Craig Lewis

Computed tomographic volumetric analysis as a predictor of local control in laryngeal cancers treated with conventional radiotherapy.

BACKGROUND There is still controversy regarding the appropriate management of large T2 and T3 laryngeal cancers, with some investigators finding little correlation between the current TNM staging system and tumour control following external beam radiotherapy. OBJECTIVE To establish the utility of computed tomography (CT)-determined tumour volume as a predictor of local control of moderately advanced (T2 and T3) squamous cell carcinoma of the larynx. MATERIALS AND METHODS A retrospective chart review and CT volumetric analysis were performed on 47 patients who were treated for T2 or T3 laryngeal squamous cell carcinoma with radiotherapy alone at the London Regional Cancer Centre between 1995 and 2000. Of these 47 patients, there were 30 with glottic tumours and 17 with supraglottic tumours. Forty-two males and five females were included in the analysis, with ages ranging from 40 to 84 years. Each patients CT scan was redigitized, and the tumours were outlined by the chief investigator and by a head and neck radiologist using anatomy modelling software. Patient demographics, tumour characteristics, and tumour stage were analyzed, with local failure rates described and related to the variables through univariate and multivariate analyses. RESULTS Tumour size ranged from 0.15 to 16.64 cm3, with a mean volume of 3.5 cm3. The local recurrence rate in this group of patients was 40% (19/47). Local control was correlated on multivariate analysis to tumour size for all patients combined (> 3 cm3 vs < 3 cm3; p = .003) and for glottic tumours alone (> 1 cm3 vs < 1 cm3; p = .001). A correlation was also demonstrated on multivariate analysis between local control and overall stage (p = .023), patient age (p = .029), and hypopharyngeal involvement (p = .032). CONCLUSIONS There is a significant and independent relationship between CT-determined tumour volume and local recurrence in moderately advanced squamous cell carcinoma of the larynx treated with conventional radiotherapy. Based on these results and those of similar studies, CT should therefore become a routine part of the staging system for T2 tumours and above.

Brachytherapy with permanent gold grain seeds for squamous cell carcinoma of the lip

PURPOSE To describe the use of radioactive gold grain implantation for squamous cell carcinoma of the lip. METHODS Retrospective review of 51 patients treated with permanent gold ((198)Au) grain implant brachytherapy. The seed arrangement delivered a dose of 5500 cGy at 0.5 cm from a single plane. Primary endpoints were local recurrence and cosmetic outcome. RESULTS Median follow-up was 27 months. Median age was 69 years. The majority (90%) were T1 lesions. None of the patients had evidence of regional lymph node or distant metastasis. Twelve patients had recurrent disease with prior surgery and five patients had previous head and neck radiation. Local control was achieved in 49 patients. Good cosmesis was achieved in 48 patients. Two-year actuarial estimates for local failure-free survival, disease-free survival and overall survival were 97.9%, 94.1% and 87.9%, respectively; no deaths were attributable to lip cancer. CONCLUSIONS Gold grain interstitial low-dose rate brachytherapy provides excellent local control and cosmesis in patients with squamous cell carcinoma of the lip. This technique provides an excellent option for patients that are elder or live remotely. It is particularly useful for lesions that are small, in previously radiated areas, or treated with prior surgery.

MIRA V: An integrated system for minimally invasive robot-assisted lung brachytherapy

An integrated system for minimally invasive robot-assisted image-guided lung brachytherapy has been developed. The system incorporates an experimental setup for accurate radioactive seed placement with commercially available dosimetry planning software. The end result is a complete system that allows planning and executing a brachytherapy procedure with increased accuracy. The results of the in vitro seed placement evaluation show that seed misplacement has a significant effect on the volume receiving more than 200% of the dose (V200), and the minimum dosage received by 90% of the volume (D90).

Lung Cancer Brachytherapy: Robotics-Assisted Minimally Invasive Approach

New technological concepts have been evolving to manage the relative poor prognosis of lung cancer. Brachytherapy is becoming an option for both unresectable and early resectable lung cancer. Three-dimensional ultrasound (US) of lung tumours and image-guided minimally invasive robotics-assisted brachytherapy are feasible for dosimetry planning and management of lung tumours. The present article reviews the current knowledge of lung brachytherapy and discusses its potential in future management of lung cancer.

Sci-Sat AM (2) Therapy-07: Feasibility of 3D ultrasound guided brachytherapy for lung cancer using a porcine lung tumour model

The standard treatment of localized early stage non‐small cell lungcancer is surgical resection. However, most patients are not candidates for surgery due to poor lung function and comorbidities. Minimally invasive interstitial brachytherapy may be an option for these patients. An in vivodosimetry test box was constructed to simulate the thoracic cavity and allow 3D ultrasound imaging of the brachytherapy needles. The box stabilizes the ultrasound probe and facilitates insertion of brachytherapy needles parallel to the probe axis. Seeds were implanted, targeted at the centre of a 1.5 cm agar sphere in 6% gelatin and then imaged using the 3D ultrasound and CT scans. The dosimetric impact of seed location was examined using Theraplan Plus. The DVH (dose volume histogram) was calculated assuming an I 125 seed activity that would cover the sphere with an arbitrary D90 of 25Gy if the seed was located at the centre of the sphere. DVH D90 values for the actual implanted seed positions will be presented comparing CT to ultrasound. This procedure was repeated in an ex vivolungtumourmodel consisting of agar spheres implanted into excised collapsed porcine lungs. Initial 3D ultrasound measurements were done with a probe designed for prostate brachytherapy. However, the measurements will be repeated with a smaller diameter thoracoscopic ultrasound probe that will be used clinically. This pilot work demonstrates the feasibility of using 3D ultrasound to target seed insertion and calculate dosimetry in a brachytherapylungtumourmodel.

Intra-operative dosimetry of trans-rectal ultrasound guided 125I prostate implants using C-arm fluoroscopic images

Permanent implantation of radioactive seeds is a viable and effective therapeutic option widely used today for early-stage prostate cancer. The implant technique has improved considerably during the recent years due to the use of image guidance; however, real-time dose distributions would allow potential cold spots to be assessed and additional seeds added. In this study, we investigate the use of a conventional C-arm fluoroscopy unit for image acquisition and evaluation of dose distribution immediately after the implant. The phantom study indicates that it is possible to obtain seed positions within ±2 mm. A pilot study carried out with three patients indicated that it is possible to obtain seed positions and calculate the dose distribution with C-arm fluoroscopy and about 95% of the seeds were reconstructed within ±2 mm. The results could be further improved with better digital imaging.

TU‐C‐J‐6B‐07: 3DUS, MRI and CT Prostate Volume Definition: 3D Evaluation of Intra‐ and Inter‐Modality and Observer Variability

Purpose: To produce a complete three-dimensional description of the accuracy, variability significance of differences in prostate volume estimation using 3DUS, MR and CT imaging. Method and Materials: Ten patients underwent 3DUS, MR (axial FSE T2-weighted) and CT imaging 28–33d after I–125 implant (74–112 seeds, mean=93.3). MR prostate volume range was 22.6–50.8cc (mean=31.9cc). Seven experienced observers contoured prostate volumes in 2.5 mm slice increments, twice for each patient, while blind to image duplication within and between modalities. Regional trends in variability and absolute differences in volume estimation between modalities were examined in 3D. Results: The average volume ratio was 1.16 for CT/MR, 0.90 for US/MR and 1.30 for CT/US. The greatest variability of CT contours occurred at the posterior and anterior portions of the mid-gland. On MR images, the overall variability was smaller, with a maximum in the anterior region. On 3DUS, high variability occurred in the anterior regions of the apex and base, while the prostate-rectum interface had the smallest variability. 3DUS contours tended to be larger than CT and MR in the anterior and posterior aspects of some patients, likely due to gland deformation by the US probe. The average percent of surface area that was significantly different (95% confidence) was 4.1%, CT-MR; 10.7% US-MR; 6.3% CT-US. Both center-of-mass registration and larger standard deviation of CT measurements increase statistical similarity of CT to other modalities. Using seeds as fiducial markers decreases this similarity. Deformation during insertion of the trans-rectal ultrasound probe, rectum and bladder filling and breathing motion also have an effect. Conclusion: Our findings suggest that improved seed recognition algorithms for 3DUS or MR, or fusion with CT may improve the accuracy of post-implant planning. Visualization of 3D trends between modalities may assist in improving the consistency of prostate delineation.

Poster — Thur Eve — 63: Planning and Phantom Study of Oblique Needle Based Low Dose Rate Prostate Brachytherapy (LDRPB) Using 3D Trans‐Rectal Ultrasound (TRUS) and Robotic Assistance

The purpose of this study was to create a phantom to validate the Low Dose Rate Prostate Brachytherapy (LDRPB) plans using oblique (angled) needles delivered using robotic guidance in overcoming pubic arch interference for large prostates. Five patient 3D Trans‐rectal Ultra Sound (TRUS)images were selected. The images were required to show a maximum pubic arch interference of <= 1 cm and prostate volume of < 50 cc. The prostate contours were artificially enlarged to 60 cc while keeping the pubic arches constant. The following three different types of plans were manually created for each 60 cc prostate: parallel needle template based, parallel needle non template based, and oblique needle non template based. One sided t‐tests between the three different types of plans were computed for DVH indices recommended by ESTRO for LDRPB. At the 1% significance level, a better DVH index for each organ (PTV, Urethra, and Rectum) was observed for oblique plans compared to the other two techniques. The feasibility of robot and 3D TRUS guided delivery of oblique plans are being tested in a phantom study. We created a phantom based on one of the 60 cc prostate contours with a plastic plate simulating pubic arch interference. Robot and 3D TRUS guided delivery of an oblique plan will be delivered. Results of CTimages of the delivered seeds will be compared to that of the planned position, validating the feasibility of delivering oblique plans.

SU-GG-T-42: Oblique Needle Based Low Dose Rate Prostate Brachytherapy (LDRPB) Using 3D Trans-Rectal Ultrasound (TRUS) and Robotic Assistance

Purpose: To validate the dosimetric benefits of Low Dose Rate Prostate Brachytherapy (LDPB) plans using oblique (angled) needles delivered using robotic guidance in overcoming pubic arch interference (PAT) for large prostates. Methods and Materials: Five patient 3D Trans‐rectal Ultra Sound (TRUS)images that showed a maximum pubic arch interference of <= 1 cm and a prostate volume of < 50 cc were selected. The prostate contours were artificially enlarged to 60 cc while keeping the pubic arches constant. The following three different types of plans were manually created for each 60 cc prostate: parallel needle template based, parallel needle non template based, and oblique needle non template based. Oblique plans were created by adapting the parallel needle non template plans, which were adapted from parallel needle template plans. ESTRO prescription dose volume histogram (DVH) index guidelines for LDRPB were used except that this study employed a more rigorous requirement of keeping the prostatic urethral dose to less than 120% of the 145 Gy prescription dose.Results: One sided t‐tests between the three different types of plans were computed for the recommended DVH indices. At the 1% significance level, a better DVH index for each organ (PTV, Urethra, and Rectum) was observed for oblique plans. For parallel non template plans, however, only a change in PTV V100 was significant with a P‐value = 0.012. Conclusions: The oblique plans conferred a significant benefit over the template plans, overcoming pubic arch interference. The parallel needle methods are not able to provide adequate PTV dose coverage for large prostates (60cc) with pubic arch interference. Phantom studies mimicking the prostate and pubic arch of patient images are underway. The feasibility of delivering oblique plans using 3D TRUS and robotic guidance will be reported.

TH‐C‐ValB‐01: Prostate Contouring Uncertainty in Mega‐Voltage Computed Tomography (MVCT) Images Acquired with a Helical Tomotherapy Unit During Image‐Guided Radiation Therapy (IGRT)

Purpose: To evaluate the image guidance capabilities of helical tomotherapy‐based MVCT, this work compares the inter‐ and intra‐observer contouring uncertainty in KVCT used for radiotherapy planning with MVCT acquired with a tomotherapy unit. Methods and Materials: Five prostate cancer patients who underwent tomotherapy treatment (with daily MVCT) at our institution were selected. One planning KVCT and one randomly selected MVCT from each patient were used. Slice spacings for KVCT and MVCT were 3 mm and 6 mm, respectively. Retrograde urethrography was performed on the KVCT studies only. For inter‐observer study, seven observers contoured the prostate on the 10 CT studies. For intra‐observer study, the same seven observers repeat‐contoured one patients KVCT and MVCT studies. Quantitative analysis of contour variations was performed using volumes and radial distances. F‐test was performed to detect statistically significant differences between KVCT and MVCT. Results: The inter‐ and intra‐observer contouring variability was larger in MVCT than KVCT. The largest variability was mainly found in the prostate apex and base regions. Up to 1 cm (SD) was found in MVCT. In the prostate apex region, interestingly, large but similar variability between KVCT and MVCT was observed. This suggest that the use of urethrography during KVCT simulation was not very helpful. For F‐test, generally, the regions with significant differences were patient‐dependent and uniformly distributed in all directions. In terms of prostate volume, observers consistenly contoured larger prostate in MVCT (by 10 %). This reflects the poorer soft‐tissue contrast in MVCT than KVCT since observers tend to over‐estimate or over‐draw target volumes under less visible conditions. Conclusions: Based on our data, the application of MVCT for estimating daily organ motion and deformation during image‐guidedradiotherapy(IGRT) is somewhat discouraging. Optimization of slice thickness and dose utilization may result in better imaging performance for prostate delineation and adaptive tomotherapy.