D Mihailidis

IMRT commissioning: Multiple institution planning and dosimetry comparisons,a report from AAPM Task Group 119

AAPM Task Group 119 has produced quantitative confidence limits as baseline expectation values for IMRT commissioning. A set of test cases was developed to assess the overall accuracy of planning and delivery of IMRT treatments. Each test uses contours of targets and avoidance structures drawn within rectangular phantoms. These tests were planned, delivered, measured, and analyzed by nine facilities using a variety of IMRT planning and delivery systems. Each facility had passed the Radiological Physics Center credentialing tests for IMRT. The agreement between the planned and measured doses was determined using ion chamber dosimetry in high and low dose regions, film dosimetry on coronal planes in the phantom with all fields delivered, and planar dosimetry for each field measured perpendicular to the central axis. The planar dose distributions were assessed using gamma criteria of 3%/3 mm. The mean values and standard deviations were used to develop confidence limits for the test results using the concept confidence limit = /mean/ + 1.96sigma. Other facilities can use the test protocol and results as a basis for comparison to this group. Locally derived confidence limits that substantially exceed these baseline values may indicate the need for improved IMRT commissioning.

Recommendations for clinical electron beam dosimetry: Supplement to the recommendations of Task Group 25

The goal of Task Group 25 (TG-25) of the Radiation Therapy Committee of the American Association of.Physicists in Medicine (AAPM) was to provide a methodology and set of procedures for a medical physicist performing clinical electron beam dosimetry in the nominal energy range of 5-25 MeV. Specifically, the task group recommended procedures for acquiring basic information required for acceptance testing and treatment planning of new accelerators with therapeutic electron beams. Since the publication of the TG-25 report, significant advances have taken place in the field of electron beam dosimetry, the most significant being that primary standards laboratories around the world have shifted from calibration standards based on exposure or air kerma to standards based on absorbed dose to water. The AAPM has published a new calibration protocol, TG-51, for the calibration of high-energy photon and electron beams. The formalism and dosimetry procedures recommended in this protocol are based on the absorbed dose to water calibration coefficient of an ionization chamber at 60Co energy, N60Co(D,w), together with the theoretical beam quality conversion coefficient k(Q) for the determination of absorbed dose to water in high-energy photon and electron beams. Task Group 70 was charged to reassess and update the recommendations in TG-25 to bring them into alignment with report TG-51 and to recommend new methodologies and procedures that would allow the practicing medical physicist to initiate and continue a high quality program in clinical electron beam dosimetry. This TG-70 report is a supplement to the TG-25 report and enhances the TG-25 report by including new topics and topics that were not covered in depth in the TG-25 report. These topics include procedures for obtaining data to commission a treatment planning computer, determining dose in irregularly shaped electron fields, and commissioning of sophisticated special procedures using high-energy electron beams. The use of radiochromic film for electrons is addressed, and radiographic film that is no longer available has been replaced by film that is available. Realistic stopping-power data are incorporated when appropriate along with enhanced tables of electron fluence data. A larger list of clinical applications of electron beams is included in the full TG-70 report available at http://www.aapm.org/pubs/reports. Descriptions of the techniques in the clinical sections are not exhaustive but do describe key elements of the procedures and how to initiate these programs in the clinic. There have been no major changes since the TG-25 report relating to flatness and symmetry, surface dose, use of thermoluminescent dosimeters or diodes, virtual source position designation, air gap corrections, oblique incidence, or corrections for inhomogeneities. Thus these topics are not addressed in the TG-70 report.

Technical note: The effect of the 4-mm-collimator output factor on gamma knife dose distributions

We present results of investigations of the clinical significance of variations in the value of the 4‐mm‐collimator output factor, OF4/18. Changes in treatment volume, dose‐volume histograms (DVHs), and isodose distributions were studied, by varying OF4/18 up to 20%. The variations were performed on a sample of clinical patient treatment plans for which the 4 mm collimator was used. Although smaller effects are noted for the prescription isodose line, greater dosimetric changes occur for higher dose regions within the target. PACS number(s): 87.53.–j, 87.52.–g

TH‐E‐M100E‐02: Superiority of Equivalent Uniform Dose (EUD)‐Based Optimization for Breast and Chest Wall IMRT

Purpose: To investigate whether IMRT optimization based on generalize equivalent uniform dose1 (gEUD) objectives for target volumes and organs at risk (OAR) alike can lead to superior plans as opposed to multiple dose‐volume (DV) based objectives plans, for intact breast and postmastectomy chest wall (CW) cancer.Methods and Materials: Four IMRT plans with six or seven coplanar 6‐MV beams were prepared for a number of chest wall and breast CA patients (10 patients). The first three plans utilized our standard in‐house physician‐set of DV objectives (phys‐plan), gEUD‐based objectives for the OARs (gEUD‐plan), and multiple, “very stringent”, DV objectives for each OAR and PTV (DV‐plan), respectively. The fourth was only beam fluence optimized plan (FO‐plan), without segmentation and utilized the same objectives as in the DV‐plan. The latter plan was to be used as an “optimum” benchmark without the effects of the segmentation for deliverability. Various dosimetric quantities, such as mean dose (Dmean) for heart, contralateral breast, and contralateral lung; and V20 (volume of organ receiving 20Gy) for the ipsilateral lung were employed to evaluate our results. Results: For all patients in this study, we have seen that the gEUD‐based plans allow greater sparing of the OARs while maintaining excellent target coverage. The use of gEUD allows selective optimization of the dose for each OAR and results in a truly individualized treatment plan. Conclusions: gEUD requires a smaller number of parameters for optimization and allows exploration of a much wider space of solutions, thereby making it easier for the optimization system to balance competing requirements in search of a better solution. Thus, gEUD optimization can be used to search for or evaluate plans of different DVHs with the same gEUDs. This method can be efficiently used in routine clinical IMRTtreatment planning.

Re: Estimating and reducing dose received by cardiac devices for patients undergoing radiotherapy

To the Editor: I read with great interest the manuscript of Bourgouin et al.,(1) describing methods to estimate and/or measure out-of-field doses to a cardiac implantable electronic device (CIED) for patients that undergo radiotherapy. This is a topic that deserves great attention in today’s radiotherapy practice since a great number of cancer patients who will receive radiation have a pacemaker or implantable cardioverter-defibrillator. For this reason, publications like the one under discussion,(1) might be used as guidance to practicing professionals. The purpose of that manuscript was the evaluation of the dosimetric effect that a sheet of lead shield over a CIED has, based on out-of-field dose measurements at the location of the CIED, as a way to reduce the dose to the CIED. There are several discrepancies and inaccuracies in the manuscript that I would like to point out. Equation (1) in the manuscript is inaccurate and is missing the radial distance dependence, r. Parameter a of Eq. (1) mostly depends on the irradiated area size, but not proportionally and, on the primary photon energy, then, parameter b is practically constant with photon energy representing the attenuation of scattered photons in water.(2) I believe Eq. (1) in the article should read

In Regard to Gomez et al

To the Editor: I read with great interest the article by Gomez et al (1), a great presentation of a survey of single-institution clinical cases regarding the noted failures of cardiac implanted electronic devices (CIEDs) of patients treated with proton beam therapy (PBT) and for various treatment sites. It is true that this article presents the largest series of CIED (42 patients with pacemakers and/or defibrillators) malfunctions in patients undergoing PBT, since the report by Oshiro et al (2) in 2008 where 8 patients with only pacemakers were considered. The observations and analysis by Gomez et al (1) are very useful to facilities that offer PBT in assisting the implementation of institutional guidelines for treating patients with CIEDs. Based on the observations reported by this study, all 4 patients who experienced device reset were receiving thoracic irradiation with passive scattering proton beam and at different dose levels (see Table 2 in Reference [1]). The authors concluded that although quantitative threshold distances and doses cannot be used for guidelines, the effect of neutron scatter on CIEDs seems to be minimal for treatment fields farther than 30 cm from the CIED. Then, they recommended that thoracic PBT be avoided for pacing-dependent patients. One possible explanation of what the authors observed in their study is that inasmuch as passive scattering mode was used for the thoracic treatments only (according to their descriptions), I would expect the out-of-field neutron scatter to be larger by a factor of 30 to 45 in the entrance region, with this factor decreasing with depth, when compared with out-of-field neutron scatter from the active scanning mode (3). For passive scattering systems, neutrons are generated in the treatment head, beam modulators, scattering devices, and patient-specific apertures or compensators and are the dominant contribution to the total dose downstream from the Bragg peak and out of field (3). The fielddefining aperture dominates as a secondary neutron production source because of its proximity to the patient, making the neutron dose dependent on the ratio of field size to aperture opening (4). The out-of-field patient neutron dose increases with beam range/energy and treatment volume (4, 5). Active and modulated scanning systems do not require scattering devices in the treatment head or patient apertures; as a result, the

Neutron physics for nuclear reactors, unpublished writings by Enrico Fermi

This article reviews Neutron physics for nuclear reactors, unpublished writings by Enrico Fermi by S. Esposito, O. Pisanti , Hackensack, NJ 2010. (Hardcover) 704 pp. Price:

Applied Physics for Radiation Oncology, Revised Edition

111.00. 978–981–4392–22–4.

Computed Tomography From Photon Statistics to Modern Cone‐Beam CT

This article reviews Applied Physics for Radiation Oncology, Revised Edition by Robert Stanton, Donna Stinson , Madison, Wisconsin, 2009,

SU-FF-T-266: Intensity Modulated Radiotherapy of Breast Cancer Using Direct-Machine-Parameter-Optimization

85.00. ISBN: 9781930524408, 292 pp. (paperback)