M. Zeverino

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.

Radiosurgery with Helical Tomotherapy Outcomes for Patients with One or Multifocal Brain Metastasis

To evaluate the feasibility and report the preliminary results for stereotactic radiosurgery (SRS) treatments of single or multiple brain metastases delivered with helical tomotherapy (HT) by means of the InterFix™ Radiosurgery kit. Between September 2010 and August 2012, thirty patients underwent SRS for treatment of 46 brain metastases with a median prescription dose of 20 Gy (range 15-21 Gy). Clinical response was assessed with 2-3 month intervals by magnetic resonance imaging (MRI). Dose distribution indexes were computed and compared with published data for SRS performed with dedicated machines. After a median follow-up of 14 months (range 4-31) the estimated overall survival (OS) rate was 70% at 6 months, 60% at 12 months and 44% at 18 months. Local control (LC) was 72% at 6 months, 65% at 12 months and 50% at 18 months. Acute toxicity as headache and epileptic crisis occurred in only two patients. The mean values of conformity, homogeneity and gradient score indexes were 1.36, 1.04 and 50 respectively. HT-SRS for single or multiple brain metastases appears a reliable technique with encouraging clinical outcomes and competitive dosimetrical results.

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.