David Sasaki

The dosimetric quality of brachytherapy implants in patients with small prostate volume depends on the experience of the brachytherapy team

PURPOSE To investigate the dosimetric outcome of brachytherapy in patients with small prostate volume (PV). METHODS AND MATERIALS Forty-three patients with small PV (<25 cm(3)) as determined using transrectal ultrasound and 120 patients with non-small PV (>25 cm(3)) that had received (125)I seed implants were reviewed in a retrospective cohort study. Implantations were performed under transrectal ultrasound guidance, and the prescription dose was 145 Gy. A CT and MRI scan of the pelvis were performed 1 month after implantation for dosimetric study. RESULTS Compared with non-small PV patients, patients with small PV experienced larger 1-month edema (p<0.001); lower dose to 90% (the isodose enclosing 90% of PV and representing a minimum dose to that volume of the prostate [D(90)]) of the prostate (p=0.03); higher intracapsular seed density (p<0.001); and were less likely to achieve D(90)>or=140 Gy (p=0.013) in a postimplant dosimetric study. The number of patients with D(90)<140 Gy decreased steadily in both subsets of patients as the implant program matured (odds ratio=0.56 per year, p<0.001), but the small prostate group exhibited more improvement compared with the non-small prostate patients over the same time period. Multivariate analysis revealed that brachytherapy team experience rather than the size of prostate was a more important predictive factor of implant quality (p<0.001). CONCLUSIONS This single institution experience demonstrated a significant learning curve in the initial years of a prostate brachytherapy program, especially for patients with small prostates. A small prostate itself is not a contraindication of brachytherapy. The quality of implant for patients with small prostates depends more on the skill of the brachytherapy team.

A quality assurance tool for high-dose-rate brachytherapy.

PURPOSE The purpose of this work was to develop a quality assurance (QA) tool for high-dose-rate (HDR) brachytherapy that would quickly and easily verify both source positioning (dwell positions) and durations (dwell times). METHODS The authors constructed a QA tool that combined radiochromic film to verify position with four photodiode detectors to verify dwell times. To characterize the temporal accuracy of the tool, a function generator powered four red light-emitting diodes that were optically coupled to the four photodiode detectors. The QA tool was used to verify the dwell positions and times of a commercial brachytherapy afterloader. Measurements of dwell time were independently verified by a one-dimensional optical camera that acquired 1000 lines/s. RESULTS The temporal accuracy of the QA tool was found to be about 1 ms. For visual assessment, the source position could be located within about 0.5 mm. Evaluating the accuracy and precision of an HDR brachytherapy afterloader, the authors found that the bias in dwell time can exceed 60 ms and the dwell time associated with the first dwell position had an unexpectedly large standard deviation of 30 ms. They found that the source locations were much easier to locate on the film if a plastic catheter was used instead of a metal treatment tube. Scanning the films enabled the dwell positions to be determined within about 0.2 mm. CONCLUSIONS For pretreatment QA, the authors found that this tool allowed verification of dwell positions and dwell times in about 6 min.

Sci‐Sat AM(2): Brachy‐06: A Comparison of MR/CT fusion versus CT alone for assessment of implant quality in permanent prostate brachytherapy

Low dose-rate permanent implant brachytherapy is widely used in the management of patients with early stage prostate cancer. An assessment of the implant quality is usually carried out 30 days after the implant is delivered, using computed tomography (CT) to identify the prostate and seeds. This is difficult due to poor contrast of the prostate and the superposition of seeds in the CT images. Magnetic resonance (MR) imaging offers superior contrast but inferior visualization of seeds. At our centre, patients are imaged using both CT and T2 weighted MR 30 days after an implant, and the image sets are fused using a commercial software package. The seeds are identified on CT and the prostate volumes are contoured on MR, with fusion performed by matching seeds on CT with seed signal voids on MR. The purpose of this study was to compare standard prostate post-implant dosimetric parameters (D90, V100, etc.) for prostates contoured on CT alone (MR blinded) versus MR/CT fusion. 25 patients were evaluated with all contouring performed by the same physician. We found that the prostate volume was overestimated using CT alone as compared to MR/CT fusion (mean: 37.2cc vs. 35.0cc respectively, p = 0.033). We also found that dosimetric parameters were underestimated for CT alone compared to MR/CT fusion, including D90 (mean: 144.3Gy vs. 150.8Gy respectively, p = 0.005) and V100 (mean: 89.2% vs. 91.0% respectively, p = 0.01). Centres using CT alone for post-implant dosimetry may therefore be underestimating their implant quality.

COMP report: CPQR technical quality control guidelines for radiation treatment centers

Abstract The Canadian Organization of Medical Physicists (COMP), in close partnership with the Canadian Partnership for Quality Radiotherapy (CPQR) has developed a series of Technical Quality Control (TQC) guidelines for radiation treatment equipment. These guidelines outline the performance objectives that equipment should meet in order to ensure an acceptable level of radiation treatment quality. The TQC guidelines have been rigorously reviewed and field tested in a variety of Canadian radiation treatment facilities. The development process enables rapid review and update to keep the guidelines current with changes in technology. This announcement provides an introduction to the guidelines, describing their scope and how they should be interpreted. Details of recommended tests can be found in separate, equipment specific TQC guidelines published in the JACMP (COMP Reports), or the website of the Canadian Partnership for Quality Radiotherapy (www.cpqr.ca).

86: Using Optical Scanner and 3D Printer Technology to Create Lead Shielding for Radiotherapy of Facial Skin Cancer with Low Energy Photons: An Exciting Innovation

Treatment of non-melanoma skin cancers of the face using ortho-voltage radiotherapy may require lead shielding to protect vulnerable organs at risk (OAR). As the human face has many complex and intricate contours, creating a lead shield can be difficult. The process can include creating a plaster mould of a patients face to create the shield. It can be difficult or impossible for a patient who is claustrophobic or medically unable to lie flat to have a shield made by this technique. Other methods have their own shortcomings. We aimed to address some of these issues using an optical scanner and 3D printer technology.

74: Innovative Approach for Generating Soft Silicone Bolus using 3D Printing for Electron Treatment of Skin Cancers in Areas with Irregular Contours

S29 _________________________________________________________________________________________________________ cardiac four-dimensional CT (4D-CT) synchronized to the electrocardiogram were obtained in treatment position, using a prospective sequential acquisition method including the extreme phases of systole and diastole. On a MimVista® image registration workstation, dose distributions were transferred to the cardiac 4D-CT. The left coronary artery, left ventricle and heart were contoured on both phases of the cardiac cycle. The maximum and minimum doses to the left coronary, left ventricle and heart were compared using a bilateral paired Student T test. Results: Preliminary data from the first eight patients enrolled are presented. Median age was 60 years (56-71) and median planned dose to the left breast was 42.56 Gy (42.56-50) in 16 fractions (16-20). For the left coronary artery, mean dose, V5 and V20 in systole versus diastole were 6.1 Gy versus 7.9 Gy (p = 0.02), 37% versus 48% (p = 0.02) and 10% versus 16% (p = 0.04), respectively. For the left ventricle, mean dose, V5 and V20 in systole versus diastole were 1.3 Gy versus 1.6 Gy (p = 0.005), 6% versus 9% (p = 0.03) and 1% versus 2% (p > 0.1), respectively. For the whole heart, mean dose, V5 and V20 in systole versus diastole were 0.9 Gy versus 1.3 Gy (p = 0.005), 21 cc versus 32 cc (p = 0.07) and 4 cc versus 5 cc (p > 0.1), respectively. Conclusions: Beyond DIBH, systolic irradiation would be associated with a further reduction in V5, V20 and mean dose to the left coronary artery, as well as a reduction in V5 and mean dose to the left ventricle and heart as a whole. The potential clinical impact of this reduction as well as the feasibility of cardiac gated irradiation are to be further investigated.

218: Using 3D Printer Technology to Manufacture Anatomic Models for Patient Education: A New Frontier

PURPOSE/OBJECTIVES The use of 3D printing technology to create precise anatomical models is well documented. These models are used by surgeons to better plan upcoming operations and to save valuable operating room time. They are also used to educate other members of the health care team, such as residents, medical students and nurses. However, the use of these anatomically accurate models to educate patients in the clinical setting has been underutilized. At our centre, we are using 3D printer technology to generate accurate clinical models of mandibles. Our objective is to use these models to better educate and prepare head and neck cancer patients for upcoming surgery where manibulectomy is part of the surgical procedure. This has been used to educate 3 consecutive patients.

Sci-Fri AM: Quality, Safety, and Professional Issues 02: Recent work on TQC Suite and Data from a National survey on Community Uptake

The Canadian Partnership for Quality Radiotherapy (CPQR) and the Canadian Organization of Medical Physicists (COMP) Quality Assurance and Radiation Safety Advisory Committee (QARSAC) have worked together in the development of a suite of Technical Quality Control (TQC) Guidelines for radiation treatment equipment and technologies, that outline specific performance objectives and criteria that equipment should meet in order to assure an acceptable level of radiation treatment quality. Early community engagement and uptake survey data showed 70% of Canadian centers are part of this process and that the data in the guideline documents reflect, and are influencing the way Canadian radiation treatment centres run their technical quality control programs. As the TQC development framework matured as a cross-country initiative, guidance documents have been developed in many clinical technologies. Recently, there have been new TQC documents initiated for Gamma Knife and Cyberknife technologies where the entire communities within Canada are involved in the review process. At the same time, QARSAC reviewed the suite as a whole for the first time and it was found that some tests and tolerances overlapped across multiple documents as single tests could pertain to multiple quality control areas. The work to streamline the entire suite has allowed for improved usability of the suite while keeping the integrity of single quality control areas. The suite will be published by the JACMP, in the coming year.

Sci‐Sat AM: Radiation Dosimetry and Practical Therapy Solutions ‐ 07: A mould room in a box – 3D scanning and printing technology in the radiotherapy clinic

Purpose: We describe the process by which our centre is currently implementing 3D printing and scanning technology for treatment accessory fabrication. This technology can increase efficiency and accuracy of accessory design, production and placement during daily use. Methods: A low-cost 3D printer and 3D optical scanner have been purchased and are being commissioned for clinical use. Commissioning includes assessing: the accuracy of the 3D scanner through comparison with high resolution CT images; the dosimetric characteristics of polylactic acid (PLA) for electron beams; the clinical utility of the technology, and; methods for quality assurance. Results: The agreement between meshes generated using the 3D scanner and CT data was within 2 millimeters for an anthropomorphic head phantom. In terms of electron beam attenuation, 1 centimetre of printed PLA was found equivalent to 1.17 cm of water. In proof-of-concept tests, several types of treatment accessories have been prototyped to date that will benefit from this technology. These include electron and photon bolus for areas with complex surface contours including the ear for electron treatments, the extremities for photon treatments and lead shielding for orthovoltage treatments. Imaging with CT and x-ray showed minimal defects, which will have no significant clinical impact. Geometric fidelity and fit to volunteers and patients was found to be excellent. Conclusions: 3D Printing and scanning can increase efficiency in the clinic for treatments requiring custom accessories. Customized boluses and shielding had excellent fit and reduced uncertainty in positioning.

Poster – 39: Using Optical Scanner and 3D Printer Technology to Create Lead Shielding for Radiotherapy of Facial Skin Cancer with Low Energy Photons

Purpose: Treatment of skin cancers of the face using orthovoltage radiotherapy often requires lead shielding. However, creating a lead shield can be difficult because the face has complex and intricate contours. The traditional process involved creating a plaster mould of the patients face can be difficult for patients. Our goal was to develop an improved process by using an optical scanner and 3D printer technology. Methods: The oncologist defined the treatment field by drawing on each patients skin. Three-dimensional images were acquired using a consumer-grade optical scanner. A 3D model of each patients face was processed with mesh editing software before being printed on a 3D printer. Using a hammer, a 3 mm thick layer of lead was formed to closely fit the contours of the model. A hole was then cut out to define the field. Results: The lead shields created were remarkably accurate and fit the contours of the patients. The hole defining the field exposed only a minimally sized site to be exposed to radiation, while the rest of the face was protected. It was easy to obtain perfect symmetry for the definition of parallel opposed beams. Conclusion: We are routinely using this technique to build lead shielding that wraps around the patient as an alternative to cut-outs. We also use it for treatment of the tip of the nose using a parallel opposed pair beams with a wax nose block. We found this technique allows more accurate delineation of the cut-out and a more reproducible set-up.