L. Montgomery

Helical tomotherapy for locoregional irradiation including the internal mammary chain in left-sided breast cancer: Dosimetric evaluation

PURPOSE To compare a standard 3- or 4-field technique to intensity modulated radiotherapy with helical tomotherapy (IMRT-HT) in the planning of locoregional breast radiation including the internal mammary chain (IMC). METHODS AND MATERIALS For 10 women with stage III left-sided breast cancer with a planning target volume (PTV) defined by the breast/chest wall and regional nodes, radiotherapy to a dose of 50 Gy in 25 fractions was planned using a standard 3- or 4-field technique and using IMRT-HT. Various metrics were extracted from dose-volume histograms, and were compared using the paired Students t-test. RESULTS The PTV receiving at least 95% of the prescribed dose did not differ between the two plans, but the VD115% was significantly lower with IMRT-HT. The dose conformality was significantly better with IMRT-HT. The cardiac V30(Gy) was reduced with IMRT-HT. The mean lungs dose was lower with IMRT-HT, as well the V20(Gy). With IMRT-HT, a greater volume of contralateral breast was irradiated to 5 Gy, but a smaller volume of soft tissue received dose above 50 Gy. CONCLUSIONS Compared to a standard technique, IMRT-HT provides similar target coverage, improves dose conformality and dose homogeneity within the PTV, decreases mean lung dose and spares heart, lung and soft tissue from high dose exposure.

On-line rapid palliation using helical tomotherapy : A prospective feasibility study

Rapid delivery of radiation therapy is expected to benefit patients requiring palliation. We investigated the feasibility of employing a helical tomotherapy unit to scan, plan, and deliver a radiation treatment in a single radiation therapy appointment. Eleven patients each had an MVCT scan acquired, a plan created, and delivery completed while the patient was on the treatment couch. Timelines for each step of the process were recorded for each patient, and compared with the conventional process for similar patients. Preliminary results show that patients routinely can be treated within a 1 hour appointment for the first fraction.

Evaluation of a Thermoplastic Immobilization System for Breast and Chest Wall Radiation Therapy

We report on the impact of a thermoplastic immobilization system on intra- and interfraction motion for patients undergoing breast or chest wall radiation therapy. Patients for this study were treated using helical tomotherapy. All patients were immobilized using a thermoplastic shell extending from the shoulders to the ribcage. Intrafraction motion was assessed by measuring maximum displacement of the skin, heart, and chest wall on a pretreatment 4D computed tomography, while inter-fraction motion was inferred from patient shift data arising from daily image guidance procedures on tomotherapy. Using thermoplastic immobilization, the average maximum motion of the external contour was 1.3 ± 1.6 mm, whereas the chest wall was found to be 1.6 ± 1.9 mm. The day-to-day setup variation was found to be large, with random errors of 4.0, 12.0, and 4.5 mm in the left-right, superior-inferior, and anterior-posterior directions, respectively, and the standard deviations of the systematic errors were found to be 2.7, 9.8, and 4.1 mm. These errors would be expected to dominate any respiratory motion but can be mitigated by daily online image guidance. Using thermoplastic immobilization can effectively reduce respiratory motion of the chest wall and external contour, but these gains can only be realized if daily image guidance is used.

Treatment planning protocols: a method to improve consistency in IMRT planning.

The Ottawa Hospital Cancer Centre (TOHCC) is a tertiary academic cancer center operating ten megavolt treatment units and treating approximately 4000 new patients per year. The treatment equipment includes 2 helical tomotherapy units (TomoTherapy HI-ART, TomoTherapy Inc., Madison, WI) and a high proportion of the more complex cases and clinical trials patients are treated with these units. The radiation therapists assigned to the tomotherapy units perform all treatment planning and treatment delivery. With this model, training in intensity-modulated radiation therapy (IMRT) treatment planning is required for each therapist assigned to the program. Although the therapists do not rotate frequently to other units, the training of new staff assigned to a tomotherapy unit is challenging. Tomotherapy is different from the other technology in the department, and the therapists assigned to these units have the additional role of treatment planning. The treatment planning process is labor-intensive and presents opportunities for error. During treatment planning, structures are classified into either tumor or sensitive structure settings. After settings are assigned, structures are prioritized on the basis of overlap between 2 or more structures of the same setting, referred to as overlap priority. Overlap priorities ensure that dose constraints and dose reporting are assigned to the appropriate structure volume, as outlined by the treatment planner. Setting the overlap priority is a source of error t TOHCC, especially for inexperienced planners. Expeience is important when selecting overlap priority and nitial optimization parameters to efficiently produce igh-quality treatment plans. This work describes a method to reduce treatment lanning time, standardize the planning process, and inimize the potential for errors, all imperative features f an efficient IMRT planning process for research trial ases.

Rapid palliative radiotherapy: comparing IG-IMRT with more conventional approaches

Purpose: To assess the efficiency of an integrated imaging, planning, and treatment delivery system to provide image-guided intensity-modulated radiotherapy (IG-IMRT) for patients requiring palliative radiotherapy (PRT). Methods: Between December 2006 and May 2008, 28 patients requiring urgent PRT were selected to undergo single-session megavoltage computed tomography (MV-CT) simulation, IMRT treatment planning, position verification and delivery of the first faction of radiotherapy on a helical Tomotherapy ® unit. The time required to complete each step was recorded and compared to our standard approach of using either fluoroscopic or CT-based simulation, simplified treatment planning and delivery on a megavoltage unit. Results: Twenty-eight patients were treated with our integrated IG-IMRT protocol. The median age was 72 years, with 61% men and 39% women. The indications for PRT were: painful bone and soft tissue metastasis (75%); bleeding lesions (14%); and other reasons (11%). The areas treated included the following: hip and/or pelvis (42%); spine (36%); and other areas (21%). The most commonly used dose prescription was 20 Gy in five fractions. Average times for the integrated IG-IMRT processes were as follows: image acquisition, 15 minutes; target delineation, 16 minutes; IMRT treatment planning, 9 minutes; treatment position verification, 10 minutes; and treatment delivery, 12 minutes. The average total time was 62 minutes compared to 66 minutes and 81 minutes for fluoroscopic and CT-simulation-based approaches, respectively. The IMRT dose distributions were also superior to simpler plans. Conclusions: PRT with an integrated IG-IMRT approach is efficient and convenient for patients, and has potential for future applications such as single-fraction radiotherapy.

Sci—Fri PM: Delivery — 08: Total Marrow Irradiation Using Helical Tomotherapy in Treating\ a Multiple Myeloma Patient: A Case Study

The Ottawa Hospital Cancer Centre has embarked on a phase I/II dose escalation study of IG‐IMRT using Helical Tomotherapy (HT) for Total Marrow Irradiation (TMI) of multiple myeloma patients prior to autologous hematopoietic stem cell transplantation. In this work we outline the technical and physical hurdles related to planning and dose delivery and summarize our experience to date. Limitations with the scanning and planning systems required that patients have two CT scans; one of the upper body and one of the lower body with at least a 20 cm overlap. They must also have a separate treatment plan for each region. PTVs and OARs were defined on both CT sets and image fusion using ImageJsoftware was used to link the two scan sets. The treatment plan for the upper body used a 2.5 cm beam to provide good sup‐inf dose conformation, while a 5.0 cm beam was used for the lower body. DQA was planned, delivered and analyzed, showing good agreement between the planned and measured dose distributions in the junction region. We demonstrate the technical feasibility of our method in overcoming the challenges related to the planning system, including junctioning and summing the dose clouds of longitudinally adjacent plans created on different CTdata sets. The treatment was well‐tolerated by the patient and no severe acute toxicity was noted. Scaling to the QUANTEC data (V20 of 30–35%) for lungs, we estimate that with the present CTV‐PTV margins it should be possible to safely deliver 25 Gy TMI.

Sci‐Thur PM Therapy‐06: Helical Tomotherapy for Adaptive Radiotherapy of Bladder Cancer: Treatment Planning Considerations

We have developed a method that leverages the image‐guidedradiotherapy capabilities of a tomotherapy unit to adapt daily treatments to changes in bladder shape and volume. Each patient receives three treatment‐planningCT scans: empty bladder; partially full bladder; and full bladder. For each scan, the radiation oncologist contours the initial and boost target volumes (PTV1 and PTV2) and organs at risk, and an initial treatment plan is generated to deliver 40 Gy in 20 fractions to PTV1. A second treatment plan is designed to deliver 20 Gy in 10 fractions to PTV2 (a total of six treatment plans per patient). Patients are asked to void immediately before each treatment. An MVCT of the pelvis is performed before each fraction to verify patient position and to assess the bladder volume. If the treating therapist concludes that the patients bladder extends to within 10 mm of the PTV contour, then the corresponding treatment plan for a larger bladder volume is downloaded and the MVCT is repeated. Approximately 20% of fractions required a treatment change based on perceived bladder volume. Three of four patients treated to‐date have required the use of a larger volume treatment plan at least once, even though they are always instructed to empty their bladders just prior to treatment. Our early experience is that relying on patient compliance for treating “empty bladder” is insufficient to ensure proper target coverage, and that generous internal margins are required to ensure target coverage in the absence of adaptive IGRT capability.

Po‐Thur Eve General‐29: Clinical Implementation of Helical Tomotherapy

In March 2005 The Ottawa Hospital Regional Cancer Center took delivery of a helical TomoTherapy Hi‐Art machine. We report our experience for installation, commissioning and training for tomotherapy relative to a conventional single energy linac as well as our experiences regarding throughput, process change and implementation of a radically different staffing model. Tomotherapy implementation was faster than a conventional single energy linac (23 vs. 31 days), but additional training requirements for tomotherapy made the overall times comparable (28 vs. 31 days). Presently, the tomotherapy team includes two physicists and two physicians, and dedicates three therapists to tomotherapy per 8 hour shift. The therapists are given responsibility for data transfer, structure contouring, planning and delivery. Mean total effort for treatment preparation per patient is 8.9 hours (median 6.6, range 3.4 to 33). We find daily machine QA for tomotherapy is more demanding than for a conventional linac, requiring approximately 1 hour for machine warm‐up, safety system testing and CT detector calibration. In addition we require approximately 45 minutes of physics time to establish output, energy, and geometric consistency. Overall system performance is verified by a daily delivery QA. The mean overall time for patient setup, MVCT, registration and treatment is 26.5 minutes (median 25.0). Eliminating the MVCT and registration reduces the mean to 18 minutes. For an 8 hour shift we anticipate that a single team (3 therapists) can maintain a patient load of at least 16 patients with daily MVCT and 24 patients with weekly MVCT.

Sci‐Sat AM (2) Therapy‐05: Early Experience with a Clinical TomoTherapy Unit

In March 2005 The Ottawa Hospital Regional Cancer Center received a helical TomoTherapy Hi‐Art machine, beginning treatment September 2005. The delivery and planning systems were subjected to rigorous daily QA. Herein we report our geometric, dosimetric and uptime analysis. Daily dosimetric QA comprises output and energy checks as well as the geometric consistency of the integrated laser and couch drive systems. At least one patient treatment plan per day is delivered to a phantom for delivery quality assurance, thereby checking all integrated tomotherapy subsystems (e.g. gantry rotation speed, couch speed, dose rate, MLC, jaw calibration and modeling within the planning system). Over the first 130 treatment days the mean output was 0.5% above reference and varied about the mean with a SD of 0.32%. Approximately 1.5% (2 of 132) of output measurements exceeded our tolerance of 2% requiring the calibration to be modified twice prior to the resumption of clinical service. The beam energy was measured by the PDD at 10 and 20 cm. We found these to vary about their expectation values with standard deviations of 0.52% and 0.59% respectively. Single point doses for the Delivery QA were normally distributed with a standard deviation of 2.4%, where 92% of all points were within 3% and 97% of all points were within 5% of expected. All coronal plane film measurements had a distance to agreement of less than 3 mm. We experienced a total of 4.5 days of downtime, 2 of which are attributed to delay in parts delivery.