The purpose of this study was to evaluate the radiation attenuation properties of PC‐ISO, a commercially available, biocompatible, sterilizable 3D printing material, and its suitability for customized, single‐use gynecologic (GYN) brachytherapy applicators that have the potential for accurate guiding of seeds through linear and curved internal channels. A custom radiochromic film dosimetry apparatus was 3D‐printed in PC‐ISO with a single catheter channel and a slit to hold a film segment. The apparatus was designed specifically to test geometry pertinent for use of this material in a clinical setting. A brachytherapy dose plan was computed to deliver a cylindrical dose distribution to the film. The dose plan used an 192Ir source and was normalized to 1500 cGy at 1 cm from the channel. The material was evaluated by comparing the film exposure to an identical test done in water. The Hounsfield unit (HU) distributions were computed from a CT scan of the apparatus and compared to the HU distribution of water and the HU distribution of a commercial GYN cylinder applicator. The dose depth curve of PC‐ISO as measured by the radiochromic film was within 1% of water between 1 cm and 6 cm from the channel. The mean HU was ‐10 for PC‐ISO and ‐1 for water. As expected, the honeycombed structure of the PC‐ISO 3D printing process created a moderate spread of HU values, but the mean was comparable to water. PC‐ISO is sufficiently water‐equivalent to be compatible with our HDR brachytherapy planning system and clinical workflow and, therefore, it is suitable for creating custom GYN brachytherapy applicators. Our current clinical practice includes the use of custom GYN applicators made of commercially available PC‐ISO when doing so can improve the patient's treatment.PACS number: none

PurposeThree-dimensional (3D) printing technology allows physicians to rapidly create customized devices for patients. We report our initial clinical experience using this technology to create custom applicators for vaginal brachytherapy.Material and methodsThree brachytherapy patients with unique clinical needs were identified as likely to benefit from a customized vaginal applicator. Patient 1 underwent intracavitary vaginal cuff brachytherapy after hysterectomy and chemotherapy for stage IA papillary serous endometrial cancer using a custom printed 2.75 cm diameter segmented vaginal cylinder with a central channel. Patient 2 underwent interstitial brachytherapy for a vaginal cuff recurrence of endometrial cancer after prior hysterectomy, whole pelvis radiotherapy, and brachytherapy boost. We printed a 2 cm diameter vaginal cylinder with one central and six peripheral catheter channels to fit a narrow vaginal canal. Patient 3 underwent interstitial brachytherapy boost for stage IIIA vulvar cancer with vaginal extension. For more secure applicator fit within a wide vaginal canal, we printed a 3.5 cm diameter solid cylinder with one central tandem channel and ten peripheral catheter channels. The applicators were printed in a biocompatible, sterilizable thermoplastic.ResultsPatient 1 received 31.5 Gy to the surface in three fractions over two weeks. Patient 2 received 36 Gy to the CTV in six fractions over two implants one week apart, with interstitial hyperthermia once per implant. Patient 3 received 18 Gy in three fractions over one implant after 45 Gy external beam radiotherapy. Brachytherapy was tolerated well with no grade 3 or higher toxicity and no local recurrences.ConclusionsWe established a workflow to rapidly manufacture and implement customized vaginal applicators that can be sterilized and are made of biocompatible material, resulting in high-quality brachytherapy for patients whose anatomy is not ideally suited for standard, commercially available applicators.

to receive 21Gy in 4 fractions; EQD2 of 26.7Gy). The resultant dosimetry was compared to the 10 prior HDR BT plans normalized to a standard dose of 34Gy in 4 fractions. Normal tissue dose tolerance limits were set using recommendations from the SBRT Task Group 101, a pelvic SBRTÀrelated RTOG trial, and guidelines from the American Brachytherapy Society. Organs at risk (OARs) evaluated were the bladder, rectum, sigmoid, femoral heads, and other bowel, including both large and small bowel. Each plan was evaluated for the uterus volume receiving 150% of the prescription dose (V150%); highest dose encompassing 95% (D95%), D90% and D50% of the uterus; D90% of the Boost CTV and PTV, and the highest dose received by 0.1cc (D0.1cc), D1cc, and D2cc of the bladder, rectum and sigmoid, among other dose points. Results: Among the 10 subjects, the contributing comorbidities to medically inoperable status included: morbid obesity (n56), cardiovascular dysfunction (n56), severe anemia (n51) and end-stage cirrhosis (n51). Perioperative complications included severe pain (n53), uterine perforation (n51), and decreased oxygen saturation (n52). Table 1 lists the average and standard deviation values for the dose-volume parameters. Compared to HDR BT, HT SBRT produced significantly greater overall target coverage to the uterus, boost CTV, and PTV, with exception of the V150% of the uterus. HT SBRT significantly increased dose to the rectum, bowel, and femoral heads compared to HDR BT, though not outside of dose tolerance limits. Conclusions: In this comparative study, SBRT for medically inoperable endometrial cancer was shown to encompass a higher percentage of the target volume by the prescription dose, but with higher doses to organs at risk and a smaller percentage of the target volume exposed to higher doses (e.g., V150%), relative to HDR BT. SBRT may be a reasonable alternative to HDR BT for medically inoperable early stage endometrial cancer patients who refuse BT or who are at high risk for complications from the device placement, anesthesia, and immobilization needed for BT. However, future studies are needed to evaluate clinical outcomes after SBRT and the comparative effectiveness relative to BT.

Purpose: (1) Evaluate the safety and radiation attenuation properties of PCISO, a bio‐compatible, sterilizable 3D printing material by Stratasys, (2) establish a method for commissioning customized multi‐ and single‐use 3D printed applicators, (3) report on use of customized vaginal cylinders used to treat a series of serous endometrial cancer patient. Methods: A custom film dosimetry apparatus was designed to hold a Gafchromic radio film segment between two blocks of PC‐ISO and 3D‐printed using a Fortus 400mc (StrataSys). A dose plan was computed using 13 dwell positions at 2.5 mm spacing and normalized to 1500 cGy at 1 cm. Film exposure was compared to control tests in only air and only water. The average Hounsfield Unit (HU) was computed and used to verify water equivalency. For the clinical use cases, the physician specifies the dimensions and geometry of a custom applicator from which a CAD model is designed and printed. Results: The doses measured from the PC‐ISO Gafchromic film test were within 1% of the dose measured in only water between 1cm and 6cm from the channel. Doses increased 7–4% measured in only air. HU range was 11–43. The applicators were sterilized using the Sterrad system multiple times without damage. As of submission 3 unique cylinders have been designed, printed, and used in the clinic. A standardizable workflow for commissioning custom 3D printed applicators was codified and will be reported. Conclusions: Quality assurance (QA) evaluation of the PC‐ISO 3D‐printing material showed that PC‐ISO is a suitable material for a gynecological brachytherapy vaginal cylinder in a clinical setting. With the material commissioning completed, if the physician determines that a better treatment would Result, a customized design is fabricated with limited additional QA necessary. Although this study was specific to PC‐ISO, the same setup can be used to evaluate other 3D‐printing materials.

Purpose: Accurate assessment of dose delivered is key to early prediction of radiation‐induced anatomic and physiologic changes vital in providing the most accurate patient‐specific treatments. We are conducting a translational small‐animal study using functional Hyperpolarized‐13C‐Urea with DCE‐MRI to evaluate tumor perfusion changes following local targeted Ir‐192 irradiation using the Leipzig applicator. The purpose of this study is to present and evaluate a novel Monte Carlo (MC) tool, which provides heterogeneous dose predictions for this specific application, and to compare the results against the TG‐43 dose calculation. Methods: CT scans were obtained with a Leipzig applicator mold (fabricated using a 3D‐printer to avoid metal artifact) centrally placed on top of the CyberKnife Ball Cube QA phantom . The CT density of the mold was overridden to be that of the applicator material, Tungsten. A Monte Carlo platform, ALGEBRA (ALgorithm for heterogeneous dosimetry based on GEANT4 for BRAchytherapy) was used for simulation. Dose measurements were done using Gafchromic EBT2 film placed orthogonally inside the Ball Cube exposed to Ir‐192 with the Leipzig applicator in place. Simple TG‐43 calculations for a free source in water was done using the Oncentra treatment planning system. Results: The two‐dimensional planar dose distributions obtained from MC simulation showed strong agreement (within 4–5%) with dose measurements while TG‐43 calculations showed differences up to 20%. Compared to TG‐43, the MC Result was attenuated less at the surface because of the Leipzig air cavity, but penetrated less due to the collimation effect. Conclusion: We have validated a new MC simulation tool using a Leipzig applicator for small animal irradiation. This tool will provide the basis for studies associating tumor response with the actual dose delivered. The tool can be further used to construct dosimetry information for clinical treatments using the Leipzig applicator as an alternative to superficial/orthovoltage radiation treatment.