BackgroundThe new TomoDirect™ modality offers a non-rotational option with discrete beam angles. We have investigated this mode for TBI with the intention to test the feasibility and to establish it as a clinical routine method. Special foci were directed onto treatment planning, dosimetric accuracy and practical aspects.Patients and methodsTBI plans were calculated with TomoDirect™ for a Rando™ phantom and all patients with an intended fractionated total body irradiation between November 2013 and May 2014 (n = 8). Finally, four of these patients were irradiated with TomoDirect™. Additionally we studied variations in the modulation factor, pitch, field width of Y-jaws and dose grid during optimization. Dose measurements were performed using thermoluminescent rods in the Rando™ phantom, with the Delta4® and with ionization chambers in a solid water phantom.ResultsFor all eight calculated plans with a prescribed dose of 12 Gy Dmean was 12.09-12.33 Gy (12,25 ± 0.08 Gy), D98 11.2-11.6 Gy (11.45 ± 0.12 Gy) and D2 12.6-13.1 Gy (12.94 ± 0.13 Gy). Dmean of inner lungs was 8.73 ± 0.22 Gy on the left side and 8.69 ± 0.27 Gy on the right side.When single planning parameters are varied with otherwise constant parameters, the modulation factor showed the greatest impact on dose homogeneity and treatment time. The impact of the pitch was marginally, and almost equal homogeneity can be obtained with field width of Y-jaws 5 cm and 2.5 cm.Measurements with thermoluminescent rods (n = 25) in the Rando™ phantom showed a mean dose deviation between measured and calculated dose of 0.66 ± 2.26%. 18 of 25 TLDs had a deviation below 3%, seven of 25 TLDs between 3% and 5%.ConclusionTBI with TomoDirect™ allows a superior homogeneity compared to conventional methods, where lung blocks are widely accepted. The treatment is performed only in supine position and is robust and comfortable for the patient.TomoDirect™ allows the implementation of organ-specific dose prescriptions. So the discussion about the balance between the need for aggressive treatment and limited toxicity can be renewed with the new potentials of TomoDirect™ - for children as well as for adults – and possibly yield a better clinical outcome in the future.

Purpose The aim of this study was to analyze the heart dose for left-sided breast cancer that can be achieved during daily practice in patients treated with multicatheter brachytherapy (MCBT) accelerated partial-breast irradiation (APBI) and deep-inspiration breath-hold (DIBH) whole-breast irradiation (WBI) using a simultaneous integrated tumor bed boost (SIB)—two different concepts which nonetheless share some patient overlap. Materials and methods We analyzed the nominal average dose (Dmean) to the heart as well as the biologically effective dose (BED) and the equivalent dose in 2‑Gy fractions (EQD2) for an α/β of 3 in 30 MCBT-APBI patients and 22 patients treated with DIBH plus SIB. For further dosimetric comparison, we contoured the breast planning target volume (PTV) in each of the brachytherapy planning CTs according to the ESTRO guidelines and computed tangential field plans. Mean dose (Dmean), EQD2 Dmean, and BED Dmean for three dosing schemes were calculated: 50 Gy/25 fractions and two hypofractionated regimens, i.e., 40.05 Gy/15 fractions and 26 Gy/5 fractions. Furthermore, we calculated tangential field plans without a boost for the 22 cases treated with SIB with the standard dosing scheme of 40.05 Gy/15 fractions. Results MCBT and DIBH radiation therapy both show low-dose exposure of the heart. As expected, hypofractionation leads to sparing of the heart dose. Although MCBT plans were not optimized regarding dose to the heart, Dmean differed significantly between MCBT and DIBH (1.28 Gy vs. 1.91 Gy, p < 0.001) in favor of MCBT, even if the Dmean in each group was very low. In MCBT radiation, the PTV–heart distance is significantly associated with the dose to the heart (p < 0.001), but it is not in DIBH radiotherapy using SIB. Conclusion In daily practice, both DIBH radiation therapy as well as MCBT show a very low heart exposure and may thus reduce long term cardiac morbidity as compared to currently available long-term clinical data of patients treated with conventional tangential field plans in free breathing. Our analysis confirms particularly good cardiac sparing with MCBT-APBI, so that this technique should be offered to patients with left-sided breast cancer if the tumor-associated eligibility criteria are fulfilled.

No abstract

Abstract:The biplanar diode arrays Delta4PT and Delta4+ has been used in our hospital since the introduction of the TomoTherapy in 2013 to ensure a good agreement between the calculated and the measured dose distributions in patientrelated QA with helical TomoTherapy. The aim of this presentation is to evaluate the quality of the measurement procedure with the Delta4 phantoms Delta4PT and (since January 2016) Delta4+. This includes the influence of a cross calibration with a treatment plan with low modulation.Two analyses were performed: (i) All treatment plans in a period of three months (n=86) were not only calculated and measured with Delta4PT or Delta4+ but also with an ionization chamber (Exradin A1SL) in the homogeneous "cheese phantom". (ii) All data measured from January 2016 to April 2017 (Delta4+, n=132) were analyzed regarding median dose deviation, Gamma analysis and others.The comparison with chamber measurements shows that all measurements with Delta4 and almost all with the ionization chambers (79 of 86) yield a deviation of measured vs. planned dose in the PTV of less than 2.5%, but with a lower variation of the Delta4 measurements. However, a strong correlation between both was not observed.The separate analysis of the measurements with the newer Delta4+ (since January 2016) shows a mean dose deviation in the PTVs of only 0.14% with a standard deviation (S.D.) of 0.69%. Before every measurement a cross calibration has been performed. Without this cross calibration, the deviation would be 0.96% with an increased standard deviation of 0.93%.It is concluded that the Delta4 systems are well suited for patient-related QA for helical TomoTherapy treatment plans.The comparison with chamber measurements shows a plausible accordance between both systems whereas the variation of single measurements is quite different.With the help of a daily cross calibration the variability of the Delta4 results is further decreased and the results show higher accuracy and reliability. According to our experience, a daily cross calibration is mandatory for a reliable patientrelated QA.