A linac-based stereotactic irradiation technique of uveal melanoma

Gantry-based pencil beam scanning proton therapy for uveal melanoma: IMPT versus proton arc therapy

BACKGROUND

This study reports the single-institution clinical experience of multifield pencil beam scanning (PBS) intensity-modulated proton therapy (IMPT) and dosimetric comparison to proton arc for uveal melanoma (UM) in a regular PBS gantry room.

METHODS

Eleven consecutive UM patients were treated with IMPT to 50 Gy in 5 fractions. A customized gaze-fixation device attached to the thermoplastic mask was used to reproduce the globe position for each patient. IMPT plans were robustly optimized with perturbations of 3 mm setup and 3.5% range uncertainties using 3-4 fields without apertures. Each plan was robustly reoptimized (using the same perturbation parameters) using two non-coplanar arc fields in the RayStation treatment planning system. Treatment quality for both plans was evaluated daily using CBCT-generated synthetic CT. Target coverage, conformity, and mean/maximum doses to adjacent organs were assessed.

RESULTS

Proton arc plans provided comparable plan quality compared to IMPT plans. Similar target coverage was achieved, with an average GTV D95% equal to 101.1% [Formula: see text] 1.0% and 101.4% [Formula: see text] 0.4% for IMPT and proton arc plans, respectively. Proton arc improves the conformity index (RTOG) compared to IMPT plans (average 0.96 [Formula: see text] 0.23 vs. 0.88 [Formula: see text] 0.18, p = 0.11). Both modalities met all the clinical goals for organs-at-risk (OARs), while proton arc significantly reduced the maximum dose for the retina from, on average, 54.5 [Formula: see text] 0.7 to 53.2 [Formula: see text] 0.3 Gy (p < 0.01). Treatment evaluation on synthetic CT showed that the doses received by patients were highly consistent with the planned doses, with a relative target coverage (D95%) difference within 3.5% for IMPT and 3.1% for proton arc, and the D95% of actual delivery exceeding 98.7% and 98.2%, respectively. The doses delivered to OARs did not exceed clinical constraints.

CONCLUSIONS

This is a novel report on proton arc for ocular tumors and gantry-based multifield PBS proton treatment for these tumors. This study demonstrated that both modalities can meet the clinical goals. The IMPT is currently clinically implanted, and 2-field non-coplanar proton arc plans can achieve comparable dosimetric metrics to those of IMPT plans when the deliver technique is matured.

Design of a compacted-sized eye-tracking system with indexed gaze target for ring gantry linear accelerators: verification study using a motorized eye phantom

Background: Eye-tracking systems and gaze targets provide effective immobilization of the eye during ocular radiation therapy treatment. This study proposes a compact-sized eye-tracking system with a gaze target to provide a simple setup in a ring gantry LINAC. The device should have accurate repositioning, while the gaze target should be easily interchangeable.Methods: A compact-sized camera was mounted on a 3D-printed stand integrated with a gaze target. The gaze target can be fixed in different positions using an indexed-positioning system. The repositioning accuracy of this system was evaluated using Computed Tomography (CT) scans. The iris center position of the eye phantom was detected using fast radial symmetry transform. The iris center shift in the camera plane was converted to the 3D absolute displacement using the approximation of the spherical rotation of the eye globe. The tolerance of iris motion from gazing toward the gaze target in the camera plane can be estimated with prior knowledge of the iris center location when gazing toward the camera. The detection accuracy was evaluated on a motorized spherical eye phantom.Results: The mean repositioning errors of the camera and the gaze target were 0.18 mm (Range: 0.08-0.36 mm) and 0.31 mm (Range: 0.03-0.56 mm), respectively. For a typical distance of 200 mm from the camera to the tracked eye, the largest absolute error of iris center detection on a motorized spherical eye phantom was 0.08 mm, while the mean absolute error was less than the resolution of one pixel.Conclusions: This study proposed a compact-sized eye-tracking system with a gaze target with an easily reproducible setup. By converting the displacement of the motorized eye phantom iris center location in the camera plane to 3D coordinate displacement, accurate tolerance of the gaze direction of the eye can be achieved.

Current and Emerging Radiotherapy Options for Uveal Melanoma

What treatment options are there for patients having uveal melanoma? A randomized, prospective, multi-institutional clinical trial (COMS) showed no difference in survival between brachytherapy and enucleation for medium-sized lesions. With the obvious benefit of retaining the eye, brachytherapy has flourished and many different approaches have been developed such as low-dose-rate sources using alternate low-energy photon-emitting radionuclides, different plaque designs and seed-loading techniques, high-dose-rate brachytherapy sources and applicators, and low- and high-dose-rate beta-emitting sources and applicators. There also have been developments of other radiation modalities like external-beam radiotherapy using linear accelerators with high-energy photons, particle accelerators for protons, and gamma stereotactic radiosurgery. This article examines the dosimetric properties, targeting capabilities, and outcomes of these approaches. The several modalities examined herein have differing attributes and it may be that no single approach would be considered optimal for all patients and all lesion characteristics.

Absorbed dose distribution in human eye simulated by FOTELP-VOX code and verified by volumetric modulated arc therapy treatment plan

This paper illustrates the potential of the FOTELP-VOX code, a modification of the general-purpose FOTELP code, combining Monte Carlo techniques to simulate particle transportation from an external source through the internal organs, resulting in a 3-D absorbed dose distribution. The study shows the comparison of results obtained by FOTELP software and the volumetric modulated arc therapy technique. This planning technique with two full arcs was applied, and the plan was created to destroy the diseased tissue in the eye tumor bed and avoid damage to surrounding healthy tissue, for one patient. The dose coverage, homogeneity index, conformity index of the target, and the dose volumes of critical structures were calculated. Good agreement of the results for absorbed dose in the human eye was obtained using these two techniques.

Clinical outcomes and secondary glaucoma after gamma-knife radiosurgery and Ruthenium-106 brachytherapy for uveal melanoma: a single institution experience

We retrospectively analyzed data from records of 48 patients (48 eyes) treated with gamma-knife (n = 18) or Ruthenium-106 brachytherapy (n = 30) for uveal melanoma, in our Ocular Oncology Unit between December 2013 and September 2019, with the aim to evaluate treatment outcomes, and incidence and risk factors for secondary glaucoma. Patients demographics and tumor characteristics at diagnosis were recorded. Follow-up data were collected regarding local tumor control, treatment complications, enucleation need, metastases occurrence and survival status. The median follow-up period was 33.7 months in the gamma-knife group and 26.2 months in the brachytherapy group. The mean tumor thickness, the largest basal diameter and the tumor volume were significantly higher in the gamma-knife group than in the brachytherapy group. The local tumor control rate was 100% in the brachytherapy group and 77.8% in the gamma-knife group. In the gamma-knife group, six patients were enucleated, no patient treated with brachytherapy underwent enucleation. The overall survival rate was 96.7% in the brachytherapy group and 94.44% in the gamma-knife group. Secondary glaucoma occurred in 10 patients after gamma-knife and in one patient after brachytherapy: it should be emphasized that larger lesions were treated with gamma-knife, whereas smaller tumors were selected for brachytherapy. We found a significative correlation of tumor thickness (P value = 0.043) and volume (P value = 0.040) with secondary glaucoma occurrence after gamma-knife treatment. Moreover, secondary glaucoma significantly correlated with radiation retinopathy in the gamma-knife group (P value = 0.009). This study shows preliminary clinical results that could be useful for further studies with more patients and longer follow-up.

Dosimetric comparison and secondary malignancy risk estimation for linac-based and robotic stereotactic radiotherapy in uveal melanoma

It was aimed to investigate the dosimetric differences among linac-based and robotic stereotactic radiotherapy (SRT) techniques for the treatment of uveal melanoma and to evaluate secondary malignancy risks for these different SRT techniques. Ten patients who received robotic SRT with CyberKnife were retrospectively included in this study. A total dose of 54 Gy in three fractions was prescribed to the planning target volume (PTV). For each patient, non-coplanar micro-multileaf collimator based dynamic conformal arc (DCA), intensity-modulated radiotherapy (IMRT) and circular cone based DCA (cDCA) plans were generated. During the analysis dose-volume histogram (DVH) parameters, homogeneity index, new conformity index, the volume received more than or equal to 30% and 50% of the prescribed dose were compared. Additionally, secondary malignancy risk for each technique was estimated using the risk factors recommended by The International Commission on Radiological Protection. Robotic SRT plans provided a high degree of conformity within the PTV and better normal tissue sparing compared to linac-based treatment plans. However, dose distribution was more heterogeneous in robotic SRT plans than that in linac-based techniques. Estimated secondary malignancy risk was also found as 3.4%, 1.4%, 1.4% and 1.6% for robotic SRT and linac-based IMRT, DCA, cDCA plans, respectively. Treatment parameters of uveal melanoma patients planned with robotic SRT had superior conformity and organ-at-risk (OAR) sparing compared with those planned with the linac-based system. However, estimated secondary malignancy risk was almost two-times higher in robotic SRT than that in linac-based techniques.

Hypofractionated stereotactic photon radiotherapy of choroidal melanoma: 20-year experience

BACKGROUND

To evaluate the long-term results after hypofractionated stereotactic photon radiotherapy (SRT) in patients with choroidal melanoma treated between 1997 and 2016.

MATERIAL AND METHODS

A total of 335 patients (183 male and 152 female) with choroidal melanoma unsuitable for ruthenium-106 brachytherapy or local resection were treated with linear accelerator-based SRT at the Medical University of Vienna. All patients received five fractions with either 10, 12 or 14 Gy per fraction. A complete ophthalmic examination including visual acuity and measurement of the tumor base and height using standardized A- and B-scan ultrasonography was performed every 3 months in the first 2 years, every 6 months until 5 years and yearly thereafter. Early and late adverse side effects were assessed at every follow-up visit.

RESULTS

The median overall follow-up was 78.6 months (39.1 to 113.7 months). Local tumor control was 95.4% after 10 and 12 years, respectively. Fifty-four patients developed metastatic disease, and 31 died during the follow-up. Mean visual acuity decreased from 0.55 Snellen at baseline to 0.05 Snellen at the last individual follow-up. Ischemic retinopathy (192/335cases) and optic neuropathy (174/335cases) were the most common radiogenic side effects, followed by radiogenic cataract (n = 127), neovascular glaucoma (n = 71) and corneal epithelium defects (n = 49). Enucleation was performed in 54 patients mostly due to neovascular glaucoma (n = 41) or tumor recurrence (n = 10) during the study period. The eye retention rate was 79.7% after 10 and 12 years.

CONCLUSION

Hypofractionated stereotactic photon radiotherapy showed a high rate of local tumor control for choroidal melanoma and an acceptable rate of radiogenic side effects.

Gamma knife radiosurgery for uveal melanomas and metastases: a systematic review and meta-analysis

BACKGROUND

Gamma knife radiosurgery is regarded as the gold-standard stereotactic radiosurgery modality for the treatment of intracranial tumours, and its use has been expanded for the treatment of intraocular malignancies. The aim of this study was to systematically evaluate the efficacy, outcomes, and complications of gamma knife radiosurgery for uveal melanomas and metastases.

METHODS

We did a systematic review and meta-analysis to aggregate the clinical outcomes of patients with uveal melanomas or intraocular metastases treated primarily with gamma knife radiosurgery. We searched MEDLINE and Embase for studies published between Sept 1, 1960, and Feb 1, 2020, reporting the use of gamma knife radiosurgery as primary treatment for uveal melanoma or uveal metastases. The search was restricted to clinical studies and relevant grey literature published in English. Studies reporting treatment of benign tumours, extraocular tumours, or other forms of stereotactic radiosurgery were excluded to reduce heterogeneity. No restrictions were placed on participant criteria. Local tumour control and tumour regression were extracted as the primary outcomes and analysed via a random-effects meta-analysis of proportions using the DerSimonian and Laird method with a Freeman-Tukey double arcsine transformation. This study is registered with PROSPERO, CRD42019148165.

FINDINGS

Our search returned 454 studies, of which 109 were assessed for full-text eligibility. 52 studies, reporting on 1010 patients with uveal melanoma and 34 intraocular metastases, were eligible for systematic review. 28 studies were included in the meta-analysis. 840 of 898 patients (0·96, 95% CI 0·94-0·97; I²=16%) from 19 studies had local control, and 378 of 478 patients (0·81, 0·70-0·90; I²=83%) from 16 studies experienced tumour regression.

INTERPRETATION

Gamma knife radiosurgery is an efficacious primary method of treating uveal melanomas and intraocular metastases, with reliable tumour control rates. Randomised controlled trials should further evaluate the safety and efficacy of gamma knife radiosurgery in this setting.

FUNDING

The Rhodes Trust and the Howard Brain Sciences Foundation.

A platform for patient positioning and motion monitoring in ocular proton therapy with a non-dedicated beamline

PURPOSE

At Centro Nazionale di Adroterapia Oncologica (CNAO, Pavia, Italy) ocular proton therapy (OPT) is delivered using a non-dedicated beamline. This paper describes the novel clinical workflow as well as technologies and methods adopted to achieve accurate target positioning and verification during ocular proton therapy at CNAO.

METHOD

The OPT clinical protocol at CNAO prescribes a treatment simulation and a delivery phase, performed in the CT and treatment rooms, respectively. The patient gaze direction is controlled and monitored during the entire workflow by means of an eye tracking system (ETS) featuring two optical cameras and an embedded fixation diode light. Thus, the accurate alignment of the fixation light provided to the patient to the prescribed gazed direction is required for an effective treatment. As such, a technological platform based on active robotic manipulators and IR optical tracking-based guidance was developed and tested. The effectiveness of patient positioning strategies was evaluated on a clinical dataset comprising twenty patients treated at CNAO.

RESULTS

According to experimental testing, the developed technologies guarantee uncertainties lower than one degree in gaze direction definition by means of ETS-guided positioning. Patient positioning and monitoring strategies during treatment effectively mitigated set-up uncertainties and exhibited sub-millimetric accuracy in radiopaque markers alignment.

CONCLUSION

Ocular proton therapy is currently delivered at CNAO with a non-dedicated beamline. The technologies developed for patient positioning and motion monitoring have proven to be compliant with the high geometrical accuracy required for the treatment of intraocular tumors.

Early ultrasonographic tumor regression after linear accelerator stereotactic fractionated photon radiotherapy of choroidal melanoma as a predictor for metastatic spread

BACKGROUND AND PURPOSE

During extended follow-up (of up to 15 years), approximately fifty percent of patients with choroidal melanoma will develop metastatic disease and eventually die. Thus, continuing research on prognostic factors, early detection and treatment is necessary. Height regression rates both after plaque brachytherapy and proton beam irradiation have been shown to have prognostic value. The purpose of this study was to analyze the influence of early tumor regression rate after treatment of choroidal melanoma with LINAC stereotactic fractionated radiotherapy (SFRT) as an independent risk factor for metastasis.

MATERIAL AND METHODS

256 patients with choroidal melanoma treated with LINAC SFRT were included. Follow-up included standardized echography yielding apical height, smallest and largest basal linear diameter, tumor volume and mean reflectivity. The influence of baseline measurements and of a longitudinal, normalized area under the curve coefficient (NAC) of the latter marker on metastasis risk was assessed.

RESULTS

NAC for tumor thickness at months 3, 6, and 12 had a statistically significant (p < 0.001) non-linear effect on risk of metastasis. Additionally, ultrasonographic baseline tumor dimensions, but not internal reflectivity were found to be statistically significant risk factors for metastasis.

CONCLUSIONS

Our results demonstrate a non-linear influence of regression rate of choroidal melanoma as independent risk factor of metastatic disease after LINAC SFRT. These prove the clinical experience that, in comparison to rather slow regressions, very quick and very slow early tumor responses to LINAC SFRT are associated with a significantly higher metastasis risk.

Incidence of secondary glaucoma after treatment of uveal melanoma with robotic radiosurgery versus brachytherapy

PURPOSE

Different modalities of radiation therapy nowadays allow for effective treatment of uveal melanoma combined with the advantage of eye preservation. However, this advantage can secondarily be impaired by radiation-related side effects. After local recurrence, secondary glaucoma (SG) has been described as second most frequent complication leading to need of enucleation. This study compares the incidence of SG after conventional Ruthenium (Ru)-106 brachytherapy (BT) versus CyberKnife robotic radiosurgery (RRS) which has been gaining importance lately as an efficient treatment option offering improved patient comfort.

METHODS

Medical records of all patients diagnosed with uveal melanoma in the Eye Clinic of the Ludwig-Maximilians-University Munich between 2007 and 2013 were reviewed. A total of 268 eyes of 268 patients treated with Ru-106 BT or CyberKnife-RRS as monotherapy were entered in this retrospective cohort study. Incidence of SG was correlated with treatment modality and baseline tumour characteristics.

RESULTS

Fifty-three patients (19.8%) developed SG. At 5 years, SG was significantly more frequent after RRS (46.7%) than BT (11.1%); however, tumour thickness (maximum apical height) as a marker of tumour progress was more pronounced in the RRS group. Subgroup analysis of 178 patients for tumours amenable to both BT and RRS (thickness ≤6 mm) revealed comparable results at 3 years (RRS: 13.8 versus BT: 11.2%), but a trend towards increased incidence after RRS beyond year three. However, this difference was not significant at 5 years (28.2% versus 11.2%, p = 0.138). Tumour thickness was significantly associated with incidence of SG.

CONCLUSION

In tumours ≤6 mm thickness, RRS and BT seem to offer a comparable safety profile in terms of SG. Beyond year three, SG was tendentially, but not significantly more frequent after RRS. Increasing tumour thickness is associated with risk of SG.

Gamma Knife Perfexion� radiosurgery and endo diode laser thermotherapy for choroidal melanoma with technical analysis: A case report

Radiosurgery serves an important function in the treatment of patients with intraocular tumors and preserves visual function via organ conservation. Therefore, it is important to ensure the safety and precision of GK-SRS as a primary treatment for intraocular tumors. The present case study described a 57-year-old female with uveal melanoma treated with GK-SRS. Retrobulbar anesthesia following fixation of the treated eye, via the suture of two of the extraocular muscles to the stereotactic frame, was performed to immobilize the eye during treatment. Computed tomography (CT) scans were performed following eye fixation, immediately prior to and following GK-SRS, to validate the accuracy of the tumor localization. The eye movement analysis revealed that the gravity center point deviations of the tumor and lens during treatment were <0.110 mm. At least 95% of the tumor volume was covered by the prescription dose according to three sets of CT images. The patient underwent a trans pars plana vitrectomy owing to a right eye vitreous hemorrhage. A 37-month follow-up assessment revealed tumor shrinkage, and the disappearance of the serous retinal detachments was noted on the basis of ophthalmoscopy and orbital magnetic resonance imaging. No major complications developed during the follow-up period. Using our treatment protocol, GK-SRS is a non-invasive procedure which is used as a brief single fraction treatment for intraocular tumor. The eye fixation method used in the present study has high accuracy.

Dosimetric advantage of volumetric modulated arc therapy in the treatment of intraocular cancer

Objective

The purpose of this study is to investigate the dosimetric advantages of volumetric modulated arc therapy (VMAT) in the treatment of intraocular cancer by comparing it directly with three-dimensional conformal radiotherapy (CRT) and intensity-modulated radiotherapy (IMRT).

Methods

CRT plan, 7f-IMRT plan, and one-arc VMAT plan were generated for 14 intraocular cancer patients. Dosimetric and biological quality indices for target volume and organs at risks (OARs) were evaluated and compared.

Results

The target coverage presented by V95 for CRT, IMRT and VMAT were 95.02% ± 0.67%, 95.51% ± 2.25%, and 95.92% ± 3.05%, respectively. The homogeneity index (HI) for CRT, IMRT and VMAT were 0.15 ± 0.05, 0.23 ± 0.05, and 0.23 ± 0.06, respectively. IMRT and VMAT greatly decreased the dose to ipsilateral lens compared with CRT with a D1 of 2972.66 ± 1407.12 cGy, 3317.82 ± 915.28 cGy and 4809.54 ± 524.60 cGy for IMRT, VMAT and CRT, respectively. Similar results were observed for ipsilateral eyeballs. IMRT and VMAT also spared better on brainstem, optical nerves and optical chiasm compared CRT. However, CRT achieved lower dose to the eyeballs compared with IMRT and VMAT. VMAT and IMRT showed mixed results on target coverage and OAR sparing. The average MUs and delivery time of IMRT and VMAT were 531.25 ± 81.21 vs. 400.99 ± 61.49 and 5.05 ± 0.53 vs.1.71 ± 0.69 min, respectively.

Conclusions

Although no clear distinction on PTV coverage among CRT, IMRT and VMAT plans was observed in the treatment of intraocular cancer, VMAT and IMRT achieved better homogeneity and conformity for target volume, and delivered fewer doses to ipsilateral lens and eyeballs compared with CRT. However, VMAT and IMRT increased the low dose volume to the contralateral OARs. Although VMAT and IMRT showed mixed results on target coverage and OAR sparing, VMAT decreased MU and delivery time significantly compared with IMRT. VMAT is a promising and feasible external beam radiotherapy technique in the treatment of intraocular cancer patients.

A pilot study on geometrical uncertainties for intra ocular cancers in radiotherapy

A system for stabilising and monitoring eye movements for linac-based stereotactic radiotherapy associated with the mobile eye, the Eye Tracker, was developed. Whilst the Eye Tracker design is based on a previously reported system, the purpose of this study was to confirm that the modified version can be used with clinically acceptable treatment margins. We report the estimates of the margin required to account for inter- and intra-fraction eye motion based on data from 12 consecutive patients treated with the Eye Tracker system in place. Patients were immobilised in a head and neck mask and were required to fixate on a light source. A camera system monitored eye movements relative to CT simulation baseline measurements. The Exactrac system (Brainlab, Feldkirchen, Germany) combined with the Varian TrueBeamSTx (Varian Medical Systems, Palo Alto, CA) confirmed pre- and intra-treatment setup of the head position. Displacement/rotation of the image of the pupil/iris was determined in the lateral and superior-inferior directions using a video display. A standard margin equation was applied to estimate the margin required to account for inter- and intra-fraction eye movement. The average displacement in both directions was 0.1-0.2 mm (0.36 mm SD). All patients maintained a position within 1 mm of the intended position during treatment. Based on a Bayesian estimation of the systematic and treatment errors, accounting for displacements in two-planes and a standard deviation of the penumbral width of 1.3 mm, the estimated margins to achieve coverage of the GTV with the 95% isodose in 90% of patients was found to be less than 1 mm. Small random and systematic uncertainties due to inter- and intra-fraction movement of the eye were achieved with the Eye Tracker. Whilst the estimated margins are small (<1 mm) they need to be considered in addition to contouring and treatment delivery uncertainties.

Feasibility study of a non-invasive eye fixation and monitoring device using a right-angle prism mirror for intensity-modulated radiotherapy for choroidal melanoma

We aimed to describe the feasibility and efficacy of a novel non-invasive fixation and monitoring (F-M) device for the eyeballs (which uses a right-angle prism mirror as the optic axis guide) in three consecutive patients with choroidal melanoma who were treated with intensity-modulated radiotherapy (IMRT). The device consists of an immobilization shell, a right-angle prism mirror, a high magnification optical zoom video camera, a guide lamp, a digital voice recorder, a personal computer, and a National Television System Committee standard analog video cable. Using the right-angle prism mirror, the antero-posterior axis was determined coincident with the optic axis connecting the centers of the cornea and pupil. The axis was then connected to the guide light and video camera installed on the couch top on the distal side. Repositioning accuracy improved using this method. Furthermore, the positional error of the lens was markedly reduced from ±1.16, ±1.68 and ±1.11 mm to ±0.23, ±0.58 and ±0.26 mm in the horizontal direction, and from ±1.50, ±1.03 and ±0.48 mm to ±0.29, ±0.30 and ±0.24 mm in the vertical direction (Patient #1, #2 and #3, respectively). Accordingly, the F-M device method decreased the planning target volume size and improved the dose-volume histogram parameters of the organ-at-risk via IMRT inverse planning. Importantly, the treatment method was well tolerated.

Reproducibility of a Noninvasive System for Eye Positioning and Monitoring in Stereotactic Radiotherapy of Ocular Melanoma

Purpose:

Our preferred treatment for juxtapapillary choroidal melanoma is stereotactic radiotherapy. We aim to describe our immobilization system and quantify its reproducibility.

Materials and Methods:

Patients were identified in our radiosurgery database. Patients were imaged at computed tomography simulator with an in-house system which allows visual monitoring of the eye as the patient fixates a small target. All patients were reimaged at least once prior to and/or during radiotherapy. The patients were treated on the CyberKnife system, 60 Gy in 10 daily fractions, using skull tracking in conjunction with our visual monitoring system. In order to quantify the reproducibility of the eye immobilization system, computed tomography scans were coregistered using rigid 6-dimensional skull registration. Using the coregistered scans, x, y, and z displacements of the lens/optic nerve insertion were measured. From these displacements, 3-dimensional vectors were calculated.

Results:

Thirty-four patients were treated from October 2010 to September 2015. Thirty-nine coregistrations were performed using 73 scans (2-3 scans per patient). The mean displacements of lens and optic nerve insertion were 0.1 and 0.0 mm. The median 3-dimensional displacements (absolute value) of lens and nerve insertion were 0.8 and 0.7 mm (standard deviation: 0.5 and 0.6 mm). Ninety-eight percent of 3-dimensional displacements were below 2 mm (maximum 2.4 mm). The calculated planning target volume (PTV) margins were 0.8, 1.4, and 1.5 mm in the anterior–posterior, craniocaudal, and right–left axes, respectively. Following this analysis, no further changes have been applied to our planning margin of 2 to 2.5 mm as it is also meant to account for uncertainties in magnetic resonance imaging to computed tomography registration, skull tracking, and also contouring variability.

Conclusion:

We have found our stereotactic eye immobilization system to be highly reproducible (<1 mm) and free of systematic error.

Optical eye tracking system for real-time noninvasive tumor localization in external beam radiotherapy

PURPOSE

External beam radiotherapy currently represents an important therapeutic strategy for the treatment of intraocular tumors. Accurate target localization and efficient compensation of involuntary eye movements are crucial to avoid deviations in dose distribution with respect to the treatment plan. This paper describes an eye tracking system (ETS) based on noninvasive infrared video imaging. The system was designed for capturing the tridimensional (3D) ocular motion and provides an on-line estimation of intraocular lesions position based on a priori knowledge coming from volumetric imaging.

METHODS

Eye tracking is performed by localizing cornea and pupil centers on stereo images captured by two calibrated video cameras, exploiting eye reflections produced by infrared illumination. Additionally, torsional eye movements are detected by template matching in the iris region of eye images. This information allows estimating the 3D position and orientation of the eye by means of an eye local reference system. By combining ETS measurements with volumetric imaging for treatment planning [computed tomography (CT) and magnetic resonance (MR)], one is able to map the position of the lesion to be treated in local eye coordinates, thus enabling real-time tumor referencing during treatment setup and irradiation. Experimental tests on an eye phantom and seven healthy subjects were performed to assess ETS tracking accuracy.

RESULTS

Measurements on phantom showed an overall median accuracy within 0.16 mm and 0.40° for translations and rotations, respectively. Torsional movements were affected by 0.28° median uncertainty. On healthy subjects, the gaze direction error ranged between 0.19° and 0.82° at a median working distance of 29 cm. The median processing time of the eye tracking algorithm was 18.60 ms, thus allowing eye monitoring up to 50 Hz.

CONCLUSIONS

A noninvasive ETS prototype was designed to perform real-time target localization and eye movement monitoring during ocular radiotherapy treatments. The device aims at improving state-of-the-art invasive procedures based on surgical implantation of radiopaque clips and repeated acquisition of X-ray images, with expected positive effects on treatment quality and patient outcome.

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.

Hypofractionated stereotactic photon radiotherapy of posteriorly located choroidal melanoma with five fractions at ten Gy--clinical results after six years of experience

PURPOSE

To evaluate long-term safety and efficacy of hypofractionated stereotactic photon radiotherapy with 5 five fractions at 10 Gy each in patients with centrally located choroidal melanoma.

MATERIALS AND METHODS

Ninety-one patients with centrally located choroidal melanoma were treated stereotactically at a linear accelerator with 6 MV photon beams with 5 fractions at 10 Gy each. Examinations were performed at baseline and every 3 months in the first 2 years, then every 6 months until 5 years and yearly thereafter. Median follow-up was 37.8 months (IQR 19.2-49.9). They included visual acuity assessment, routine ophthalmological examinations with fundoscopy, echography for measurement of tumor dimensions, medical examinations and, if necessary, fluorescein angiography.

RESULTS

Initial tumor base diameters, height and volume were 11.20mm (IQR 9.10-13.70), 9.80 mm (IQR 7.80-11.70), 4.53 mm (IQR 3.33-6.43) and 253.8mm(3) (IQR 127.5-477.0). Local tumor control and eye retention rates were 97.7% and 86.4% after 5 years, respectively. Eight patients developed metastatic disease and 3 of them died due to metastatic disease during the follow-up period. Median visual acuity decreased from 0.67 initially to 0.05 at the last individual follow-up (p<0.001). The most common toxicities (any grade) were radiation retinopathy (n=39), optic neuropathy (n=32), radiogenic cataract (n=21), neovascular glaucoma (n=15) and dry eye syndrome (n=10). The 5 year probabilities to remain free of these side effects (any grade) were 26.0%, 45.4%, 55.4%, 72.6% and 80.5%, respectively. The most important prognostic factors for toxicities were the largest tumor base diameter, tumor height and tumor distance to the optic disk.

CONCLUSION

Hypofractionated stereotactic photon radiotherapy with a total dose of 50 Gy delivered in 5 fractions is a highly effective treatment option in patients with centrally located choroidal melanoma and has a moderate toxicity profile.

Dosimetry of (125)I and (103)Pd COMS eye plaques for intraocular tumors: report of Task Group 129 by the AAPM and ABS

Dosimetry of eye plaques for ocular tumors presents unique challenges in brachytherapy. The challenges in accurate dosimetry are in part related to the steep dose gradient in the tumor and critical structures that are within millimeters of radioactive sources. In most clinical applications, calculations of dose distributions around eye plaques assume a homogenous water medium and full scatter conditions. Recent Monte Carlo (MC)-based eye-plaque dosimetry simulations have demonstrated that the perturbation effects of heterogeneous materials in eye plaques, including the gold-alloy backing and Silastic insert, can be calculated with reasonable accuracy. Even additional levels of complexity introduced through the use of gold foil "seed-guides" and custom-designed plaques can be calculated accurately using modern MC techniques. Simulations accounting for the aforementioned complexities indicate dose discrepancies exceeding a factor of ten to selected critical structures compared to conventional dose calculations. Task Group 129 was formed to review the literature; re-examine the current dosimetry calculation formalism; and make recommendations for eye-plaque dosimetry, including evaluation of brachytherapy source dosimetry parameters and heterogeneity correction factors. A literature review identified modern assessments of dose calculations for Collaborative Ocular Melanoma Study (COMS) design plaques, including MC analyses and an intercomparison of treatment planning systems (TPS) detailing differences between homogeneous and heterogeneous plaque calculations using the American Association of Physicists in Medicine (AAPM) TG-43U1 brachytherapy dosimetry formalism and MC techniques. This review identified that a commonly used prescription dose of 85 Gy at 5 mm depth in homogeneous medium delivers about 75 Gy and 69 Gy at the same 5 mm depth for specific (125)I and (103)Pd sources, respectively, when accounting for COMS plaque heterogeneities. Thus, the adoption of heterogeneous dose calculation methods in clinical practice would result in dose differences >10% and warrant a careful evaluation of the corresponding changes in prescription doses. Doses to normal ocular structures vary with choice of radionuclide, plaque location, and prescription depth, such that further dosimetric evaluations of the adoption of MC-based dosimetry methods are needed. The AAPM and American Brachytherapy Society (ABS) recommend that clinical medical physicists should make concurrent estimates of heterogeneity-corrected delivered dose using the information in this report's tables to prepare for brachytherapy TPS that can account for material heterogeneities and for a transition to heterogeneity-corrected prescriptive goals. It is recommended that brachytherapy TPS vendors include material heterogeneity corrections in their systems and take steps to integrate planned plaque localization and image guidance. In the interim, before the availability of commercial MC-based brachytherapy TPS, it is recommended that clinical medical physicists use the line-source approximation in homogeneous water medium and the 2D AAPM TG-43U1 dosimetry formalism and brachytherapy source dosimetry parameter datasets for treatment planning calculations. Furthermore, this report includes quality management program recommendations for eye-plaque brachytherapy.

Eye tracking and gating system for proton therapy of orbital tumors

PURPOSE

A new motion-based gated proton therapy for the treatment of orbital tumors using real-time eye-tracking system was designed and evaluated.

METHODS

We developed our system by image-pattern matching, using a normalized cross-correlation technique with LabVIEW 8.6 and Vision Assistant 8.6 (National Instruments, Austin, TX). To measure the pixel spacing of an image consistently, four different calibration modes such as the point-detection, the edge-detection, the line-measurement, and the manual measurement mode were suggested and used. After these methods were applied to proton therapy, gating was performed, and radiation dose distributions were evaluated.

RESULTS

Moving phantom verification measurements resulted in errors of less than 0.1 mm for given ranges of translation. Dosimetric evaluation of the beam-gating system versus nongated treatment delivery with a moving phantom shows that while there was only 0.83 mm growth in lateral penumbra for gated radiotherapy, there was 4.95 mm growth in lateral penumbra in case of nongated exposure. The analysis from clinical results suggests that the average of eye movements depends distinctively on each patient by showing 0.44 mm, 0.45 mm, and 0.86 mm for three patients, respectively.

CONCLUSIONS

The developed automatic eye-tracking based beam-gating system enabled us to perform high-precision proton radiotherapy of orbital tumors.

Optical eye tracking system for noninvasive and automatic monitoring of eye position and movements in radiotherapy treatments of ocular tumors

A noninvasive eye tracking system based on infrared 3-D video-oculographic techniques is proposed for the automatic monitoring of eye position and orientation in external beam radiotherapy of ocular tumors. The presented method can be applied for the real-time estimation of lesion position and tumor-beam misalignments, allowing automatic patient setup and eye movement gated treatments. A prototypal eye tracker was developed and tested on five subjects, achieving gaze estimation errors of 0.5° and eye monitoring frequencies of 125 Hz. The proposed application can potentially improve quality and efficacy of ocular radiotherapy treatments, currently based on invasive, qualitative, and manual control procedures.

Current status and future perspective of flattening filter free photon beams

PURPOSE

Flattening filters (FFs) have been considered as an integral part of the treatment head of a medical accelerator for more than 50 years. The reasons for the longstanding use are, however, historical ones. Advanced treatment techniques, such as stereotactic radiotherapy or intensity modulated radiotherapy have stimulated the interest in operating linear accelerators in a flattening filter free (FFF) mode. The current manuscript reviews treatment head physics of FFF beams, describes their characteristics and the resulting potential advantages in their medical use, and closes with an outlook.

METHODS

A number of dosimetric benefits have been determined for FFF beams, which range from increased dose rate and dose per pulse to favorable output ratio in-air variation with field size, reduced energy variation across the beam, and reduced leakage and out-of-field dose, respectively. Finally, the softer photon spectrum of unflattened beams has implications on imaging strategies and radiation protection.

RESULTS

The dosimetric characteristics of FFF beams have an effect on treatment delivery, patient comfort, dose calculation accuracy, beam matching, absorbed dose determination, treatment planning, machine specific quality assurance, imaging, and radiation protection. When considering conventional C-arm linacs in a FFF mode, more studies are needed to specify and quantify the clinical advantages, especially with respect to treatment plan quality and quality assurance.

CONCLUSIONS

New treatment units are already on the market that operate without a FF or can be operated in a dedicated clinical FFF mode. Due to the convincing arguments of removing the FF, it is expected that more vendors will offer dedicated treatment units for advanced photon beam therapy in the near future. Several aspects related to standardization, dosimetry, treatment planning, and optimization need to be addressed in more detail in order to facilitate the clinical implementation of unflattened beams.

Local tumor control, visual acuity, and survival after hypofractionated stereotactic photon radiotherapy of choroidal melanoma in 212 patients treated between 1997 and 2007

PURPOSE

To evaluate long-term local tumor control, visual acuity, and survival after hypofractionated linear accelerator-based stereotactic photon radiotherapy in patients with choroidal melanoma.

METHODS AND MATERIALS

Between 1997 and 2007, 212 patients with choroidal melanoma unsuitable for ruthenium-106 brachytherapy or local resection were treated stereotactically at a linear accelerator with 6-MV photon beams at the Medical University of Vienna in five fractions over 7 days. Twenty-four patients received a total dose of 70 Gy (five fractions of 14 Gy), 158 a total dose of 60 Gy (five fractions of 12 Gy) and 30 patients a total dose of 50 Gy (five fractions of 10 Gy) applied on the 80% isodose. Ophthalmologic examinations were performed at baseline and every 3 months in the first 2 years, every 6 months until 5 years, and once a year thereafter until 10 years after radiotherapy. Assessment of visual acuity, routine ophthalmologic examinations, and measurement of tumor base dimension and height using standardized A-scan and B-scan echography were done at each visit. Funduscopy and fluorescein angiography were done when necessary to document tumor response.

RESULTS

Median tumor height and volume decreased from 4.8 mm and 270.7 mm3 at baseline to 2.6 mm and 86.6 mm3 at the last individual follow-up, respectively (p<0.001, p<0.001). Median visual acuity decreased from 0.55 at baseline to hand motion at the last individual follow-up (p<0.001). Local tumor control was 95.9% after 5 years and 92.6% after 10 years. Thirty-two patients developed metastatic disease, and 22 of these patients died during the follow-up period.

CONCLUSION

Hypofractionated stereotactic photon radiotherapy with 70 to 50 Gy delivered in five fractions in 7 days is sufficient to achieve excellent local tumor control in patients with malignant melanoma of the choroid. Disease outcome and vision are comparable to those achieved with proton beam radiotherapy. Decreasing the total dose below 60 Gy seems to be possible.

Development of a streamlined, non-invasive robotic radiosurgery method for treatment of uveal melanoma

To analyze the feasibility and safety of frameless, image-guided robotic radiosurgery against uveal melanoma, we developed a streamlined procedure that is completed within 3 hours under retrobulbar anesthesia without immobilization. Twenty patients (10 men and 10 women) with medium (3-5-mm prominence) and large (>5-mm prominence) unilateral uveal melanomas were treated with a frameless robotic radiosurgery system. Median age was 61 years (range 32-78 years). All patients underwent a single-session procedure beginning with retrobulbar anaesthesia, followed by computerized tomography (CT) scanning that was used in the generation of a treatment plan, and then the delivery of a radiosurgical tumor dose between 18 and 22 Gy to the 70% isodose line. Three-dimensional treatment planning was aimed at securing the optical lens and the optic disc as much as possible. Follow-up occurred at 3, 6, 12, and 18 months after the radiosurgery with clinical, ultrasound, and CT studies. We were able to treat all patients in the frameless setup within 3 hours. In five patients with lateral and dorsal tumors, the dose to the optic lens could be kept below 2 Gy. The clinical response was evaluated for the first seven patients treated with a follow-up of at least 6 months. No local recurrences occurred with any of the clinically evaluated patients for a mean 13-month follow-up (range 6-22 months). Maximum median apical tumor height according to standardized A-scan ultrasound evaluations decreased from 7.7 to 5.6 mm (p < 0.1). The median reflectivity increased from 41% to 70% (p < 0.01). None of the patients developed a secondary glaucoma during the short-term follow-up period. Frameless, single-session, image-guided robotic radiosurgery is a feasible, safe and comfortable treatment option for patients with uveal melanoma. Longer follow-up and analysis of a larger patient series is required for definitive clinical recommendations.

Stereotactic arc therapy for small elongated tumors using cones and collimator jaws; dosimetric and planning aspects

Stereotactic arc treatment of small intracranial tumors is usually performed with arcs collimated by circular cones, resulting in treatment volumes which are basically spherical. For nonspherical lesions this results in a suboptimal dose distribution. Multiple isocenters may improve the dose conformity for these lesions, at the cost of large overdosages in the target volume. To achieve improved dose conformity as well as dose homogeneity, the linac jaws (with a minimum distance of 1.0 cm to the central beam axis) can routinely be used to block part of the circular beams. The purpose of this study was to investigate the feasibility of blocking cones with diameters as small as 1.0 cm and a minimum distance between the jaw and the central beam axis of 0.3 cm. First, the reproducibility in jaw positioning and resulting dose delivery on the treatment unit were assessed. Second, the accuracy of the TPS dose calculation for these small fields was established. Finally, clinically applied treatment plans using nonblocked cones were compared with plans using the partially blocked cones for several treatment sites. The reproducibility in dose delivery on our Varian Clinac 2300 C/D machines on the central beam axis is 0.8% (1 SD). The accuracy of the treatment planning system dose calculation algorithm is critically dependent on the used fits for the penumbra and the phantom scatter. The average deviation of calculated from measured dose on the central beam axis is -1.0%+/-1.4% (1 SD), which is clinically acceptable. Partial cone blocking results in improved dose distributions for elongated tumors, such as vestibular schwannoma and uveal melanoma. Multiple isocenters may be avoided. The technique is easy to implement and requires no additional workload.

Automatic real-time surveillance of eye position and gating for stereotactic radiotherapy of uveal melanoma

A new prototype (hardware and software) for monitoring eye movements using a noninvasive technique for gated linac-based stereotactic radiotherapy (SRT) of uveal melanoma was developed. The prototype was tested within the scope of a study for 11 patients. Eye immobilization was achieved by having the patient fixate a light source integrated into the system. The system is used in conjunction with a Head&Neck mask system for immobilization, and uses infrared tracking technology for positioning (both BrainLAB AG Heimstetten/Germany). It was used during CT and MR image acquisition as well as during all of five treatment fractions (6 MeV, 5 x 12 Gy to 80% isodose) to guarantee identical patient setup and eye rotational state during treatment planning and treatment delivery. Maximum temporal and angular deviations tolerated during treatment delivery can be chosen by the physician, the radiation then being interrupted automatically and instantaneously if those criteria are being exceeded during irradiation. A graphical user interface displays life video images of the treated eye and information about the current and previous rotational deviation of the eye from its reference treatment position. The physician thus has online access to data directly linked to the success of the treatment and possible side effects. Mean angular deviations during CT/MR scans and treatment deliveries ranged from 1.61 degrees to 3.64 degrees (standard deviations 0.87 degrees to 2.09 degrees ) which is in accordance with precision requirements for SRT. Typical situations when preset deviation criteria were exceeded are slow drifts (fatigue), sudden large eye movements (irritation), or if patients closed their eyes (fatigue). In these cases radiation was reliably interrupted by the gating system. In our clinical setup the novel system for computer-controlled eye movement gated treatments was well tolerated by all patients. The system yields quantitative real-time information about the eye's rotational state with respect to a reference position (treatment planning situation). Together with the possibility of performing movement-gated treatments of uveal melanoma, the system thus greatly improves the quality of this treatment.

Influence of uveal melanoma therapy on patients' quality of life: a psychological study

PURPOSE

The objective of this study ws to describe the quality of life of 98 patients treated with brachytherapy or stereotactic external beam irradiation, either with the Leksell Gamma Knife or a 6-MV LINAC.

METHODS

The EORTC QLQ-C30 and the EORTC QLQ-OPT37 psychological questionnaires and the HADS-D scale were used. Two visual analogue scales (VASs) were applied to compare overall quality of life before and after treatment.

RESULTS

The results revealed no significant differences in quality of life (p=0.215) among treatments with different methods of radiotherapy. Comparison of quality of life before and after therapy did, however, indicate a decrease in quality of following radiotherapy. The average binocular visual acuity (VA) was 0.8 (range 0.3-1). Complication arising from the treatment included a reduction in VA in the affected eye, keratitis, cataract, scleral and corneal necrosis, radiation retinopathy, radiation optic neuropathy, retinal detachment and glaucoma.

CONCLUSIONS

Due to the diagnosis revealed and the subsequent radiotherapy, patients with uveal melanoma experienced a reduced quality of life. However, compared to patients with other types of cancer, they seemed to feel relatively well and showed fewer signs of deterioration.

A modified relocatable stereotactic frame for irradiation of eye melanoma: design and evaluation of treatment accuracy

PURPOSE

To describe a reliable, patient-friendly relocatable stereotactic frame for irradiation of eye melanoma and to evaluate the repositioning accuracy of the stereotactic treatment.

METHODS AND MATERIALS

An extra construction with a blinking light and a camera is attached to a noninvasive relocatable Gill-Thomas-Cosman stereotactic frame. The position of the blinking light is in front of the unaffected eye and can be adjusted to achieve an optimal position for irradiation. The position of the diseased eye is monitored with a small camera. A planning CT scan is performed with the affected eye in treatment position and is matched with an MR scan to improve the accuracy of the delineation of the tumor. Both the translation and rotation of the affected eye are calculated by comparing the planning CT scan with a control CT scan, performed after the radiation therapy is completed.

RESULTS

Nineteen irradiated eye melanoma patients were analyzed. All patients received 5 fractions of 10 Gy within 5 days. The depth-confirmation helmet measurements of the day-to-day treatment position of the skull within the Gill-Thomas-Cosman frame were analyzed in the anteroposterior, lateral, and vertical directions and were 0.1 +/- 0.3, 0.0 +/- 0.2, and 0.2 +/- 0.2 mm (mean +/- SD), respectively. The average translations of the eye on the planning and control CT scan were 0.1 +/- 0.3 mm, 0.1 +/- 0.4, and 0.1 +/- 0.5 mm, respectively. The median rotation of the diseased eye was 8.3 degrees.

CONCLUSIONS

The described Rotterdam eye fixation system turned out to be a feasible, reliable, and patient-friendly system.

A noninvasive eye fixation and computer-aided eye monitoring system for linear accelerator-based stereotactic radiotherapy of uveal melanoma

PURPOSE

To introduce a noninvasive eye fixation and computer-aided eye monitoring system for linear accelerator-based stereotactic radiotherapy for uveal melanoma.

METHODS AND MATERIALS

At the Department of Radiotherapy and Radiobiology, University of Vienna, stereotactic radiotherapy is offered to patients with uveal melanoma considered unsuitable for (106)Ru brachytherapy or local resection. For the present feasibility study, 8 patients were carefully selected according to their ability to fixate a small light source with the diseased eye and whether they had a rather small head to meet the limited geometric space available. A polymethyl methacrylate tube was attached to a stereotactic mask system in craniocaudal orientation supporting a 45 degrees mirror, which was placed in front of the diseased eye. At the other end of the tube, the patient was given a small fixation light, and a small camera was positioned beneath, which was shielded for use during MRI. A computer interface calculated and visualized the spatial difference of the actual and a given reference pupil position, which was defined before CT scanning, during the MRI sequences, and during treatment delivery at the linear accelerator.

RESULTS

The described system can be attached to a conventional stereotactic mask system with minor modifications. Because of the large distance between the eye and the fixation light, the optical fixation system was well tolerated by all patients, and a stable position of the eye was obtained. The camera system can be used during CT and MRI without interference. Absorption of the 6-MV photon beam by the mirror and the polymethyl methacrylate tube was negligible. The computer interface designed to determine the pupil position uses an image-processing algorithm that correlates a template of the reference image with the actual image of the eye. Provided sufficient illumination of the pupil, the correlation function showed a pronounced minimum at the reference position. The precision of the algorithm was tested by phantom measurements. For a given 1 mm or 2 mm displacement, the interface reported a mean shift of 0.96 +/- 0.18 mm or 2.07 +/- 0.11 mm, respectively.

CONCLUSION

The results of this study demonstrated the feasibility of a new optical fixation system for linear accelerator-based stereotaxis. The artifact-free application of the camera system during image acquisition and irradiation and the use of the computer interface, which automatically monitored eye movements with submillimeter precision, provided large improvements compared with existing techniques. Given well-defined interruption criteria and accelerated image processing, the described system has a high potential to perform automatically gated treatment beam delivery in the near future.

LINAC based stereotactic radiotherapy of uveal melanoma: 4 years clinical experience

PURPOSE

To study local tumor control and radiogenic side effects after fractionated LINAC based stereotactic radiotherapy for selected uveal melanoma.

PATIENTS AND METHODS

Between June 1997 and March 2001, 90 patients suffering from uveal melanoma were treated at a LINAC with 6 MV. The head was immobilized with a modified stereotactic frame system (BrainLAB). For stabilization of the eye position a light source was integrated into the mask system in front of the healthy or the diseased eye. A mini-video camera was used for on-line eye movement control. Tumors included in the study were either located unfavorably with respect to macula and optical disc (<3 mm distance) or presented with a thickness >7 mm. Median tumor volume was 305+/-234 mm3 (range 70-1430 mm3), and mean tumor height was 5.4+/-2.3 mm (range 2.7-15.9 mm). Total doses of 70 (single dose 14 Gy @ 80% isodose) or 60 Gy (single dose 12 Gy @ 80% isodose) were applied in five fractions within 10 days. The first fractionation results in total dose (TD) (2 Gy) of 175 Gy for tumor and 238 Gy for normal tissue, corresponding values for the second fractionation schedule are 135 and 180 Gy, respectively.

RESULTS

After a median follow-up of 20 months (range 1-48 months) local control was achieved in 98% (n=88). The mean relative tumor reductions were 24, 27, and 37% after 12, 24 and 36 months. Three patients (3.3%) developed metastases. Secondary enucleation was performed in seven patients (7.7%). Long term side effects were retinopathy (25.5%), cataract (18.9%), optic neuropathy (20%), and secondary neovascular glaucoma (8.8%).

CONCLUSION

Fractionated LINAC based stereotactic photon beam therapy in conjunction with a dedicated eye movement control system is a highly effective method to treat unfavorably located uveal melanoma. Total doses of 60 Gy (single dose 12 Gy) are considered to be sufficient to achieve good local tumor control.

Ocular melanoma

This article reviews the current pathogenesis, molecular changes, diagnosis, and treatment of ocular melanomas. Ocular melanomas can involve the eyelid, conjunctiva, intraocular structures, and the orbit. The most common eye melanoma involves the uveal tract and is responsible for approximately 13% of melanoma deaths. Uveal melanomas account for 10% of all melanomas.

Impact of a micromultileaf collimator on stereotactic radiotherapy of uveal melanoma

PURPOSE

To evaluate the impact of a micro multileaf collimator (mMLC) on Linac-based stereotactic radiotherapy (SRT) of uveal melanoma by comparing circular arc with static conformal, dynamic arc, and intensity-modulated SRT.

MATERIALS AND METHODS

Forty uveal melanoma patients were selected from approximately 100 patients treated with SRT since 1996. For each patient, four treatment plans (BrainSCAN XL, V5.0) were made: conventional arc, static conformal, dynamic arc plan, and intensity-modulated radiotherapy (IMRT). The goal of treatment planning was to fully encompass the planning target volume (PTV) by the 80% isodose while minimizing doses to the optic nerve and lens. The following parameters were evaluated: target conformity; target homogeneity; ratio of the target volume and 50% isodose volume; normal tissue receiving doses >/=80%, >/=50%, and >/=20%; central nervous system volume irradiated to >/=20%; optical nerve volume irradiated >/=50%, D(max) of the lens; lens volume receiving >/=20%; and monitor units.

RESULTS

PTVs ranged from 0.68 to 4.90 cm(3) (mean 1.97 +/- 0.97 cm(3)). The average reduction of the prescription isodose volume was 1-1.5 cm(3) for conformal (range 2.6-0.3 cm(3)), dynamic arc (range 2.5-0.3 cm(3)), and IMRT plans (range 3.9-0.1 cm(3)), compared with conventional arc therapy. Central nervous system volumes irradiated to doses >/=20% were smallest for conventional or dynamic arc treatments. Average target dose homogeneity values were 1.74 +/- 0.50 for arc, 1.27 +/- 0.02 for static mMLC, 1.26 +/- 0.01 for dynamic arc, and 1.15 +/- 0.03 for IMRT plans. IMRT helped to reduce doses to the lens but did not provide an advantage for optical nerve sparing. When applying IMRT, the monitor units increased by approximately one-third compared with static mMLC-based SRT.

CONCLUSIONS

Conformal mMLC and dynamic arc SRT are the treatment options of choice for Linac-based SRT of uveal melanoma. They present dosimetric advantages, while being highly efficient in treatment planning and delivery.

Stereotactic radiotherapy in the treatment of ocular melanoma: a noninvasive eye fixation aid and tracking system

Ocular melanoma is frequently treated using brachytherapy implants (such as 125I and 60Co plaques or 184Ta wire), surgery, or external beam radiotherapy using small 60Co beams, high energy x-rays, or proton therapy. The last technique, though very expensive, provides improved dose distributions and dose localizations in the treatment of tumours adjacent to critical normal tissues. The technique of fractionated stereotactic radiotherapy is now being used at an increasingly large number of centers in the treatment of lesions in the brain, and the head and neck. This article describes the successful extension of the stereotactic technique to the treatment of ocular melanoma: an eye fixation aid is attached to a noninvasive, relocatable Gill-Thomas-Cosman head frame together with a simple eye-movement tracking system.

Leksell gamma knife treatment of uveal melanoma

Object. The purpose of this study was to analyze treatment results, radiation-induced side effects, and prognostic survival factors for patients with uveal melanoma.

Methods. Eighty-one patients with uveal melanoma were treated using the Leksell gamma knife during a period of 6 years (1996–2001). There were 45 men and 36 women with a median age of 59 years (range 22–85 years). Seventyfive of these patients underwent minimal follow up 10 months after treatment. After patient eye immobilization, magnetic resonance (MR) imaging was performed to enable stereotactic localization. A scoring system was used to measure radiation side effects. The median target volume was 640 mm3, and the median applied minimal dose was 31.4 Gy. All patients were examined by an ophthalmologist and with MR imaging at regular intervals. Factors influencing posttreatment survival and side effects were statistically analyzed.

Conclusions. Local tumor control in the 75 patients who underwent minimal follow up after 10 months was achieved in 63 patients (84%), whereas progression was observed in 12 patients (16%). The most frequent side effect was secondary glaucoma, which was detected in 18 patients (25%). The incidence of this side effect was significantly higher when the total volume of peripheral isodose was greater than 1000 mm3 (p = 0.015). Toxicity in the optic nerve here was also significantly higher when the maximum dose to this structure was higher than 9 Gy (p = 0.011), in the cornea when the maximum dose was higher than 15 Gy (p = 0.010), and in the lens when the maximum dose was higher than 10 Gy (p = 0.035). Altogether three pretreatment variables (patient age, tumor location, and dissemination of the disease) and one treatment variable (the minimum dose applied) were identified as having a significant influence on a patient's survival.