Preventing radiation retinopathy with hyperfractionation

Comparison of stereotactic radiotherapy and protons for uveal melanoma patients

Background and purpose

Uveal melanoma (UM) is the most common primary ocular malignancy. We compared fractionated stereotactic radiotherapy (SRT) with proton therapy, including toxicity risks for UM patients.

Materials and methods

For a total of 66 UM patients from a single center, SRT dose distributions were compared to protons using the same planning CT. Fourteen dose-volume parameters were compared in 2-Gy equivalent dose per fraction (EQD2). Four toxicity profiles were evaluated: maculopathy, optic-neuropathy, visual acuity impairment (Profile I); neovascular glaucoma (Profile II); radiation-induced retinopathy (Profile III); and dry-eye syndrome (Profile IV). For Profile III, retina Mercator maps were generated to visualize the geographical location of dose differences.

Results

In 9/66 cases, (14 %) proton plans were superior for all dose-volume parameters. Higher T stages benefited more from protons in Profile I, especially tumors located within 3 mm or less from the optic nerve. In Profile II, only 9/66 cases resulted in a better proton plan. In Profile III, better retina volume sparing was always achievable with protons, with a larger gain for T3 tumors. In Profile IV, protons always reduced the risk of toxicity with a median RBE-weighted EQD2 reduction of 15.3 Gy.

Conclusions

This study reports the first side-by-side imaging-based planning comparison between protons and SRT for UM patients. Globally, while protons appear almost always better regarding the risk of optic-neuropathy, retinopathy and dry-eye syndrome, for other toxicity like neovascular glaucoma, a plan comparison is warranted. Choice would depend on the prioritization of risks.

International Consensus Statement on Allergy and Rhinology: Sinonasal Tumors

BACKGROUND

Sinonasal neoplasms, whether benign and malignant, pose a significant challenge to clinicians and represent a model area for multidisciplinary collaboration in order to optimize patient care. The International Consensus Statement on Allergy and Rhinology: Sinonasal Tumors (ICSNT) aims to summarize the best available evidence and presents 48 thematic and histopathology-based topics spanning the field.

METHODS

In accordance with prior International Consensus Statement on Allergy and Rhinology documents, ICSNT assigned each topic as an Evidence-Based Review with Recommendations, Evidence-Based Review, and Literature Review based on the level of evidence. An international group of multidisciplinary author teams were assembled for the topic reviews using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses format, and completed sections underwent a thorough and iterative consensus-building process. The final document underwent rigorous synthesis and review prior to publication.

RESULTS

The ICSNT document consists of four major sections: general principles, benign neoplasms and lesions, malignant neoplasms, and quality of life and surveillance. It covers 48 conceptual and/or histopathology-based topics relevant to sinonasal neoplasms and masses. Topics with a high level of evidence provided specific recommendations, while other areas summarized the current state of evidence. A final section highlights research opportunities and future directions, contributing to advancing knowledge and community intervention.

CONCLUSION

As an embodiment of the multidisciplinary and collaborative model of care in sinonasal neoplasms and masses, ICSNT was designed as a comprehensive, international, and multidisciplinary collaborative endeavor. Its primary objective is to summarize the existing evidence in the field of sinonasal neoplasms and masses.

OCT-A evaluation of the retinal and choroidal structures of patients with a history of radiotherapy due to nasopharyngeal carcinoma

BACKGROUND

To perform the optical coherence tomography angiography (OCT-A) evaluation of the microvascular structures of the retina and choroidal tissue in asymptomatic patients who received radiotherapy for nasopharyngeal carcinoma and to compare the results to those of healthy individuals.

METHODS

Ophthalmological examinations were performed in all asymptomatic patients without vascular or systemic diseases, or fundus findings who had received radiotherapy at least two years earlier. Then, OCT-A scans were obtained. Foveal, parafoveal, and whole retinal thicknesses, vessel densities in the superficial and deep capillary plexuses, subfoveal choroidal thickness, the non-flow area in the superficial capillary plexus, and the choriocapillaris flow area were measured and compared to the values of the healthy control group.

RESULTS

The radiotherapy group had significantly lower deep capillary plexus vascular density and subfoveal choroidal thickness values and significantly higher choriocapillaris flow area values compared to the control group.

CONCLUSIONS

We consider that OCT-A is useful in the early diagnosis of radiation retinopathy that may develop during follow-up in patients with nasopharyngeal carcinoma who have received radiotherapy.

Radiation-Induced Retinopathy and Optic Neuropathy after Radiation Therapy for Brain, Head, and Neck Tumors: A Systematic Review

Background: Patients with brain, head, and neck tumors experience a decline in their quality of life due to radiation retinopathy and optic neuropathy. Little is known about the dose–response relationship and patient characteristics. We aimed to systematically review the prevalence of radiation retinopathy and optic neuropathy. Method: The primary outcome was the pooled prevalence of radiation retinopathy and optic neuropathy. The secondary outcome included the effect of the total radiation dose prescribed for the tumor according to the patient’s characteristics. Furthermore, we aimed to evaluate the radiation dose parameters for organs at risk of radiation retinopathy and optic neuropathy. Results: The pooled prevalence was 3.8%. No retinopathy was reported for the tumor’s prescribed dose of <50 Gy. Optic neuropathy was more prevalent for a prescribed dose of >50 Gy than <50 Gy. We observed a higher prevalence rate for retinopathy (6.0%) than optic neuropathy (2.0%). Insufficient data on the dose for organs at risk were reported. Conclusion: The prevalence of radiation retinopathy was higher compared to optic neuropathy. This review emphasizes the need for future studies considering retinopathy and optic neuropathy as primary objective parameters.

Long-term follow-up and health-related quality of life among cancer survivors with stage IEA orbital-type lymphoma after external photon-beam radiotherapy: Results from a longitudinal study

We assessed the long-term outcomes and treatment-related adverse effects of patients with Stage I, "orbital-type" lymphomas that were uniformly treated with photons. All consecutive patients diagnosed with low-grade, Ann Arbor Stage IEA orbital lymphoma treated between 1999 and 2020 at our department were retrospectively reviewed. We excluded patients with exclusive conjunctival involvement, typically treated with en face electrons. In order to quantify radiotherapy related side effects we applied the CTCAE criteria, analyzed changes in visual acuity, quantified dry eye symptoms by use of the Ocular Surface Disease Index (OSDI) score and applied the EORTC QLQ-C30 questionnaire for quality of life (QoL) assessment. In total 66 eyes of 62 patients were irradiated with a median dose of 30.6 Gy. The median follow-up was 43.5 months. The predominant histological subtype were MALT lymphomas. No local failure occurred in this cohort. Of nine outfield relapses, six solely occurred in the contralateral eye. The 5- and 10- years distant progression free survival rates (PFS) were 81.4% and 63.5%. The 5- and 10-years overall survival rates were 85.1% and 71.9% without any tumor related death. Of the acute toxicities none was higher than CTCAE grade 1. The predominant late toxicities were dry eyes (21.2%) of CTCAE Grade <2 and radiation induced cataracts (19.7%). During long-term follow up the average visual acuity did not deteriorate. The global QoL was worst before treatment and improved significantly after 24 months (p = 0.007). External beam radiotherapy of "orbital-type" lymphomas with photons is an effective and gentle treatment option with excellent local control rates. From the high control rates the trend to use slightly lower total doses of 24-27 Gy with conventional fractionation is supported. As non-coplanar radiotherapy techniques improved and total doses can slightly be reduced, the current status of radiotherapy as first line therapy is provided.

[Radiation-induced retinopathy: actual knowledge and new concepts]

Radiation retinopathy is an occlusive vascular pathology following radiotherapy, generally targeted on the eye or peri-ocular structures. Despite increasingly precise techniques (stereotactic radiosurgery, proton therapy, etc.), the inclusion of the retina in the radiation field is sometimes unavoidable. This can lead to a severe pathology, which can ultimately cause blindness or even the anatomical loss of the eye when neovascular glaucoma occurs, due to the abnormal proliferation of neovessels. Radiation retinopathy have been described for more than a century, but it has recently seen great advances in both diagnosis and treatment. The advances of efficient and less invasive examinations in our clinical practice, such as OCT-angiography, allows for easier screening and diagnosis at earlier stages. Thus a new approach to the pathology is necessary, first of all through new definitions and classifications including previously undetected minimal forms. Furthermore, the recent appearance of intravitreal therapies by injection of anti-VEGF or dexamethasone implants has drastically changed the visual prognosis of these patients, who were previously treated only by retinal photocoagulation of the ischaemic areas. Recent studies have even shown the effectiveness of these new molecules in preventing the development of radiation retinopathy. This review of the literature provides an update on this disease and details how these recent diagnostic and therapeutic developments may play a role in the management of this complication.

Granular Cell Tumor of the Orbit: Review of the Literature and a Proposed Treatment Modality

PURPOSE

To document a unique case of granular cell tumor of the orbit, located lateral to and abutting the optic nerve, that benefited from treatment with proton beam irradiation, with a comprehensive review of the literature on granular cell tumor of the orbit.

METHODS

Clinicopathologic case report with detailed imaging features and histopathologic and immunohistochemical evaluation for cytoplasmic tumor biomarkers differentiating granular cell tumor (GCT) from it mimicking lesions with relevant literature citations. The authors reviewed 20 cases of orbital GCT from 2011 to 2020 in addition to 40 cases from 1948 to 2011 and included a summary of imaging and clinical features, outcomes, and recommended treatment modalities.

RESULTS

A 32-year-old man with 1-year history of left retrobulbar pain and diplopia on lateral gaze, intermittent left eyelid swelling, and a tonic left pupil was found to have a fusiform intraconal mass extending toward the orbital apex and abutting the optic nerve. Histopathologic and immunohistochemical investigations collectively supplied data diagnostic of a GCT with an initial low proliferation rate. GCT is a soft tissue neoplasm that originates in the nervous system and can occur anywhere in the body. This enhancing tumor is isointense to gray matter on T1-weighted MRI, hypointense on T2. After an incisional biopsy, the patient's symptoms persisted, and follow-up imaging several months later revealed further growth of the mass. The impossibility of complete surgical removal prompted the decision to treat with proton beam radiation therapy, which resulted in substantial regression in the size of the residual tumor. Most frequently involving the inferior rectus muscle (42%), orbital GCT is usually benign with only 4 reported cases of malignant orbital GCT (7%). Wide surgical resection with complete removal is usually curative for benign orbital GCT, and proton beam radiation therapy can aid in tumor shrinkage.

CONCLUSIONS

GCT should be considered in the differential diagnosis when encountering patients with mass lesions involving the extraocular muscles, peripheral nerves, or less frequently, the optic nerve or orbital apex. Immunohistochemical analysis of biopsied tissue is required for the definitive diagnosis of GCT. Consideration of adjuvant therapies such as proton beam radiation therapy may be appropriate in cases of incomplete surgical resection of benign GCT. Proton beam radiation therapy can be an excellent therapeutic option for symptomatic relief and residual tumor size reduction with an acceptable toxicity profile.

Ocular, Orbital, and Adnexal Toxicity With High-dose Volumetric Modulated Arc Radiation Therapy for Orbital Malignancies

PURPOSE

Conventional modalities of external-beam radiation therapy (EBRT) are associated with high incidences of severe vision-threatening ocular and orbital toxicities when used to treat orbital malignancies. We investigate toxicities associated with high-dose volumetric modulated arc therapy (VMAT), a commonly used contemporary treatment modality for these tumors.

METHODS

Retrospective analysis of malignant orbital tumors managed with adjuvant high-dose VMAT preceded by globe-salvaging surgical therapy (GST) or exenteration. Dosimetric quantitation of target volumes and critical structures was performed. Incidence and severity of ocular, orbital, and adnexal toxicities were evaluated and assessed with regard to conventional EBRT toxicities for orbital malignancies described in the literature.

RESULTS

Eighty-four subjects (mean age = 65.9 ± 9.7 years) were included (N = 48 and N = 36 in GST and exenteration subgroups, respectively). Mean dose was 64.8 ± 2.1 Gy to the planning target volume. Dosing to critical structures typically did not surpass known tissue tolerance limits. Median follow up was 18.3 months. Visual acuity in the GST subgroup was not significantly different after VMAT (0.25 ± 0.06) compared with baseline (0.23 ± 0.02; P = 0.302). Whereas severe toxicities reported by major systematic analyses in the literature with older EBRT modalities were relatively common-for example, retinopathy (16-40%), optic neuropathy (16%), and corneal perforation (13%)-toxicities with VMAT were typically mild and less common. The most common toxicities with VMAT were mild dry eye (81.3%; 39/48), cataract (21.1%; 8/38 phakic eyes), and periocular dermatitis (15.5%; 13/84). Vision-threatening toxicities, including severe corneal pathologies, retinopathy, or optic neuropathy, were rare. There were no contralateral ocular or adnexal toxicities.

CONCLUSIONS

High-dose VMAT for orbital malignancies demonstrated low incidence and severity of eye-related toxicity, in contradistinction to adverse events reported from conventional forms of radiotherapy.

Non-Cancer Effects following Ionizing Irradiation Involving the Eye and Orbit

Simple Summary

The irradiation of tumors involving the eye or orbit represents a complex therapeutic challenge due to the proximity between the tumor and organs that are susceptible to radiation. The challenges include tumor control, as it is often a surrogate for survival; organ (usually the eyeball) preservation; and the minimization of damage of sensitive tissues surrounding the tumor in order to preserve vision. Anticipation of the spectrum and severity of radiation-induced complications is crucial to the decision of which technique to use for a given tumor. The aim of the present review is to report the non-cancer effects that may occur following ionizing irradiation involving the eye and orbit and their specific patterns of toxicity for a given radiotherapy modality. The pros and cons of conventional and advanced forms of radiation techniques and their clinical implementation are provided with a clinical perspective.

Abstract

The eye is an exemplarily challenging organ to treat when considering ocular tumors. It is at the crossroads of several major aims in oncology: tumor control, organ preservation, and functional outcomes including vision and quality of life. The proximity between the tumor and organs that are susceptible to radiation damage explain these challenges. Given a high enough dose of radiation, virtually any cancer will be destroyed with radiotherapy. Yet, the doses inevitably absorbed by normal tissues may lead to complications, the likelihood of which increases with the radiation dose and volume of normal tissues irradiated. Precision radiotherapy allows personalized decision-making algorithms based on patient and tumor characteristics by exploiting the full knowledge of the physics, radiobiology, and the modifications made to the radiotherapy equipment to adapt to the various ocular tumors. Anticipation of the spectrum and severity of radiation-induced complications is crucial to the decision of which technique to use for a given tumor. Radiation can damage the lacrimal gland, eyelashes/eyelids, cornea, lens, macula/retina, optic nerves and chiasma, each having specific dose–response characteristics. The present review is a report of non-cancer effects that may occur following ionizing irradiation involving the eye and orbit and their specific patterns of toxicity for a given radiotherapy modality.

Orbital Metastases: A Systematic Review of Clinical Characteristics, Management Strategies, and Treatment Outcomes

BACKGROUND

Orbital metastases often lead to severe functional impairment. The role of resection, orbital exenteration, and complementary treatments is still debated. We systematically reviewed the literature on orbital metastases.

METHODS

PubMed, Scopus, Web-of-Science, and Cochrane were searched upon PRISMA guidelines to identify studies on orbital metastases. Clinical characteristics, management strategies, and survival were analyzed.

RESULTS

We included 262 studies comprising 873 patients. Median age was 59 years. The most frequent primary tumors were breast (36.3%), melanoma (10.1%), and prostate (8.5%) cancers, with median time interval of 12 months (range, 0-420). The most common symptoms were proptosis (52.3%) and relative-afferent-pupillary-defect (38.7%). Most metastases showed a diffuse location within the orbit (19%), with preferential infiltration of orbital soft tissues (40.2%). In 47 cases (5.4%), tumors extended intracranially. Incisional biopsy (63.7%) was preferred over fine-needle aspiration (10.2%), with partial resection (16.6%) preferred over complete (9.5%). Orbital exenteration was pursued in 26 patients (3%). A total of 305 patients (39.4%) received chemotherapy, and 506 (58%) received orbital radiotherapy. Post-treatment symptom improvement was significantly superior after resection (p = 0.005) and orbital radiotherapy (p = 0.032). Mean follow-up was 14.3 months, and median overall survival was 6 months. Fifteen cases (1.7%) demonstrated recurrence with median local control of six months. Overall survival was statistically increased in patients with breast cancer (p < 0.001) and in patients undergoing resection (p = 0.024) but was not correlated with orbital location (p = 0.174), intracranial extension (p = 0.073), biopsy approach (p = 0.344), extent-of-resection (p = 0.429), or orbital exenteration (p = 0.153).

CONCLUSIONS

Orbital metastases severely impair patient quality of life. Surgical resection safely provides symptom and survival benefit compared to biopsy, while orbital radiotherapy significantly improves symptoms compared to not receiving radiotherapy.

Radiation Retinopathy: Detection and Management Strategies

A gradual shift in trend from primary enucleation to globe salvaging radiation therapy for the management of ocular tumors has resulted in the rise of several post-treatment ocular complications including radiation retinopathy. Radiation retinopathy is a chronic, progressive, and occlusive vasculopathy that can manifest anytime between 1 month to 15 years after starting radiation therapy. The aim of treatment in most of these cases is to prevent further vision loss. Treatment options such as laser photocoagulation, anti-vascular endothelial growth factor and intraviral steroids have been described. However, despite several advances in diagnostic and therapeutic modalities, a significant proportion of eyes with radiation retinopathy eventually go blind. This review summarises some of the clinical features, investigative modalities, and recent therapeutic strategies used in the management of radiation retinopathy.

Cancer of the Paranasal Sinuses

Sinonasal malignancies rare and pathologically diverse and make up <1% of all malignancies. Due to their anatomical location, they can cause significant morbidity with involvement of surrounding critical structures. They often present at a late stage with insidious onset of symptoms. Treatment of sinonasal malignancies is challenging and they often require a multimodality approach with surgery, radiation, and chemotherapy. Outcomes are poor with 5-year overall survival around 32%, but this varies greatly depending on histologic subtype. There is an urgent need for more randomized controlled trials to better define the appropriate therapeutic regimens and to improve clinical outcomes.

Passively Scattered Proton Therapy for Nonmelanoma Skin Cancer with Clinical Perineural Invasion

Purpose

To report our experience with the delivery of passively scattered proton therapy in the management of nonmelanoma skin cancers with clinical perineural invasion.

Materials and Methods

We reviewed the medical records of patients who received definitive or postoperative proton therapy for nonmelanoma skin cancer with clinical perineural invasion at our institution and updated patient follow-up when possible. All patients were treated with curative intent with or without the delivery of concurrent systemic therapy. We report disease control rates and the rates of late toxicity among this cohort.

Results

Twenty-six patients treated between 2008 and 2017 were included in the analysis. Following proton therapy, the 3-year overall, cause-specific, and disease-free survival rates were 59%, 73%, and 60%, respectively. The 3-year local control, local regional control, and distant metastasis-free survival rates were 80%, 65%, and 96%, respectively. On univariate analysis, surgical resection before radiation therapy significantly improved local regional control rates at 3 years (55% versus 86%; P = .04). Grade 3+ late toxicities occurred in 13 patients (50%) and the most common toxicities included grade 3+ keratitis of the ipsilateral eye, which occurred in 4 patients (15%) and grade 3+ brain necrosis in 4 patients (15%).

Conclusion

Proton therapy is effective in the management of nonmelanoma skin cancer with clinical perineural invasion. Although disease control and complication rates compare favorably to those previously published for photon-based radiation therapy, the risk for late toxicity is significant and patients should be appropriately counseled.

Long-term Outcomes from Proton Therapy for Sinonasal Cancers

PURPOSE

To report long-term disease control, survival, and toxicity after proton therapy for sinonasal cancer.

PATIENTS AND METHODS

We reviewed 143 cases of adults with nonmetastatic sinonasal cancers treated with primary (18%; n = 26) or adjuvant (82%; n = 117) proton therapy. The most common histologies were squamous cell carcinoma (29%; n = 42), olfactory neuroblastoma (23%; n = 33), and adenoid cystic carcinoma (16%; n = 23). Patients had predominantly advanced-stage disease (T3, 24%, n = 35; T4, 66%, n = 94) and high-grade histology (52%; n = 74). Surgery included endoscopic resection alone (50%) with craniotomy (10%) or open resection (40%), and 31% had gross disease present at radiotherapy. Most (91%) received high-dose (median, 73.6 Gy radiobiological equivalent [GyRBE]; 84% >70 GyRBE) passive-scatter proton therapy using accelerated hyperfractionation (1.2 GyRBE twice daily) and concurrent chemotherapy (70%). Univariate and multivariate models assessed prognostic factors. Grade 3+ toxicities were recorded per Common Terminology Criteria, version 4. Median follow-up was 3.4 years (range, 0.1-12.5 years) overall and 4.9 years (range, 0.9-12.5 years) for living patients.

RESULTS

The 5-year outcomes were as follows: local control (LC), 80%; neck control, 96%; local-regional control, 78%; freedom from distant metastases, 71%; and disease-free survival, 62%; cause-specific survival, 64%; and overall survival, 59%. Surgery improved LC, but only with gross total resection (5-year LC 87% versus subtotal resection 62.9%, and biopsy alone 55% (P < 0.001). Gross residual disease was the only significant prognostic factor for local-regional control on multivariate analysis. High-grade, T4, and local recurrence were associated with decreased overall survival. Late (G3+) toxicity occurred in 22% (32 of 143), including central nervous system necrosis and vision loss in 6% (9 of 143) and 3.5% (5 of 143), respectively.

CONCLUSION

Proton therapy after gross-total resection provides excellent long-term LC in patients with locally advanced, high-grade sinonasal cancer. Moreover, LC remains strongly associated with long-term survival. With gross disease, about 60% of patients had long-term LC with proton therapy and induction or concurrent chemotherapy.

Radiation-Induced Ocular Surface Disorders and Retinopathy: Ocular Structures and Radiation Dose-Volume Effect

Purpose

This study aimed to evaluate the radiation-induced adverse effects on ocular structures in head and neck cancer patients and investigate the radiation dose-volume effects on the cornea, lacrimal gland, retina, optic nerve and chiasm.

Materials and Methods

A total of 38 eyes of 19 patients were included in this prospective, cohort study. All patients underwent complete ophthalmological examination in addition to contrast sensitivity, visual field and visual evoked potentials (VEP) tests. Ophthalmological examinations and psychophysical tests were performed in 6th, 12th, 18th, 24th months and in the last visit. The relationship between the ophthalmologic findings, and the radiation doses below and above the cut-off values was evaluated.

Results

Contrast sensitivity decrease and visual field deterioration were observed in 42% of the patients in the last visit (median 26 months) whereas a prolonged latency and decreased amplitude of P100 wave in VEP was observed in 58% and 33% of the eyes, respectively at 24th month. Totally 16 patients (84.2%) developed dry eye disease and eight of them received radiotherapy below tolerance doses and had mild to moderate dry eye findings. Radiation-induced retinopathy was observed in three of the eyes in eight patients who received radiation above tolerance dose.

Conclusion

Head and neck cancers treated with radiotherapy, resulted in various ophthalmic complications. All patients who are treating with radiotherapy should be evaluated by an ophthalmologist in terms of anterior and posterior segment damage, even if the radiation dose is below the tolerance limit.

Management of periocular cutaneous squamous cell carcinoma with perineural invasion: a case series and literature review

Purpose: To review and elucidate the complex, multimodal management of periocular cutaneous squamous cell carcinoma (SCC) with perineural invasion (PNI), and offer practical, evidence-based patient care recommendations.Methods: Three exemplary cases of high-risk periocular cutaneous SCC with PNI were selected from a single surgeon's experience. The clinical courses, management, and clinical outcomes, with follow-up intervals of 19, 19, and 24 months after presentation, were reviewed. The English-language literature on PNI, with attention to the management of cutaneous SCC of the head and neck (SCCHN), was reviewed.Results: PNI of cutaneous SCCHN portends aggressive tumor behavior and a worsened prognosis. Treatment is multimodal, with varied combinations of surgical excision, radiotherapy (RT), and systemic chemotherapy. Retrospective reports from multiple institutions involve heterogenous patient populations, treatment strategies, and confounding variables that preclude formulation of a standardized treatment paradigm. Newer, comparative studies of advanced RT techniques (e.g., hyper-fractionation), novel systemic chemotherapeutic agents (e.g., cetuximab, cemiplimab), and varied integrative regimens are providing additional insights. Prompt initiation of adjuvant therapies (within 6-8 weeks of surgery), and careful evaluation of lymphatic basins can increase oncologic control. Utilizing deep-tissue fixation of advancement flaps and eyelid stabilization can enhance functional and aesthetic results.Conclusion: Management of cutaneous SCC with PNI remains complex and in most cases requires combined-modality therapy directed by a multidisciplinary tumor board. With novel therapies and new treatment patterns, optimal combinations and intensities of individual modalities require further elucidation. The oculofacial plastic surgeon plays a pivotal role - in diagnosis, coordination of interdisciplinary management, thoughtful surgical reconstruction, and postoperative surveillance.

Radiation-induced neuropathies in head and neck cancer: prevention and treatment modalities

Head and neck cancer (HNC) is the sixth most common human malignancy with a global incidence of 650,000 cases per year. Radiotherapy (RT) is commonly used as an effective therapy to treat tumours as a definitive or adjuvant treatment. Despite the substantial advances in RT contouring and dosage delivery, patients suffer from various radiation-induced complications, among which are toxicities to the nervous tissues in the head and neck area. Radiation-mediated neuropathies manifest as a result of increased oxidative stress-mediated apoptosis, neuroinflammation and altered cellular function in the nervous tissues. Eventually, molecular damage results in the formation of fibrotic tissues leading to susceptible loss of function of numerous neuronal substructures. Neuropathic sequelae following irradiation in the head and neck area include sensorineural hearing loss, alterations in taste and smell functions along with brachial plexopathy, and cranial nerves palsies. Numerous management options are available to relieve radiation-associated neurotoxicities notwithstanding treatment alternatives that remain restricted with limited benefits. In the scope of this review, we discuss the use of variable management and therapeutic modalities to palliate common radiation-induced neuropathies in head and neck cancers.

Evolution of Care of Orbital Tumors with Radiation Therapy

Orbital tumors are rare lesions comprising 0.1% of all tumors and less than 20% of all ocular diseases. These lesions in children and adults differ significantly in their incidence, tumor type, and treatment management. Although surgery and systemic therapies are commonly used in the management of these diseases, radiation therapy has become a widely used treatment for both benign and malignant tumors of the orbit. Radiotherapy is used as a definitive treatment to provide local control while avoiding morbidity associated with surgery for some tumors while it is used as an adjuvant treatment following surgical resection for others. For many tumors, radiation provides excellent tumor control with preservation of visual function. This article is dedicated for presenting the most common applications of orbital radiotherapy. A brief overview of the commonly available radiation therapy modalities is given. Dose constraint goals are reviewed and acute and long-term side effects are discussed. Orbital tumors covered in this article include optic glioma, ocular melanoma, retinoblastoma, orbital rhabdomyosarcoma, orbital lymphoma, and lacrimal gland tumors. Background information, indications for radiotherapy, and goals of treatment for each case example are described.

Treatment of radiation maculopathy and radiation-induced macular edema: A systematic review

Radiation maculopathy and radiation-induced macular edema are common, sight-threatening complications after radiotherapy, especially that used for uveal melanoma. While many treatment and preventive strategies have been proposed, management of these conditions is still challenging. Initially, treatments were based on the use of retinal laser, but the outcomes were poor. Subsequently, management has shifted toward injection of intravitreal antivascular endothelial growth factor or corticosteroids. We reviewed current clinical evidence, which mostly relies on small sample-sized and retrospective studies, for the management of radiation maculopathy and, in particular, radiation-induced macular edema. At present, the first-line approach is usually intravitreal antivascular endothelial growth factor. Intravitreal dexamethasone implantation may be an option for those with suboptimal response or contraindications to antivascular endothelial growth factor agents. Possible preventive treatments that require future study are intravitreal bevacizumab and ranibizumab, peripheral laser photocoagulation, and subtenon triamcinolone acetonide.

The Role of Adjuvant Treatment in Craniofacial Malignancy: A Critical Review

Background: Tumors originating from the craniofacial region usually present in a locally advanced stage with frequent involvement of adjacent sites and have a strong tendency for local recurrence in the absence of adjuvant therapy, even when the original surgical resection was presumed to be radical. In the past decades, several advances in the radiological diagnosis and treatment of craniofacial malignancies have been introduced. There are, however, no randomized trials that define the optimal multimodal treatment of these tumors because of their rarity as well as heterogeneity in both histology and site of origin. The aim of this study was to conduct a critical review of the role of adjuvant therapy in the treatment of craniofacial malignancy. Method: We conducted a critical review of the past and contemporary literature available, focusing on adjuvant oncological treatments of the most common craniofacial malignancies. Results: Preoperative radiotherapy can have a documented role in the treatment of olfactory neuroblastoma and soft tissue sarcoma, while preoperative chemotherapy can be advocated in the treatment of sinonasal undifferentiated carcinoma, neuroendocrine carcinoma, olfactory neuroblastoma, and craniofacial sarcoma (both soft-tissue and high-grade osteosarcoma). Postoperative radiotherapy has a well-established role in the treatment of most craniofacial malignancies. The role of postoperative chemotherapy is unclear in most histologies, but is commonly used during the treatment of well-selected cases of paranasal sinus carcinoma, olfactory neuroblastoma, mucosal melanoma, soft tissue sarcoma and high-grade craniofacial osteosarcoma. Discussion: Alongside developments in surgery, there have also been improvements in diagnostics, radiotherapy, and chemotherapy. Implementation of novel radiation techniques allows delivery of higher radiation doses while minimizing irradiation-related morbidity. Better understanding of tumor biology allows the construction of more complex treatment strategies, incorporating adjuvant chemotherapy either pre- or postoperatively. In the era of personalized targeted therapy, rapid strides are being made to identify specific tumor-targets for use of novel biologic agents, with the potential to change current management paradigms.

Predictors of Free Flap Volume Loss in Nonosseous Reconstruction of Head and Neck Oncologic Defects

OBJECTIVES

Free tissue reconstruction of the head and neck must be initially overcorrected due to expected postoperative free flap volume loss, which can be accelerated by adjuvant radiation therapy. In this study, we aim to identify patient and treatment-specific factors that may significantly contribute to this phenomenon and translate these characteristics into a predictive model for expected percent free flap volume loss in a given patient.

METHODS

Patients with a history of oral cavity and/or oropharyngeal cancer who underwent nonosseous free flap reconstruction were reviewed between January 2009 and November 2018 at a tertiary care center. Demographics/characteristics, total radiation dose, radiation fractionation (RF), and pre/postradiation free flap volume as evaluated by computed tomography imaging were collected. Free flap volume was measured by a fellowship-trained neuroradiologist in all cases. Only patients receiving adjuvant radiotherapy with available pre/postradiation imaging were included. Multivariable linear regression modeling for prediction of free flap volume loss was performed with optimization via stepwise elimination.

RESULTS

Thirty patients were included for analysis. Mean flap volume loss was 42.7% ± 17.4%. The model predicted flap volume loss in a significant fashion (P = .004, R² = 0.49) with a mean magnitude of error of 9.8% ± 7.5%. Age (β = 0.01, P = .003) and RF (β = -0.01, P = .009) were individual predictors of flap volume loss.

CONCLUSIONS

Our model predicts percent free flap volume loss in a significant fashion. Age and RF are individual predictors of free flap volume loss, the latter being a novel finding that is also modifiable through hyperfractionation radiotherapy schedules.

Glioma-associated radiation retinopathy treated successfully with aflibercept

Radiation retinopathy is a chronic, progressive retinal microangiopathy which can occur with variable latency after retina exposure to ionizing radiation used for cancer treatment. It can occur secondary to treatment of nasopharyngeal tumors, as well as intraocular tumors, such as uveal melanoma and retinoblastoma. Several treatment modalities have been reported including intravitreal corticosteroids, intravitreal anti-VEGFs and argon laser photocoagulation. Our purpose is to present a case report of bilateral radiation retinopathy with macular edema in one eye that was revealed 6 years after glioma therapy and treated successfully by using monotherapy of aflibercept. A 59-year-old male patient presented with gradually deteriorating visual acuity in his left eye for the past 12 months. Best corrected visual acuity in his right eye was 20/25 and in his left eye 20/100. Fundoscopy and fluorescein angiography revealed severe non-proliferative retinopathy in his right eye and proliferative retinopathy in his left eye with macular edema. Following complete work-up and due to his past medical history, he was diagnosed with radiation retinopathy. The patient received 6 intravitreal injections of aflibercept in a period of 9 months in order to treat macular edema and radiation retinopathy. According to the literature, there is minimal experience using aflibercept monotherapy to successfully treat macular edema due to radiation retinopathy. In addition, radiotherapy for glioma is a rather rare cause of radiation retinopathy compared to other more common causes, such as nasopharyngeal tumors, meningiomas, and uveal melanomas.

Risk of ocular complications following radiation therapy in patients with nasopharyngeal carcinoma

OBJECTIVE

To examine the risk of ocular complications following radiotherapy in patients with nasopharyngeal carcinoma (NPC).

METHODS

We adopted 1:1 propensity score matching and identified an NPC cohort (n = 736) and a comparison cohort (n = 736) that comprised non-NPC head and neck cancer patients who received radiotherapy in the National Health Insurance Research Database from 1997 to 2010. The follow-up period was terminated upon developing ocular complications (International Classification of Diseases, Ninth Revision, Clinical Modification [ICD-9-CM]360-379) or on December 31, 2010.

RESULTS

After adjusting for the confounding factors of the study, the NPC cohort had a higher adjusted hazard ratio (HR) for developing ocular complications than the comparison cohort (adjusted HR = 2.786, 95% confidence interval [CI] = 1.805-4.112, P < 0.001). The NPC cohort was associated with a significantly higher risk of developing ocular complications compared with the comparison cohort within 12 and after 24 months of follow-up (P < 0.05). The most common associated ocular complications were optic nerve disorder and retinopathy.

CONCLUSIONS

Patients with NPC might be at higher risk of developing ocular complications after radiotherapy than non-NPC head and neck cancer patients in Taiwan. Either further investigation or routine assessments by ophthalmological physician is recommended.

LEVEL OF EVIDENCE

NA Laryngoscope, 130:1270-1277, 2020.

Exposing primary rat retina cell cultures to γ-rays: An in vitro model for evaluating radiation responses

Retinal tissue can receive incidental γ-rays exposure during radiotherapy either of tumors of the eye and optic nerve or of head-and-neck tumors, and during medical diagnostic procedures. Healthy retina is therefore at risk of suffering radiation-related side effects and the knowledge of pathophysiological response of retinal cells to ionizing radiations could be useful to design possible strategies of prevention and management of radiotoxicity. In this study, we have exploited an in vitro model (primary rat retinal cell culture) to study an array of biological effects induced on retinal neurons by γ-rays. Most of the different cell types present in retinal tissue - either of the neuronal or glial lineages - are preserved in primary rat retinal cultures. Similar to the retina in situ, neuronal cells undergo in vitro a maturational development shown by the formation of polarized neuritic trees and operating synapses. Since 2 Gy is the incidental dose received by the healthy retina per fraction when the standard treatment is delivered to the brain, retina cell cultures have been exposed to 1 or 2 Gy of γ-rays at different level of neuronal differentiation in vitro: days in vitro (DIV)2 or DIV8. At DIV9, retinal cultures were analyzed in terms of viability, apoptosis and characterized by immunocytochemistry to identify alterations in neuronal differentiation. After irradiation at DIV2, MTT assay revealed an evident loss of cell viability and βIII-tubulin immunostaining highlighted a marked neuritic damage, indicating that survived neurons showed an impaired differentiation. Differentiated cultures (DIV8) appeared to be more resistant with respect to undifferentiated, DIV2 cultures, both in terms of cell viability and differentiation. Apoptosis evaluated with TUNEL assay showed that irradiation at both DIV2 and DIV8 induced a significant increase in the apoptotic rate. To further investigate the effects of γ-rays on retinal neurons, we evaluated the expression of synaptic proteins, such as SNAP25 and synaptophysin. WB and immunofluorescence analysis showed an altered expression of these proteins in particular when cultures were irradiated at DIV2. To evaluate the effect of γ-rays on photoreceptors, we studied the expression of rhodopsin in WB analysis and immunofluorescence. Our results confirm data from the literature that differentiated photoreceptors appear to be more resistant to irradiation respect to other retinal cell types present in cultures. The results obtained suggest that γ-rays exposure of primary retinal cultures may contribute to shed further light on the mechanisms involved in γ-radiation-induced neurodegeneration.

[Unusual complication of radiation therapy, corneal perforation: about a case]

Les complications oculaires post radiques sont fréquentes au cours de l'irradiation des tumeurs de la tête et du cou. Certaines sont bénignes et transitoires, d'autres peuvent être très graves pouvant mettre en jeu la fonction visuelle. Nous discuterons à travers ce cas rare et inhabituel, les différentes manifestations et complications oculaires et surtout cornéenne de la radiothérapie ainsi que les modalités diagnostiques et thérapeutiques d'une perforation cornéenne qui représente une complication redoutable de la radiothérapie.

The Role of Radiation Therapy in the Management of Sinonasal and Ventral Skull Base Malignancies

Sinonasal and ventral skull base malignancies are rare tumors that arise in a complex anatomic location juxtaposed with critically important normal tissues. The standard treatment paradigm for most histologies has been surgery followed by postoperative radiation therapy. Because of their propensity to present at an advanced stage and the presence of nearby critical structures, patients are at risk for severe radiation-induced long-term toxicity. Recent advances in radiotherapy technique have improved the therapeutic ratio between tumor control and normal tissue toxicity. This article reviews issues pertinent to the use of radiotherapy in the management of these tumors.

Rapid onset of radiation maculopathy after whole-brain radiation therapy: A case report

BACKGROUND

Radiation maculopathy is a phenomenon that occurs after radiation exposure. The rapid onset of unilateral macular atrophy without peripheral retinopathy after radiation has rarely been described.

METHODS

A case report and literature review.

RESULTS

We report a case of stage 4 non-small cell lung cancer under targeted therapy using Gefitinib who presented with severely impaired visual acuity related to rapid onset of unilateral macular atrophy and diminished photoreceptor inner segment/outer segment (IS/OS) junction 1 month after whole-brain radiation therapy. The fundus fluorescein angiography revealed an enlarged diamond-shaped clear-cut foveal avascular zone in the macula without peripheral retinal vascular changes that differed from typical radiation retinopathy. We confirmed the diagnosis by evaluating the total radiation dosage and by excluding target therapy-induced maculopathy based on a review of the medical literature.

CONCLUSION

Current therapeutic interventions for macular atrophy after radiation therapy remain a challenge. Vasodilators or antiplatelet medication may be beneficial; however, long-term follow-up is needed. Further studies are required to support the use of early aggressive therapy for the prevention of radiation retinopathy.

Optimization of the fractionated irradiation scheme considering physical doses to tumor and organ at risk based on dose-volume histograms

PURPOSE

Radiotherapy of solid tumors has been performed with various fractionation regimens such as multi- and hypofractionations. However, the ability to optimize the fractionation regimen considering the physical dose distribution remains insufficient. This study aims to optimize the fractionation regimen, in which the authors propose a graphical method for selecting the optimal number of fractions (n) and dose per fraction (d) based on dose-volume histograms for tumor and normal tissues of organs around the tumor.

METHODS

Modified linear-quadratic models were employed to estimate the radiation effects on the tumor and an organ at risk (OAR), where the repopulation of the tumor cells and the linearity of the dose-response curve in the high dose range of the surviving fraction were considered. The minimization problem for the damage effect on the OAR was solved under the constraint that the radiation effect on the tumor is fixed by a graphical method. Here, the damage effect on the OAR was estimated based on the dose-volume histogram.

RESULTS

It was found that the optimization of fractionation scheme incorporating the dose-volume histogram is possible by employing appropriate cell surviving models. The graphical method considering the repopulation of tumor cells and a rectilinear response in the high dose range enables them to derive the optimal number of fractions and dose per fraction. For example, in the treatment of prostate cancer, the optimal fractionation was suggested to lie in the range of 8-32 fractions with a daily dose of 2.2-6.3 Gy.

CONCLUSIONS

It is possible to optimize the number of fractions and dose per fraction based on the physical dose distribution (i.e., dose-volume histogram) by the graphical method considering the effects on tumor and OARs around the tumor. This method may stipulate a new guideline to optimize the fractionation regimen for physics-guided fractionation.

Definitive Radiotherapy for Skin and Adenoid Cystic Carcinoma with Perineural Invasion

Adenoid cystic carcinomas (ACC) and, to a lesser extent, cutaneous squamous cell carcinomas and basal cell carcinomas may exhibit perineural invasion (PNI). A subset of patients have tumors with extensive PNI tracking to the skull base that are incompletely resectable and are treated with definitive radiotherapy (RT). RT may be administered with intensity-modulated RT or proton RT. Patients with ACC may also be considered for neutron RT, although the number of available neutron facilities is limited. A substantial proportion of patients with incompletely resectable ACCs and cutaneous carcinomas may be cured with definitive RT. Proton RT provides a more conformal dose distribution compared with other modalities and is likely associated with a lower risk of complications.

Outcomes of Sinonasal Cancer Treated With Proton Therapy

PURPOSE

To report disease outcomes after proton therapy (PT) for sinonasal cancer.

METHODS AND MATERIALS

Eighty-four adult patients without metastases received primary (13%) or adjuvant (87%) PT for sinonasal cancers (excluding melanoma, sarcoma, and lymphoma). Common histologies were olfactory neuroblastoma (23%), squamous cell carcinoma (22%), and adenoid cystic carcinoma (17%). Advanced stage (T3 in 25% and T4 in 69%) and high-grade histology (51%) were common. Surgical procedures included endoscopic resection alone (45%), endoscopic resection with craniotomy (12%), or open resection (30%). Gross residual disease was present in 26% of patients. Most patients received hyperfractionated PT (1.2 Gy [relative biological effectiveness (RBE)] twice daily, 99%) and chemotherapy (75%). The median PT dose was 73.8 Gy (RBE), with 85% of patients receiving more than 70 Gy (RBE). Prognostic factors were analyzed using Kaplan-Meier analysis and proportional hazards regression for multiple regression. Dosimetric parameters were evaluated using logistic regression. Serious, late grade 3 or higher toxicity was reported using the National Cancer Institute Common Terminology Criteria for Adverse Events, version 4. The median follow-up was 2.4 years for all patients and 2.7 years among living patients.

RESULTS

The local control (LC), neck control, freedom from distant metastasis, disease-free survival, cause-specific survival, and overall survival rates were 83%, 94%, 73%, 63%, 70%, and 68%, respectively, at 3 years. Gross total resection and PT resulted in a 90% 3-year LC rate. The 3-year LC rate was 61% for primary radiation therapy and 59% for patients with gross disease. Gross disease was the only significant factor for LC on multivariate analysis, whereas grade and continuous LC were prognostic for overall survival. Six of 12 local recurrences were marginal. Dural dissemination represented 26% of distant recurrences. Late toxicity occurred in 24% of patients (with grade 3 or higher unilateral vision loss in 2%).

CONCLUSIONS

Dose-intensified, hyperfractionated PT with or without concurrent chemotherapy results in excellent LC after gross total resection, and results in patients with gross disease are encouraging. Patients with high-grade histology are at greater risk of death from distant dissemination. Continuous LC is a major determinant of survival justifying aggressive local therapy in nearly all cases.

Dose-response of critical structures in the posterior eye segment to hypofractioned stereotactic photon radiotherapy of choroidal melanoma

PURPOSE

To identify modifying factors and dose-/volume-response relationships for the retina and optic nerve related to highly conformal hypofractionated radiotherapy.

PATIENTS AND METHODS

Seventy-three patients undergoing hypofractionated stereotactic photon radiotherapy of choroidal melanoma were included in this retrospective study. The volumes of the optic nerve receiving doses of more than 7.5 or 12 Gy, respectively, were defined. Optic nerve circumference included in the 30%, 40%, 50%, or 80% isodose (ON%) and retina included in 30% or 40% were determined as quantal effects. Univariate and multivariate analyses were performed for clinical variables as well as probit analysis to define EDx (doses where a positive response is expected in x% of the cases).

RESULTS

Median follow-up was 90.0 (interquartile range 69.0-98.0) months. Fifty-two (71%) and 49 (67%) patients developed radiation retinopathy and optic neuropathy (any grade). Age, length of follow-up and diabetes were significant parameters regarding retinopathy. Optic neuropathy was significantly influenced by age, length of follow-up, and ON30. The probability of optic neuropathy (any grade and grade ≥ 2) significantly increases with the dose (p ranges from 0.0126 to 0.0211).

CONCLUSION

Treatment planning should aim at minimizing encompassing isodoses particularly in the low dose region, without compromising PTV coverage.

External beam radiotherapy for head and neck cancers is associated with increased variability in retinal vascular oxygenation

BACKGROUND

Radiation retinopathy is a possible post-treatment complication of radiation therapy. The pathophysiologic mechanism is hypothesized to be microvascular in origin, but evidence is limited. In an effort to study retinal oxygenation in these patients, we herein evaluate the repeatability and variability of retinal oximetry measurements in subjects who had previously received radiation and make comparisons to a cohort of unirradiated subjects.

METHODS

Using retinal oximetry, a non-invasive imaging modality, we performed in vivo measurements of arteriole (SaO2) and venule SO2 (SvO2) in subjects (n = 9, 18 retinas) who had received incidental radiation to their retinas (≥ 45 Gy to one retina) and in healthy subjects (n = 20, 40 retinas). A total of 1367 SO2 observations on 593 vessels in 29 persons were analyzed to assess three sources of variance in vessel SO2: 1) variance in repeated measurements of the same vessel ("repeatability"), 2) variance in different vessels within the same subject ("within-subject variability"), and 3) variance between subjects ("between-subject variability").

RESULTS

Retinal oximetry measurements were highly repeatable in both irradiated patients and unirradiated subjects. The within-subject variability of SvO2 and SaO2 measurements constituted the highest component of variance in both groups and was significantly higher in venules vs. arterioles (relative effect size 1.8, p<0.001) and in irradiated subjects vs. unirradiated subjects (relative effect size 1.6, p<0.001).

CONCLUSIONS

Retinal oximetry is a highly repeatable technology and can be reliably used to study vascular oxygenation in irradiated subjects. Different vessels within the same subject exhibit a high degree of variability, suggesting that pooled analyses of multiple vessels are most likely to be informative of regional retinal oxygenation. Finally, irradiated subjects exhibited significantly higher within-subject variability in SO2 measurements, suggesting that radiation may cause regional alterations in retinal oxygen delivery and/or metabolism.

Standard fractionation low-dose proton radiotherapy for diffuse choroidal hemangiomas in pediatric Sturge-Weber syndrome

Sturge-Weber syndrome is a nonhereditary congenital neurocutaneous syndrome characterized by leptomeningeal angiomatosis, facial nevus flammeus, and diffuse choroidal hemangioma, which when complicated by total retinal detachment, portend a poor prognosis. Management is often limited to salvage external beam irradiation. We present a modified proton therapy technique for young children with total bullous retinal detachments that uses standard fractionation low-dose proton radiotherapy to decrease the risk of radiation complications. Treatment techniques for young children who cannot cooperate with conventional radiation protocols are also described.

Skin carcinoma of the head and neck with perineural invasion

PURPOSE

The aim of the study was to update the experience treating cutaneous squamous cell and basal cell carcinomas of the head and neck with incidental or clinical perineural invasion (PNI) with radiotherapy (RT).

MATERIALS AND METHODS

From 1965 to 2007, 216 patients received RT alone or with surgery and/or chemotherapy.

RESULTS

The 5-year overall, cause-specific, and disease-free survivals for incidental and clinical PNIs were 55% vs 54%, 73% vs 64%, and 67% vs 51%. The 5-year local control, local-regional control, and freedom from distant metastases for incidental and clinical PNIs were 80% vs 54%, 70% vs 51%, and 90% vs 94%. On univariate and multivariate (P = .0038 and .0047) analyses, clinical PNI was a poor prognostic factor for local control. The rates of grade 3 or higher complication in the incidental and clinical PNI groups were 16% and 36%, respectively.

CONCLUSIONS

Radiotherapy plays a critical role in the treatment of this disease. Clinical PNI should be adequately irradiated to include the involved nerves to the skull base.

Sinonasal malignancies and charged particle radiation treatment: a systematic literature review

Background. Paranasal and nasal cavity malignancies are rare tumors that frequently present at advanced stages. Tumor extension and anatomic complexity pose a challenge for their treatment. Due to their peculiar physical and biological properties particle radiation therapy, i.e. protons and ions can have a role in their management. We performed a systematic literature review to gather clinical evidence about their use to treat sinonasal malignancies. Materials and Methods. We searched the browsers PubMed and Medline as well as specific journals and conference proceedings. Inclusion criteria were: at least 10 patients, English language, reporting outcome and/or toxicity data. Results. We found six studies with data on clinical outcome. Carbon and helium ions were each used in one study, protons in four. Toxicity was specifically described in five studies. One reported acute toxicity of carbon ions, one dealt with brain toxicity from both carbon ions and protons. Three papers reported on visual toxicity: one from carbon ions, one from protons and one from both. Specific data were extracted and compared with the most pertinent literature. Conclusion. Particle radiation therapy is in its early phase of development. Promising results achieved so far must be confirmed in further studies.

A mathematical study to select fractionation regimen based on physical dose distribution and the linear-quadratic model

PURPOSE

Hypofractionated irradiation is often used in precise radiotherapy instead of conventional multifractionated irradiation. We propose a novel mathematical method for selecting a hypofractionated or multifractionated irradiation regimen based on physical dose distribution adding to biologic consideration.

METHODS AND MATERIALS

The linear-quadratic model was used for the radiation effects on tumor and normal tissues, especially organs at risk (OARs). On the basis of the assumption that the OAR receives a fraction of the dose intended for the tumor, the minimization problem for the damage effect on the OAR was treated under the constraint that the radiation effect on the tumor is fixed.

RESULTS

For an N-time fractionated irradiation regimen, the constraint of tumor lethality was described by an N-dimensional hypersphere. The total dose of the fractionated irradiations was considered for minimizing the damage effect on the OAR under the hypersphere condition. It was found that the advantage of hypofractionated or multifractionated irradiation therapies depends on the magnitude of the ratio of α/β parameters for the OAR and tumor in the linear-quadratic model and the ratio of the dose for the OAR and tumor.

CONCLUSIONS

Our mathematical method shows that multifractionated irradiation with a constant dose is better if the ratio of α/β for the OAR and tumor is less than the ratio of the dose for the OAR and tumor, whereas hypofractionated irradiation is better otherwise.