AAPM WGTG51 Report 374: Guidance for TG-51 reference dosimetry.

Practical guidelines that are not explicit in the TG-51 protocol and its Addendum for photon beam dosimetry are presented for the implementation of the TG-51 protocol for reference dosimetry of external high-energy photon and electron beams. These guidelines pertain to: (i) measurement of depth-ionization curves required to obtain beam quality specifiers for the selection of beam quality conversion factors, (ii) considerations for the dosimetry system and specifications of a reference-class ionization chamber, (iii) commissioning a dosimetry system and frequency of measurements, (iv) positioning/aligning the water tank and ionization chamber for depth ionization and reference dose measurements, (v) requirements for ancillary equipment needed to measure charge (triaxial cables and electrometers) and to correct for environmental conditions, and (vi) translation from dose at the reference depth to that at the depth required by the treatment planning system. Procedures are identified to achieve the most accurate results (errors up to 8% have been observed) and, where applicable, a commonly used simplified procedure is described and the impact on reference dosimetry measurements is discussed so that the medical physicist can be informed on where to allocate resources.

A collapsed-cone based transit EPID dosimetry method.

Purpose: To develop a transit-dose portal dosimetry method based on a commercial collapsed-cone algorithm.

Methods: A Varian Clinac21EX (Varian Medical Systems, USA), equipped with an amorphous-silicon EPID aS1000, was used. Dose calculations were performed with the collapsed-cone algorithm of Pinnacle v8.

Insight gained from responses to surveys on reference dosimetry practices.

Purpose: To present the results and discuss potential insights gained through surveys on reference dosimetry practices.

Methods: Two surveys were sent to medical physicists to learn about the current state of reference dosimetry practices at radiation oncology clinics worldwide. A short survey designed to maximize response rate was made publicly available and distributed via the AAPM website and a medical physics list server.

Radiation for Hodgkin's lymphoma in young female patients: a new technique to avoid the breasts and decrease the dose to the heart.

Purpose: To demonstrate how, in young female patients with Hodgkin's lymphoma, using an inclined board technique can further decrease the volume of breasts and heart in the treatment field.

Methods And Materials: An inclined board was constructed with the ability to mount an Aquaplast face mask, a Vacu-Lock, and a hip stopper. Eight female patients with early-stage Hodgkin's lymphoma were planned and compared using the conventional flat position and the inclined board position.

Dosimetric characterization of a 131Cs brachytherapy source by thermoluminescence dosimetry in liquid water.

Dosimetry measurements of a 131Cs brachytherapy source have been performed in liquid water employing thermoluminescence dosimeters. A search of the literature reveals that this is the first time a complete set of dosimetric parameters for a brachytherapy "seed" source has been measured in liquid water. This method avoids the medium correction uncertainties introduced by the use of water-equivalent plastic phantoms.

Patient dosimetry for total body irradiation using single-use MOSFET detectors.

We studied the usefulness of a new type of solid-state detector, the OneDose single-use MOSFET (metal oxide semiconductor field effect transistor) dosimeter, for entrance dose measurements for total body irradiation (TBI). The factory calibration factors supplied by the manufacturer are applicable to conventional radiotherapy beam arrangements and therefore may not be expected to be valid for TBI dosimetry because of the large field sizes and extended source-to-axis distances used. OneDose detectors were placed under a 1-cm thick bolus at the head, neck, and umbilicus of 9 patients undergoing TBI procedures.

Thermoluminescence dosimetry measurements of brachytherapy sources in liquid water.

Radiation therapy dose measurements are customarily performed in liquid water. The characterization of brachytherapy sources is, however, generally based on measurements made with thermoluminescence dosimeters (TLDs), for which contact with water may lead to erroneous readings. Consequently, most dosimetry parameters reported in the literature have been based on measurements in water-equivalent plastics, such as Solid Water.

Comparison of breath-hold and free-breathing positions of an external fiducial by analysis of respiratory traces.

An internal target volume (ITV) accounting for respiratory-induced tumor motion is best obtained using 4DCT. However, when 4DCT is not available, inspiratory/expiratory breath-hold (BH insp, BH exp) CT images have been suggested as an alternative. In such cases, an external fiducial on the abdomen can be used as a substitute for tumor motion and CT images are acquired when the marker position matches - as judged by the therapist/physicist - its positions at previously determined free-breathing (FB) respiratory extrema (FB insp, FB exp).

4D-CT imaging with synchronized intravenous contrast injection to improve delineation of liver tumors for treatment planning.

We have developed a tumor-specific protocol for the 4D-CT imaging of liver tumors using synchronized intravenous (IV) contrast injection to improve the accuracy of tumor delineation for treatment planning. Most liver metastases and cholangiocarcinomas can be imaged in the portal venous phase, while hepatocellular carcinomas are most visible in the delayed phase. Combined 4D-CT imaging with synchronized IV contrast allows for both enhancement of tumor contrast and coverage over the entire breathing cycle.

Respiration-correlated treatment delivery using feedback-guided breath hold: a technical study.

Respiratory motion causes movement of internal structures in the thorax and abdomen, making accurate delivery of radiation therapy to tumors in those areas a challenge. To reduce the uncertainties caused by this motion, we have developed feedback-guided breath hold (FGBH), a novel delivery technique in which radiation is delivered only during a voluntary breath hold that is sustained for as long as the patient feels comfortable. Here we present the technical aspects of FGBH, which involve (1) fabricating the hardware so the respiratory trace can be displayed to the patient, (2) assembling a delay box to be used as a breath-hold detector, and (3) performing quality control tests to ensure that FGBH can be delivered accurately and safely.