Christopher L. Deufel

Total skin electron therapy in the lying-on-the-floor position using a customized flattening filter to accommodate frail patients

A total skin electron (TSE) floor technique is presented for treating patients who are unable to safely stand for extended durations. A customized flattening filter is used to eliminate the need for field junctioning, improve field uniformity, and reduce setup time. The flattening filter is constructed from copper and polycarbonate, fits into the linacs accessory slot, and is optimized to extend the useful height and width of the beam such that no field junctions are needed during treatment. A TSE floor with flattening filter (TSE FF) treatment course consisted of six patient positions: three supine and three prone. For all treatment fields, electron beam energy was 6 MeV; collimator settings were an x of 30 cm, y of 40 cm, and θcoll of 0°; and a 0.4 cm thick polycarbonate spoiler was positioned in front of the patient. Percent depth dose (PDD) and photon contamination for the TSE FF technique were compared with our standard technique, which is similar to the Stanford technique. Beam profiles were measured using radiochromic film, and dose uniformity was verified using an anthropomorphic radiological phantom. The TSE FF technique met field uniformity requirements specified by the American Association of Physicists in Medicine Task Group 30. TSE FF R80 ranges from 4 to 4.8 mm. TSE FF photon contamination was ~ 3%. Anthropomorphic radiological phantom verification demonstrated that dose to the entire skin surface was expected to be within about ±15% of the prescription dose, except for the perineum, scalp vertex, top of shoulder, and soles of the feet. The TSE floor technique presented herein eliminates field junctioning, is suitable for patients who cannot safely stand during treatment, and provides comparable quality and uniformity to the Stanford technique. PACS number: 87

Mathematical solutions of the TG-43 geometry function for curved line, ring, disk, sphere, dome and annulus sources, and applications for quality assurance

Analytic solutions for the TG-43 geometry function for curved line, ring, disk, sphere, dome and annulus shapes containing uniform distributions of air-kerma are derived. These geometry functions describe how dose distributions vary strictly due to source geometry and not including attenuation or scatter effects. This work extends the use of geometry functions for individual sources to applicators containing multiple sources. Such geometry functions may be used to verify dose distributions computed using advanced techniques, including QA of model-based dose calculation algorithms. The impact of source curvature on linear and planar implants is considered along with the specific clinical case of brachytherapy eye plaques. For eye plaques, the geometry function for a domed distribution is used with published Monte Carlo dose distributions to determine a radial dose function and anisotropy function which includes all the scatter and attenuation effects due to the phantom, eye plaque and sources. This TG-43 model of brachytherapy eye plaques exactly reproduces azimuthally averaged Monte Carlo calculations, both inside and outside the eye.

Quality assurance for high dose rate brachytherapy treatment planning optimization: using a simple optimization to verify a complex optimization

As dose optimization for high dose rate brachytherapy becomes more complex, it becomes increasingly important to have a means of verifying that optimization results are reasonable. A method is presented for using a simple optimization as quality assurance for the more complex optimization algorithms typically found in commercial brachytherapy treatment planning systems. Quality assurance tests may be performed during commissioning, at regular intervals, and/or on a patient specific basis. A simple optimization method is provided that optimizes conformal target coverage using an exact, variance-based, algebraic approach. Metrics such as dose volume histogram, conformality index, and total reference air kerma agree closely between simple and complex optimizations for breast, cervix, prostate, and planar applicators. The simple optimization is shown to be a sensitive measure for identifying failures in a commercial treatment planning system that are possibly due to operator error or weaknesses in planning system optimization algorithms. Results from the simple optimization are surprisingly similar to the results from a more complex, commercial optimization for several clinical applications. This suggests that there are only modest gains to be made from making brachytherapy optimization more complex. The improvements expected from sophisticated linear optimizations, such as PARETO methods, will largely be in making systems more user friendly and efficient, rather than in finding dramatically better source strength distributions.

Intraoperative high-dose-rate brachytherapy: An American Brachytherapy Society consensus report

PURPOSE This report presents recommendations from the American Brachytherapy Society for the use of intraoperative high-dose-rate (IOHDR) brachytherapy. METHODS AND MATERIALS Members of the American Brachytherapy Society with expertise in IOHDR formulated this document based on their clinical experience and a review of the literature. This report covers the use of IOHDR in colorectal cancer, soft tissue sarcoma, gynecologic cancers, head and neck cancers, and pediatric cancers. This report does not cover intraoperative brachytherapy for breast cancer. Details about treatment planning and delivery are emphasized so this document can serve as a guide to practices implementing this technique. RESULTS IOHDR brachytherapy is generally most beneficial for patients with either close or positive margins and/or recurrent disease in a previous resection bed or previously irradiated area. IOHDR brachytherapy requires a well-coordinated multidisciplinary team. IOHDR brachytherapy is recommended in the treatment of both recurrent and primary locally advanced disease for colorectal and gynecologic malignancies, soft tissue sarcoma, and selected head and neck and pediatric malignancies. Other techniques such as perioperative fractionated brachytherapy are also acceptable in many cases with some advantages and disadvantages compared to IOHDR. CONCLUSIONS IOHDR brachytherapy is a specialized technique in radiation therapy with unique properties and advantages in cancer control. Special considerations for treatment planning and delivery are outlined herein.

Clinical application of lying-on-the-floor total skin electron irradiation for frail patients with cutaneous lymphoma: An emphasis on the importance of in vivo dosimetry

Total skin electron irradiation (TSEI) is an effective option for cutaneous T-cell lymphoma (CTCL). Two conventional methods used to deliver TSEI are the Stanford multiple dual field technique and the McGill rotational technique; however, both techniques require patients to stand for 10 to 30 minutes and cannot be used in nonambulatory patients. Our group has previously described technical parameters for “lying-on-the-floor” total skin electron beam therapy for nonambulatory patients.Wenow report clinical implementation of this technique in a nonambulatory patient with progressive CTCL with particular emphasis on the critical importance of in vivo dosimetry.

Technique for the administration of high-dose-rate brachytherapy to the bile duct using a nasobiliary catheter

PURPOSE Cholangiocarcinoma patients who are potential candidates for liver transplantation may be treated with high-dose-rate (HDR) brachytherapy using a minimally invasive nasobiliary catheter in an effort to escalate the radiotherapy dose to the tumor and maximize local control rates. This work describes the equipment, procedures, and quality assurance (QA) that enables successful administration. METHODS AND MATERIALS This work describes the nasobiliary catheter placement, simulation, treatment planning, treatment delivery, and QA. In addition, a chart review was performed of all patients who received endoscopic retrograde cholangiopancreatography for HDR bile duct brachytherapy at our institution from 2007 to 2017. The review evaluated how many patients were treated and the number of patients who could not be treated because of anatomic and/or equipment limitations. RESULTS From 2007 to 2017, 122 cholangiocarcinoma patients have been treated with HDR brachytherapy using a nasobiliary catheter. Three patients underwent catheter placement but did not receive brachytherapy treatment due to catheter migration between placement and treatment or because the HDR afterloader was unable to extend the source wire into the treatment site. Periodic QA is recommended for ensuring whether the HDR afterloader is capable of extending the source wire through an extensive and curved path. CONCLUSIONS Intraluminal HDR brachytherapy with a nasobiliary catheter can be successfully administered. Procedures and QA are described for ensuring safety and overcoming technical challenges.

Brachytherapy in the Management of Prostate Cancer

Brachytherapy is performed by directly inserting radioactive sources into the prostate gland and is an important treatment option for appropriately selected men with prostate adenocarcinoma. Brachytherapy provides highly conformal radiotherapy and delivers tumoricidal doses that exceed those administered with external beam radiation therapy. There is a significant body of literature supporting the excellent long-term oncologic and safety outcomes achieved when brachytherapy is used for men in all risk categories of nonmetastatic prostate cancer. This article highlights some important considerations and published outcomes that relate to brachytherapy and its role in the treatment of prostate cancer.

A method to improve dose uniformity during total skin electron beam therapy in patients with pendulous breasts

Cutaneous lymphomas are particularly radiosensitive and amenable to palliative radiation therapy. Total skin electron beam therapy (TSEB) is effective for palliation of Sézary syndrome and cutaneous T-cell lymphoma with large body surface area involvement. Focal radiation therapy is often used for treatment of localized disease. Treatment of cutaneous T-cell lymphoma can often pose technical challenges that require creative, patient-specific solutions. The electron beam used in TSEB is superficially penetrating. Although technique-dependent variation exists in the depth of penetration, delivery of an effective dose is generally limited to a depth of less than 1 cm. The inframammary fold of a pendulous breast is generally deeper than 1 cm and therefore will not receive an adequate radiation dose when treated by this technique. The use of a thin brassiere, as suggested in American Association of Physicists Report 23, may overcome this problem in some patients. We report the use of a sling made from nylon stockings to suspend large, pendulous

Investigating the dosimetric impact of seed location uncertainties in Collaborative Ocular Melanoma Study-based eye plaques.

PURPOSE To quantify the dosimetric effects of random and systematic seed position uncertainties in Collaborative Ocular Melanoma Study-based eye plaques. METHODS AND MATERIALS An eye plaque dose calculation routine was created using Task Group 43 formalism. A variety of clinical configurations were simulated, including two seed models: (125)I and (103)Pd, three eye plaque sizes, and eight plaque/eye orientations. Dose was calculated at four ocular anatomic sites and three central axis plaque depths. Random seed positional uncertainty was modeled by adding Gaussian random displacements, in one of three seed-motion degrees of freedom, to each seeds nominal coordinate. Distributions of dosimetric outcomes were obtained and fitted after 10(6) randomizations. Similar analysis was performed for deterministic, systematic shifts of the plaque along the eye surface and radially from the globe center. RESULTS Random seed placement uncertainties of 0.2-mm root mean square (RMS) (amplitude) produce dose changes that are typically <4% for each degree of freedom (95% confidence interval). Systematic seed placement uncertainties are generally greater than random uncertainty 95% confidence intervals (factor of 0.72-2.15), with the relative magnitudes depending on plaque size and location of interest. Eye plaque dosimetry is most sensitive to seed movement toward the center of the eye. Dosimetric uncertainty also increases with increasing dose gradients, which are typically greatest near the inner sclera, with smaller plaques, and with lower energy radionuclides (e.g., (103)Pd). CONCLUSIONS Dosimetric uncertainties due to the random seed positional displacements anticipated in the clinic are expected to be <4% for each degree of freedom in most circumstances.

Heterogeneous dose calculations for Collaborative Ocular Melanoma Study eye plaques using actual seed configurations and Task Group Report 43 formalism.

PURPOSE Collaborative Ocular Melanoma Study (COMS) eye plaques (EPs) contain silastic and Modulay materials that introduce 15-30% dose differences compared with all-water dosimetry. A Task Group Report 43 (TG43) dose rate calculation method is presented that includes silastic and Modulay heterogeneous effects, uses the actual plaque seed configuration, is not restricted to a particular commercial treatment planning system, and does not require purchase of additional software. METHODS AND MATERIALS Dose rate is calculated using TG43 formalism: Dos˙e(EP)(r,θ)=S(K)Λ(G(L)(r,θ)/G(L)(r0,θ0))g(EP)(r)F(EP)(r,θ), with revised radial dose, g(EP)(r), and anisotropy, F(EP)(r,θ), functions specific to (125)I or (103)Pd seeds in COMS EPs. The EP signifies that the functions are specific to COMS EPs. The g(EP)(r) is obtained from Monte Carlo (MC) data for EPs that contain just a single center seed. The F(EP)(r,θ) is obtained by performing a Nelder-Mead Simplex routine to find a least squares solution that minimizes differences between MC dose rate and Do˙seEP(r,θ). RESULTS The TG43 formalism calculations agree with MC results, for 10-22-mm (125)I and (103)Pd EPs, to within 2% along and near the plaque central axis and within 4% in the penumbra region for depths of 1 mm or greater. Methods and data are provided for COMS plaque calculations using seed models other than (125)I Model 6711 and (103)Pd Model 200. Because actual seed configurations are used in dose rate calculations, this formalism may also be used to estimate dosimetry for nonstandard seed loadings. CONCLUSION This manuscript enables the clinical user to perform accurate heterogeneity-corrected dose rate calculations for COMS EPs using TG43 formalism in a spreadsheet or commercial treatment planning system that has a TG43 line source geometry function calculation capabilities.