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Purpose: To perform adaptive radiation therapytreatments for lungcancer using IMRT; to show that adjusting the target dose after each fraction, in order to‘react’ to errors in the dosedelivered in prior fractions, can lead to significant changes in the daily tumordose over the treatment.Method and Materials: Before the start of treatment, the beamlet intensities are optimized to deliver the current target dose distribution for a target set of breathing patterns at minimal healthy tissuedose. In each fraction, the current beamlet intensities are delivered, and the patient's breathing pattern is measured. The breathing pattern set is updated using the breathing pattern, and the target dose distribution is updated to account for dose errors realized in the previous fraction. The beamlet intensities are then re‐optimized for the updated dose distribution and uncertainty set, to be used in the next fraction. This process continues until the end of the treatment. We consider three types of updates to the target dose distribution: the reactive± update, which responds to both under and overdose; the reactive‐ update, which responds only to underdose; and the reactive+ update, which responds only to overdose. Results: On breathing pattern sequences obtained from real patients, dose‐reactive methods result in final dose performance comparable to non‐dose‐reactive methods. However, as the treatment progresses, the reactive± update results in growing daily underdose and overdose, the reactive‐ update results in growing daily overdose, and the reactive+ update results in growing daily underdose. In contrast, non‐reactive methods have stable or decreasing tumor underdose and overdose. Conclusions: By incorporating dose‐reaction, the final tumordose distribution can be made to conform closely to the target dose distribution, but at the cost of increasing tumor underdose and/or overdose. This increasing heterogeneity may have implications for the biological effectiveness of treatments obtained by dose‐reaction.

In prostate brachytherapy, radioactive seeds are permanently implanted in the prostate for delivering a tumorocidal dose to the cancerous tissues. These seeds provide a significant radiation dose to a relatively small volume, requiring that the seeds be placed accurately to ensure complete treatment. Sensitivity of the urethra and rectal mucosa to radiation are other factors that heighten the need for careful placement of the seeds. In currently practiced manual procedures, the needles are inserted into the patient through fixed holes of a physical template where the maneuverability of the needle is extremely difficult. In contrast, a robotic system can not only provide flexibility in positioning and orientating along with improved consistency and accuracy of needle insertion and seed deposition but may also assist less skillful/inexperienced clinicians to treat patients with higher quality. Thus, it is important to develop an automated (or a semiautomated) seed delivery device which can provide enhanced consistency, accuracy and efficiency.

In this paper we present a semi-automated device designed and developed to deliver radio-active seeds for treating prostate cancer. In the brachytherapy procedure a slander needle is inserted through the perineum and passed through different types of tissues. Thus, the needle experiences significant amount of force which may cause it to buckle and bend. In our design, we have considered the buckling force and insertion force on needle by collecting in-vivo data from real patient and performing in-vitro experiments. Techniques to reduce force and organ/tissue deformation have been implemented into this new design. To track the axial force on the needle for detecting pubic arch interference and to improve robotic control, we have incorporated three force sensors. Rigidity and factor of safety of the device has been analyzed using finite element method which was very useful for iterative design process

In contemporary brachytherapy procedures, needle placement at the desired target is challenging due to a variety of reasons. A robot-assisted brachytherapy system can improve the needle placement and seed delivery resulting in enhanced patient care. In this paper we present a 16 DOF (degrees-of-freedom) robotic system (9DOF positioning module and 7DOF surgery module) developed and fabricated for prostate brachytherapy. Techniques to reduce needle deflection and target movement have been incorporated after verifying with extensive experiments. Provisions for needle motion and force feedback have been included into the system for improving the robot control and seed delivery. Preliminary experimental results reveal that the prototype system is quite accurate (sub-millimeter) in placing brachytherapy needles.

Purpose: As IGRT strategies evolve from localization to adaptive planning, it becomes more important to acquire guidance images of higher quality. We utilized a CATPHAN to subject radiotherapyCBCTimages acquired under various conditions to the same rigorous tests and evaluation that diagnostic CTs undergo. This study reports on the evaluation of image qualities of diagnostic CT and radiotherapyCBCT and identifies the area of quality differences between the images.Method and Materials: RT‐CBCT scans were performed on Elekta XVI using pelvis scan settings on a CATPHAN Model 600. They were then compared to results from a GE Lightspeed16 multidetector CT scanner. The phantom contained modules allowing measurement of slice thickness, spatial resolution, low contrast resolution, Hounsfield Unit (HU) sensitivity and image uniformity. HU uniformity in the axial direction and geometric distortion were also measured. Results: For low contrast resolution tests, no targets could be clearly defined in the medium resolution reconstruction on RT‐CBCT. Only three spheres could be seen with the high resolution reconstruction (not used clinically) compared to six on diagnostic CTs. Calculated thicknesses for a 1.0 mm slice varied from 1.33 to 2.45 mm. The HU sensitometry test showed large variation from accepted HU values of the targets. These variations were not linear or affected by the reconstruction method. Spatial resolution for clinical settings (medium resolution) was constant at three lp/cm and improved to ten lp/cm with the high resolution acceptance testing reconstruction. This is comparable to diagnostic CT resolution. Axial direction HU uniformity varied in a stepwise fashion as the uniformity module moved away from the CBCT isocenter. No measurable geometric distortion was found as a function of distance from isocenter. Conclusion: A consolidated CBCT QA procedure is feasible for monitoring changes in image acquisition systems over time for image quality evaluation in adaptive therapy.

Purpose: In image‐guidedbrachytherapy (IGBT), accurate placement of needles and radiation sources is a major challenge. In traditional prostate brachytherapy, for example, needles are introduced through fixed, parallel holes of a template where the maneuverability of the needle is extremely limited. The accuracy of needle placement and seed delivery is subject to variation with clinician technique, such as deflection force and needle rotation. We present a robotic platform for IGBT, a semi‐automated 14 degree‐of‐freedom (DOF) robotic system, designed and fabricated for performing prostate brachytherapy with radioactive seeds. Method and Materials: The IGBT system consists of two main modules: (1) a 7 DOF positioning module, and (2) a 7 DOF surgery module. The positioning module has a 2 DOF cart and a 5 DOF platform. The surgery module includes a 2 DOF ultrasound probe driver, a 3 DOF gantry robot, a 2 DOF needle inserter and a seed pusher. All motions of the surgery module are motorized. This system incorporated numerous important data and methods garnered from in‐vivo measurements during actual brachytherapy procedures. Various techniques to enhance precision of needle insertion and seed delivery have been implemented into the system, after extensive verification via phantom experiments. Three force‐torque sensors were incorporated for tracking the forces on the needle to detect pubic arch interference and to improve robot control. Rigidity and factor of safety of the mechanical structures have been analyzed using finite element method. The system has provisions for feedback of various states (position, velocity and force), which will be useful to improve needle insertion and seed delivery accuracy, consistency and efficiency. Results and Conclusion: Preliminary experimental results demonstrate highly accurate (sub‐millimeter) and consistent placement of brachytherapy needle. Extensive experiments have been conducted to evaluate performance of this prototype system for IGBT. Acknowledgment: Work supported by NIH/NCI Grant No. R01‐CA91763.

During the prostate brachytherapy procedure, multiple needles are inserted into the prostate and radioactive seeds are deposited. Stabilizing needles are first inserted to provide some rigidity and support to the prostate, ideally this will provide better seed placement and an overall improved treatment. However, there is much speculation regarding the effectiveness of using regular brachytherapy needles as stabilizers. In this study, we explored the efficacy of (1) two types of needles - 18 gauge brachytherapy needle vs. 18 gauge hooked needle; and (2) parallel vs. angulated needle configurations to stabilize the prostate. Prostate phantom movement and needle insertion progression were imaged using ultrasound (US). The recorded images were analyzed and prostate displacement was computed from images using implanted artifacts. Experimentation allowed us to further understand the mechanics behind prostate stabilization. We observed superior stabilization by the hooked needles compared to the regular brachytherapy needles (more than 40% for parallel stabilization). Prostate movement was also reduced significantly when regular brachytherapy needles were in an angulated configuration as compared to the parallel configuration (approximately 40%). When the hooked needles were angled for stabilization, further improvement in decreased displacement was observed. In general, for convenience of dosimetric planning, all needles are desired to be in parallel and in this case, hooked needles are better suited to improve stabilization of the prostate. On the other hand, both regular and hooked needles appear to be equally effective in reducing prostate movement when they are in angulated configurations, which will be useful in robotic permanent seed implantation (PSI).