TomoTherapy

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 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.

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.