Allan Wilkinson

Lung Dose Calculation With SPECT/CT for 90Yittrium Radioembolization of Liver Cancer

PURPOSE To propose a new method to estimate lung mean dose (LMD) using technetium-99m labeled macroaggregated albumin ((99m)Tc-MAA) single photon emission CT (SPECT)/CT for (90)Yttrium radioembolization of liver tumors and to compare the LMD estimated using SPECT/CT with clinical estimates of LMD using planar gamma scintigraphy (PS). METHODS AND MATERIALS Images of 71 patients who had SPECT/CT and PS images of (99m)Tc-MAA acquired before TheraSphere radioembolization of liver cancer were analyzed retrospectively. LMD was calculated from the PS-based lung shunt assuming a lung mass of 1 kg and 50 Gy per GBq of injected activity shunted to the lung. For the SPECT/CT-based estimate, the LMD was calculated with the activity concentration and lung volume derived from SPECT/CT. The effect of attenuation correction and the patients breathing on the calculated LMD was studied with the SPECT/CT. With these effects correctly taken into account in a more rigorous fashion, we compared the LMD calculated with SPECT/CT with the LMD calculated with PS. RESULTS The mean dose to the central region of the lung leads to a more accurate estimate of LMD. Inclusion of the lung region around the diaphragm in the calculation leads to an overestimate of LMD due to the misregistration of the liver activity to the lung from the patients breathing. LMD calculated based on PS is a poor predictor of the actual LMD. For the subpopulation with large lung shunt, the mean overestimation from the PS method for the lung shunt was 170%. CONCLUSIONS A new method of calculating the LMD for TheraSphere and SIR-Spheres radioembolization of liver cancer based on (99m)Tc-MAA SPECT/CT is presented. The new method provides a more accurate estimate of radiation risk to the lungs. For patients with a large lung shunt calculated from PS, a recalculation of LMD based on SPECT/CT is recommended.

Dosimetric Benefit of a New Ophthalmic Radiation Plaque

PURPOSE To determine whether the computed dosimetry of a new ophthalmic plaque, EP917, when compared with the standard Collaborative Ocular Melanoma Study (COMS) plaques, could reduce radiation exposure to vision critical structures of the eye. METHODS AND MATERIALS One hundred consecutive patients with uveal melanoma treated with COMS radiation plaques between 2007 and 2010 were included in this study. These treatment plans were generated with the use of Bebig Plaque Simulator treatment-planning software, both for COMS plaques and for EP917 plaques using I-125. Dose distributions were calculated for a prescription of 85 Gy to the tumor apex. Doses to the optic disc, opposite retina, lens, and macula were obtained, and differences between the 2 groups were analyzed by standard parametric methods. RESULTS When compared with the COMS plaques, the EP917 plaques used fewer radiation seeds by an average difference of 1.94 (P<.001; 95% confidence interval [CI], -2.8 to -1.06) and required less total strength of radiation sources by an average of 17.74 U (air kerma units) (P<.001; 95% CI, -20.16 to -15.32). The total radiation doses delivered to the optic disc, opposite retina, and macula were significantly less by 4.57 Gy, 0.50 Gy, and 11.18 Gy, respectively, with the EP917 plaques vs the COMS plaques. CONCLUSION EP917 plaques deliver less overall radiation exposure to critical vision structures than COMS treatment plaques while still delivering the same total therapeutic dose to the tumor.

Episcleral brachytherapy of uveal melanoma: role of intraoperative echographic confirmation

Purpose To compare the rates of tumour recurrence following episcleral brachytherapy for uveal melanoma before and after implementation of intraoperative echographic confirmation of plaque placement. Materials and methods All patients with primary single ciliary body or choroidal melanoma treated with iodine-125 or ruthenium-106 plaque brachytherapy between 1 January 2004 and 30 December 2013 were included. Exclusion criteria were patients with previous radiation treatment and patients who received adjuvant transpupillary thermotherapy. Since February 2007, intraoperative echographic confirmation was initiated to ensure that the plaque was centred on the tumour base and/or all tumour margins were covered by the plaque. Results 252 patients were included in the study. Local tumour control after primary brachytherapy was achieved in 242/252 (96.0%). Of the 10 patients with treatment failure, 8 patients had local recurrence and 2 patients had failure to response. With the incorporation of the intraoperative echographic confirmation for plaque positioning the treatment failure rate decreased from 9.3% (5/54 patients) to 1.5% (3/198 patients). Continuous and categorical univariable predictors of recurrence were analysed for statistical significance. The only statistically significant variable was the intraoperative echographic confirmation (HR: 0.16; p=0.032) for recurrence within the first 24 months. Conclusions Intraoperative echographic confirmation of plaque placement during episcleral brachytherapy for choroidal melanoma reduces the risk of early local recurrence.

Vision Loss Following Episcleral Brachytherapy for Uveal Melanoma: Development of a Vision Prognostication Tool

IMPORTANCE Vision loss following episcleral brachytherapy for uveal melanoma is difficult to predict for individual patients. OBJECTIVE To generate a risk calculator for vision loss following episcleral brachytherapy for uveal melanoma. DESIGN, SETTING, AND PARTICIPANTS A retrospective review of data was conducted at a multispecialty tertiary care center in Cleveland, Ohio. All patients with primary ciliary body or choroidal melanoma treated with iodine 125 or ruthenium 106 episcleral brachytherapy between January 1, 2004, and December 30, 2013, were included. Univariate and multivariable Cox proportional hazards were used to determine the influence of baseline patient factors on vision loss. Kaplan-Meier curves (log-rank analyses) were used to estimate freedom from vision loss. Bootstrap resampling was performed to bias correct this estimate. MAIN OUTCOMES AND MEASURES Vision loss (to visual acuity [VA] worse than 20/50 and worse than 20/200). RESULTS A total of 311 patients were included in the study, with a mean (SD) age of 62 (14.7) years at start of treatment and a median follow-up of 36 months (interquartile range, 18-60 months). At presentation, VA was better than or equal to 20/50 in 199 patients (64%) and better than or equal to 20/200 in 289 patients (93%). By Kaplan-Meier analysis, VA less than 20/200 at 3 years was not associated with sex, diabetes, systemic hypertension, or hypercholesterolemia but was associated with history of ocular comorbidities, type of isotope (ruthenium 106 or iodine 125), and initial VA ( >20/50 or <20/50). By multivariable analysis, age (hazard ratio [HR], 0.97; 95% CI, 0.94-1.00; P = .06), largest basal diameter (HR, 1.25; 95% CI, 1.16-1.34; P = <.001), total radiation dose to the fovea (HR, 1.03; 95% CI, 1.01-1.04; P = .001) and optic disc (HR, 1.01; 95% CI, 1.00-1.01; P = .005), and initial VA worse than 20/50 (HR, 1.85; 95% CI, 1.20-2.85; P = .005) were predictive of vision loss to a VA of less than 20/200. The concordance index for the full data set was 0.77. Using these data, an online risk calculator was developed to predict vision loss following episcleral brachytherapy. CONCLUSIONS AND RELEVANCE The vision prognostication tool presented herein needs to be validated by independent data sets. This tool may improve counseling for patients being evaluated for episcleral brachytherapy. At-risk individuals identified by this tool could be considered for inclusion into trials exploring prevention or treatment of radiation retinopathy and alternative therapies of uveal melanoma.

Principles of Radiation Therapy

Radioactivity was first described by Henri Becquerel and Pierre and Marie Curie in the late 1890s. Wilhelm Roentgen discovered x-rays in 1895, and subsequent physics and biology research revealed the therapeutic properties of radiation. X-rays were first used to treat cancer in 1897. Soon after, the concept of brachytherapy was developed when radium was implanted into tumors for therapeutic effect. Low-voltage x-ray machines were built in the 1920s for the external treatment of superficial tumors. External beam radiation therapy was further refined in 1953 with the development of linear accelerators (linacs) that could produce megavoltage electron and x-ray photon beams using pulsed microwaves and an electron gun. Three-dimensional conformal radiation therapy (3D-CRT), intensity-modulated radiation therapy (IMRT), stereotactic radiosurgery, and charged particle therapy focus therapeutic dose while minimizing damage to surrounding normal structures. In this chapter we will review the basic principles of radiation therapy and its application as the definitive, adjuvant, salvage, and palliative management of a variety of ophthalmic cancers.

Principles and practice of high-dose rate penile brachytherapy: Planning and delivery techniques

PURPOSE To allow for organ preservation, high-dose rate (HDR) brachytherapy may be used in the treatment of localized penile cancer. Penile cancer is a rare malignancy that accounts for <1% of cancers in men in the United States. The standard treatment for localized disease is partial amputation of the penis. However, patients with T1b or T2 disease <4 cm in maximum dimension and confined to the glans penis may be treated with brachytherapy as an organ-sparing approach. Previous works have described the technique involved for low-dose rate brachytherapy; however, we detail the techniques involved with HDR brachytherapy. METHODS AND MATERIALS Circumcision should precede brachytherapy. Interstitial brachytherapy needles are placed in the operating room under general anesthesia with the goal to allow for appropriate target coverage. Target definition is done via computed tomography-based simulation and planning. Radiation is delivered using a prescription dose of 3840 cGy in 12 fractions twice daily over a course of 6 days. RESULTS Acute toxicities peak upon completion of the radiation therapy and may include dermatitis, sterile urethritis, and adhesions in the urethra. These toxicities are reversible and generally take 2 to 3 months to heal. The two most common and significant late complications of radiation therapy for penile cancer are soft tissue necrosis and meatal stenosis. An increased risk of necrosis has been reported with T3 tumors and higher-volume implants (>30 cm3). Erectile function is generally maintained because the erectile tissues including the penile shaft and corpora have not been irradiated. CONCLUSIONS Organ preservation is feasible using HDR brachytherapy with favorable acute and late toxicities.