Glenn P. Glasgow

The American Brachytherapy Society recommendations for high-dose-rate brachytherapy for carcinoma of the endometrium

PURPOSE To develop recommendations for use of high-dose-rate (HDR) brachytherapy in patients with endometrial cancer. METHODS A panel of members of the American Brachytherapy Society (ABS) performed a literature review, supplemented their clinical experience, and formulated recommendations for endometrial HDR brachytherapy. RESULTS The ABS endorses the National Comprehensive Cancer Network (NCCN) guidelines for indications for radiation therapy for patients with endometrial cancer and the guidelines on HDR quality assurance of the American Association on Physicists in Medicine (AAPM). The ABS made specific recommendations for HDR applicator selection, insertion techniques, target volume definition, dose fractionation, and specifications for postoperative adjuvant vaginal cuff therapy, for vaginal recurrences, and for medically inoperable primary endometrial cancer patients. The ABS recommends that applicator selection should be based on patient and target volume geometry. The dose prescription point should be clearly specified. The treatment plan should be optimized to conform to the target volume whenever possible while recognizing the limitations of computer optimization. Suggested doses were tabulated for treatment with HDR alone, and in combination with external beam radiation therapy (EBRT), when applicable. For intravaginal brachytherapy, the largest diameter applicator should be selected to ensure close mucosal apposition. Doses should be reported both at the vaginal surface and at 0.5-cm depth irrespective of the dose prescription point. For vaginal recurrences, intracavitary brachytherapy should be restricted to patients with nonbulky (< 0.5-cm thick) disease. Patients with bulky (> 0.5-cm thick) recurrences should be treated with interstitial techniques. For medically inoperable patients, an appropriate applicator that will allow adequate irradiation of the entire uterus should be selected. CONCLUSION Recommendations are made for HDR brachytherapy for endometrial cancer. Practitioners and cooperative groups are encouraged to use these recommendations to formulate their treatment and dose reporting policies. This will lead to meaningful comparisons of reports from different institutions and lead to advances and appropriate use of HDR.

High dose-rate brachytherapy treatment delivery: Report of the AAPM Radiation Therapy Committee Task Group No. 59

The goals of this task group are to examine the current high dose-rate (HDR) treatment delivery practices and to prepare a document to assure safe delivery of HDR treatments. The document consists of detailed HDR procedures for design of an HDR brachytherapy program, staffing and training, treatment specific quality assurance, and emergency procedures. The document provides an extensive quality assurance (QA) check list. It reviews all aspects of HDR treatment delivery safety, including prescription, treatment plan, treatment delivery, and radiation safety.

Surface and build-up region dosimetry for obliquely incident intensity modulated radiotherapy 6 MV x rays.

This study investigates the surface dose and build-up region dosimetry for oblique IMRT beams. The dependence of surface and build-up region doses of 0 degrees (perpendicular incidence) and 75 degrees (oblique incidence) IMRT fields on field size was measured and compared with open field dosimetry. Measurements were performed using a parallel-plate chamber and KODAK EDR2 films in a polystyrene phantom for a 6 cm x 6 cm and a 12 cm x 12 cm, 6 MV photon beam at depths of 0 mm (surface) through dmax. Data were normalized to the dmax value of each field. Four intensity modulated delivery patterns were created and delivered using step-and-shoot IMRT: (1) six static 1 cm x 6 cm strips (IMRTstrip), (2) 12 static 1 cm x 12 cm strips (IMRTstrip), (3) intensity modulated beam patterns created by using the inverse planning optimization software (IMRTopt) for 6 cm x 6 cm, and (4) IMRTopt for 12 cm x 12 cm field sizes. The percent depth doses (PDDs) of 0 degrees, 6 cm x 6 cm IMRTstrip beam at the surface and 5 mm were lower by 8.8% and 1.6%, respectively, compared to the open field. The PDDs of 75 degrees, 6 cm x 6 cm IMRTstrip beam at the surface and 5 mm were lower by 6.7% and 2.4%, respectively, compared to the open field. This study showed that IMRT itself is not contributing to greater skin doses.

Patient dosimetry quality assurance program with a commercial diode system

PURPOSE To evaluate a commercial silicone diode dosimeter for a patient dosimetry quality assurance program. METHODS AND MATERIALS The diode dosimeter was calibrated against an ion chamber and percentage depth dose, linearity, anisotropy, virtual source position, and field size factor studies were performed. Correction factors for lack of full scatter medium in the diode entrance and exit dose measurements were acquired. Dosimetry equations were proposed for calculation of dose delivered at isocenter. Diode dose accuracy and reproducibility were tested on phantom and on four patients. A patient dosimetry quality assurance program based on diode measured dose was instituted and patient dose data were collected. RESULTS Diode measured percentage depth dose and field factors agreed to within 3% with those measured with an ion chamber. The diode exhibited less than 1.7% angular dose anisotropy and less than 0.5% nonlinearity up to 4 Gy. Diode dose measurements in phantom showed that the calculated doses differed from the prescribed dose by less than 1.5%; the diode exhibited a daily dose reproducibility of better than 0.2%. On four selected patients, the measured dose reproducibility was 1.5%; the average calculated doses were all within +/- 7% of the prescribed doses. For 33 of 40 patients treated with a 6 MV beam, measured doses were within +/- 7% of the prescribed doses. For 58 of 63 patients treated with an 18 MV beam, measured doses were within +/- 7% of the prescribed doses. For 11 out of 12 patients, a second repeat measurements yielded doses within +/- 7% of the prescribed doses. CONCLUSIONS The proposed diode-based patient dosimetry quality assurance program with dose tolerance at +/- 7% is simple and feasible. It is capable of detecting certain serious treatment errors such as incorrect daily dose greater than 7%, incorrect wedge use, incorrect photon energy and patient setup errors involving some incorrect source-to-surface-distance vs. source-to-axis-distance treatments.

Inter-society standards for the performance of brachytherapy: a joint report from ABS, ACMP and ACRO

PURPOSE The proliferation of various brachytherapy modalities for different anatomical sites necessitates the creation of standards for brachytherapy. METHODS A panel consisting of members of The American Brachytherapy Society (ABS), The American College of Medical Physics (ACMP) and The American College of Radiation Oncology (ACRO) developed standards for the clinical practice and quality assurance (QA) of brachytherapy. These were based upon their clinical experience and a review of the literature. RESULTS Recommended practice standards are presented for clinical processes, treatment planning, equipment, facilities, QA, dose evaluation, dose specification, dose reporting, the training, and credentialing of personnel, and radiation control/safety/protection. Safe and efficacious performance of brachytherapy requires a highly structured QA program and carefully designed treatment delivery processes, as well as a coordinated effort amongst the team members. CONCLUSION Standards for clinical brachytherapy are proposed. Practitioners are encouraged to use these standards to design and implement a consistent and efficacious brachytherapy program.

Field matching of electron beams using plastic wedge penumbra generators

We describe the use of polystyrene wedges to match adjacent electron beams with improved dose uniformity. These wedges were designed to increase the penumbra width at the field junction from about 1.5 to about 3.5 cm, to achieve dose uniformity. Measurements using thermoluminescent dosimeters (TLD) and therapy localization film showed that the use of polystyrene wedges (penumbra generators) produced only a small increase (less than 3%) in the surface dose and a small increase (less than 1%) in the x-ray contamination. Without wedges at the field junction, lateral mismatching of beam edges by 2 or 3 mm may introduce high dose variations (120% or more or 50% or less). Similar 2-3 mm set-up errors did not cause more than +/- 5% dose variations when plastic wedges were used to match the fields. These wedges are particularly useful when matching fields of different beam energies or matching fields on curved surfaces, such as the chest wall.

Dosimetry of Small Circular Fields for 6-MeV Electron Beams

Small field electron beams used in the clinic present complex dosimetry. This investigation reports dosimetric characteristics of small 6-MeV electron field measurements and Monte Carlo calculations, and examines their impact on patient dosimetry. Radiographic film and ionization chamber were used for dosimetric measurements for a 6-MeV electron beam from a Varian 21EX linac. A set of circular cerrobend cutouts with diameters ranging from 2 to 3.0 cm was made. A clinical Monte Carlo algorithm was used to calculate dosimetric parameters. As the cutout diameter decreased, the build-up portion of the percentage depth dose (PDD) curves shifted toward the phantom surface, the depth of maximum dose, d(max,) decreased from 1.2 cm to 0.6 cm, but the practical range, R(p), remained constant at about 3.1 cm. The absorbed dose rate, D(r), decreased linearly with decreasing diameter. Profile coverage ratios CR (ie, the ratio of a given isodose line to the cutout diameter) at d(max), for 90% and 80%, CR(90), CR(80), are approximately 55% and 73%, respectively. As the cutout diameter decreased, the 90% to 10% penumbra to diameter ratio, PR, increased from 0.49 to 0.56 for 3- to 2-cm cutouts. The total 90% to 10% penumbra was about the same size as the cutout diameter. The measured output factors were in good agreement with Monte Carlo calculation within 2.2%. Accurate small electron field measurements were performed using parallel plate ion chamber and film. The data were well supported by Monte Carlo calculations. These data facilitate routine clinical treatments for small cutouts as d(max), D(r), and other data can be quickly obtained instead of performing labor-intensive individual patient measurements.

TECHNIQUE CHARTS FOR KODAK'S NEW FILM-SCREEN SYSTEMS FOR PORTAL LOCALIZATION

In July 1996, Kodak released new film-screen systems with enhanced contrast (EC) for portal localization with megavoltage therapeutic beams. This study presents the generation of general-purpose technique charts for Kodaks new film-screen combinations: the Enhanced-Contrast localization (EC-L) film in EC-L cassette and the EC-L film in fast ECL (fECL) cassette for use with cobalt-60, 6 MV, 10 MV, and 18 MV beams. These technique charts were based on the assumption that a film with an optical density (OD) of 1.8 provides the best viewing density. The doses to produce such as OD, Dexp, were obtained from the H & D curves and were 1.5, 1.6, 1.7, and 1.8 cGy for cobalt-60, 6 MV, 10 MV, and 18 MV beams, respectively, with the EC-L-film + EC-L-cassette combination. The corresponding values were 1.3, 1.3, 1.3, and 1.4 cGy, respectively, for the above four beams with the EC-L-film + fEC-L-cassette combination. The dose to the film is assumed to be proportional to the calibrated dose rate (D0), field size factor (FSF), inverse square factor relative to 100.0 cm (INV), and the transmission factor through the patient, which is equal to e-uT, where u is the broad beam attenuation coefficient and T is the patient thickness. With the above assumptions, the exposure time or monitor unit, t, is then calculated from the following equation: t = Dexp/(D0*FSF*INV*e-uT). For an average port size of 15 x 15 cm, the attenuation coefficients were obtained from the fitting of TAR (cobalt-60) or TMR (6 MV, 10 MV, and 18 MV) as a function of depth from 10 to 30 cm and were 0.0564 cm-1, 0.03714 cm-1, and 0.02271 cm-1 for cobalt-60, 6 MV, 10 MV, and 18 MV beams, respectively. The FSF were explicitly obtained from the clinical physics data books and were 1.028, 1.032, 1.036, and 1.053 for cobalt-60, 6 MV, 10 MV, and 18 MV, respectively. For cobalt-60 beam, the D0 was assumed to be 100.0 cGy/min. For the 6 MV, 10 MV, and 18 MV beams, the D0 in cGy per monitor unit is 1.030, 1.051, and 1.061, respectively. Technique charts were then generated as a function of patient thickness from 10 to 45 cm for filming distance from 110 to 140 cm for all four beams. These technique charts can be easily customized to portal localization practices in a radiation therapy department.

A total body irradiation stand for bone marrow transplant patients

A stand designed for the immobilization of patients standing during total body irradiation (TBI) with horizontal 10 MV X rays is described. The stand reduces patient movement and facilitates the initial positioning and repositioning of patients during 11 fractions of TBI over a 3 2/3 day period. Details of design and use are presented. The stand is regularly used to treat TBI patients.

Design of electron beam wedges for increasing the penumbra of abutting fields

Polystyrene electron beam wedges increase the beam penumbra of electron beams and can reduce the dose non-uniformity of field junctions of abutted adjacent electron fields. The authors have investigated the dependence of the electron beam penumbra on the physical angle of polystyrene wedges for various electron beam energies and field sizes. Square, individual, and uniformly thick (1-15 mm) polystyrene inserts which covered the entire field were placed in electron applicators. Beam profiles, central-axis depth doses, and isodose curves were obtained using a water-phantom scanning system. The dependence of the beam penumbra widths, beam energy and practical range on the thickness of the polystyrene inserts are reported. These data yield the design parameters for polystyrene physical wedge angles which would increase beam penumbra from about 15 mm to about 35 mm.