The latent period in clinical radiation myelopathy

Predictive Factors Associated With Radiation Myelopathy in Pediatric Patients With Cancer: A PENTEC Comprehensive Review

PURPOSE

Radiation myelitis (RM) is a rare complication of radiation therapy (RT). The Pediatric Normal Tissue Effects in the Clinic spinal cord task force aimed to identify RT dose effects and assess risk factors for RM in children. Through systematic review, we analyzed RT dose, fraction size, latency between completion of RT and toxicity, chemotherapy use, age when irradiated, and sex.

METHODS AND MATERIALS

We conducted literature searches of peer-reviewed manuscripts published from 1964 to June 2017 evaluating RM among children. Normality of variables was assessed with Kolmogorov-Smirnov or Shapiro-Wilk tests. Spearman's rank correlation coefficients were used to test correlations between RT dose/fraction size and latency between RT and development of toxicity.

RESULTS

Of 1329 identified and screened reports, 144 reports were fully reviewed and determined to have adequate data for analysis; 16 of these reports had a total of 33 cases of RM with a median age of 13 years (range, 0.2-18) at the time of RT. The most common primary tumor histologies were rhabdomyosarcoma (n = 9), medulloblastoma (n = 5), and Hodgkin lymphoma (n = 2); the most common chemotherapy agents given were vincristine (n = 15), intrathecal methotrexate (n = 12), and intrathecal cytarabine (n = 10). The median RT dose and fraction size were 40 Gy (range, 24-57.4 Gy) and 1.8 Gy (range, 1.3-2.6 Gy), respectively. RT dose resulting in RM in patients who also received chemotherapy was lower than in those not receiving chemotherapy (mean 39.6 vs 49.7 Gy; P = .04). There was no association of age with RT dose. The median latency period was 7 months (range, 1-29). Higher RT dose was correlated with longer latency periods (P = .03) to RM whereas sex, age, fraction size, and chemotherapy use were not. Two of 17 patients with adequate follow-up recovered from RM; unfortunately, it was fatal in 6 of 15 evaluable patients. Complication probability modeling was not possible because of the rarity of events.

CONCLUSIONS

This report demonstrates a relatively short latency from RT (with or without chemotherapy) to RM and a wide range of doses (including fraction sizes) associated with RM. No apparent association with age at the time of RT could be discerned. Chemotherapy appears to reduce spinal cord tolerance. Recovery from RM is rare, and it is often fatal.

Spinal Cord Delineation Based on Computed Tomography Myelogram Versus T2 Magnetic Resonance Imaging in Spinal Stereotactic Body Radiation Therapy

Purpose

Spinal cord delineation is critical to the delivery of stereotactic body radiation therapy (SBRT). Although underestimating the spinal cord can lead to irreversible myelopathy, overestimating the spinal cord may compromise the planning target volume coverage. We compare spinal cord contours based on computed tomography (CT) simulation with a myelogram to spinal cord contours based on fused axial T2 magnetic resonance imaging (MRI).

Methods and Materials

Eight patients with 9 spinal metastases treated with spinal SBRT were contoured by 8 radiation oncologists, neurosurgeons, and physicists, with spinal cord definition based on (1) fused axial T2 MRI and (2) CT-myelogram simulation images, yielding 72 sets of spinal cord contours. The spinal cord volume was contoured at the target vertebral body volume based on both images. The mixed-effect model assessed comparisons of T2 MRI- to myelogram-defined spinal cord in centroid deviations (deviations in the center point of the cord) through the vertebral body target volume, spinal cord volumes, and maximum doses (0.035 cc point) to the spinal cord applying the patient's SBRT treatment plan, in addition to in-between and within-subject variabilities.

Results

The estimate for the fixed effect from the mixed model showed that the mean difference between 72 CT volumes and 72 MRI volumes was 0.06 cc and was not statistically significant (95% confidence interval, -0.034, 0.153; P = .1832). The mixed model showed that the mean dose at 0.035 cc for CT-defined spinal cord contours was 1.24 Gy lower than that of MRI-defined spinal cord contours and was statistically significant (95% confidence interval, -2.292, -0.180; P = .0271). Also, the mixed model indicated no statistical significance for deviations in any of the axes between MRI-defined spinal cord contours and CT-defined spinal cord contours.

Conclusions

CT myelogram may not be required when MRI imaging is feasible, although uncertainty at the cord-to-treatment volume interface may result in overcontouring and hence higher estimated cord dose-maximums with axial T2 MRI-based cord definition.

Analysis of deep inspiration breath-hold technique to improve dosimetric and clinical advantages in postoperative intensity-modulated radiation therapy for thymomas

Background

Radiation therapy is one of the essential treatment modalities for invasive thymomas. Clinically, respiratory motion poses a challenge for the radiotherapy of thoracic tumors. One method to address this issue is to train patients to hold their breath at the end of deep inspiration. The purpose of this retrospective cohort study was to investigate the dosimetric and clinical advantages of the deep inspiration breath-hold (DIBH) technique in postoperative intensity-modulated radiation therapy (IMRT) for thymomas.

Methods

Thymoma patients undergoing postoperative IMRT were included. Each patient underwent two computed tomography (CT) scans, one under free breath (FB) and the other under DIBH. Dosimetric parameters of organs at risk (OARs) were evaluated in three series plans. Dose analysis and volume comparisons were conducted during FB-3 mm (FB with 3 mm internal target volume margin), FB-10 mm (FB with 10 mm internal target volume margin), and DIBH and compared using a paired sample Student’s t-test. Normal tissue complication probabilities (NTCP) for lungs and heart were calculated and compared.

Results

The total lung volume significantly increased by 31% (4,216±198 vs. 2,884±166 mL) and the heart volume reduced by 12% (552±25 vs. 636±35 mL) between DIBH acquisitions compared to FB. A significant improvement was observed in all the dosimetric parameters (D_mean, V20, V5) of the lung on DIBH compared to FB-3 mm (54%±2.85% vs. 47%±2.90%, P<0.001; 15%±1.37% vs. 12%±1.32%, P=0.004; and 10.28±0.58 vs. 8.76±0.57 Gy, P<0.001, respectively), as well as in the D_max and D2% of the esophagus and spine. The lung volume increment was related to a reduction in the mean dose of lungs, with a correlation coefficient of r=0.27, P=0.03. The NTCP values for pneumonitis significantly reduced with DIBH compared to the FB state (0.6% vs. 1.1%, P<0.001).

Conclusions

The radiation dose to the OARs can be significantly reduced by using the DIBH technique in postoperative IMRT for thymomas. The increased volume of lungs using DIBH acquisitions can significantly reduce the incidence of pneumonitis.

Models for Translational Proton Radiobiology-From Bench to Bedside and Back

The number of proton therapy centers worldwide are increasing steadily, with more than two million cancer patients treated so far. Despite this development, pending questions on proton radiobiology still call for basic and translational preclinical research. Open issues are the on-going discussion on an energy-dependent varying proton RBE (relative biological effectiveness), a better characterization of normal tissue side effects and combination treatments with drugs originally developed for photon therapy. At the same time, novel possibilities arise, such as radioimmunotherapy, and new proton therapy schemata, such as FLASH irradiation and proton mini-beams. The study of those aspects demands for radiobiological models at different stages along the translational chain, allowing the investigation of mechanisms from the molecular level to whole organisms. Focusing on the challenges and specifics of proton research, this review summarizes the different available models, ranging from in vitro systems to animal studies of increasing complexity as well as complementing in silico approaches.

Radiotherapy-Specific Chronic Pain Syndromes in the Cancer Population: An Evidence-Based Narrative Review

While radiation therapy is increasingly utilized in the treatment paradigm of many solid cancers, the chronic effects of radiation therapies are poorly characterized. Notably, understanding radiation-specific chronic pain syndromes is paramount given that the diagnosis and management of these conditions can serve to prevent long-standing functional impairments, optimize quality of life, and even allow for continued radiotherapy candidacy. These radiation-specific chronic pain phenomena include dermatitis, mucositis, enteritis, connective tissue fibrosis, lymphedema, and neuropathic pain syndromes. It is necessary to maintain a low threshold of suspicion for appropriately diagnosing these conditions as there exists a variance in when these symptoms arise after radiation. However, we present key epidemiological data delineating vulnerable cancer populations for each pain syndrome along with the available evidence for the management for each specific condition.

Ramipril reduces incidence and prolongates latency time of radiation-induced rat myelopathy after photon and carbon ion irradiation

To test the hypothesis that the use of an angiotensin-converting enzyme inhibitor (ACEi) during radiotherapy may be ameliorative for treatment-related normal tissue damage, a pilot study was conducted with the clinically approved (ACE) inhibitor ramipril on the outcome of radiation-induced myelopathy in the rat cervical spinal cord model. Female Sprague Dawley rats were irradiated with single doses of either carbon ions (LET 45 keV/μm) at the center of a 6 cm spread-out Bragg peak (SOBP) or 6 MeV photons. The rats were randomly distributed into 4 experimental arms: (i) photons; (ii) photons + ramipril; (iii) carbon ions and (iv) carbon ions + ramipril. Ramipril administration (2 mg/kg/day) started directly after irradiation and was maintained during the entire follow-up. Complete dose-response curves were generated for the biological endpoint radiation-induced myelopathy (paresis grade II) within an observation time of 300 days. Administration of ramipril reduced the rate of paralysis at high dose levels for photons and for the first time a similar finding for high-LET particles was demonstrated, which indicates that the effect of ramipril is independent from radiation quality. The reduced rate of myelopathy is accompanied by a general prolongation of latency time for photons and for carbon ions. Although the already clinical approved drug ramipril can be considered as a mitigator of radiation-induced normal tissue toxicity in the central nervous system, further examinations of the underlying pathological mechanisms leading to radiation-induced myelopathy are necessary to increase and sustain its mitigative effectiveness.

Fulminant spinal cord compression caused by postradiation inflammatory pseudotumor with rapid response to steroids: case report

Radiation therapy continues to play an extremely valuable role in the treatment of malignancy. The effects of radiation therapy on normal tissue can present in a delayed fashion, resulting in localized damage with pseudomalignant transformation, producing a compressive effect on the spinal cord or exiting nerve roots. Infiltration of inflammatory cells and the subsequent fibrotic response can result in the development of an inflammatory pseudotumor (benign tumor-like lesion) with subsequent mass effect. Herein, the authors present a rare case of inflammatory pseudotumor with fulminant cervicothoracic cord compression, developing 7 years after radiation therapy for breast cancer. The lesion recurred following resection but subsequently displayed complete and rapid resolution following steroid therapy. To the best of the authors' knowledge, no previous studies have reported such an incident.

Effects of Radiation on Spinal Dura Mater and Surrounding Tissue in Mice

PURPOSE

Spinal surgery in a previously irradiated field carries increased risk of perioperative complications, such as delayed wound healing or wound infection. In addition, adhesion around the dura mater is often observed clinically. Therefore, similar to radiation-induced fibrosis--a major late-stage radiation injury in other tissue--epidural fibrosis is anticipated to occur after spinal radiation. In this study, we performed histopathologic assessment of postirradiation changes in the spinal dura mater and peridural tissue in mice.

MATERIALS AND METHODS

The thoracolumbar transition of ddY mice was irradiated with a single dose of 10 or 20 Gy. After resection of the irradiated spine, occurrence of epidural fibrosis and expression of transforming growth factor beta 1 in the spinal dura mater were evaluated. In addition, microstructures in the spinal dura mater and peridural tissue were assessed using an electron microscope.

RESULTS

In the 20-Gy irradiated mice, epidural fibrosis first occurred around 12 weeks postirradiation, and was observed in all cases from 16 weeks postirradiation. In contrast, epidural fibrosis was not observed in the nonirradiated mice. Compared with the nonirradiated mice, the 10- and 20-Gy irradiated mice had significantly more overexpression of transforming growth factor beta 1 at 1 week postirradiation and in the late stages after irradiation. In microstructural assessment, the arachnoid barrier cell layer was thinned at 12 and 24 weeks postirradiation compared with that in the nonirradiated mice.

CONCLUSION

In mice, spinal epidural fibrosis develops in the late stages after high-dose irradiation, and overexpression of transforming growth factor beta 1 occurs in a manner similar to that seen in radiation-induced fibrosis in other tissue. Additionally, thinning of the arachnoid barrier cell layer was observed in the late stages after irradiation. Thus, consideration should be given to the possibility that these phenomena can occur as radiation-induced injuries of the spine.

Comparison of supine and prone craniospinal irradiation in children with medulloblastoma

PURPOSE

To compare port film rejection and treatment outcome according to craniospinal irradiation (CSI) position for medulloblastoma.

METHODS AND MATERIALS

We retrospectively searched for patients ≤19 years treated with CSI for medulloblastoma at 1 department. We collected the following data: age; sex; risk group; need for general anesthesia; radiation therapy (RT) dose and fractionation; and the acceptance or rejection of weekly port films during treatment. We also collected data on outcomes, including neuraxis recurrence and possible complications such as myelitis.

RESULTS

Of 46 children identified, 23 were treated prone (median age, 8.1 years) and 23 supine (median age, 7.2 years). High-risk disease was seen in 26% of prone and 35% of supine patients (P = .25). There was no difference in use of general anesthesia between those treated prone versus supine (57% vs 61%). The rejection rate of cranial port films in the prone position was 35%, which was significantly higher than the rate of 8% in patients treated supine (P < .0001). The 5-year progression-free (P = .37) and overall survival (P = .18) rates were 62% and 67% for prone and 76% and 84% for supine patients. There were no isolated junctional failures or radiation myelitis in either CSI position.

CONCLUSIONS

The supine position for CSI was found to have similar survival outcomes compared with the prone position. A higher proportion of rejected cranial port films was seen in children treated in the prone position.

Spinal cord glioblastoma induced by radiation therapy of nasopharyngeal rhabdomyosarcoma with MRI findings: case report

Radiation-induced spinal cord gliomas are extremely rare. Since the first case was reported in 1980, only six additional cases have been reported.; The radiation-induced gliomas were related to the treatment of Hodgkin's lymphoma, thyroid cancer, and medullomyoblastoma, and to multiple chest fluoroscopic examinations in pulmonary tuberculosis patient. We report a case of radiation-induced spinal cord glioblastoma developed in a 17-year-old girl after a 13-year latency period following radiotherapy for nasopharyngeal rhabdomyosarcoma. MRI findings of our case are described.

Biological mechanisms of normal tissue damage: importance for the design of NTCP models

The normal tissue complication probability (NTCP) models that are currently being proposed for estimation of risk of harm following radiotherapy are mainly based on simplified empirical models, consisting of dose distribution parameters, possibly combined with clinical or other treatment-related factors. These are fitted to data from retrospective or prospective clinical studies. Although these models sometimes provide useful guidance for clinical practice, their predictive power on individuals seems to be limited. This paper examines the radiobiological mechanisms underlying the most important complications induced by radiotherapy, with the aim of identifying the essential parameters and functional relationships needed for effective predictive NTCP models. The clinical features of the complications are identified and reduced as much as possible into component parts. In a second step, experimental and clinical data are considered in order to identify the gross anatomical structures involved, and which dose distributions lead to these complications. Finally, the pathogenic pathways and cellular and more specific anatomical parameters that have to be considered in this pathway are determined. This analysis is carried out for some of the most critical organs and sites in radiotherapy, i.e. spinal cord, lung, rectum, oropharynx and heart. Signs and symptoms of severe late normal tissue complications present a very variable picture in the different organs at risk. Only in rare instances is the entire organ the critical target which elicits the particular complication. Moreover, the biological mechanisms that are involved in the pathogenesis differ between the different complications, even in the same organ. Different mechanisms are likely to be related to different shapes of dose effect relationships and different relationships between dose per fraction, dose rate, and overall treatment time and effects. There is good reason to conclude that each type of late complication after radiotherapy depends on its own specific mechanism which is triggered by the radiation exposure of particular structures or sub-volumes of (or related to) the respective organ at risk. Hence each complication will need the development of an NTCP model designed to accommodate this structure.

Neurocytomas: long-term experience of a single institution

There is a lack of studies reporting on outcomes of control and treatment toxicities for neurocytomas. A 25-year retrospective review of a tertiary center's experience with neurocytomas was completed to report on these outcomes. All cerebral neurocytoma cases (19 patients; median age, 31 years; range, 18-62 years; 18 intraventricular and 1 extraventricular) treated between 1984 and 2009 were analyzed, including central pathology and radiology reviews. Median follow-up was 104.5 months (range, 0.75-261.7 months). Primary treatment was surgery alone (n = 18 patients), followed by surgery and adjuvant radiotherapy (n = 1). The crude local control rate after surgery was 68% for all cases (cerebral neurocytomas) and 74% for central neurocytomas. Salvage therapies included further surgery (n = 4), radiation (n = 3), and chemotherapy (n = 1). Ten-year Kaplan-Meier overall and relapse-free survival rates were 82% and 62% and 81% and 57%, respectively, for all cases and for central neurocytomas only. The median overall survival and relapse-free survival were 104.5 and 79.3 months, respectively, for all cases and for central neurocytomas. Ten patients had grade 3/4 toxicity, and 1 patient had a grade 5 perioperative hemorrhage that resulted in death 23 days after surgery. Late grade 3/4 toxicities occurred in 9 patients. Three patients had permanent grade 2 motor or cognitive deficits. We provide the first report outlining toxicities and survival outcomes in a series of 19 patients. Our experience suggests that initial surgery provides durable local control rates in two-thirds of patients, with low risk for significant permanent deficits. Salvage therapy with surgery and/or radiation provides durable local control in tumors that recur after surgery.

Increased vulnerability of the spinal cord to radiation or intrathecal chemotherapy during adolescence: A report from the Children's Oncology Group

PURPOSE

To assess the rate of spinal cord toxicity in adolescents resulting from chemoradiotherapy of parameningeal sarcoma.

METHODS AND MATERIALS

Of 152 patients with parameningeal sarcoma treated per the Intergroup Rhabdomyosarcoma Study Group protocol from 1977 through 1989, eight developed paralyzing ascending myelitis after intrathecal chemotherapy with cytosine arabinoside, methotrexate, and hydrocortisone administered during and after radiation therapy to volumes that included part of the spinal cord. The eight cases include three not previously published.

RESULTS

Of eight patients who developed CNS toxicity after intrathecal chemotherapy and radiotherapy for parameningeal rhabdomyosarcoma, all but one were between 13 and 18 years of age when treated. This severe toxicity occurred in one quarter of 28 adolescents treated with the regimen in comparison with one of 123 children 12 years of age or less (P < 0.0001), a rate that was as much as 30 times higher in the adolescents. Lengthening of the spinal cord during the pubertal growth spurt may account for the apparent increased vulnerability.

CONCLUSIONS

Chemoradiotoxicity-associated spinal cord injury appears to be more likely to occur in adolescents than in younger or older ages. This observation appears to reverse a conventional wisdom in which the central nervous system is thought to become more resistant to the neurotoxic effects of chemoradiotherapy as it matures.

Myelopathy After Radiation Therapy and Chemotherapy with Capecitabine and Gemcitabine

This article describes a woman with metastatic upper gastrointestinal cancer who developed thoracic myelopathy unexpectedly after standard dosage and fractionation radiotherapy. She also was receiving capecitabine and gemcitabine concomitantly. There are few reported cases of chemotherapy potentiation of spinal cord radiation toxicity. These agents are known radiosensitizers, making it likely that they contributed to this adverse outcome. As these agents are increasingly incorporated into clinical trials of combined therapy, caution will be necessary in both trial design and clinical management.

Dose-volume effects in rat thoracolumbar spinal cord: the effects of nonuniform dose distribution

PURPOSE

To investigate dose-volume effects in rat spinal cord irradiated with nonuniform dose distributions and to assess regional differences in radiosensitivity.

METHODS AND MATERIALS

A total of 106 rats divided into three groups were irradiated with (192)Ir gamma-rays at a high dose rate. The groups were irradiated with one, two, or six catheters distributed around the thoracolumbar spinal cord to create different dose distributions. After irradiation, the animals were tested for motor function for 9 months. The response was defined as motor dysfunction and WM or nerve root necrosis. Dose-response data were analyzed with a probit analysis as function of the dose level at a percentage of the volume (D(%)) and with different normal tissue complication probability models. Additionally, the histologic responses of the individual dose voxels were analyzed after registration with the histologic sections.

RESULTS

The probit analysis at D(24) (24% of the volume) gave the best fit results. In addition, the Lyman Kutcher Burman model and the relative seriality model showed acceptable fits, with volume parameters of 0.17 and 0.53, respectively. The histology-based analysis revealed a lower radiosensitivity for the dorsal (50% isoeffective dose [ED(50)] = 32.3) and lateral WM (ED(50) = 33.7 Gy) compared with the dorsal (ED(50) = 25.9 Gy) and ventral nerve roots (ED(50) = 24.1 Gy).

CONCLUSIONS

For this nonuniform irradiation, the spinal cord did not show typical serial behavior. No migration terms were needed for an acceptable fit of the dose-response curves. A higher radiosensitivity for the lumbar nerve roots than for the thoracic WM was found.

Toward improving the therapeutic ratio in stereotactic radiosurgery: selective modulation of the radiation responses of both normal tissues and tumor

✓A review of the radiobiological factors that influence the response of the brain to radiation is provided in relation to stereotactic radiosurgery (SRS). The prospects for intervention after radiation treatment to selectively modulate the expression of late central nervous system (CNS) injury is considered, as well as an account of recent interest in the use of radiation enhancers to selectively increase the response of tumors to radiation.

Brain necrosis in humans, after conventional irradiation, indicates that the risk of necrosis increases rapidly after an equivalent single dose of 12 or 13 Gy. When single-dose treatments are extended due to 60Co decay or planned extension of treatment times, account should be taken of the effects of the repair of sublethal radiation damage to DNA on the efficacy of treatment. Both repair capacity and repair kinetics will also influence tumor control, but parameters to quantify this effect have not yet been established.

The volume of CNS tissue that has been irradiated affects the tissue response, but this effect is only significant for volumes less than 0.05 cm3. The gain obtained from irradiation of small volumes is reduced, however, when focal irradiation is given within a wider field of irradiation.

Based on a vascular hypothesis explaining the pathogenesis of late CNS damage, approaches designed to selectively modulate the frequency of late CNS damage have been validated. Given the high intrinsic radioresistance of some tumors, as opposed to the presence of hypoxia, an interest has developed in the use of selective radiation enhancers in the treatment of tumors. The compound presently available has proved to be disappointing clinically due to toxicity at effective doses, when repeated administration is required. However, when given at high single doses it is less toxic and may be more effective. Less toxic radiation enhancers need to be developed.

Significant response of radiation induced CNS toxicity to high dose steroid administration

Treatment of radiation myelopathy remains a challenge. Supportive and rehabilitative therapy is the mainstay of treatment. This article describes a case of central nervous system (CNS) toxicity of radiation with a progressive improvement in the clinicoradiological picture following high dose steroid treatment. A female patient was admitted to the neurology department of our hospital 7 months after a course of radiotherapy in another centre for lingual epidermoid cancer. Neurological examination revealed a heavy spastic quadriplegia syndrome. On MRI examination, T2 weighted hyperintensities were observed in cerebral and cerebellar peduncles, periventricular regions and medulla spinalis at Th1-Th2 levels. The patient was treated with high dose methylprednisolone, 1 g day(-1) for 5 days (pulse therapy) followed by oral methylprednisolone 80 mg day(-1) for a week, tapered over 3 weeks. Within the first week of pulse therapy, she regained muscle strength of upper limbs against gravity. At the 2 year follow-up, MRI demonstrated obvious regression of the lesions in the medulla and cerebellum with disappearance of contrast enhancement. This case report is notable with the complete disappearance of MRI lesions at the 2 year follow-up after the treatment with high dose steroid.

Clinical Outcomes After Reirradiation of Paraspinal Tumors

OBJECTIVE

We present our experience with reirradiation of locally recurrent paraspinal tumors using image-guided intensity modulated radiotherapy (IG-IMRT).

METHODS

We performed a retrospective review of 37 patients who were reirradiated using IG-IMRT for recurrent paraspinal tumors between 2000 and 2005. We evaluated radiation dose to the spinal cord or cauda equina in first and second radiation treatments, time to first recurrence, and clinical outcomes after reirradiation including second recurrence, survival, pain, functional status, and toxicity.

RESULTS

Median time to local failure after first radiation was 13 months. All patients underwent salvage reirradiation, postoperatively or with IG-IMRT alone. Median radiation dose to the planning target volume (PTV) was 2000 cGy; median spinal cord or cauda equina dose was 990 cGy. Median cumulative spinal cord or cauda equina dose was 4198 cGy. Local control probability at a median follow-up of 8 months was 60%; median interval to second failure was 13 months. Survival probability at a median follow up of 12 months was 72%; median survival was 18 months. Thirty-four patients (91%) reported stable or improved pain after second radiation, and 26 (70%) had a stable or improved functional status. Mild acute toxicity occurred in 3 patients (8%). No long-term toxicity has been identified.

CONCLUSIONS

Reirradiation using IG-IMRT is safe and achieves a meaningful interval of local control with improved symptoms. Further studies with more patients and longer follow up are needed to evaluate toxicity, predictors of failure, and timing of radiation after surgical salvage.

Transverse myelitis after therapy for primitive neuroectodermal tumors

Traditional therapy for malignant primitive neuroectodermal tumors in children includes surgery, multi-agent chemotherapy, and radiation. Given the poor prognosis with conventional therapy alone, newer treatment approaches have incorporated high-dose chemotherapy followed by autologous stem cell rescue. Treatment with chemotherapy and radiation is not without unanticipated and unwanted side effects. Specifically, radiation-induced damage to the central nervous system can occur, though the frequency is thought to be acceptably low. This report describes two cases of treatment-related transverse myelitis in patients who received induction chemotherapy and craniospinal irradiation followed by high-dose chemotherapy with autologous stem cell rescue. Other patients treated with a similar strategy but different sequence and timing of treatment did not experience symptoms of myelitis, suggesting that the specific timing of radiation in relationship to the chemotherapy may be of critical importance.

The Effect of Radiation Therapy on Normal Tissue Function

As more patients are treated for their primary malignancy with cure or increased disease-free intervals, injury to normal tissues will become more detectable and an important endpoint for study. Future protocols will probably be modified based on toxicity endpoints. In Hodgkin's disease, current protocols use response-based treatment strategies to limit therapy. The objective is to provide the same level of tumor control and follow normal tissue endpoints for outcome analysis. DVH analysis has improved the ability to analyze endpoint data for normal tissues. These image-guided platforms will provide the infrastructure needed to continue efforts in improving the delivery of radiation therapy.

Fatal radiation myelopathy after high-dose busulfan and melphalan chemotherapy and radiotherapy for Ewing's sarcoma: a review of the literature and implications for practice

Radiation myelopathy is a rare, devastating, late effect of radiotherapy to the spinal cord. Spinal cord tolerance is currently accepted as about 50 Gy in 1.8-2 Gy fractions. However, the effect of chemotherapy on cord tolerance is unclear. This issue is important, given the increasing use of chemotherapy in combination with radiotherapy. We describe the case of a 17-year-old boy with a right apical paraspinal Ewing's tumour in the neck treated with induction chemotherapy, high-dose chemotherapy (busulfan and melphalan) with peripheral stem-cell rescue and, 4 months later, radiotherapy to the primary tumour site (cervical cord received 50 Gy in 30 fractions). After a latent period of 4 months, he developed a progressive, severe and ultimately fatal radiation myelopathy, which we suggest was due to a synergistic interaction between the high-dose chemotherapy and the radiotherapy. The use of such chemotherapy regimens in Ewing's tumours should be carefully considered, particularly when radiotherapy encompassing the spinal cord is an essential component of management.

Lhermitte's sign among nasopharyngeal cancer patients after radiotherapy

BACKGROUND

Lhermitte's sign (LS) is a side effect of radiotherapy (RT) on the spinal cord and typically occurs shortly after the procedure has been conducted. When treating patients with cancer of the head and neck region with irradiation, it remains difficult to avoid exposing the cervical spinal cord to unintended radiation. In this study, we focused on nasopharyngeal cancer (NPC) alone and looked for various parameters that might influence the occurrence of LS associated with this disease after RT.

METHODS

From 1979 through 1990, 1171 patients with NPC completed RT either with or without chemotherapy at the Lin-Kou Medical Center, Chang Gung Memorial Hospital (CGMH), Tao-Yuan, Taiwan; the RT regimens for these treated patients were very similar. The nasopharyngeal tumor was treated to 75 Gy by photon teletherapy and after-loading brachytherapy. The neck lymphatics were irradiated with photon irradiation to 46.8 Gy and then boosted with electron beams to 10 to 30 Gy, in accordance with the patient's nodal status, either unilaterally or bilaterally. Every patient was followed monthly for the first 3 months after therapy and subsequently every 2 to 3 months for the next 2 years and, finally, every 6 months thereafter. At follow-up, a neurologic checkup of each patient was performed to determine whether any injury to the spinal cord or brain stem had arisen.

RESULTS

LS was observed for 121 patients (10.3%). The median development time for such signs was 3.0 months after the completion of RT (range, 0.2-72 months), and the appearance of such a sign lasted 1 to 82 weeks (median, 17 weeks). No statistically significant differences between the sexes were noted in the development of such a sign (p = .5263),or among various T classifications (p = .0757) and N classifications (p = .4412). The incidence of LS was significantly lower for those patients who had also received chemotherapy than it was for those who had not (p = .003), and it was also lower for patients older than 60 years than for those younger than 60 years (p = .0061). Of the subjects who did not undergo neck-lymphatic boosting or who had undergone only unilateral neck-lymphatic boosting, 7.2% had LS develop, whereas 11.5% of patients who had been boosted bilaterally had LS develop (p = .0285).

CONCLUSIONS

The incidence of LS associated with NPC and after RT was higher in patients who underwent bilateral neck-lymphatic boosting by electron beams than for those who underwent unilateral boosting or who did not undergo boosting. A correlation between increased incidence of LS and RT dose on the cervical spinal cord was noted when the cord dose exceeded 48.9 Gy. Therefore, wherever possible, a CT simulator and a three-dimensional treatment-planning system should necessarily be used to verify the dose distribution of electron-beam RT to diminish the chance of radiation overdose on the cervical cord.

Characterization of late radiation effects in the rat thoracolumbar spinal cord by MR imaging using USPIO

The aim of this study was to detect late radiation effects in the rat spinal cord using MR imaging with ultra-small particles of iron oxide (USPIO) contrast agent to better understand the development of late radiation damage with emphasis on the period preceding neurological signs. Additionally, the role of an inflammatory reaction was assessed by measuring macrophages that internalized USPIO. T2-weighted spin echo MR measurements were performed at 7T in six rats before paresis was expected (130-150 days post-irradiation, early group), and in six paretic rats (150-190 days post-irradiation, late group). Measurements were performed before, directly after and, only in the early group, 40 h after USPIO administration and compared with histology. In the early group, MR images showed focal regions in grey matter (GM) and white matter (WM) with signal intensity reduction after USPIO injection. Larger lesions with contrast enhancement were located in and around edematous GM of three animals of the early group and five of the late group. Forty hours after injection, additional lesions in WM, GM and nerve roots appeared in animals with GM edema. In the late paretic group, MR imaging showed WM necrosis adjacent to areas with large contrast enhancement. In conclusion, detection of early focal lesions was improved by contrast administration. In the animals with extended radiation damage, large hypo-intense regions appeared due to USPIO, which might be attributed to blood spinal cord barrier breakdown, but the involvement of blood-derived iron-loaded macrophages could not be excluded.

Dose-volume effects in rat thoracolumbar spinal cord: an evaluation of NTCP models

PURPOSE

To evaluate models for normal-tissue-complication probability (NTCP) on describing the dose-volume effect in rat thoracolumbar spinal cord.

METHODS AND MATERIALS

Single-dose irradiation of four field lengths (4, 1.5, 1.0, and 0.5 cm) was evaluated by the endpoints paresis and white-matter necrosis. The resulting dose-response data were used to rank phenomenological and tissue architecture NTCP models.

RESULTS

The 0.5-cm field length showed a steep increase in radiation tolerance. Statistical analysis of the model fits, which included evaluation of goodness of fit (GOF) and confidence intervals, resulted in the rejection of all the models considered. Excluding the smallest field length, the Schultheiss (D(50) = 21.5 Gy, k = 26.5), the relative seriality (D(50) = 21.4 Gy, s = 1.6, gamma(50) = 6.3), and the critical element (D(50,FSU) = 26.6 Gy, gamma(50,FSU) = 2.3, n = 1.3) model gave the best fit.

CONCLUSION

A thorough statistical analysis resulted in a serial or critical-element behavior for the field lengths of 1.0 cm and greater. Including the 0.5-cm field length, the radiation response markedly diverged from serial properties, but none of the models applied acceptably described this dose-response relationship. This study suggests that the commonly assumed serial behavior of the spinal cord might be valid for daily use in external- beam irradiation.

Characteristics of radiogenic lower motor neurone disease, a possible link with a preceding viral infection

OBJECTIVE

To investigate the pathogenesis of the rare radiogenic lower motor neurone disease (LMND) on the basis of a meta-analysis of the published case histories.

MATERIALS AND METHODS

The authors reviewed 47 well-documented radiogenic LMND cases from the English literature.

RESULTS

The disease typically occurs following the irradiation of radiosensitive cancers situated near the spinal cord. It arises predominantly (46 cases) in the lower extremities; only one case involved the upper extremities. There is a male predominance (male:female ratio 7.8:1), and the patients are characteristically young (13-40 years, with four exceptions). An overdose does not seem to be a particular risk factor for the development of the disease, as total dose, fraction size and biologically effective dose are typically below 50 Gy, 2 Gy and 128 Gy2, respectively, which are regarded as safe doses. Other risk factors (chemotherapy, operations, etc) have been identified only rarely. Radiogenic LMND is manifested in an apparently random manner, 4-312 (mean 48.7) months after the completion of radiotherapy.

DISCUSSION

The complete lack of a dose-effect relationship argues strongly against a pure radiogenic nature of the pathological process. The latency period is typically several years and it varies extremely, which excludes a direct and complete causal relationship between radiotherapy and LMND. As the interaction of ionizing radiation with living tissues is highly unspecific, thus a selective motor injury due to irradiation alone, without comparable effects on the sensory and vegetative fibers, seems improbable.

CONCLUSIONS

On analogy with the viral motor neurone diseases, we suppose that radiogenic LMND may be preceded by viral (enterovirus/poliovirus) infection. Based on the meta-analysis, it is suggested that irradiation may be only a single component of the set of factors jointly resulting in the clinical state regarded as radiogenic LMND.

Normal-tissue toxicities of thoracic radiation therapy: esophagus, lung, and spinal cord as organs at risk

The evolution of therapeutic approaches for lung cancer illustrates the trend for treatment intensification, with hopes that dose-intense chemotherapy regimens, higher radiation therapy (RT) doses, or novel fractionation schemes will result in prolongation of survival. Current chemotherapy- and RT-intense regimens may not be intensified further without addressing dose-limiting toxicities such as esophagitis. It is important to understand factors pre-disposing to esophagitis so that strategies to minimize its severity can be investigated. Pulmonary complications such as pneumonitis and fibrosis from RT (with or without chemotherapy) are dose and volume dependent. Methods to better identify the target tissues and improved RT-delivery systems may facilitate increasing target doses or reducing doses to adjacent normal tissues. Biologic predictors may allow clinicians in the future to individualize RT treatment based on a patient's toxicity risk profile. Radiation myelopathy is still the most feared radiation complication of lung cancer treatment. The authors address the known parameters that influence the incidence of thoracic radiation myelopathy and the putative factors that could be considered when a clinician may be required to push the spinal cord dose in favor of tumor control.

Autopsy verifies demyelination and lack of vascular damage in partially reversible radiation myelopathy

STUDY DESIGN

Case report of recovering radiation myelopathy.

OBJECTIVE

To present autopsy and functional imaging findings on a unique case of slowly recovering radiation myelopathy with the aim of the clarification of the underlying mechanism.

PATIENT

The cervical spinal cord and the distal part of the medulla oblongata of a 36-year-old thyroid cancer patient had been incorrectly irradiated with a total dose of 61 Gy and a fraction size of 3.4 Gy (J Neurol Sci 1999; 163:39-43), resulting in incomplete cervical transection with a 5-month latency period following the termination of radiotherapy. This was followed by a 9.5-year spontaneous improvement until her demise, during which the check-ups were supplemented by positron emission tomography (PET) investigations; these indicated increased [18F]deoxyglucose and [15O]butanol uptakes, but a diminished [11C]methionine accumulation by the irradiated spinal cord segment.

RESULTS

Autopsy revealed demyelination (with axonal loss) and neuronal damage in the cervical spinal cord and the distal part of the medulla oblongata. In the same region, only minimal vascular injury (thickening of some of the capillary walls) was detected, but not cell proliferation or chronic inflammation. Bilateral, secondary pyramidal tract degeneration caudal to the irradiated segment was observed. The PET and autopsy findings, although separated by 2 years, are consistent.

CONCLUSIONS

The pathological state of the spinal cord revealed by the autopsy is concordant with the incomplete cervical transection, implying that the functional recovery is supported by a process that probably differs from the restoration of the mechanism destroyed by the radiotherapy. For the restoration of the function, we suggest an altered conduction mechanism of the action potential, involving an increased number of sodium channels along the demyelinated segments of the injured axons, which is fully congruent with the PET findings.

A PET study on the characterization of partially reversible radiogenic lower motor neurone disease

OBJECTIVE

To investigate the pathomechanism of the rare radiogenic lower motor neurone disease (LMND) on the basis of a case history involving a partial functional recovery.

PATIENT

A 31-year-old seminoma patient received postoperative para-aortic and para-iliac telecobalt irradiation with a biologically effective dose of 88 Gy(2) (44 Gy in 2 Gy fractions/day, with an estimated alpha/beta of 2 Gy) delivered to the spinal cord following a single cycle of chemotherapy. LMND developed 4 months after the completion of radiotherapy. The patient exhibited flaccid paraparesis of the lower extremities (without sensory or vegetative signs), followed by a worsening after further chemotherapy, due to pulmonary metastatization. A gradual spontaneous functional improvement commenced and led several years later to a stabilized state involving moderately severe symptoms.

METHODS

In the 15th year of the clinical course, magnetic resonance imaging (MRI) and positron emission tomography (PET) with [(18)F]fluorodeoxyglucose (FDG) and [(11)C] methionine were conducted. Four lines of experiments (clonogenic assay using fibroblasts isolated from a skin biopsy sample of the patient, comet assay, micronucleus assay, and the testing of chromosome aberrations after in vitro irradiation of peripheral blood samples) were performed in a search for an increased individual radiosensitivity.

RESULTS

MRI investigations failed to reveal any pathological change. PET demonstrated an increased FDG accumulation, but a negligible [(11)C] methionine uptake in the irradiated spinal cord segments. The radiobiological investigations did not indicate any sign of an increased individual radiosensitivity.

CONCLUSIONS

We suggest that the observed partial functional recovery and stabilization of the symptoms of radiogenic LMND may be explained by the higher than normal density of sodium channels expressed along the demyelinated axons of the restored conduction. The increased energy demands of this type of conduction are proved by a higher metabolic rate (increased FDG uptake) of the irradiated spinal cord segments without a substantial regenerative process (lack of detectable protein synthesis).

Radiation myelitis in a 5-year-old girl

Myelopathy is an uncommon complication of radiotherapy, particularly in the pediatric age group. A 5-year-old girl with acute lymphoblastic leukemia developed a severe but transient radiculopathy after intrathecal administration of methotrexate and cytarabine for an isolated central nervous system relapse. Chemotherapy was then given through an intraventricular catheter. Owing to a second central nervous system recurrence, she was treated with craniospinal radiation. The whole brain down to the level of C2 received a dose of 2400 cGy. Two months after completion of radiation, the child developed a progressive tetraparesis, and magnetic resonance imaging revealed an enhancing lesion involving the medulla and upper cervical cord. A biopsy was consistent with a treatment-related necrotizing leukoencephalopathy. This case suggests that patients who develop neurologic dysfunction when treated with methotrexate can also be particularly susceptible to radiation-related injury.

Clinical radiation doses for spinal cord: the 1998 international questionnaire

BACKGROUND AND PURPOSE

Emmanuel van der Schueren gave a keynote lecture at the 1988 ASTRO annual conference pointing out that the spinal cord 'tolerance doses' then prescribed were probably unnecessarily cautious, resulting in probable underdosing of some tumours. This lecture was supported both by an international questionnaire which he and two of the present authors had conducted, and by animal experimental data. In 1997 he initiated a 10-year follow-up questionnaire, the results of which are summarised here.

MATERIALS AND METHODS

The present report analyses the change in prescriptions from 1988 to 1998 and the variation in prescriptions among various regions of the World.

RESULTS AND CONCLUSIONS

The main conclusion is that prescribed dose levels have increased significantly in this period. Large geographical variations still exist. Among responders who use a formula to correct for changed dose per fraction, 90% are now using the linear-quadratic model vs. 33% in 1988. The current status of clinically acceptable doses to spinal cord in 2-Gy fractions is discussed briefly. Further details from the responses to the 1998 questionnaire will be presented in another publication.

Neuropathic pain in cancer patients: mechanisms, syndromes, and clinical controversies

The identification of a neuropathic pain syndrome in a cancer patient requires a focused clinical evaluation based on knowledge of common neuropathic pain syndromes. If a tumor is directly involved in the etiology of the pain, oncologic treatment is an initial consideration and may include surgery, radiation, or chemotherapy. There is no single accepted algorithm for the analgesic treatment of neuropathic pain and a systematic approach utilizing therapeutic trials of specific agents at gradually increasing doses is warranted. A trial of opioids, perhaps in combination with an NSAID, is warranted. If the pain is relatively unresponsive to an opioid, a trial with an adjuvant analgesic is reasonable. For example, a tricyclic antidepressant might be selected early for patients with continuous dysesthesia, and early treatment with an anticonvulsant might be used if the pain is predominantly lancinating or paroxysmal. Other adjuvant analgesics can be selected if there is insufficient response to these agents. A trial of sympathetic blockade, pharmacologic, anesthetic or surgical, should be considered in patients with evidence of causalgia or reflex sympathetic dystrophy. Physiatric modalities such as massage, heat, or cold; counterstimulation or transcutaneous electrical nerve stimulation (TENS), and orthopedic interventions, such as braces and splints may be useful. Epidural injections or neurostimulation of the spinal cord or brain can be considered in selected cases where appropriate expertise is available. Treatment of neuropathic pain remains a challenge for both clinicians and patients. The complexity of syndromes and underlying etiologic mechanisms warrants further clinical trials to determine the best treatment modalities for individual pain syndromes.

Delayed radiation myelopathy: serial MR-imaging and pathology

Clinical data, MR-scans, time-dose fractionation schemes and neuropathologic findings of two cases of delayed radiation myelopathy (DRM), are presented. Both patients, a 72-year-old diabetic woman with cervical lymphnode metastasis from a squamous cell carcinoma and a 46-year-old woman with tonsillar carcinoma, developed paraparesis followed by quadriplegia, at 7 and at 10 months following radiation. The spinal cord received 46 and 49 Gy. (Fraction dose 2.25 Gy and 2.0 Gy, 4 times/week). Serial MR-scans showed spinal cord enlargement and focally increased signal intensity (T1-gd). The second patient survived and stabilized following therapy with coumarins. The first patient died 13 months after radiotherapy. At autopsy necrosis, local calcium deposits, lipid macrophages and swollen astrocytes were observed in the white matter. There was slight hyalinosis of the intramedullary vessel walls. We conclude that serial MRI may be helpful to distinguish DRM from other causes of spinal cord injury. DRM may occur at a total dose less than 50 Gy. Additional risk factors (diabetes, hypertension), and fraction doses above 2 Gy contribute to the development of DRM.

Radiation response of the central nervous system

This report reviews the anatomical, pathophysiological, and clinical aspects of radiation injury to the central nervous system (CNS). Despite the lack of pathognomonic characteristics for CNS radiation lesions, demyelination and malacia are consistently the dominant morphological features of radiation myelopathy. In addition, cerebral atrophy is commonly observed in patients with neurological deficits related to chemotherapy and radiation, and neurocognitive deficits are associated with diffuse white matter changes. Clinical and experimental dose-response information have been evaluated and summarized into specific recommendations for the spinal cord and brain. The common spinal cord dose limit of 45 Gy in 22 to 25 fractions is conservative and can be relaxed if respecting this limit materially reduces the probability of tumor control. It is suggested that the 5% incidence of radiation myelopathy probably lies between 57 and 61 Gy to the spinal cord in the absence of dose modifying chemotherapy. A clinically detectable length effect for the spinal cord has not been observed. The effects of chemotherapy and altered fractionation are also discussed. Brain necrosis in adults is rarely noted below 60 Gy in conventional fractionation, with imaging and clinical changes being observed generally only above 50 Gy. However, neurocognitive effects are observed at lower doses, especially in children. A more pronounced volume effect is believed to exist in the brain than in the spinal cord. Tumor progression may be hard to distinguish from radiation and chemotherapy effects. Diffuse white matter injury can be attributed to radiation and associated with neurological deficits, but leukoencephalopathy is rarely observed in the absence of chemotherapy. Subjective, objective, management, and analytic (SOMA) parameters related to radiation spinal cord and brain injury have been developed and presented on ordinal scales.

The radiation response of the cervical spinal cord of the pig: effects of changing the irradiated volume

PURPOSE

An investigation of the field size effect for the cervical spinal cord of the pig after single doses of gamma-rays. In this study, clinically relevant volumes of the spinal cord were irradiated.

METHODS AND MATERIALS

The effects of the local irradiation of different lengths of the spinal cord (2.5 cm, 5.0 cm, and 10.0 cm) have been evaluated in mature pigs (37-43 weeks). Single doses of 25-31 Gy were given using a 60Co gamma-source, at a dose rate of 0.21-0.30 Gy/min. The incidence of radiation-induced paralysis was used as the endpoint. The data were analyzed using probit analysis and a normal tissue complication probability (NTCP)-model.

RESULTS

Twenty-five animals out of a total of 53 developed paralysis, with histological evidence of parenchymal and vascular changes in their white matter. The slope of the dose-response curves decreased with the decrease in field size; however, there was no significant difference at the radiation dose associated with a 50% incidence of paralysis (ED50) irrespective of the method of analysis. The ED50 values +/- standard errors (+/- SE) were 27.02 +/- 0.36 Gy, 27.68 +/- 0.57 Gy, and 28.28 +/- 0.78 Gy for field lengths of 10, 5, and 2.5 cm, respectively. Analysis of the data with a normal tissue complication probability (NCTP) model gave similar results. The latent period for paralysis was 7.5-16.5 weeks with no significant differences between dose and field size.

CONCLUSION

No significant field size-related differences in response were detectable in the cervical spinal cord of mature pigs after single dose irradiations, specifically at a clinically relevant level of effect (< ED10).

The extent, time course, and fraction size dependence of mouse spinal cord recovery from radiation injury

PURPOSE

This experiment was designed to assess: (a) the influence of fraction size and time interval between fractions on the tolerance of the spinal cord to high cumulative doses of radiation; and (b) the influence of the long-term recovery process on the tolerance of the spinal cord to reirradiation.

METHODS AND MATERIALS

The T10-L2 level of the spinal cord of C3Hf mice was irradiated using a conventionally fractionated regimen of 2.0 Gy once daily, a prolonged fractionated regimen of 1.2 Gy once daily, a hyperfractionated regimen of 1.2 Gy twice daily, or a single dose of 12 Gy followed 0-190 days later by a second dose of 5-20 Gy. Mice in the multifractionated regimen groups were given a single 15 Gy top-up dose 24 h after reaching a cumulative fractionated dose of 24-70 Gy. Hind limb strength was measured weekly for 2 years after the completion of irradiation.

RESULTS

Paralysis occurred in a bimodal time distribution, with peaks at 5-10 months and 15-23 months after the completion of irradiation. The cumulative radiation dose was directly associated with the incidence of paralysis in each radiation schedule (p < 0.0001) and inversely associated with the time to onset of paralysis in the 1.2 Gy b.i.d. (p = 0.0001) and 2.0 Gy q.d. schedules (p = 0.03). The median latency of paralysis in each group was inversely associated with the incidence of paralysis in that group (p < 0.001). Decreasing the fraction size from 2.0 to 1.2 Gy once daily markedly increased the radiation tolerance of the spinal cord (p < 0.0001), consistent with a very small alpha-beta value of -0.30 Gy (approximately 95% confidence interval -0.72, +0.18) in the linear-quadratic model. Decreasing the time interval from 24 h to alternating 8 and 16 h periods produced an offsetting diminuation in cord tolerance (p < 0.0001). The 1.2 Gy once daily schedule resulted in ED20 and ED50 values that were approximately double those of the 2.0 Gy once daily and the 1.2 Gy twice daily schedules and a relative risk of paralysis from a given dose that was 0.03 times the risk associated with the other two regimens (p < 0.0001). There was no significant difference between the 2.0 Gy once daily and the 1.2 Gy twice daily dose-paralysis curves (p = 0.86). The residual from a single 12 Gy radiation dose was 17% after 190 days, leaving the retreatment ED50 only 10% below the ED50 of previously unirradiated spinal cord. The relative risk of paralysis after 12 Gy plus a second radiation dose decreased from 1.00 with no time interval between doses to 0.51-0.73 with a 0.25, 1 or 3 day interval, 0.32 with a 7 day interval, 0.11 with a 30 day interval, and 0.06 with a 190 day interval.

CONCLUSION

The increased radiation tolerance of the murine spinal cord produced by decreasing the fraction size from 2.0 to 1.2 Gy was offset by the diminished tolerance produced by decreasing the time interval between fractions from 24 to 8-16 h, resulting in no significant difference in the dose-paralysis curves of conventional and hyperfractionated radiation schedules. The rodent spinal cord eliminates the majority of the occult radiation injury produced by a radiation dose equal to half the ED50 during the months following irradiation. This permits retreatment of previously irradiated spinal cord to high doses without the induction of myelopathy.

Radiation myelopathy following single courses of radiotherapy and retreatment

PURPOSE

To assess the latent time, survival and dose-fractionation factors associated with permanent radiation myelopathy following single and multiple courses of radiotherapy to the spinal cord.

METHODS AND MATERIALS

A retrospective analysis was undertaken of all patients who were registered at the Princess Margaret Hospital between 1955 and 1985, and who developed permanent radiation myelopathy. There were 22 males and 13 females with ages ranging from 30 to 72 years. Twenty-four patients developed permanent myelopathy after one course of radiation therapy and 11 patients following retreatment. Seven patients had histological confirmation of radiation myelopathy at autopsy.

RESULTS

The actuarial survival was 14% at 5 years (median: 8.3 months) from the date of diagnosis of radiation myelopathy. Latent times for myelopathy following a single course of treatment (mean: 18.5 months, 7-57 months), were significantly longer than those after reirradiation (mean: 11.4 months, 4-25 months), p = 0.03. There was not a single incident of myelopathy in patients who received fractionated radiotherapy given once daily to an extrapolated response dose (ERD) of < or = 100 Gy2 (equivalent to 50 Gy in 25 daily fractions). Four patients who developed myelopathy after an ERD of < 100 Gy2 were all treated on accelerated fractionation protocols with multiple fractions given per day. Patients who were reirradiated received significantly higher doses (mean ERD of 148 Gy2) than those who had a single course of treatment (mean ERD of 121 Gy2), p = 0.001.

CONCLUSION

We conclude that the risk of radiation myelopathy following conventionally fractionated radiotherapy to the spinal cord is extremely small; giving multiple fractions per day reduces the spinal cord tolerance; latent time to myelopathy decreases following retreatment; and there is possible long-term recovery of radiation damage in the human spinal cord.