Optic disc dose reduction in ocular brachytherapy using 125 I notched COMS plaques: A simulation study based on current clinical practice

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.

Monte Carlo investigation of dose distribution of uniformly and non-uniformly loaded standard and notched eye plaques

To investigate the effect of using non-uniform loading and notched plaques on dose distribution for eye plaques. Using EGSnrc Monte Carlo (MC) simulations, we investigate eye plaque dose distributions in water and in an anatomically representative eye phantom. Simulations were performed in accordance with TG43 formalism and compared against full MC simulations which account for inter-seed and inhomogeneity effects. For standard plaque configurations, uniformly and non-uniformly loaded plaque dose distributions in water showed virtually no difference between each other. For standard plaque, the MC calculated dose distribution in planes parallel to the plaque is narrower than the TG43 calculation due to attenuation at the periphery of the plaque by the modulay. MC calculated the dose behind the plaque is fully attenuated. Similar results were found for the notched plaque, with asymmetric attenuation along the plane of the notch. Cumulative dose volume histograms showed significant reductions in the calculated MC doses for both tumor and eye structures, compared to TG43 calculations. The effect was most pronounced for the notch plaque where the MC dose to the optic nerve was greatly attenuated by the modulay surrounding the optic nerve compared to the TG43. Thus, a reduction of optic nerve D95% from 14 to 0.2 Gy was observed, when comparing the TG43 calculation to the MC result. The tumor D95% reduced from 89.2 to 79.95 Gy for TG43 and MC calculations, respectively. TG43 calculations overestimate the absolute dose and the lateral dose distribution of both standard and notched eye plaques, leading to the dose overestimation for the target and organs at risk. The dose matching along the central axis for the non-uniformly loaded plaques to that of uniformly loaded ones was found to be sufficient for providing comparable coverage and can be clinically used in eye-cancer-busy centers.

Prognosis of adenoid cystic carcinoma in head and neck region treated with different regimens-A single-centre study

BACKGROUND

No study has evaluated the impact of regimen on recurrence, metastasis and survival in patients with adenoid cystic carcinoma (ACC). The present study aimed to compare the efficacy of radioactive seed implantation and other regimens in treating ACC, so as to investigate the clinical applicability of radioactive seed implantation and determine the indications for this regimen.

METHODS

A total of 188 patients with ACC in oromaxillofacial region were allocated to four groups according to the treatment regimen: group 1 was treated with a combination of surgery and ¹²⁵ I seed therapy, group 2 with a combination of surgery and external radiotherapy, group 3 with surgery, whereas group 4 was untreated. The Kaplan-Meier method was used to assess the survival rates, and the Cox regression analyses were used to identify the associated prognostic factors.

RESULTS

The overall survival rates of 188 patients and groups 1, 2, 3 and 4 were 85.7%, 75%, 68.2% and 37.5%, respectively. Cox regression analysis revealed that age, T stage, N stage and regimen were independent prognostic factors of survival. Amongst patients with primary ACC, the efficacy of radioactive seed implantation was higher in those with perineural invasion than in those without.

CONCLUSION

Patient age, T stage, N stage and regimen are independent prognostic factors of survival in patients with ACC. Patients treated with surgery combined with postoperative ¹²⁵ I seed radiotherapy have a higher overall survival rate, and those with perineural invasion are more suitable for radioactive seed implantation therapy.

How to design, fabricate, and validate a customized COMS-style eye plaque: Illustrated with a narrow-slotted plaque example

PURPOSE

A customized Collaborative Ocular Melanoma Study (COMS)-style eye plaque may provide superior dosimetric coverage compared with standard models for certain intraocular tumor locations and shapes. This work provides a recipe for developing and validating such customized plaques.

METHODS AND MATERIALS

The concept-into-clinical treatment process for a customized COMS-style eye plaque begins with a CAD model design that meets the specifications of the radiation oncologist and surgeon based on magnetic resonance, ultrasound, and clinical measurements, as well as a TG-43 hybrid heterogeneity-corrected dose prediction to model the dose distribution. Next, a 3D printed plastic prototype is created and reviewed. After design approval, a Modulay plaque is commercially fabricated. Quality assurance (QA) is subsequently performed to verify the physical measurements of the Modulay and Silastic and also includes dosimetric measurement of the calibration, depth dose, and dose profiles. Sterilization instructions are provided by the commercial fabricator. This customization procedure and QA methodology is demonstrated with a narrow-slotted plaque that was recently constructed for the treatment of a circumpapillary (e.g., surrounding the optic disk) ocular tumor.

RESULTS

The production of a customized COMS-style eye plaque is a multistep process. Dosimetric modeling is recommended to ensure that the design will meet the patient's needs, and QA is essential to confirm that the plaque has the proper dimensions and dose distribution. The customized narrow-slotted plaque presented herein was successfully implemented in the clinic, and provided superior dose coverage of juxtapapillary and circumpapillary tumors compared with standard or notched COMS-style plaques. Plaque development required approximately 30 h of physicist time and a fabrication cost of $1500.

CONCLUSION

Customized eye plaques may be used to treat intraocular tumors that cannot be adequately managed with standard models. The procedure by which a customized COMS-style plaque may be designed, fabricated, and validated was presented along with a clinical example.

Optic Disc Dose Comparison Between 125I and 103Pd Collaborative Ocular Melanoma Study (COMS) Plaques Based on Current Clinical Practice

Purpose

The purpose of this study is to compare optic disc dose (ODD) between ¹²⁵I and ¹⁰³Pd Collaborative Ocular Melanoma Study (COMS) plaques in ocular brachytherapy.

Methods

A previously validated in-house brachytherapy dose calculation program was used for ODD calculations. ODD was calculated as a function of tumor margin-to-optic disc distance (DT) up to 5 mm for various tumor basal dimensions (BDs), for a prescription depth of 5 mm, and for standard and notched COMS plaques loaded with ¹²⁵I (model: IAI-125A) and ¹⁰³Pd (model: IAPd-103A) seeds. ODD calculations were repeated for prescription depths from 2 mm to 10 mm in 1 mm intervals. A prescribed dose of 85 Gy (irradiation time: 120 hours) was normalized to each prescription depth. Dose conversion factors (DCFs) for each prescription depth were calculated by taking a ratio of [total reference air kerma (TRAK) per seed]_{prescription depth} to [TRAK per seed]_{5 mm}. ODD reduction by notched COMS plaques was calculated for each prescription depth by subtracting ODD for notched COMS plaques from ODD for standard COMS plaques.

Results

Trends of ODD as a function of DT for various BDs are similar between the two seed types in both standard and notched COMS plaques. However, due to the energy difference, there exists a transition distance (d_t) for each BD in each plaque at which ODD for ¹²⁵I COMS plaques equals that for ¹⁰³Pd COMS plaques. For small BDs, at DT <d_t, ODD for ¹⁰³Pd COMS plaques is higher than that for ¹²⁵I COMS plaques while at DT >d_t, the opposite is observed. For the largest 1-3 BD(s), contrarily, d_t occurs within the tumor, and thus, ODD for ¹²⁵I COMS plaquesis always higher. Trends of ODD reduction by notched COMS plaques as a function of DT for various BDs are the same for the two seed types except that maximum ODD reduction by ¹⁰³Pd COMS notched plaques is larger. DCF increases with increasing prescription depth for both seed types.

Conclusions

There exist ODD differences between ¹²⁵I and ¹⁰³Pd COMS plaques and the differences depend on DT, BD, plaque size, and prescription depth.