approach should be investigated further in a phase III trial.

Stereotactic conformal radiotherapy for posterior fossa tumours: a modelling study for potential improvement in therapeutic ratio

PURPOSE

To investigate the optimal technique of stereotactic conformal radiotherapy (SCRT) for posterior fossa tumours.

MATERIAL AND METHODS

SCRT planning image data sets of four patients with posterior fossa tumours constituted the study material. Based on the operative notes and preoperative imaging, a clinical target volume (CTV) was drawn for each patient. An additional CTV representative of a typical posterior fossa tumour was also drawn on each patient's localisation scans. Therefore a total of eight CTVs differing in their size and location were used for further work. A margin of 5 mm was grown in three dimensions to result in a final planning target volume (PTV). Beam arrangements studied were conformal bilateral parallel pair, a three-field coplanar arrangement with two bilateral and a vertex beam, two three-field non-coplanar techniques and a six-field non-coplanar technique with conformation achieved by micromultileaf collimator (mMLC). Normal structures contoured included normal posterior fossa brain (excluding PTV), brain stem, cochleae, optic apparatus, pituitary-hypothalamic axis (PHA), supratentorial brain and the temporal lobes. Comparative evaluation of plans was done with dose volume histograms (DVH), conformity index (CI) and dose heterogeneity (DH).

RESULTS

In all plans, the 95% isodose line covered at least 99% of the PTV with acceptable dose heterogeneity. As compared to the baseline bilateral conformal parallel pair plan, all other plans achieved significantly more sparing of the normal posterior fossa brain at the 95 and 80% dose prescription levels with superior CI (at 95% isodose). The six-field technique resulted in maximum sparing as compared to the bilateral plan with a mean additional sparing of 74% (46.2 cm3) and 55% (33.83) at 95 and 80% dose prescription level, respectively (P<0.0001). Among the three field plans, the technique of bilateral and vertex fields resulted in least doses to cochlea and also irradiated the least volume of brain stem and PHA. Comparison of this technique to the six-field technique did not show any significant difference in sparing of normal structures in the posteriorly placed tumours. In anteriorly placed tumours, the six-field technique was the most optimal irrespective of the size of the target volumes.

CONCLUSIONS

A six-field plan SCRT achieves the most significant sparing of the normal tissues for localised irradiation in posterior fossa tumours, particularly for anteriorly located tumours. A relatively simpler three-field plan with bilateral and a vertex beam is equally good for tumours that are placed posteriorly and away from the brain stem.

Intensity-modulated radiation therapy in the treatment of children

Intensity-modulated radiation therapy (IMRT) is a relatively new method of conformal radiotherapy delivery that is rapidly being incorporated in clinical practice. Of all patients treated with conformal techniques, children are the most likely to benefit as normal, developing structures can be minimized in the radiation field. The advantages of IMRT, including increased conformality and possible dose escalation, are discussed in this review. Possible disadvantages of IMRT in children are also discussed, such as lack of dose homogeneity in the target volume, increased dose to nontarget tissues, reliability of treatment setup, increased anesthesia time in younger children, and prolonged treatment planning. The issue of increased risk of second malignancy in this very young population is important, as many of these children will be long-term survivors with current multimodality therapy.

Results of three-dimensional stereotactically-guided radiotherapy in recurrent medulloblastoma

PURPOSE

To evaluate survival rates and side effects after stereotactically-guided radiotherapy (SRT) in patients with recurrent medulloblastoma of the brain.

METHODS AND MATERIALS

Between 1992 and 2000, 20 patients with 29 radiological manifestations were treated with fractionated SRT (n = 21) or radiosurgery (n = 8). Median age was 16 years with 6 patients < or = 14 years. All patients had prior cranio-spinal radiotherapy plus boost to the posterior fossa with a total dose of 54 Gy. Time to recurrence was 33 months mean. Eighteen of the 29 lesions were located within the boost volume. Chemotherapy was given according to current international study protocols (HIT) in all patients. Mean total dose for re-irradiation was 24 Gy for fractionated stereotactically-guided radiotherapy, and 15 Gy for radiosurgery. Mean follow-up was 88.5 months.

RESULTS

Overall local control was 89.7%. Thirteen recurrences showed partial or complete response in CT/MR-imaging, 13 showed stable disease. Local tumor progression was seen 5 months mean after radiotherapy in three cases. A multifocal intracranial progression was seen in 9 patients, 5 patients developed additional spinal metastases. Thirteen patients died with disseminated cranio-spinal progression, after 72.6 months median. No late toxicity > CTC II(o) especially no brain radionecrosis was seen after radiotherapy.

CONCLUSION

SRT is effective and safe in the treatment of recurrent medulloblastoma to improve local control without evident side effects. The main problem remains the control of subclinical cranio-spinal dissemination.

Intensity-modulated radiation therapy for pediatric medulloblastoma: early report on the reduction of ototoxicity

PURPOSE

The combination of cisplatin chemotherapy and radiation therapy for the treatment of medulloblastoma has been shown to cause significant ototoxicity, impairing a child's cognitive function and quality of life. Our purpose is to determine whether the new conformal technique of intensity-modulated radiation therapy (IMRT) can achieve lower rates of hearing loss by decreasing the radiation dose delivered to the cochlea and eighth cranial nerve (auditory apparatus).

PATIENTS AND METHODS

Twenty-six pediatric patients treated for medulloblastoma were retrospectively divided into two groups that received either conventional radiotherapy (Conventional-RT Group) or IMRT (IMRT Group). One hundred thirteen pure-tone audiograms were evaluated retrospectively, and hearing function was graded on a scale of 0 to 4 according to the Pediatric Oncology Group's toxicity criteria. Statistical analysis comparing the rates of ototoxicity was performed using Fisher's exact test with two-tailed analysis.

RESULTS

When compared to conventional radiotherapy, IMRT delivered 68% of the radiation dose to the auditory apparatus (mean dose: 36.7 vs. 54.2 Gy). Audiometric evaluation showed that mean decibel hearing thresholds of the IMRT Group were lower at every frequency compared to those of the Conventional-RT Group, despite having higher cumulative doses of cisplatin. The overall incidence of ototoxicity was lower in the IMRT Group. Thirteen percent of the IMRT Group had Grade 3 or 4 hearing loss, compared to 64% of the Conventional-RT Group (p < 0.014).

CONCLUSION

The conformal technique of IMRT delivered much lower doses of radiation to the auditory apparatus, while still delivering full doses to the desired target volume. Our findings suggest that, despite higher doses of cisplatin, and despite radiotherapy before cisplatin therapy, treatment with IMRT can achieve a lower rate of hearing loss.

Conformal radiotherapy for brain tumors

The technical improvements of three-dimensional conformal radiotherapy can decrease the toxicity of brain treatment to acceptable levels. The adoption of the technique by more centers would allow for the potential advantages of three-dimensional radiotherapy to be employed in a greater number of patients. Further studies evaluating the use of three-dimensional conformal radiotherapy in patients with nervous system neoplasms should focus on determining the effects on quality of life for the patient and survival compared with more standard treatment techniques.

Three-dimensional conformal radiation treatment planning and delivery for low- and intermediate-grade gliomas

Three-Dimensional conformal radiation treatment (3D-CRT) planning and delivery is an external beam radiation therapy modality that has the general goal of conforming the shape of a prescribed dose volume to the shape of a 3-dimensional target volume, simultaneously limiting dose to critical normal structures. 3-Dimensional conformal therapy should include at least one volumetric imaging study of the patient. This image should be obtained in the treatment position for visualizing the target and normal anatomic structures that are potentially within the irradiated volume. Most often, computed tomography (CT) and/or magnetic resonance imaging (MRI) are used; however, recently, other imaging modalities such as functional MRI, MR spectroscopy, and positron emission tomography (PET) scans have been used to visualize the clinically relevant volumes. This article will address the clinically relevant issues with regard to low- and intermediate-grade gliomas and the role of 3D-CRT planning. Specific issues that will be addressed will include normal tissue tolerance, target definition, treatment field design in regard to isodose curves and dose-volume histograms, and immobilization.

The local field in infratentorial ependymoma: does the entire posterior fossa need to be treated?

INTRODUCTION

In the past decade, there have been multiple reports indicating that the predominant problem in the curative treatment of intracranial ependymoma is local failure. As a result, many have recommended local field radiotherapy. For infratentorial ependymoma, there is controversy regarding what constitutes the local field. Some radiation oncologists advocate coverage of the entire posterior fossa, whereas others recommend radiotherapy to the tumor bed and a safety margin.

METHODS AND MATERIALS

From 1984 to 1998, 28 patients with posterior fossa ependymoma were diagnosed at our institution. There were 18 males and 10 females with a median age of 12 years (range, 2-81 years). Four patients (14%) had high-grade ependymoma and 3 (11%) had M+ disease at initial diagnosis. Gross total resection was achieved in 17 (61%) and postoperative radiotherapy (RT) was given to 22 (77%). Radiotherapy fields were craniospinal in 10, whole brain in 1, posterior fossa in 2, and tumor bed with a 2-cm. margin in 9. Median dose to the primary site was 54 Gy (range, 45-55 Gy). All 4 patients with high-grade ependymoma received craniospinal RT. Six patients did not receive RT after surgery. Magnetic resonance imaging (MRI) or computed tomography (CT) scans of the brain at initial diagnosis were compared to MRI or CT scans of patients at relapse to determine if the local relapse was in the tumor bed or nontumor bed posterior fossa. Median follow-up was 127 months (range, 14-188 months).

RESULTS

Six patients have relapsed. For the 11 patients who had craniospinal or whole brain radiotherapy (RT), 3 recurred (tumor bed 1, spine 1, nontumor bed posterior fossa + spine 1). Both patients who failed in the spine had high-grade tumors. Neither of the 2 treated with posterior fossa fields relapsed. For the 9 patients who had tumor bed RT alone and the 6 who did not receive RT, there were 3 relapses; all were in the tumor bed. There were no relapses in the nontumor bed posterior fossa.

CONCLUSION

For nondisseminated, low-grade infratentorial ependymoma, the radiotherapy volume does not need to include the entire posterior fossa. This information can be used to minimize late effects of RT in the era of three-dimensional (conformal) radiotherapy. No conclusion can be reached regarding the appropriate local field for high-grade infratentorial ependymoma because of the small number of patients.