G. Taccini

Helical tomotherapy targeting total bone marrow after total body irradiation for patients with relapsed acute leukemia undergoing an allogeneic stem cell transplant

BACKGROUND AND PURPOSE To report our clinical experience in planning and delivering total marrow irradiation (TMI) after total body irradiation (TBI) in patients with relapsed acute leukemia undergoing an allogeneic stem-cell transplant (SCT). MATERIALS AND METHODS Patients received conventional TBI as 2 Gy BID/day for 3 days boosted the next day by TMI (2 Gy in a single fraction) and followed by cyclophosphamide (Cy) 60 mg/kg for 2 days. While TBI was delivered with linear accelerator, TMI was performed with helical tomotherapy (HT). RESULTS Fifteen patients were treated from July 2009 till May 2010, ten with acute myeloid leukemia, and five with acute lymphoid leukemia. At the time of radiotherapy eight patients were in relapse and seven in second or third complete remission (CR) after relapse. The donor was a matched sibling in 7 cases and an unrelated donor in 8 cases. Median organ-at-risk dose reduction with TMI ranged from 30% to 65% with the largest reduction (-50%-65%) achieved for brain, larynx, liver, lungs and kidneys. Target areas (bone marrow sites and spleen in selected cases) were irradiated with an optimal conformity and an excellent homogeneity. Follow-up is short ranging from 180 to 510 days (median 310 days). However, tolerance was not different from a conventional TBI-Cy. All patients treated with TBI/TMI reached CR after SCT. Three patients have died (2 for severe GvHD, 1 for infection) and 2 patients showed relapsed leukemia. Twelve patients are alive with ten survivors in clinical remission of disease. CONCLUSIONS This study confirms the clinical feasibility of using HT to deliver TMI as selective dose boost modality after TBI. For patients with advanced leukemia targeted TMI after TBI may be a novel approach to increase radiation dose with low risk of severe toxicity.

Determination of the correction factors for different ionization chambers used for the calibration of the helical tomotherapy static beam.

BACKGROUND AND PURPOSE To determine the machine-specific correction factors for three commercial ionization chambers (Exradin A1SL, PTW Semiflex and PTW PinPoint) to be applied in the dose calibration of a helical tomotherapy (HT) unit. MATERIALS AND METHODS Machine-specific reference (msr) conditions for HT unit involved a 10 × 5 cm(2) (IEC x×y) radiation field at 85 cm SSD with the ionization chamber (IC) positioned at 10 cm depth in Virtual Water. Each msr correction factor was determined using the formalism proposed by the AAPM Task Group 148 (i.e. k(Q[HT)(TG-51])) and was compared to direct calibration of the ICs against radiochromic films, calibrated in absolute dose at our institute, following the formalism proposed by the IAEA-AAPM joint committee (i.e. [Formula: see text] ). RESULTS TPR(20,10) values under HT msr conditions were 0.608, 0.608 and 0.615 corresponding to %dd(10)(x[HT)(Ref]) of 0.606, 0.606 and 0.613 for A1SL, Semiflex and PinPoint ICs, respectively. Based on these findings, k(Q[HT)(TG-51]) determination resulted 0.998±0.001, 0.998±0.001 and 0.991±0.002 for A1SL, Semiflex and PinPoint ICs, respectively. The [Formula: see text] correction factors obtained through direct calibration were 1.000±0.010, 1.004±0.007 and 0.998±0.006 for A1SL, Semiflex and PinPoint ICs, respectively. CONCLUSIONS Direct calibration of ICs versus radiochromic films provided correction factors equivalent to those obtained following the TG-148 formalism. This study showed that ICs calibrated for conventional linear accelerators can be used for the calibration of the static beam delivered by a HT unit taking into account the particular reference conditions.

Clinical evaluation of the accuracy of an invasive frame designed for stereotactic intracranial radiosurgery treatment with helical tomotherapy

AIMS AND BACKGROUND The study focused on the evaluation of the accuracy of intracranial stereotactic radiosurgery treatments delivered with helical tomotherapy by means of the InterFix™ Radiosurgery kit. METHODS AND STUDY DESIGN Twenty-two patients received stereotactic radiosurgery treatments with single fraction dose ranging from 13 to 20 Gy depending on diagnosis. Megavoltage computed tomography scans performed prior the treatments were analyzed in order to determine the position accuracy. For 8 selected cases, they were also performed at the end of the treatment to evaluate the intra-fraction motion. RESULTS Mean setup errors and standard deviations were -1.6 ± 2.2 mm, -0.2 ± 1.2 mm, 0.4 ± 1.3 mm, 0.2 ± 0.5° for the lateral (IEC-x), longitudinal (IEC-y), vertical (IEC-z) directions and rotational variation (roll), respectively. Setup error was found to be greater than 3 mm-PTV expansion in 36% of the cases. Mean intra-fraction motion was 0.5 ± 0.7 mm, -0.3 ± 0.4 mm, 0.1 ± 0.5 mm and 0.1 ± 0.2° for the IEC-x, IEC-y, IEC-z and roll, respectively. CONCLUSIONS Observed intra-fraction movements of less than 1 mm suggested the use of the tested fixation device for stereotactic radiosurgery treatment on helical tomotherapy providing that the image-guidance procedure is always performed prior to treatment.

Dosimetric analysis of Tomotherapy-based intracranial stereotactic radiosurgery of brain metastasis

PURPOSE This paper analyzes Tomotherapy-based intracranial stereotactic radiosurgery (HTSRS) of brain metastasis targeting two end-points: 1) evaluation of dose homogeneity, conformity and gradient scores for single and multiple lesions and 2) assay of dosimetric criticality of completion of HTSRS procedures. METHODS 42 treatment plans of 33 patients (53 brain lesions) treated with HTSRS were analyzed. Dose to healthy brain, homogeneity, conformity and gradient indexes were evaluated for each lesion. Influence of Field Length and multiple lesions cross-talk effect were assessed. Treatment interruption and completion was investigated using radiochromic films in order to examine the delivered dose and its robustness to patient intrafraction movement. RESULTS The average dose homogeneity index was 1.04 ± 0.02 (SD). Average dose conformity and gradient score indexes were 1.4 ± 0.2 and 50 ± 14 respectively. We found a strong correlation of the dose to healthy brain and conformity and gradient indexes with target(s) volume for which analytical functions were obtained. Field Length and cross-talk effect were significantly correlated with poor gradient scores, but were found not to affect dose conformity. CONCLUSIONS Homogeneity and conformity of HTSRS plans achieved excellent scores, while dose falloff and dose to healthy brain were slightly larger when compared with non-coplanar SRS techniques. Care should be given if treating large (>3 cc) or multiple near in-plane lesions in order to reduce dose to healthy brain. Analysis of interrupted treatments suggests splitting HTSRS treatments in two consecutive fractions in order to prevent target miss and overdosage due to patient intrafraction movement.