Retinoblastoma—comparative analysis of external radiotherapy techniques, including an IMRT technique

Physics Considerations for Evaluation of Dose for Dose-Response Models of Pediatric Late Effects From Radiation Therapy: A PENTEC Introductory Review

PURPOSE

We describe the methods used to estimate the accuracy of dosimetric data found in literature sources used to construct the Pediatric Normal Tissue Effects in the Clinic (PENTEC) dose-response models, summarize these findings of each organ-specific task force, describe some of the dosimetric challenges and the extent to which these efforts affected the final modeling results, and provide guidance on the interpretation of the dose-response results given the various dosimetric uncertainties.

METHODS AND MATERIALS

Each of the PENTEC task force medical physicists reviewed all the journal articles used for dose-response modeling to identify, categorize, and quantify dosimetric uncertainties. These uncertainties fell into 6 broad categories. A uniform nomenclature was developed for describing the "dosimetric quality" of the articles used in the PENTEC reviews. Among the multidisciplinary experts in the PENTEC effort, the medical physicists were charged with the dosimetric evaluation, as they are most expert in this subject.

RESULTS

The percentage dosimetric uncertainty was estimated for each late effect endpoint for all PENTEC organ reports. Twelve specific sources of dose uncertainty were identified related to the 6 broad categories. The most common reason for organ dose uncertainty was that prescribed dose rather than organ dose was reported. Percentage dose uncertainties ranged from 5% to 200%. Systematic uncertainties were used to correct the dose component of the models. Random uncertainties were also described in each report and in some cases used to modify dose axis error bars. In addition, the potential effects of dose binning were described.

CONCLUSIONS

PENTEC reports are designed to provide guidance to radiation oncologists and treatment planners for organ dose constraints. It is critical that these dose constraint recommendations are as accurate as possible, acknowledging the large error bars for many. Achieving this accuracy is important as it enables clinicians to better balance target dose coverage with risk of late effects. Evidence-based dose constraints for pediatric patients have been lacking and, in this regard, PENTEC fills an important unmet need. One must be aware of the limitations of our recommendations, and that for some organ systems, large uncertainties exist in the dose-response model because of clinical endpoint uncertainty, dosimetric uncertainty, or both.

Stereotactic Gamma Knife® Radiosurgery of Intraocular Retinoblastoma: Six-Year Experience

Background

External beam radiotherapy for resistant retinoblastoma is now seen as a last resort to saving the eye because of the risk of severe side effects: secondary cancers and cosmetic problems of orbital bone growth retardation. To reduce such complications, treatment modalities have shifted towards new radiation therapy techniques. No information on single fraction Gamma Knife® radiosurgery (GKRS) for intraocular retinoblastoma exists.

Materials and methods

Eighteen children (19 eyes) with retinoblastoma were treated with GKRS. The mean age at the time of treatment was 35 months (from 12 to 114 months). Before GKRS, all routes of chemotherapy delivery were held in all cases. The eligibility criteria for GKRS were retinoblastomas not amenable either to systemic or local chemotherapy and local ophthalmological treatment, retinoblastomas too large for conventional local methods, and inability to perform intraarterial chemotherapy. Conventional external beam radiotherapy was excluded in the presented cases, given the possible complications mentioned above. In every case, eye removal was suggested to the child's parents, but they flatly refused. GKRS was proposed as the last chance to save the eye (in four cases, it was performed on the only eye). The median prescribed dose was 22 Gy (interquartile range [IQR]: 18-35 Gy), and the median prescribed isodose was 50% (IQR: 36-90%).

Results

Local control was achieved in 79% of cases (complete tumor regression in 69%, incomplete regression in 10%). Two eyes (10.5%) could not be preserved and had to be enucleated due to the tumor recurrence. Two eyes (10.5%) developed secondary complications (total vitreous hemorrhage, retinal detachment, and iris neovascularization), making adequate tumor control nearly impossible. Overall, 15 eyes (79%) were preserved, and four eyes (21%) were enucleated after GKRS with no signs of tumor recurrence and metastasis in the mean follow-up of 41 months. No acute radiation side effects occurred in any patient after GKRS. Ten children (10 eyes, 53%) were diagnosed with vitreous hemorrhage from mild to severe. Three eyes presented with optic neuropathy one year after GKRS, and four eyes developed retinopathy. Radiation-induced cataract occurred in two eyes. There were no cases of secondary glaucoma or keratopathy in our study. All patients and eyes treated by GKRS were stable within 41 months (from seven to 74 months).

Conclusions

Single fraction Gamma Knife® radiosurgery may be a reasonable salvage treatment for resistant and recurrent retinoblastoma as an alternative approach to enucleation in selected cases. GKRS should be considered in retinoblastoma management.

Retinoblastoma and vision

The assessment of vision has a growing importance in the management of retinoblastoma in the era of globe-conserving therapy, both prior to and after treatment. As survival rates approach 98-99% and globe salvage rates reach ever-higher levels, it is important to provide families with information regarding the visual outcomes of different treatments. We present an overview of the role of vision in determining the treatment given and the impact of complications of treatment. We also discuss screening and treatment strategies that can be used to maximise vision.

Clinical outcomes and prognosis of Thai retinoblastoma patients

BACKGROUND

Retinoblastoma (RB) outcomes in Thailand are unfavorable compared to those of developed countries. This study aims to determine whether the clinical outcomes of patients with RB significantly improved after the implementation of new therapeutic approaches and which clinical factors affect survival and globe-saving outcomes.

METHODS

The medical records of patients newly diagnosed with RB and treated at Siriraj Hospital between January 2005 and December 2018 were reviewed retrospectively. Clinical data, treatments, and outcomes were collected and analyzed.

RESULTS

In 194 eyes (144 patients), leukocoria was the most common presenting feature (76.8%); 129 (66.5%) eyes were staged in group E of the International Classification of Intraocular Retinoblastoma. Of the 149 enucleated eyes, 35 had high-risk histopathological features, mostly choroidal invasion; 45 eyes (23.2%) could be salvaged. The 5-year overall survival rate was 90.3%, an improvement compared to the previous study. The 5-year enucleation-free survival rates of Groups A and B, C, D and E were 100%, 83.1%, 36.7% and 16.6% respectively. Factors associated with a lower survival rate were interval from symptom onset to diagnosis >3 months (hazard ratio (HR): 5.8: 95% confidence interval (CI): 1.637, 20.579) and buphthalmos (HR: 12.57: 95% CI: 3.936, 40.153). Factors associated with high-risk features were secondary glaucoma (HR: 11.016: 95% CI: 1.24, 98.10) and pseudohypopyon (HR: 14.110: 95% CI: 2.16, 92.05).

CONCLUSIONS

Survival rates and globe-saving rates appear to have improved; however, advanced-stage presentation remains the major hindrance. Further studies with a larger cohort and longer follow-up are warranted.

Lens Dose-Response Prediction Modeling and Cataract Incidence in Patients With Retinoblastoma After Lens-Sparing or Whole-Eye Radiation Therapy

PURPOSE

We retrospectively assessed the incidence of cataracts in patients with retinoblastoma (Rb) treated with either lens-sparing radiation therapy (LSRT) or whole-eye radiation therapy (WERT). A secondary aim of this study was to model the dose-response risk of cataract.

METHODS AND MATERIALS

We reviewed 65 patients with Rb treated with radiation therapy (RT) at Children's Hospital, Los Angeles from 1997 to 2015. Eyes that were enucleated before RT or lacked follow-up eye examinations were excluded. All patients underwent computed tomography simulation, and mean lens dose data were collected. Follow-up ophthalmologic examinations and intraocular lens implant history were reviewed for cataracts. The primary event-free survival (EFS) outcome was cataract development. Eyes without cataracts were censored on the last date of eye examination or post-RT enucleation, if applicable. Kaplan-Meier estimates were used to compare EFS outcomes, and dose response was projected with Cox regression and logistic regression models.

RESULTS

Sixty-one patients (94 eyes) were analyzed with a median follow-up of 51.8 months. For eyes treated with WERT, cataracts developed in 71.7% versus 35.3% for LSRT. Median EFS for WERT and LSRT were 20.8 and 67.9 months, respectively. Compared with WERT, a significant EFS benefit was demonstrated for LSRT (P < .001). Mean lens dose had a significant effect on cataracts in both Cox regression and logistic regression models (P < .01). The mean lens dose of 7 Gy was projected to have a 5-year cataract incidence of 20% and 25% with the logistic and Cox regression models, respectively.

CONCLUSIONS

We report the first clinical data demonstrating significantly improved EFS in patients with Rb treated with LSRT. Through lens dose-response modeling, we validate a mean lens dose threshold of 7 Gy to keep cataract risk below 25%. Although RT is used less often for Rb owing to advances in chemotherapy delivery options, these findings are relevant for refining lens dose constraints, particularly in children who have received radiation dose near the orbit.

Challenges and differences in external radiation therapy for retinoblastoma: from standard techniques to new developments

AIMS

The purpose of this study is to calculate the treatment plans and to compare the dose distributions and dose-volume histograms (DVH) for 6 external radiotherapy techniques for the treatment of retinoblastoma as well as intensity-modulated radiotherapy (IMRT) and fractionated stereotactic radiotherapy (Cyberknife).

METHODS

Treatment plans were developed using 6 techniques, including an en face electron technique (ET), an anterior and lateral wedge photon technique (LFT), a 3D conformal (6 fields) technique (CRT), an inverse plan IMRT, tomotherapy, and conventional focal stereotactic external beam radiotherapy with Cyberknife (SBRT). Dose volume analyses were carried out for each technique.

RESULTS

All techniques except electron provided similar target coverage. When comparing conformal plan with IMRT and SBRT, there was no significant difference in planning target volume dose distribution. The mean volume of ipsilateral bony orbit received more than 20 Gy, a suggested threshold for bone growth inhibition. The V20 Gy was 73% for the ET, 57% for the LFT, 87% for the CRT, 65% for the IMRT, 66% for the tomotherapy, and 2.7% for the SBRT.

CONCLUSIONS

This work supports the potential use of IMRT and SBRT to spare normal tissues in these patients.

Analysis of patient outcomes following proton radiation therapy for retinoblastoma

PURPOSE

Proton radiotherapy (PRT) is used in the treatment of retinoblastoma (RB) and has the potential to minimize exposure of normal tissue to radiation and thus decrease risk of toxicity and second malignancies. However, comprehensive analyses of long-term patient outcomes are not available.

METHODS

RB patients treated with PRT at our institution between 1986 and 2012 were invited to return for participation in a study designed to assess long-term outcomes. Enrolled patients underwent comprehensive analysis including oncologic, ophthalmic, endocrine, cephalometric, and quality of life (QOL) assessments.

RESULTS

A total of 12 patients were enrolled in this study, and the average length of follow-up among enrolled patients was 12.9 years (range 4.8-22.2 years). All enrolled patients had bilateral disease, and the disease and visual outcomes for enrolled patients were similar to outcomes for all RB patients treated with PRT over the same time period at our institution. Endocrine evaluation revealed no growth abnormalities or hormonal deficiencies across the cohort. Based on MRI and external cephalometry, PRT was associated with less facial hypoplasia than enucleation. Patient and parent-proxy QOL assessments revealed that RB treatment did not appear to severely impact long-term QOL.

CONCLUSIONS

In addition to providing an opportunity for long-term disease control and functional eye preservation, PRT does not appear to be associated with unexpected late visual, endocrine, or QOL effects in this cohort.

Incidence of second cancers after radiotherapy and systemic chemotherapy in heritable retinoblastoma survivors: A report from the German reference center

BACKGROUND

Survivors of heritable retinoblastoma carry a high risk to develop second cancers. Eye-preserving radiotherapy raises this risk, while the impact of chemotherapy remains less defined.

PROCEDURE

This population-based study characterizes the impact of all treatment modalities on second cancers incidence and type after retinoblastoma treatment in Germany. Data on second cancer incidence in 648 patients with heritable retinoblastoma treated between 1940 and 2008 at the German national reference center for retinoblastoma were analyzed to identify associations with treatment.

RESULTS

The cumulative incidence ratio (per 1,000 person years) of second cancers was 8.6 (95% confidence interval 7.0-10.4). Second cancer incidence was influenced by type of retinoblastoma treatment but not by the year of diagnosis or by sex. Radiotherapy and systemic chemotherapy increased the incidence of second cancers (by 3.0- and 1.8-fold, respectively). While radiotherapy was specifically associated with second cancers arising within the periorbital region in the previously irradiated field, chemotherapy was the strongest risk factor for second cancers in other localizations. Soft tissue sarcomas and osteosarcomas were the most prevalent second cancers (standardized incidence ratio 179.35 compared to the German population).

CONCLUSIONS

Second cancers remain a major concern in heritable retinoblastoma survivors. Consistent with previous reports, radiotherapy increased second cancer incidence and influenced type and localization. However, chemotherapy was the strongest risk factor for second malignancies outside the periorbital region. Our results provide screening priorities during life-long oncological follow-up based on the curative therapy the patient has received and emphasize the need for less-detrimental therapies for children with heritable retinoblastoma.

Fractionated stereotactic radiotherapy using Novalis for confined intra-orbital optic nerve glioma in pediatric patient

INTRODUCTION

Optic gliomas are the most common tumors in the optic pathways during childhood. Among them, about 10 % are located within intra-orbital cavity. However, the optimal management for intra-orbital optic nerve gliomas remains controversial. An 11-year-old male complained about progressive decline of vision in his right eye. Brain MRI revealed a fusiform enlargement of right optic nerve within intra-orbital cavity.

MATERIALS AND METHODS

A presumptive diagnosis of optic nerve glioma was made. Therefore, we performed fractionated stereotactic radiotherapy (FSRT) using Novalis.

DISCUSSION

Five years after FSRT treatment, follow-up MRI revealed size reduction of tumor and visual acuity improvement without radiation-related complications.

Long-term outcomes of Group D eyes in bilateral retinoblastoma patients treated with chemoreduction and low-dose IMRT salvage

BACKGROUND

To evaluate outcomes of Group D eyes of bilateral retinoblastoma patients treated with primary chemoreduction and external beam radiation as salvage.

PROCEDURE

Retrospective chart review of patients diagnosed with bilateral retinoblastoma and designated Group D in at least one eye from January 1, 2000 to December 31, 2009. Overall, 62 Group D eyes of 49 patients were included; 13 had bilateral Group D disease. Primary chemoreduction with vincristine, etoposide, and carboplatin with local consolidation was administered, followed by external beam radiation in the form of intensity-modulated radiation therapy (IMRT) as salvage for recurrent tumor. Primary outcome measure was globe salvage.

RESULTS

Of 62 Group D eyes, 7 were enucleated primarily; 55 were treated with systemic chemoreduction, and local therapy. Chemoreduction cured 26 of 55 eyes (47%). Recurrences were found in 29 eyes; 5 underwent enucleation and 24 were treated with IMRT at a dose of 24 Gy (2 eyes) or 36 Gy (22 eyes). Of the 24 irradiated eyes, 19 (79%) were salvaged and 5 required enucleation. Final visual acuity ranged from 20/20 to light perception with 10 eyes having 20/80 or better visual acuity. Average follow-up was 54.2 months.

CONCLUSION

Kaplan-Meier estimates of eye survival of Group D eyes in bilateral patients at 12 months is 82% (95% confidence interval [CI] 70.1-89.7%); at 60 months eye survival is estimated to be 68% (95% confidence interval [CI] 55.4-82.8%). Systemic treatment for retinoblastoma demonstrated a high rate of globe preservation with acceptable complications and many eyes retaining functional vision.

Retinoblastoma: an overview

Retinoblastoma, the most common intraocular malignancy of childhood arises due to mutation of the retinoblastoma gene on chromosome 13q14. In the hereditary setting this mutation is present in all germ line cells and can occur as early as during development; however it requires a mandatory second "hit" or mutation of the remaining allele for retinoblastoma to develop. The non-hereditary form arises from spontaneous mutation affecting both alleles in a somatic cell of the retina. The tumor may present with leucocoria or strabismus. The diagnosis is best made by an ophthalmologist who examines the patient under sedation. Although tissue biopsy is not routinely performed, imaging studies like ultrasound and MRI scan can serve as useful adjuncts to help in establishing the diagnosis and also aid in staging. Group A tumors are smaller than 3 mm while group B tumors are >3 mm or those located in the macula. Groups C and D tumors are associated with localized and diffuse vitreous seeds respectively. Group E tumors occupy >50% of the globe and are generally not salvagable. Despite the fact that great advances have been made in the treatment of retinoblastoma in the last two decades, a large number patients undergo procedures associated with significant morbidity such as enucleation. We recommend large multi institutional studies using newer therapeutic models and targeting novel pathways to improve the outcome in advanced stage retinoblastoma.

Abnormal orbital growth in children submitted to enucleation for retinoblastoma treatment

Enucleation is typically performed for the treatment of advanced retinoblastoma in children. After enucleation, the orbit undergoes abnormal development. In this study, orbital asymmetry was calculated using computed tomography measurements obtained from patients who experienced enucleation for unilateral retinoblastoma. Influence factors analyzed included: type of treatment, use of orbital implants, and patient's age at diagnosis. A total of 42 children underwent enucleation with a mean follow-up period of 4.8 years. For 28 patients, treatment included enucleation alone, 14 patients received enucleation plus radiation therapy. Thirty patients kept orbital implants long term. The mean orbital volume asymmetry for treated versus contralateral orbits was 16.8%. Mean asymmetry in orbital volume was greater for patients who underwent enucleation combined to radiation therapy (23.7% vs. 13.3%, P=0.05) and for patients without long-term maintenance of the prosthetic implants (29.3% vs. 11.8%, P<0.01). In conclusion, orbital volume is abnormally affected in children after enucleation of 1 eye for the treatment of retinoblastoma, and computed tomography can precisely quantify the asymmetry that develops. Orbital implants improve volumetric growth after enucleation, with 2-fold greater orbital asymmetry achieved without an implant.

Consideraciones clínicas, diagnósticas y de tratamiento en retinoblastoma

El  retinoblastoma es el  tumor  intraocular  primario más frecuente en la infancia. Su detección temprana y el inicio del tratamiento adecuado permiten mejorar  dramáticamente la sobrevida en estos niños. En este artículo se hace una revisión general de la enfermedad. Se empleó PubMed y se revisaron artículos representativos del tema, que permitieran dar una idea general de los diferentes avances alcanzados. Dada su clínica característica, el médico de atención primaria, es pieza fundamental en la captación inicial del paciente.

Preliminary experience in treatment of papillary and macular retinoblastoma: evaluation of local control and local complications after treatment with linear accelerator-based stereotactic radiotherapy with micromultileaf collimator as second-line or salvage treatment after chemotherapy

PURPOSE

To determine the local control and complication rates for children with papillary and/or macular retinoblastoma progressing after chemotherapy and undergoing stereotactic radiotherapy (SRT) with a micromultileaf collimator.

METHODS AND MATERIALS

Between 2004 and 2008, 11 children (15 eyes) with macular and/or papillary retinoblastoma were treated with SRT. The mean age was 19 months (range, 2-111). Of the 15 eyes, 7, 6, and 2 were classified as International Classification of Intraocular Retinoblastoma Group B, C, and E, respectively. The delivered dose of SRT was 50.4 Gy in 28 fractions using a dedicated micromultileaf collimator linear accelerator.

RESULTS

The median follow-up was 20 months (range, 13-39). Local control was achieved in 13 eyes (87%). The actuarial 1- and 2-year local control rates were both 82%. SRT was well tolerated. Late adverse events were reported in 4 patients. Of the 4 patients, 2 had developed focal microangiopathy 20 months after SRT; 1 had developed a transient recurrence of retinal detachment; and 1 had developed bilateral cataracts. No optic neuropathy was observed.

CONCLUSIONS

Linear accelerator-based SRT for papillary and/or macular retinoblastoma in children resulted in excellent tumor control rates with acceptable toxicity. Additional research regarding SRT and its intrinsic organ-at-risk sparing capability is justified in the framework of prospective trials.

Intensity modulated radiotherapy (IMRT) in bilateral retinoblastoma

Background

External beam radiotherapy (EBRT) for retinoblastoma has traditionally been done with conventional radiotherapy techniques which resulted high doses to the surrounding normal tissues.

Case report

A 20 month-old girl with group D bilateral retinoblastoma underwent intensity modulated radiotherapy (IMRT) to both eyes after failing chemoreduction and focal therapies including cryotherapy and transpupillary thermotherapy. In this report, we discuss the use of IMRT as a method for reducing doses to adjacent normal tissues while delivering therapeutic doses to the tumour tissues compared with 3-dimensional conformal radiotherapy (3DCRT). At one year follow-up, the patient remained free of any obvious radiation complications.

Conclusions

Image guided IMRT provides better dose distribution than 3DCRT in retinoblastoma eyes, delivering the therapeutic dose to the tumours and minimizing adjacent tissue damage.

Long term follow-up results of external beam radiotherapy as primary treatment for retinoblastoma

The authors reviewed their experiences of external beam radiotherapy (EBR) as an initial treatment in retinoblastoma patients to determine its long-term effect on subsequent tumor control and complications. A total of 32 eyes in 25 patients that underwent EBR for retinoblastoma were reviewed retrospectively. The patients consisted of 21 boys and 4 girls of median age at treatment of 7.1 months. Radiation doses ranged from 35 to 59.4 Gy. The 10-yr ocular and patient survivals were 75.4% and 92.3%, respectively. Nine of the 32 eyes progressed; 7 of these were enucleated and 2 were salvaged by focal treatment. According to the Reese-Ellsworth classification, 4 of 5 eyes of Group II, 13 of 16 Group III eyes, 2 of 4 Group IV eyes, and 5 of 7 Group V eyes were retained, and of the 32 eyes, 13 had visual acuity better than 20/200. Eleven patients experienced a radiation-induced complication. No patient developed a second malignancy during follow-up. Despite the limited number of patients enrolled, EBR may provide a mean of preserving eyeball and vision for some advanced lesions.

Intensity-modulated radiation therapy for orbital lymphoma

PURPOSE

Orbital manifestations of non-Hodgkin's lymphoma (NHL) are rare and accounts for only 1% of all cases of NHL. There have been no reports of treating orbital lymphoma using intensity-modulated radiotherapy (IMRT).

MATERIALS AND METHODS

Four patients were treated at our institution for orbital lymphoma using IMRT. Radiotherapy (RT) plans using wedged pair fields were developed for comparison. Clinical results using IMRT are presented and a dosimetric analysis between IMRT and RT was performed.

RESULTS

All patients had a complete response based on their physical examinations and post-IMRT imaging. Symptoms that had been present at initial presentation resolved in all patients during the course of the treatment. All four patients experienced only grade 1 dry eye syndrome and keratitis. The average dose to the contralateral orbit, lacrimal gland, and lens were all significantly reduced (P < 0.01) in IMRT patients as compared to the RT patients. IMRT reduced the V5 and V10 for the contralateral lens, orbit, and lacrimal gland and the optic chiasm (P < 0.05).

CONCLUSION

IMRT is feasible when treating orbital lymphoma and reduces dose to critical structures while providing excellent dose coverage of target volumes. IMRT offers patients with orbital lymphoma excellent clinical outcomes, similar to conventional RT, with no increased toxicity.