Risk Of Radiation-induced Malignancies Research Articles

Extracranial Dose and the Risk of Radiation-Induced Malignancy after Intracranial Stereotactic Radiosurgery: is it Time to Establish a Therapeutic Reference Level?

Background. To measure extracranial doses from Gamma Knife Perfexion (GKP) intracranial stereotactic radiosurgery (SRS) and model the risk of malignancy after SRS for different treatment platforms.
 Methods. Doses were measured for 20 patients undergoing SRS on a GKP at distances of 18, 43 and 75 cm from the target, corresponding to the approximate positions of the thyroid, breast and gonads respectively. The National Cancer Institute (NCI) RadRAT calculator was used to estimate excess lifetime cancer risk from this exposure. Five different age groups covering childhood and younger adults were modelled for both sexes.
 Results. Extracranial doses delivered during SRS with the GKP were a median 0.04 %, 0.008 % and 0.002 % of prescription dose at 18 cm, 43 cm and 70 cm from the isocentre respectively. Comparison with the literature revealed that the extracranial dose was lowest from GKP, then linacs equipped with micro-multileaf collimators (mMLC), then linacs equipped with circular collimators (cones), and highest from Cyberknife (CK). Estimated lifetime risks of radiation-induced malignancy in the body for patients treated with SRS aged 5–45 years were 0.03 0.88 %, 0.36–11 %, 0.61–18 % and 2.2–39 % for GKP, mMLC, cones and CK respectively.
 Conclusions. We have compared typical extracranial doses from different platforms and quantified the lifetime risk of radiation-induced malignancy. The risk varies with platform. This should be taken into account when treating children and young adults with SRS. The concept of a therapeutic reference level (TRL), similar to the diagnostic reference level (DRL) established in radiology, is proposed.

Frequency of radiation-induced malignancies post-adjuvant radiotherapy for breast cancer in patients with Li-Fraumeni syndrome.

Women with Li-Fraumeni syndrome (LFS), a cancer predisposition syndrome caused by germline mutations in TP53, have an over 50% risk of developing breast cancer by age 70. Patients with LFS are at risk for radiation-induced malignancies; however, only small case series have prior investigated radiation risks in the treatment of breast cancer. We therefore aimed to investigate the risk of malignancy in breast cancer patients with LFS following adjuvant radiotherapy. A single-institution retrospective chart review was conducted for female breast cancer patients with confirmed germline TP53 mutation. The frequency of radiation-induced malignancies in LFS patients was compared to non-LFS breast cancer cases reported in the Penn Medicine Cancer Registry via statistical analyses. We identified 51 female LFS breast cancer patients with 74 primary diagnoses. Fifty-seven% had a history of breast cancer only, and 25% had breast cancer as their presenting diagnosis of LFS. LFS-associated breast cancers were predominantly invasive ductal carcinoma (48%) and HER2+ (58%). Twenty patients underwent adjuvant radiotherapy with a median follow-up of 12.5 (2-20) years. Of 18 patients who received radiation in a curative setting, one (6%) patient developed thyroid cancer, and one (6%) patient developed sarcoma in the radiation field. This risk for radiation-induced malignancy associated with LFS was higher for both sarcoma and thyroid cancer in comparison with thecontrol cohort. We found a lower risk of radiation-induced secondary malignancies in LFS breast cancer patients than previously reported in the literature (33% risk of radiation-induced sarcoma). These findings suggest that LFS may not be an absolute contraindication for radiotherapy in breast cancer. The potential risk for locoregional recurrence without radiotherapy must be weighed against the long-term risk for radiation-induced malignancies in consideration of adjuvant radiotherapy for LFS breast cancer patients.

Abstract P4-12-33: Frequency of radiation-induced malignancies post-adjuvant radiotherapy for breast cancer in patients with Li-Fraumeni syndrome

Abstract Background. Women with Li-Fraumeni syndrome (LFS), a cancer predisposition syndrome caused by germline mutations in TP53, have an over 50% risk of developing breast cancer (BC) by age 70. Providers often avoid adjuvant radiotherapy to treat BC in LFS patients due to a reported high risk of radiation-induced malignancies of over 30%. We aimed to investigate the characteristics of LFS-associated BC and the risk of subsequent malignancy in BC patients with LFS following adjuvant radiotherapy. Methods. A single institution retrospective chart review was conducted for female BC patients with a confirmed germline TP53 mutation. Statistical analyses were performed to compare the frequency of radiation-induced malignancies in LFS patients to non-LFS BC cases reported in the Penn Medicine Cancer Registry (PMCR) (n=6607 patients total, 3863 who received radiation). Results. Among 95 patients with LFS, we identified 51 female BC patients with 74 primary BC diagnoses. Of 51 patients, 57% had a history of BC only, and 25% had BC as their presenting diagnosis of LFS. LFS-associated BCs were predominantly invasive ductal carcinoma (48%) and HER2+ (58%). We analyzed 20 LFS BC patients who underwent adjuvant radiotherapy with an average follow up of 11.1 (2-20) years. Of 18 patients who received radiation in a curative setting, one (6%) patient developed thyroid cancer and one (6%) patient developed sarcoma in the radiation field. The incidence of thyroid cancer did not significantly differ between LFS-associated and non-LFS BCs. The incidence of radiation-induced sarcoma in patients with LFS is significantly higher than in non-LFS BC patients (0.03%, p=0.01). Conclusion. We found a 6% (one in 18 patients) risk of radiation-induced sarcoma in LFS BC patients, lower than the previously reported rate of 33%. Adjuvant radiotherapy should be considered in LFS BC patients when the potential risk for locoregional recurrence (LRR) or the mortality benefit to radiation is greater than 6%. Citation Format: Anh N Le, Jacquelyn Powers, Kristin Zelley, Angela Bradbury, Payal Shah, Gary Freedman, Katherine Nathanson, Susan M Domchek, Suzanne P MacFarland, Kara N Maxwell. Frequency of radiation-induced malignancies post-adjuvant radiotherapy for breast cancer in patients with Li-Fraumeni syndrome [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P4-12-33.

Intent of health care providers to adopt a clinical decision support tool in the management of minor pediatric head injuries

Radiographic neuroimaging in minor pediatric head injuries contains risks of radiation-induced malignancy. The Pediatric Emergency Care Applied Research Network (PECARN) head injury protocol identifies head-injured children who are at very low risk of clinically important traumatic brain injuries and can safely not receive a head computed tomography (CT) scan. The identified urgent care facility had no facility-wide protocol to manage head injuries. The purpose of the evidence-based practice project was to educate health care providers on the risks of indiscriminate head CT prescription and the utility of the PECARN head injury protocol in the management of minor pediatric head injuries. A knowledge assessment was conducted using pre- and posttests and the likelihood to adopt the PECARN head injury protocol in clinical practice was evaluated using the Evidence-Based Practice Attitude Scale. Additionally, rates of head CT scans ordered that were inappropriate according to the PECARN head injury protocol were calculated postproject and compared with preproject rates. Data analysis was performed using descriptive statistics. Findings included increase in provider knowledge on the use of the PECARN head injury protocol and high likelihood of intent to adopt the PECARN head injury protocol in clinical practice. In addition, rates of head CT prescription postproject were lower than preproject rates, and 82.61% of CT scans ordered postproject were appropriate according to the PECARN head injury protocol. Using the PECARN head injury protocol was associated with consistency of care, reduced unnecessary health care resource utilization, and health care costs.

EDITORIAL COMMENT

The authors present data using a model to estimate the risk vs benefit of using computed tomography urography (CTU) in the evaluation of gross hematuria. Various models and data sources were used to construct the models used in this paper. The risk of radiation-induced malignancy was modeled using the Biological Effects of Ionizing Radiation VII Phase 2 report which assumes a linear, cumulative risk with no upper limit. The literature was then queried to assess the risk of an upper tract urothelial cell carcinoma (UTUC) in a patient with gross hematuria. The sensitivity and specificity of renal ultrasound (RUS) and CTU were included in the model. Finally the loss of life expectancy was used to assess how a potential radiation-induced malignancy might limit the life span of patients. The data were then analyzed by gender as well as age (younger than age 50 vs those older than 50). The authors conclude that RUS may be the best study for females under the age of 50 with gross hematuria.

Does the incidence of thoracic aortic injury warrant the routine use of chest computed tomography in children?

Thoracic aortic injury is a potentially life-threatening injury associated with rapid deceleration mechanisms. Diagnosis is made by chest computed tomography (CT), which is associated with a risk of radiation-induced malignancy. We sought to determine the incidence of aortic injuries in the pediatric population to weigh against the risk of CT imaging. The Pediatric Health Information Systems was queried for children ≤18 years with discharge diagnosis code of thoracic aortic injury (901.0) between December 2004 and 2014. Data abstracted included patient age, gender, diagnosis and procedure codes, and discharge disposition, where available. We also queried for imaging codes to determine what type of chest imaging the child received. Between December 2004 and 2014, 311,850 children were admitted to Pediatric Health Information Systems hospitals with traumatic injury. Of these patients, 46 (0.015%) were coded with a thoracic aortic injury and an accompanying E-code. Twenty-seven patients (58.7%) were male, and the median age was 13 years. The most common mechanism of injury was motor vehicle collision (63%, n = 29). Eighteen hospitals (41.9%) had no patients with a thoracic aortic injury in the 10-year period. In children with a thoracic aortic injury, the mortality rate was 11% (n = 5) and 22 (47.8%) underwent a chest CT during their hospitalization. Forty percent (124,909) of all trauma patients underwent chest CT, with a positive rate for aortic injury of 1.8/10,000. The reported estimated cancer risk from a chest CT scan is 25/10,000 for girls and 7.5/10, 000 in boys, greater than the positive CT rate. Thoracic aortic injuries are rare in children in the United States. The risk of cancer associated with screening chest CT is greater than the likelihood of identifying an aortic injury. Therefore, screening chest CT scans are unwarranted in injured children. Therapeutic/Care Management, level IV.

Current controversies in screening mammography.

Current controversies in screening mammography.

Risk of radiation-induced malignancies from CT scanning in children who underwent shunt treatment before 6 years of age: a retrospective cohort study with a minimum 10-year follow-up

A number of mathematical models predict the risk of future cancer from the ionizing radiation exposure of CT scanning. The predictions are alarming. Some models predict 29,000 future cancers and 14,500 deaths in the US will be directly caused by 1 year's worth of CT scanning. However, there are very few clinical data to justify or refute these claims. Young children are theoretically highly susceptible to the damaging effects of radiation. In this study, the authors examined children who underwent CSF shunt placement before 6 years of age. The authors chose to study shunt-treated patients with the assumption that these patients would undergo future imaging, facilitating surveillance. They chose a study period of 1991-2001 to allow more than 10 years of follow-up data. The authors studied 104 consecutive children who underwent CSF shunt placement prior to 6 years of age and who had at least 10 years of follow-up data. Sixty-two of these patients underwent shunt placement prior to 1 year of age. The age at the initial scanning session, the number of future CT scanning sessions, diagnosis, and results of any future studies were recorded. The age-specific radiation dose was calculated for children younger than 1 year. Children younger than 1 year at the time of shunt placement were evaluated separately, based on the assumption that they represented the highest risk cohort. The authors examined all data for any evidence of future leukemia or head/neck tumor (benign or malignant). These children underwent a total of 1584 CT scanning sessions over a follow-up period of 1622 person-years. A total of 517 scanning sessions were performed prior to 6 years of age, including 260 in the 1st year of life. Children who underwent shunt placement before 1 year of age underwent an average of 16.3 ± 13.5 CT sessions (range 1-41). Children undergoing placement between 1 and 6 years of age received an average of 14.1 ± 12.5 CT studies (range 5-52). There were no subsequent tumors (benign or malignant) or leukemia detected. Previously published models predict a significant number of future cancers directly caused by CT scanning. However, there are very few published clinical data. In the authors' study, zero future radiation-induced malignancies were detected after routine CT scanning in a high-risk group. While the authors do not consider their single-institution study adequate to define the actual risk, their data suggest that the overall risk is low. The authors hope this study encourages future collaborative efforts to define the actual risk to patients.

Peripheral organ doses from radiotherapy for heterotopic ossification of non-hip joints: Is there a risk for radiation-induced malignancies?

Radiotherapy, used for heterotopic ossification (HO) management, may increase radiation risk to patients. This study aimed to determine the peripheral dose to radiosensitive organs and the associated cancer risks due to radiotherapy of HO in common non-hip joints. A Monte Carlo model of a medical linear accelerator combined with a mathematical phantom representing an average adult patient were employed to simulate radiotherapy for HO with standard AP and PA fields in the regions of shoulder, elbow and knee. Radiation dose to all out-of-field radiosensitive organs defined by the International Commission on Radiological Protection was calculated. Cancer induction risk was estimated using organ-specific risk coefficients. Organ dose change with increased field dimensions was also evaluated. Radiation therapy for HO with a 7 Gy target dose in the sites of shoulder, elbow and knee, resulted in the following equivalent organ dose ranges of 0.85–62 mSv, 0.28–1.6 mSv and 0.04–1.6 mSv, respectively. Respective ranges for cancer risk were 0–5.1, 0–0.6 and 0–1.3 cases per 104 persons. Increasing the field size caused an average increase of peripheral doses by 15–20%. Individual organ dose increase depends upon the primary treatment site and the distance between organ of interest and treatment volume. Relatively increased risks of more than 1 case per 10,000 patients were found for skin, breast and thyroid malignancies after treatment in the region of shoulder and for skin cancer following elbow irradiation. The estimated risk for inducing any other malignant disease ranges from negligible to low.

The Risk of Radiation-Induced Malignancy With Heterotopic Ossification Prophylaxis: A Case–Control Analysis

Heterotopic ossification (HO) is a debilitating complication following traumatic fracture or hip surgery. Prior research has shown that prophylactic RT given in a single fraction is more effective and more tolerable in the prevention of HO in the perioperative elderly population than six weeks of indomethacin. Given treatment efficacy, more cases of younger patients with traumatic fractures are being referred for prophylactic RT for HO. A recent case report documented the first incidence of radiation induced sarcoma in a 37 year old male following RT for a traumatic acetabular fracture.

Risks of radiation versus risks from injury: A clinical decision analysis for the management of penetrating palatal trauma in children

Penetrating palatal trauma in children presents a diagnostic dilemma regarding the small but severe risk of injury to carotid vessels. Decisions regarding which children require computed tomography with angiography must be balanced against the risk of radiation-induced malignancy. Our objectives were to compare outcomes between children with and without computed tomography with angiography in the evaluation of palatal trauma and to identify thresholds where the ideal strategy changes in the management of children with palatal trauma through sensitivity analyses. Decision analytic techniques were used to compare management strategies for penetrating palatal trauma. We assigned utilities to the following outcomes: 1) perfect health, 2) future malignancy, 3) carotid injury diagnosed by computed tomography with angiography, and 4) delayed diagnosis of stroke. We calculated outcomes when the risk of stroke ranged from 0.01% to 5.0% for a hypothetical cohort of 10,000 injured children. Not obtaining computed tomography with angiography is the optimal strategy when the stroke risk is less than 4.5%. In two-way sensitivity analyses that consider a range of probabilities of radiation-induced malignancy and stroke, not obtaining computed tomography with angiography on all patients dominates as a strategy until the risk of stroke exceeds 2.3%, and the risk of malignancy is under 0.24%. Routine imaging would introduce 20 additional malignancies for each additional stroke diagnosed. Routine use of computed tomography with angiography for well-appearing children with palatal trauma should be reconsidered, as the risk of radiation-induced malignancy may outweigh the benefit of identifying the rare carotid injury. 2b.

Radiotherapy-induced malignancies: review of clinical features, pathobiology, and evolving approaches for mitigating risk.

One of the most significant effects of radiation therapy on normal tissues is mutagenesis, which is the basis for radiation-induced malignancies. Radiation-induced malignancies are late complications arising after radiotherapy, increasing in frequency among survivors of both pediatric and adult cancers. Genetic backgrounds harboring germline mutations in tumor suppressor genes are recognized risk factors. Some success has been found with using genome wide association studies to identify germline polymorphisms associated with susceptibility. The insights generated by genetics, epidemiology, and the development of experimental models are defining potential strategies to offer to individuals at risk for radiation-induced malignancies. Concurrent technological efforts are developing novel radiotherapy delivery to reduce irradiation of normal tissues, and thereby, to mitigate the risk of radiation-induced malignancies. The goal of this review is to discuss epidemiologic, modeling, and radiotherapy delivery data, where these lines of research intersect and their potential impact on patient care.

The Dosimetric Effects of Different Beam Energy on Physical Dose Distributions in IMRT Based on Analysis of Physical Indices

This work aimed at evaluating the effect of 6- and 10-MV photon energies on intensity-modulated radiation therapy (IMRT) treatment plan outcome in different selected diagnostic cases. For such purpose, 19 patients, with different types of non CNS solid tumers, were selected. Clinical step-and-shoot IMRT treatment plans were designed for delivery on a Siemens Oncor accelerator with 82 leafs; multi-leaf collimators (MLCs). To ensure that the similarity or difference among the plans is due to energy alone, the same optimization constraints were applied for both energy plans. All the parameters like beam angles, number of beams, were kept constant to achieve the same clinical objectives. The Comparative evaluation was based on dose-volumetric analysis of both energy IMRT plans. Both qualitative and quantitative methods were used. Several physical indices for Planning Target Volume (PTV), the relevant Organs at Risk (OARs) as mean dose (Dmean), maximum dose (Dmax), 95% dose (D95), integral dose, total number of segments, and the number of MU were applied. Homogeneity index and conformation number were two other evaluation parameters that were considered in this study. Collectively, the use of 6 MV photons was dosimetrically comparable with 10 MV photons in terms of target coverage, homogeneity, conformity, and OAR savings. While 10-MV plans showed a significant reduction in the number of MUs that varied between 4.2% and 16.6% (P-value = 0.0001) for the different cases compared to 6-MV. The percentage volumes of each patient receiving 2 Gy and 5 Gy were compared for the two energies. The general trend was that 6-MV plans had the highest percentage volume, (P-value = 0.0001, P-value = 0.006) respectively. 10-MV beams actually decreased the integral dose (from average 183.27 ± 152.38 Gy-Kg to 178.08 ± 147.71 Gy-Kg, P-value = 0.004) compared with 6-MV. In general, comparison of the above parameters showed statistically significant differences between 6-MV and 10-MV groups. Based on the present results, the 10-MV is the optimal energy for IMRT, regardless of the concerns about a potential risk of radiation-induced malignancies. It is recommended that the choice to treat at 10 MV be taken as a risk vs. benefit as the clinical significance remains to be determined on case by case basis.

Pediatric Traumatic Brain Injury and Radiation Risks: A Clinical Decision Analysis

To determine the optimal imaging strategy for young children with minor head injury considering health-related quality of life and radiation risk. In children with minor head trauma, the risk of missing a clinically important traumatic brain injury (ciTBI) must be weighed against the risk of radiation-induced malignancy from computed tomography (CT) to assess impact on public health. We included children <2 years old with minor blunt head trauma defined by a Glasgow Coma Scale score of 14-15. We used decision analysis to model a CT-all versus no-CT strategy and assigned values to clinical outcomes based on a validated health-related quality of life scale: (1) baseline health; (2) non-ciTBI; (3) ciTBI without neurosurgery, death, or intubation; and (4) ciTBI with neurosurgery, death, or intubation >24 hours with probabilities from a prospective study of 10000 children. Sensitivity analysis determined the optimal management strategy over a range of ciTBI risk. The no-CT strategy resulted in less risk with the expected probability of a ciTBI of 0.9%. Sensitivity analysis for the probability of ciTBI identified 4.8% as the threshold above which CT all becomes the preferred strategy and shows that the threshold decreases with less radiation. The CT all strategy represents the preferred approach for children identified as high-risk. Among children <2 years old with minor head trauma, the no-CT strategy is preferable for those at low risk, reserving CT for children at higher risk.

The best method for dose escalation: Prostate brachytherapy

The best method for dose escalation: Prostate brachytherapy

Understanding the Cancer-CT Conundrum

It is imperative that responsible clinicians understand the relationship between computed tomography imaging and radiation-induced malignancy risk. As the concept of computed tomography-induced malignancy risk becomes more widespread, it is important that clinicians are well informed and are able to intelligently answer questions and concerns posed by their patients and are able to understand and discuss the issues with their radiologist colleagues. The purpose of this article is to review the history of ionizing radiation exposure growth in diagnostic imaging, to understand the biologic effects of radiation exposure, to define the growth of ionizing radiation from computed tomography in the United States, and to explore available mechanisms that can be used to control excessive patient radiation exposure.

Identification of children at very low risk of clinically-important brain injuries after head trauma: a prospective cohort study

CT imaging of head-injured children has risks of radiation-induced malignancy. Our aim was to identify children at very low risk of clinically-important traumatic brain injuries (ciTBI) for whom CT might be unnecessary. We enrolled patients younger than 18 years presenting within 24 h of head trauma with Glasgow Coma Scale scores of 14-15 in 25 North American emergency departments. We derived and validated age-specific prediction rules for ciTBI (death from traumatic brain injury, neurosurgery, intubation >24 h, or hospital admission >or=2 nights). We enrolled and analysed 42 412 children (derivation and validation populations: 8502 and 2216 younger than 2 years, and 25 283 and 6411 aged 2 years and older). We obtained CT scans on 14 969 (35.3%); ciTBIs occurred in 376 (0.9%), and 60 (0.1%) underwent neurosurgery. In the validation population, the prediction rule for children younger than 2 years (normal mental status, no scalp haematoma except frontal, no loss of consciousness or loss of consciousness for less than 5 s, non-severe injury mechanism, no palpable skull fracture, and acting normally according to the parents) had a negative predictive value for ciTBI of 1176/1176 (100.0%, 95% CI 99.7-100 0) and sensitivity of 25/25 (100%, 86.3-100.0). 167 (24.1%) of 694 CT-imaged patients younger than 2 years were in this low-risk group. The prediction rule for children aged 2 years and older (normal mental status, no loss of consciousness, no vomiting, non-severe injury mechanism, no signs of basilar skull fracture, and no severe headache) had a negative predictive value of 3798/3800 (99.95%, 99.81-99.99) and sensitivity of 61/63 (96.8%, 89.0-99.6). 446 (20.1%) of 2223 CT-imaged patients aged 2 years and older were in this low-risk group. Neither rule missed neurosurgery in validation populations. These validated prediction rules identified children at very low risk of ciTBIs for whom CT can routinely be obviated. The Emergency Medical Services for Children Programme of the Maternal and Child Health Bureau, and the Maternal and Child Health Bureau Research Programme, Health Resources and Services Administration, US Department of Health and Human Services.

Osteosarcoma After External Beam Radiation Therapy for Recurrent Choroidal Melanoma

A 59-year-old woman underwent enucleation for choroidal melanoma. She had a late recurrence of the melanoma, which was treated with surgery and radiotherapy. Nine years after radiation treatment, she presented with pain and an orbital mass. Biopsy of the mass revealed an osteoblastic osteosarcoma. This report describes the late recurrence of choroidal melanoma and subsequent radiation-induced osteosarcoma. The risk of radiation-induced malignancy should be considered in all patients receiving radiotherapy. Despite yearly review, osteosarcoma was diagnosed only when the patient had symptoms, thus raising questions about the merits of long-term follow-up in detecting recurrence or emergence of secondary tumors.

SU-FF-T-384: The Impact of Prostate IMRT On Radiation Induced Malignancies

Introduction: The application of intensity-modulated radiation therapy (IMRT) in the treatment of prostate cancer has provided a tool to deliver high doses to the target volume while sparing surrounding critical structures. The drawback of intensity modulation, as implemented using computer-controlled multileaf collimators (MLC), is the larger number of monitor units (MU) and more beam directions used compared to conventional radiotherapy. Concerns have been raised that the widespread use of IMRT could lead to an increase in radiation-induced malignancies (RIM) due to more normal tissues being exposed to low dose radiation. Method and Materials: The EGS4/BEAM code was used to simulate detailed accelerator geometry to generate phase space data for the clinical beams in our department. Using patient CT data with the EGS4/MCSIM code, we calculated the dose to the patient for IMRT and conventional treatments. Based on the doses received by the risk organs away from the target we calculated the total whole-body dose equivalent and estimated the risk of RIM. Results: IMRT increases the leakage dose but not the scatter dose to risk organs. IMRT uses more MUs (3–8 times) than conventional treatments. For a 10MV photon beam, the estimated percent likelihood of a fatal second cancer due to 72 Gy was 0.5% for conventional treatment and it ranged from 0.6% to 1.6% for prostate IMRT depending on the energy, the accelerator/MLC design and the optimization/leaf sequence algorithms used. Conclusion: The increased leakage radiation due to IMRT results in an increased risk of RIM. Analysis of the dose volume histograms and the corresponding TCP, NTCP and the relative risk of RIM may help develop guidelines for IMRT treatment planning in selecting treatment technique, beam energy, beam delivery methods and plan acceptance criteria.

Osteosarcoma of the Skull Base after Radiation Therapy in a Patient with McCune-Albright Syndrome: Case Report

Sarcomas of the skull base occurring in the field of prior radiotherapy are rare; only a few have been reported in the English literature. We report a fatal osteosarcoma of the skull base arising in a patient with McCune-Albright syndrome and severe fibrous dysplasia of the skull base 22 years after radiation therapy for a pituitary adenoma. This malignancy fulfills Cahan's criteria for a radiation-induced tumor in that it arose in the radiation field of a pituitary adenoma with a latency of 22 years. The literature on radiation-induced sarcomas of the skull base is reviewed, and the predisposition of patients with isolated fibrous dysplasia or McCune-Albright syndrome to develop radiation-induced tumors is discussed. Although the risk of radiation-induced malignancy is low in the general population, special consideration should be given when contemplating the use of radiotherapy for benign disease in patients with McCune-Albright syndrome or isolated fibrous dysplasia.