TomoTherapy

Background and purpose: Investigation of the use of TomoTherapy and TomoDirect versus conventional radiotherapy for the treatment of post-operative breast carcinoma. This study concentrates on the evaluation of the planning protocol for the TomoTherapy and TomoDirect TPS, dose verification and the implementation of in vivo dosimetry. Materials and methods: Eight patients with different breast cancer indications (left/right tumor, axillary nodes involvement (N+)/no nodes (N0), tumorectomy/mastectomy) were enrolled. TomoTherapy, Tomo-Direct and conventional plans were generated for prone and supine positions leading to six or seven plans per patient. Dose prescription was 42 Gy in 15 fractions over 3 weeks. Dose verification of a TomoTherapy plan is performed using TLDs and EDR2 film inside a home-made wax breast phantom fixed on a randoalderson phantom. In vivo dosimetry was performed with TLDs. Results: It is possible to create clinically acceptable plans with TomoTherapy and TomoDirect. TLD calibration protocol with a water equivalent phantom is accurate. TLD verification with the phantom shows measured over calculated ratios within 2.2% (PTV). An overresponse of the TLDs was observed in the low dose regions (<0.1 Gy). The film measurements show good agreement for high and low dose regions inside the phantom. A sharp gradient can be created to the thoracic wall. In vivo dosimetry with TLDs was clinically feasible. Conclusions: The TomoTherapy and TomoDirect modalities can deliver dose distributions which the radiotherapist judges to be equal to or better than conventional treatment of breast carcinoma according to the organ to be protected.

A feasibility study of total body irradiation (TBI) using tomotherapy (TTBI) at Liverpool Cancer Therapy Centre was undertaken, using phantom-based dosimetry. TBI is used to kill malignant white blood cells in leukaemia patients. Unlike wide-field TBI, TTBI enables dose sculpting to complex treatment volumes from multi-leaf collimator motions with minimal chance of gantry-patient collision, as with volumetric modulated arc therapy.

The phantom was scanned with CT and contoured in MiM. Dose calculation and optimisation was performed in the Tomotherapy Hi-Art planning station. Ionisation chambers, thermoluminescent dosimeters (TLDs), radiochromic film and the in-house exit dosimetry tool were used for dose verification. Dose metrics included expected-measured dose difference for ionisation chambers, exit dosimetry and TLDs, 2D gamma pass rate (3mm/3% criteria) for film and 3D gamma pass rate (2mm/2% criteria) for the exit dosimetry tool.

Differences between the planned and measured doses for ionisation chambers and TLDs were 0.54 % and -0.56 % respectively. The 2D
gamma pass rate was 86.8 % (left lung) and 93.7 % (right lung) and 3D
gamma pass rate 99.9 %.

Dose differences were all within the recommended 5 % by ICRU. From
this, TTBI is viable in delivering controlled doses to complex treatment volumes.

Purpose: Glioblastoma Multiforme (GBM) is the most common malignant brain tumor and frequently recurs in the same location after radiotherapy. Intensive treatment targeting localized lesion is required to improve GBM outcome, but dose escalation using conventional methods is limited by healthy tissue tolerance. Helical Tomotherapy (HT) Dose Painting (DP) treatments were simulated to safely deliver high doses in the recurrent regions. Materials and methods: Apparent Diffusion Coefficient (ADC) data from five recurrent GBM were retrospectively considered for planning. Hypo-fractionated (25À50 Gy, 5 fractions) voxel-based prescriptions were opportunely converted to personalized structured-based dose maps to create DP plans with a commercial Treatment Planning System. Optimized plans were generated and analyzed in terms of plan conformity to dose prescription (Q 0.90–1.10), tolerance of the healthy tissues (D MAX), and dosimetry accuracy of the deliverable plans (c-index). Results: Only three of the five cases could receive a safe retreatment without violating the maximum critical organs dose constraints. The conformity of the simulated plans was between 40.9% and 79.9% (Q 0.90–1.10), their delivery time was in the range of 38.3–63.6 min, while the dosimetry showed c-index of 82.4–92.4%. Conclusions: This study proved the ability of our method to simulate personalized, deliverable and dosi-metrically accurate DPBN plans. HT hypo-fractionated treatments guided by ADC maps can be realized and applied to deliver high doses in the GBM recurrent regions, although there are some critical issues related to low Q 0.90–1.10 values, to exceeding of healthy-tissue dose constraints for some patients and long delivery times.

The purpose of this study was to compare 2 adaptive radiotherapy strategies with helical tomotherapy. A patient having mesothelioma with mediastinal nodes was treated using helical tomotherapy with pretreatment megavoltage CT (MVCT) imaging. Gross tumor volumes (GTVs) were outlined on every MVCT study. Two alternatives for adapting the treatment were investigated: (1) keeping the prescribed dose to the targets while reducing the dose to the OARs and (2) escalating the target dose while maintaining the original level of healthy tissue sparing. Intensity modulated radiotherapy (step-and-shoot IMRT) and 3D conformal radiotherapy (3DCRT) plans for the patient were generated and compared. The primary lesion and nodal mass regressed by 16.2% and 32.5%, respectively. Adapted GTVs and reduced planning target volume (PTV) margins of 4 mm after 22 fractions decrease the planned mean lung dose by 19.4%. For dose escalation, the planned prescribed doses may be increased from 50.0 to 58.7 Gy in PTV1 and from 60.0 to 70.5 Gy in PTV2. The step-and-shoot IMRT plan was better in sparing healthy tissue but did not provide target coverage as well as the helical tomotherapy plan. The 3DCRT plan resulted in a prohibitively high planned dose to the spinal cord. MVCT studies provide information both for setup correction and plan adaptation. Improved healthy tissue sparing and/or dose escalation can be achieved by adaptive planning.

PURPOSE: To describe a clinical pilot case of renal lymphoma successfully treated using helical tomotherapy, and to evaluate alternative hypofractionated treatment schedules and their potential applicability to future cases of renal cell carcinoma (RCC).

PATIENTS AND METHODS: An 82-year-old female patient with a large right perinephric mass encircling the lower pole of the right kidney was treated on the Hi-ART unit (TomoTherapy Inc. Madison, WI, USA) with daily pretreatment megavoltage CT imaging. Gross tumor volumes (GTVs) were outlined on every MVCT study. The Planned Adaptive software was used for calculation of dosimetric parameters for both the target and organs at risk (OARs). In response to observed GTV regression, a hypothetical anatomy changes adjusted plan was generated and analyzed. Six alternative treatment schedules were investigated: 48 Gy in 4 and 3 fractions, and 60 Gy in 30, 5, 4 and 3 fractions, as possible clinical scenarios for RCC. Normal tissue complication probability (NTCP) and tumor control probability (TCP) values were estimated for each scenario in the study.

RESULTS: During 30 days, the GTV was reduced by 50.6%. The smaller GTV and the reduced planning target volume (PTV) margins from 15 mm to 10 mm after 12 fractions would allow for a decrease of the planned mean liver and spinal cord dose by 3.8 Gy and 4 Gy, respectively. Improvements to portions of the colon include a 3.3 Gy and 9.2 Gy reduction in planned mean dose to the descending and ascending colons, respectively. NTCP and TCP estimates have shown that hypofractionated treatment schedules provide a much higher probability of local control, but the risk of tissue complication rises simultaneously. For this particular case, hypofractionation would not be suitable due to the potential adverse affects brought on to the liver.

CONCLUSIONS: Caution should be observed in high dose hypofractionated radiotherapy in right sided, whole kidney carcinoma due to increased risk of liver complication. The accelerated treatment may however be justified by the significantly higher TCP rates for left sided kidney cases. Further investigation of small renal tumors is needed to evaluate control rates, vasculopathy, and residual normal function.

Purpose: To evaluate feasibility and accuracy of skin dose measurements in helical tomotherapy treatments with EBT radiochromic films (ISP, Wayne, NJ). Method and Materials: EBT films were cut into pieces and irradiated for calibration with a static Tomotherapy field at 1cm depth of a solid water phantom. Calibration doses, ranging from 25 to 1200 cGy, were calculated from thimble ionisation chambermeasurements at 1.5cm depth and PDD data. We taped small cuts (1 cm2) of EBT films on the inner side of masks used for patients immobilization. Films were removed from mask after 1–3 sessions of tomotherapy treatment performed with HI‐ART Tomotherapy System (Tomotherapy Incorporated, Madison, WI). EBT films were read with an Epson 1680 Scanner using only the central 10×15cm2scanner region for better homogeneity. Calibration curve and conversion to dose for EBT scans were made following Devic et al1. We tested the method on four patients treated for cranial and head and neck diseases with tomotherapy. To check measurement accuracy, we compared film doses with dose calculated by the treatment planningsoftware on patient surface.Results:Measured and calculated doses on patient surface show an average difference, calculated on the four patients, of 3.54% and a mean standard deviation of 2.99%. Conclusions: A simple, non‐invasive method to measure patient skin dose in helical tomotherapy treatments has been implemented. Preliminary results of measurements on three cranial patients show a good agreement with surface dose calculated by the treatment planning system. Further data need to be collected to confirm accuracy of measurements.

Purpose: In Tomotherapy dose is dependant on the output and shape of the beam (‘cone’). Variations in these can have huge influences on IMRT‐treatments and daily monitoring is required, but time consuming using conventional methods. Method and Materials: A software package was developed to run independently on the system and retrieve the integrated CT‐detector and dose‐chamber data. The ability to monitor daily output changes was tested by using static fields and ionization chamber(IC). To validate the link between output, cone and daily patient QA a dedicated IMRT‐plan containing disjunctive targets was used and a regression model was built to check the effect variations of cone and output have on this. Results : Results show that the in‐house tool can be used to monitor output and cone shape on tomotherapy in a fast and reliable way. Furthermore, the system has the ability of separating effects of output and cone in one single measurement. The static beam measurements using IC show a correspondence within 2% after elimination of the cone effect. Using a 6D‐linear regression the software can predict IMRT‐ionization chamber measurements within 0.7%. Early results show that the model&#39;s instabilities model could predict problems such as target failure prematurely. Conclusion : The in‐house developed software tool based on direct detector and dose‐chamber monitoring can be used to monitor output‐ and cone‐variation in 1 procedure. By using a regression the tool can also replace IMRT‐QA measurements. Combined, this allows for daily QA‐time reduction from 50 to 5 minutes.

PURPOSE To verify a Tomotherapy plan for a typical head and neck treatment against experimental measurements. METHODS The treatment plan for a head and neck case was generated by the Tomotherapy treatment planning system (TPS) to deliver ∼70 Gy in 33 sessions to the contoured PTV. The plan was calculated on a CIRS ATOM anthropomorphic phantom that provides a grid spacing of 3×3 cm2 holes to accommodate thermoluminescent detectors (TLD). The plan was verified against experimental measurements carried out by 7 LiF:Mg,Ti (TLD-700) TLD. Up to 20 locations were selected within the irradiated region and three detectors were used simultaneously at each point to decrease the statistical uncertainty. TLD locations were labeled in the planning system and dose comparisons between TPS prediction and experimental measurements were performed in terms of absolute dose to water for a single fraction. We examined the dose from (i) the corresponding 3.5MV Tomo-scan alone and (ii) the complete treatment. TLD-700 were found to fulfill the requirements of reproducibility, linearity and flat energy response in a previous study. In particular, TLD energy response was previously checked for 6 MV flattening filter free and conventional radiation beams under reference conditions. RESULTS Doses derived from the TPS were in most cases in good agreement (4% on average) with TLD dose measurements within TLD statistical uncertainties (about 3%). Larger discrepancies up to 7% were found for points close to complex tissue inhomogeneities, such as bony structures. Dose from the scanning procedure alone is about 1 % of the dose per fraction. CONCLUSIONS This work indicates that dose delivery plans created with Tomotherapy TPS are accurate for head and neck tumor localizations.

This study highlights the use of adaptive planning to accommodate testicular shielding in helical tomotherapy for malignancies of the proximal thigh. Two cases of young men with large soft tissue sarcomas of the proximal thigh are presented. After multidisciplinary evaluation, preoperative radiation therapy was recommended. Both patients were referred for sperm banking and lead shields were used to minimize testicular dose during radiation therapy. To minimize imaging artifacts, kilovoltage CT (kVCT) treatment planning was conducted without shielding. Generous hypothetical contours were generated on each "planning scan" to estimate the location of the lead shield and generate a directionally blocked helical tomotherapy plan. To ensure the accuracy of each plan, megavoltage fan-beam CT (MVCT) scans were obtained at the first treatment and adaptive planning was performed to account for lead shield placement. Two important regions of interest in these cases were femurs and femoral heads. During adaptive planning for the first patient, it was observed that the virtual lead shield contour on kVCT planning images was significantly larger than the actual lead shield used for treatment. However, for the second patient, it was noted that the size of the virtual lead shield contoured on the kVCT image was significantly smaller than the actual shield size. Thus, new adaptive plans based on MVCT images were generated and used for treatment. The planning target volume was underdosed up to 2% and had higher maximum doses without adaptive planning. In conclusion, the treatment of the upper thigh, particularly in young men, presents several clinical challenges, including preservation of gonadal function. In such circumstances, adaptive planning using MVCT can ensure accurate dose delivery even in the presence of high-density testicular shields.

The aims of this study were to investigate the variability between physicians in delineation of head and neck tumors on original tomotherapy megavoltage CT (MVCT) studies and corresponding software enhanced MVCT images, and to establish an optimal approach for evaluation of image improvement. Five physicians contoured the gross tumor volume (GTV) for three head and neck cancer patients on 34 original and enhanced MVCT studies. Variation between original and enhanced MVCT studies was quantified by DICE coefficient and the coefficient of variance. Based on volume of agreement between physicians, higher correlation in terms of average DICE coefficients was observed in GTV delineation for enhanced MVCT for patients 1, 2, and 3 by 15%, 3%, and 7%, respectively, while delineation variance among physicians was reduced using enhanced MVCT for 12 of 17 weekly image studies. Enhanced MVCT provides advantages in reduction of variance among physicians in delineation of the GTV. Agreement on contouring by the same physician on both original and enhanced MVCT was equally high.