In our institution, patient‐specific quality assurance (QA) for intensity‐modulated radiation therapy (IMRT) is usually performed by measuring the dose to a point using an ion chamber and by measuring the dose to a plane using film. In order to perform absolute dose comparison measurements using film, an accurate calibration curve should be used. In this paper, we investigate the film response curve uncertainty factors, including film batch differences, film processor temperature effect, film digitization, and treatment unit. In addition, we reviewed 50 patient‐specific IMRT QA procedures performed in our institution in order to quantify the sources of error in film‐based dosimetry. Our study showed that the EDR2 film dosimetry can be done with less than 3% uncertainty. The EDR2 film response was not affected by the choice of treatment unit provided the nominal energy was the same. This investigation of the different sources of uncertainties in the film calibration procedure can provide a better understanding of the film‐based dosimetry and can improve quality control for IMRT QA.PACS numbers: 87.86.Cd, 87.53.Xd, 87.57.Nk

Film dosimetry offers an advantageous in-phantom planar dose verification tool in terms of spatial resolution and ease of handling for quality assurance (QA) of intensity modulated radiation therapy (IMRT) plans. A critical step in the success of such a technique is that the film calibration be appropriately conducted. This paper presents a fast and efficient film calibration method for a helical tomotherapy unit using a single sheet of film. Considering the unique un-flattened cone shaped profile from a helical tomotherapy beam, a custom leaf control file (sinogram) was created, to produce a valley shaped intensity pattern. There are eleven intensity steps in the valley pattern, representing varying dose values from 38 to 265 cGy. This dose range covers the most commonly prescribed doses in fractionated IMRT treatments. An ion chamber in a solid water phantom was used to measure the dose in each of the eleven steps. For daily film calibration the whole procedure, including film exposure, processing, digitization and analysis, can be completed within 15 min, making it practical to use this technique routinely. This method is applicable to film calibration on a helical tomotherapy unit and is particularly useful in IMRT planar dose verification due to its efficiency and reproducibility. In this work, we characterized the dose response of the KODAK EDR2 ready-pack film which was used to develop the step valley dose maps and the IMRT QA planar doses. A comparison between the step valley technique and multifilm based calibration showed that both calibration methods agreed with less than 0.4% deviation in the clinically useful dose ranges.

How to speed up Monte Carlo (MC) simulation in dose calculation without losing its intrinsic accuracy is one of the key issues of making a clinical MC dose engine. In this study we intensively investigated a special parallel computation technique, the vectorization technique, to boost simulation efficiency on a personal computer (PC) without extra hardware investment. A MC code, dose planning method (DPM), was extensively modified into a vectorized code, V-DPM, using the streaming single-instruction-multiple-data extension (SSE) parallel computation model. Comparative simulations were conducted for typical simulation cases in both DPM and V-DPM codes. We found that in every case the V-DPM code runs 1.5 times faster than the DPM code with variance of 0.6%.

Purpose: To present an enhanced DICOM‐RT viewer for clinical practitioners and R&D scientists and engineers in radiation therapy. Methods and Materials: DICOM‐RT is a set of DICOM extensions for radiotherapy. Despite the fact that DICOM‐RT was devised in 1997 and has currently been adopted by all major manufacturers, the DICOM‐RT viewer is not readily available to many healthcare providers and R&D scientists and engineers in radiation therapy. Triggered by clinical needs, a DICOM/DICOM‐RT viewer, DICOMan, was developed on Microsoft Windows XP platform started from scratch three years ago. It supports all kinds of DICOM‐RT objects, namely RT Image, RT Structure Set, RT Plan, RT Dose and RT Record. Added to the viewer, a set of built‐in tools were also implemented, such as DICOM Decompressor, DICOM Pusher, DICOM Retriever, DICOM editor, DICOM Anonymizer, DICOM Format Converter and so on. Some RT information that is not explicitly expressed in RT objects, such as incident energy fluence and isodose curves, can be reproduced and rendered to facilitate plan review. Results: DICOMan has been tested, routinely used and constantly upgraded for about three years. It has been frequently used to view DICOM CD‐ROMs, push DICOM images to treatment planning systems, retrieve images from RT PACS, review treatment plans and help perform dose summation. The anonymizer, format converter and editor are handy tools for R&D scientists and engineers who need to handle DICOM/DICOM‐RT objects. Conclusion: DICOM RT extension models radiation therapy practice in many modules related to clinical components of radiation therapy. Many of them are cross‐referenced and coexist with the referenced ones in different objects. The regular DICOM viewer can not render RT objects appropriately. A dedicated DICOM RT viewer is needed.

Purpose: To assess the accuracy of self‐developing Gafchromic XR‐RV2 film for the dosimetry of small animal kilovoltage x‐ray irradiation. Method and Materials: Two kilovoltage x‐ray beams (100kVp and 150kVp) for small animal irradiation from a Faxitron machine were employed in this study. The doses of a point at the center of a round field with diameter of 20cm in a 30×30×10 cm3 solid water phantom at a depth of 1cm were measured via Gafchromic XR‐RV2 films and a Farmer ion chamber. The films, cut into small samples (3.5×1.5cm2 in size), were from the same batch to remove the variability between batches. Two film calibration curves were established for the two beams. The films were scanned with an Epson V700 flat‐bed scanner 24 hours after exposure and analyzed with FilmQA software. The doses of the same point for a round field with diameter of 1cm were also measured. Results: The Gafchromic XR‐RV2 film calibration curves were found to be weak dependent of beam energy (<8% difference of the pixel values between 100kVp and 150kVp). The agreement of measured doses for big field between Gafchromic XR‐RV2 films and Framer chamber were within 5% (−4.0% to 5.0%). While for small field irradiation, large difference (up to 75%) of measured doses was observed, which indicates that Farmer chamber underestimated the point dose due to field size is not big enough to cover chamber body. Conclusion: The Gafchromic XR‐RV2 film can provide acceptable accuracy of dose measurements for kilovoltage x‐ray irradiation and it is more accurate than Farmer ion chamber for small field irradiation that are often used in small animal treatments. The combination of Gafchromic XR‐RV2 film with flat‐bed scanner represents a low‐cost and viable dosimetry tool for small animal irradiation.