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

Radiotherapy-associated Sensorineural Hearing Loss in Pediatric Oncology Patients

During the radiotherapeutic treatment of pediatric oncology patients, they would be at a latent risk of developing ionizing radiation-induced ototoxicity when the cochlea or auditory nerve is located within the radiation field. Sensorineural hearing loss (SNHL) is an irreversible late complication of radiotherapy, and its incidence depends on various factors such as the patient's hearing sensitivity, total radiation dose to the cochlea, radiotherapy fractionation regimen, age and chemoradiation. Importantly, this complication exhibits serious challenges to adult survivors of childhood cancer, as it has been linked to impairments in academic achievement, psychosocial development, independent living skills, and employment in the survivor population. Therefore, early detection and proper management can alleviate academic, speech, language, social, and psychological morbidity arising from hearing deficits. In the present review, we have addressed issues such as underlying mechanisms of radiation-induced SNHL, audiometric findings of pediatric cancer patients treated with radiotherapy, and management and protection measures against radiation-induced ototoxicity.

Highly Conformal Craniospinal Radiotherapy Techniques Can Underdose the Cranial Clinical Target Volume if Leptomeningeal Extension through Skull Base Exit Foramina is not Contoured

AIMS

Craniospinal irradiation (CSI) remains a crucial treatment for patients with medulloblastoma. There is uncertainty about how to manage meningeal surfaces and cerebrospinal fluid (CSF) that follows cranial nerves exiting skull base foramina. The purpose of this study was to assess plan quality and dose coverage of posterior cranial fossa foramina with both photon and proton therapy.

MATERIALS AND METHODS

We analysed the radiotherapy plans of seven patients treated with CSI for medulloblastoma and primitive neuro-ectodermal tumours and three with ependymoma (total n = 10). Four had been treated with a field-based technique and six with TomoTherapy™. The internal acoustic meatus (IAM), jugular foramen (JF) and hypoglossal canal (HC) were contoured and added to the original treatment clinical target volume (Plan_CTV) to create a Test_CTV. This was grown to a test planning target volume (Test_PTV) for comparison with a Plan_PTV. Using Plan_CTV and Plan_PTV, proton plans were generated for all 10 cases. The following dosimetry data were recorded: conformity (dice similarity coefficient) and homogeneity index (D₂ - D₉₈/D₅₀) as well as median and maximum dose (D_2%) to Plan_PTV, V_95% and minimum dose (D_99.9%) to Plan_CTV and Test_CTV and Plan_PTV and Test_PTV, V_95% and minimum dose (D_98%) to foramina PTVs.

RESULTS

Proton and TomoTherapy™ plans were more conformal (0.87, 0.86) and homogeneous (0.07, 0.04) than field-photon plans (0.79, 0.17). However, field-photon plans covered the IAM, JF and HC PTVs better than proton plans (P = 0.002, 0.004, 0.003, respectively). TomoTherapy™ plans covered the IAM and JF better than proton plans (P = 0.000, 0.002, respectively) but the result for the HC was not significant. Adding foramen CTVs/PTVs made no difference for field plans. The mean D_min dropped 3.4% from Plan_PTV to Test_PTV for TomoTherapy™ (not significant) and 14.8% for protons (P = 0.001).

CONCLUSIONS

Highly conformal CSI techniques may underdose meninges and CSF in the dural reflections of posterior fossa cranial nerves unless these structures are specifically included in the CTV.

Fast imaging employing steady-state acquisition (FIESTA) MRI to investigate cerebrospinal fluid (CSF) within dural reflections of posterior fossa cranial nerves

OBJECTIVE

There is no consensus approach to covering skull base meningeal reflections-and cerebrospinal fluid (CSF) therein-of the posterior fossa cranial nerves (CNs VII-XII) when planning radiotherapy (RT) for medulloblastoma and ependymoma. We sought to determine whether MRI and specifically fast imaging employing steady-state acquisition (FIESTA) sequences can answer this anatomical question and guide RT planning.

METHODS

96 posterior fossa FIESTA sequences were reviewed. Following exclusions, measurements were made on the following scans for each foramen respectively (left, right); internal acoustic meatus (IAM) (86, 84), jugular foramen (JF) (83, 85) and hypoglossal canal (HC) (42, 45). A protocol describes measurement procedure. Two observers measured distances for five cases and agreement was assessed. One observer measured all the remaining cases.

RESULTS

IAM and JF measurement interobserver variability was compared. Mean measurement difference between observers was -0.275 mm (standard deviation 0.557). IAM and JF measurements were normally distributed. Mean IAM distance was 12.2 mm [95% confidence interval (CI) 8.8-15.6]; JF was 7.3 mm (95% CI 4.0-10.6). The HC was difficult to visualize on many images and data followed a bimodal distribution.

CONCLUSION

Dural reflections of posterior fossa CNs are well demonstrated by FIESTA MRI. Measuring CSF extension into these structures is feasible and robust; mean CSF extension into IAM and JF was measured. We plan further work to assess coverage of these structures with photon and proton RT plans. Advances in knowledge: We have described CSF extension beyond the internal table of the skull into the IAM, JF and HC. Oncologists planning RT for patients with medulloblastoma and ependymoma may use these data to guide contouring.

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.

New perspectives in the treatment of adult medulloblastoma in the era of molecular oncology

Medulloblastoma is the most common central nervous system tumor in children, while it is extremely rare in adults. Multimodal treatment involving surgery, radiotherapy and chemotherapy can improve the prognosis of this disease, and recent advances in molecular biology have allowed the identification of molecular subgroups (WNT, SHH, Groups 3 and 4), each of which have different cytogenetic, mutational and gene expression signatures, demographics, histology and prognosis. The present review focuses on the state of the art for adult medulloblastoma treatment and on novel molecular advances and their future implications in the treatment of this disease.

SIOP PODC adapted treatment recommendations for standard-risk medulloblastoma in low and middle income settings

Effective treatment of children with medulloblastoma requires a functioning multi-disciplinary team with adequate neurosurgical, neuroradiological, pathological, radiotherapy and chemotherapy facilities and personnel. In addition the treating centre should have the capacity to effectively screen and manage any tumour and treatment-associated complications. These requirements have made it difficult for many low and middle-income countries (LMIC) centres to offer curative treatment. This article provides management recommendations for children with standard-risk medulloblastoma (localised tumours in children over the age of 3-5 years) according to the level of facilities available.

Prospective longitudinal assessment of sensorineural hearing loss with hyperfractionated radiation therapy alone in patients with average-risk medulloblastoma

Background

To report on sensorineural hearing loss (SNHL) in a cohort of patients treated with hyperfractionated radiation therapy (HFRT) without upfront platinum-based chemotherapy in average-risk medulloblastoma.

Methods

Hearing thresholds were assessed by ear-specific pure-tone audiograms at stimulus frequencies of 0.25, 0.5, 1, 2, 4, and 8 kilohertz. Audiometric assessments were done serially longitudinally at baseline, between 6-12 months after HFRT, and annually thereafter. Pure-tone audiograms were analyzed and graded according to Brock pediatric ototoxicity grading criteria.

Results

Five of 20 (25%) children had communicatively and developmentally significant SNHL (Brock grade 2 or worse) even before starting radiotherapy. On follow-up, new-onset Brock grade 2 or worse ototoxicity was documented in 6 previously normal ears. Eleven patients had preserved hearing in both ears on last audiometric follow-up. Compared with baseline testing, post-HFRT audiometry at 2-3 years showed modest decline in hearing threshold across all frequencies. Age at diagnosis and sex did not significantly impact hearing, while higher cochlear doses trended towards worse hearing outcomes. Tumors that extended more towards one side expectedly showed significant worsening in the ipsilateral ear. There was a differential impact of treatment on the right and left ears with the right ear (and not the left ear) showing significantly worse hearing thresholds in the low-to-intermediate speech frequency range over time.

Conclusion

The use of HFRT for craniospinal irradiation and conformal tumor bed boost without upfront platinum-based chemotherapy in children with average-risk medulloblastoma results in preserved hearing in a large proportion of patients in the audible speech range.

Single Arc Volumetric Modulated Arc Therapy for Complex Brain Gliomas: Is There an Advantage as Compared to Intensity Modulated Radiotherapy or by Adding a Partial Arc?

The objective of this study was to determine if volumetric modulated arc therapy (VMAT) offers advantages over intensity modulated radiotherapy (IMRT) for complex brain gliomas and evaluate the role of an additional partial arc. Twelve patients with glioma involving critical organs at risk (OAR) were selected [six low grade brainstem glioma (BG) and six glioblastoma (GB) cases]. BGs were prescribed 54 Gy/30 fractions (frx), and GB treated to 50 Gy/30 frx to a lower dose PTV (PTV50) with a simultaneous integrated boost delivering a total dose of 60 Gy/30 frx to a higher dose PTV (PTV60). VMAT was planned with a single arc (VMAT1) and with an additional coplanar partial arc spanning 90° (VMAT2). We observed VMATI improving the PTV equivalent uniform dose (EUD) for BG cases (p = 0.027), improving the V95 for the PTV50 in GB cases (p = 0.026) and resulting in more conformal GB plans (p = 0.008) as compare to IMRT. However, for the GB PTV60, IMRT achieved favorable V95 over VMAT1 and VMAT2 (0.0046 and 0.008, respectively). The GB total integral dose (ID) was significantly lower with VMAT1 and VMAT2 (p = 0.049 and p = 0.006, respectively). Both VMAT1 and VMAT2 reduced the ID, however, only at the 5 Gy threshold for BG cases (p = 0.011 and 0.005, respectively). VMAT achieved a lower spinal cord maximum dose and EUD for BG cases and higher optic nerve doses, otherwise no significant differences were observed. VMAT1 yielded the fastest treatment times and least MU. We conclude that VMAT offers faster treatment delivery for complex brain tumors while maintaining similar dosimetric qualities to IMRT. Selective dosimetric advantages in terms of spinal cord sparing and lowering the ID are observed favoring the use of an additional coplanar partial arc.

Disease control and ototoxicity using intensity-modulated radiation therapy tumor-bed boost for medulloblastoma

PURPOSE

We previously reported excellent local control for treating medulloblastoma with a limited boost to the tumor bed. In order to decrease ototoxicity, we subsequently implemented a tumor-bed boost using intensity-modulated radiation therapy (IMRT), the clinical results of which we report here.

PATIENTS AND METHODS

A total of 33 patients with newly diagnosed medulloblastoma, 25 with standard risk, and 8 with high risk, were treated on an IMRT tumor-bed boost following craniospinal irradiation (CSI). Six standard-risk patients were treated with an institutional protocol with 18 Gy CSI in conjunction with intrathecal iodine-131-labeled monoclonal antibody. The majority of patients received concurrent vincristine and standard adjuvant chemotherapy. Pure-tone audiograms were graded according to National Cancer Institute Common Terminology Criteria for Adverse Events version 3.0.

RESULTS

Median age was 9 years old (range, 4-46 years old). Median follow-up was 63 months. Kaplan-Meier estimates of progression-free survival (PFS) and overall survival (OS) rates for standard-risk patients who received 23.4 or 36 Gy CSI (not including those who received 18 Gy CSI with radioimmunotherapy) were 81.4% and 88.4%, respectively, at 5 years; 5-year PFS and OS rates for high-risk patients were both 87.5%. There were no isolated posterior fossa failures outside of the boost volume. Posttreatment audiograms were available for 31 patients, of whom 6%, at a median follow-up of 19 months, had developed Grade 3 hearing loss.

CONCLUSION

An IMRT tumor-bed boost results in excellent local control while delivering a low mean dose to the cochlea, resulting in a low rate of ototoxicity.

Neuropsychological differences between survivors of supratentorial and infratentorial brain tumours

BACKGROUND

The purpose of this study is to evaluate the relationship between brain tumour location and core areas of cognitive and behavioural functioning for paediatric brain tumour survivors. The extant literature both supports and refutes an association between paediatric brain tumour location and neurocognitive outcomes. We examined neuropsychological test data to identify any differences in neurocognitive and behavioural profile associated with supratentorial versus infratentorial tumour location.

METHODS

Following Institutional Review Board approval, the medical records and neuropsychological test data collected between 1997 and 2002 for 70 children treated for brain tumour at Children's Hospital Los Angeles were reviewed. Fifty-one per cent of the participants had tumours located in the supratentorial regions of the brain, whereas 49% had infratentorial tumours. Primary medical treatments involved tumour resection (90%), cranial radiation therapy (76%), chemotherapy (71%), and 59% all three medical procedures. The two tumour location groups did not differ significantly in the cumulative treatment dose of irradiation to the tumour bed or in the dose delivered to the whole brain. Neuropsychological test data included measures of verbal and non-verbal intellectual functioning, attention/working memory, processing speed, verbal and visual memory, fine motor skills, visual-motor integration, academic achievement, and social-emotional functioning. Differences between the two groups were evaluated using anova, t-tests and chi-squared statistical tests.

RESULTS

The supratentorial and infratentorial tumour location groups did not differ on measures of intellectual functioning. However, survivors of infratentorial tumours performed more poorly on selected measures of more specific cognitive functions and on parent-report of social-emotional functioning relative to survivors of supratentorial tumours, even when age at diagnosis was held as a covariate. Higher frequency of auditory deficits was noted in the infratentorial tumour group and was associated with lowered academic achievement scores.

CONCLUSIONS

The differences by location found in more specific neurocognitive and social-emotional variables, after controlling for age at diagnosis, may possibly reflect tumour location-specific effects. However, this interpretation remains tentative given the limitations in our study and inability to control for the range of medical and treatment-related factors that may have contributed towards the outcomes observed in our sample. At the same time, most of our findings appear consistent with reports from recent studies in this area.

First quinquennial review of intensity-modulated radiotherapy at St Bartholomew's Hospital, London

Intensity-modulated radiotherapy (IMRT) is a relatively new technique of delivering external beam radiotherapy that is becoming increasingly available in the UK. This paper summarises the introduction and initial clinical work in IMRT over the period 2004-2009. Physics aspects of commissioning are described, including the development of a robust method of quality control using a sweeping gap test. Details of the organisational changes necessary to introduce IMRT are given. The clinical selection and practice in head and neck sites are described, together with promising early results on the maintenance of salivary flow after IMRT. A summary of research into optimal planning for pelvic cancer follows. The controversial areas of breast and paediatric IMRT are discussed with recommendations on practice. The potential for concomitant boost therapy is exemplified in the treatment of brain metastatic disease.

Intensity-modulated and 3D-conformal radiotherapy for whole-ventricular irradiation as compared with conventional whole-brain irradiation in the management of localized central nervous system germ cell tumors

PURPOSE

To compare the sparing potential of cerebral hemispheres with intensity-modulated radiotherapy (IMRT) and three-dimensional conformal radiotherapy (3D-CRT) for whole-ventricular irradiation (WVI) and conventional whole-brain irradiation (WBI) in the management of localized central nervous system germ cell tumors (CNSGCTs).

METHODS AND MATERIALS

Ten cases of patients with localized CNSGCTs and submitted to WVI by use of IMRT with or without a "boost" to the primary lesion were selected. For comparison purposes, similar treatment plans were produced by use of 3D-CRT (WVI with or without boost) and WBI (opposed lateral fields with or without boost), and cerebral hemisphere sparing was evaluated at dose levels ranging from 2 Gy to 40 Gy.

RESULTS

The median prescription dose for WVI was 30.6 Gy (range, 25.2-37.5 Gy), and that for the boost was 16.5 Gy (range, 0-23.4 Gy). Mean irradiated cerebral hemisphere volumes were lower for WVI with IMRT than for 3D-CRT and were lower for WVI with 3D-CRT than for WBI. Intensity-modulated radiotherapy was associated with the lowest irradiated volumes, with reductions of 7.5%, 12.2%, and 9.0% at dose levels of 20, 30, and 40 Gy, respectively, compared with 3D-CRT. Intensity-modulated radiotherapy provided statistically significant reductions of median irradiated volumes at all dose levels (p = 0.002 or less). However, estimated radiation doses to peripheral areas of the body were 1.9 times higher with IMRT than with 3D-CRT.

CONCLUSIONS

Although IMRT is associated with increased radiation doses to peripheral areas of the body, its use can spare a significant amount of normal central nervous system tissue compared with 3D-CRT or WBI in the setting of CNSGCT treatment.

Multicentre quality assurance of intensity-modulated radiation therapy plans: A precursor to clinical trials

A multicentre planning study comparing intensity-modulated radiation therapy (IMRT) plans for the treatment of a head and neck cancer has been carried out. Three Australian radiotherapy centres, each with a different planning system, were supplied a fully contoured CT dataset and requested to generate an IMRT plan in accordance with the requirements of an IMRT-based radiation therapy oncology group clinical trial. Plan analysis was carried out using software developed specifically for reviewing multicentre clinical trial data. Two out of the three plans failed to meet the prescription requirements with one misinterpreting the prescription and the third failed to meet one of the constraints. Only one plan achieved all of the dose objectives for the critical structures and normal tissues. Although each centre used very similar planning parameters and beam arrangements the resulting plans were quite different. The subjective interpretation and application of the prescription and planning objectives emphasize one of the many difficulties in carrying out multicentre IMRT planning studies. The treatment prescription protocol in a clinical trial must be both lucid and unequivocally stated to avoid misinterpretation. Australian radiotherapy centres must show that they can produce a quality IMRT plan and that they can adhere to protocols for IMRT planning before using it in a clinical trial.

Intensity-modulated radiotherapy (IMRT) and conventional three-dimensional conformal radiotherapy for high-grade gliomas: does IMRT increase the integral dose to normal brain?

PURPOSE

To determine whether intensity-modulated radiotherapy (IMRT) treatment increases the total integral dose of nontarget tissue relative to the conventional three-dimensional conformal radiotherapy (3D-CRT) technique for high-grade gliomas.

METHODS AND MATERIALS

Twenty patients treated with 3D-CRT for glioblastoma multiforme were selected for a comparative dosimetric evaluation with IMRT. Original target volumes, organs at risk (OAR), and dose-volume constraints were used for replanning with IMRT. Predicted isodose distributions, cumulative dose-volume histograms of target volumes and OAR, normal tissue integral dose, target coverage, dose conformity, and normal tissue sparing with 3D-CRT and IMRT planning were compared. Statistical analyses were performed to determine differences.

RESULTS

In all 20 patients, IMRT maintained equivalent target coverage, improved target conformity (conformity index [CI] 95% 1.52 vs. 1.38, p < 0.001), and enabled dose reductions of normal tissues, including brainstem (D(mean) by 19.8% and D(max) by 10.7%), optic chiasm (D(mean) by 25.3% and D(max) by 22.6%), right optic nerve (D(mean) by 37.3% and D(max) by 28.5%), and left optic nerve (D(mean) by 40.6% and D(max) by 36.7%), p < or = 0.01. This was achieved without increasing the total nontarget integral dose by greater than 0.5%. Overall, total integral dose was reduced by 7-10% with IMRT, p < 0.001, without significantly increasing the 0.5-5 Gy low-dose volume.

CONCLUSIONS

These results indicate that IMRT treatment for high-grade gliomas allows for improved target conformity, better critical tissue sparing, and importantly does so without increasing integral dose and the volume of normal tissue exposed to low doses of radiation.

Dynamic intensity-modulated non-coplanar arc radiotherapy (INCA) for head and neck cancer

BACKGROUND AND PURPOSE

To define the potential advantages of intensity-modulated radiotherapy (IMRT) applied using a non-coplanar dynamic arc technique for the treatment of head and neck cancer.

MATERIALS AND METHODS

External beam radiotherapy (EBRT) was planned in ten patients with head and neck cancer using coplanar IMRT and non-coplanar arc techniques, termed intensity modulated non-coplanar arc EBRT (INCA). Planning target volumes (PTV1) of first order covered the gross tumor volume and surrounding clinical target volume treated with 68-70 Gy, whereas PTV2 covered the elective lymph nodes with 54-55 Gy using a simultaneous internal boost. Treatment plan comparison between IMRT and INCA was carried out using dose-volume histogram and "equivalent uniform dose" (EUD).

RESULTS

INCA resulted in better dose coverage and homogeneity of the PTV1, PTV2, and reduced dose delivered to most of the organs at risk (OAR). For the parotid glands, a reduction of the mean dose of 2.9 (+/- 2.0) Gy was observed (p = 0.002), the mean dose to the larynx was reduced by 6.9 (+/- 2.9) Gy (p = 0.003), the oral mucosa by 2.4 (+/- 1.1) Gy (p < 0.001), and the maximal dose to the spinal cord by 3.2 (+/- 1.7) Gy (p = 0.004). The mean dose to the brain was increased by 3.0 (+/- 1.4) Gy (p = 0.002) and the mean lung dose increased by 0.2 (+/- 0.4) Gy (p = 0.87). The EUD suggested better avoidance of the OAR, except for the lung, and better coverage and dose uniformity were achieved with INCA compared to IMRT.

CONCLUSION

Dose delivery accuracy with IMRT using a non-coplanar dynamic arc beam geometry potentially improves treatment of head and neck cancer.

Current role of radiation therapy in the management of malignant brain tumors

The objective of this article is to explain how the current management of malignant brain tumors has evolved, using the foundation of evidence-based literature. Radiotherapy plays a central role in the multidisciplinary management of primary brain tumors and brain metastases. The techniques of radiotherapy continue to be refined to optimize local control while minimizing potential treatment-related neurocognitive toxicities.