Reference dosimetry for helical tomotherapy: practical implementation and a multicenter validation.

PURPOSE: The aim of this study was to implement a protocol for reference dosimetry in tomotherapy and to validate the beam output measurements with an independent dosimetry system. METHODS: Beam output was measured at the reference depth of 10 cm in water for the following three cases: (1) a 5 × 10 cm(2) static machine specific reference field (MSR), (2) a rotational 5 × 10 cm(2) field without modulation and no tabletop in the beam, (3) a plan class specific reference (PCSR) field defined as a rotational homogeneous dose delivery to a cylindrical shaped target volume: plan with modulation and table-top movement. The formalism for reference dosimetry of small and nonstandard fields [Med.Phys.35: 5179-5186, 2008] and QA recommendations [Med.Phys.37: 4817-4853, 2010] were adopted in the dose measurement protocol. All ionization chamber measurements were verified independently using alanine∕EPR dosimetry. As a pilot study, the beam output was measured on tomotherapy Hi-art systems at three other centers and directly compared to the centers specifications and to alanine dosimetry. RESULTS: For the four centers, the mean static output at a depth of 10 cm in water and SAD = 85 cm, measured with an A1SL chamber following the TG-148 report was 6.238 Gy∕min ± 0.058 (1 SD); the rotational output was 6.255 Gy∕min ± 0.069 (1 SD). The dose stated by the center was found in good agreement with the measurements of the visiting team: D(center)∕D(visit) = 1.000 ± 0.003 (1 SD). The A1SL chamber measurements were all in good agreement with Alanine∕EPR dosimetry. Going from the static reference field to the rotational ∕ non modulated field the dose rate remains constant within 0.2% except for one center where a deviation of 1.3% was detected. CONCLUSIONS: Following the TG-148 report, beam output measurements in water at the reference depth using a local protocol, as developed at different centers, was verified. The measurements were found in good agreement with alanine∕EPR dosimetry. The presented methodology may provide a good concept for reference dosimetry.

Impact of complementary oral enzyme application on the postoperative treatment results of breast cancer patients--results of an epidemiological multicentre retrolective cohort study.

PURPOSE: [corrected] To evaluate the impact of postoperative treatment with an oral enzyme (OE) preparation given complementary to an antineoplastic therapy in patients with breast cancer. METHODS: The design of this epidemiological study was a retrolective cohort analysis with parallel groups. Design and conduct of the study were performed to current standards for prospective, controlled clinical trials. A cohort of 2,339 breast cancer patients undergoing surgical intervention and radio-, chemo- or hormonal therapy were studied in 216 centres. Of the 2,339 patients, 1,283 received complementary treatment with OE and 1,056 did not receive OE. Patients with other complementary medications were excluded and the final analysis was performed with the data from 649 patients, of whom 239 (37%) were additionally treated with OE (test group) and 410 (63%) without OE (control group). The median follow-up time for the test group was 485 days and for the control group 213 days. The primary endpoint of the study was to determine whether complementary treatment with OE can reduce typical disease- or therapy-associated signs and symptoms (gastrointestinal symptoms, mental symptoms, dyspnoea, headache, tumour pain, cachexia, skin disorders, infections, and side effects associated with the antineoplastic therapy) in patients with breast cancer. Imbalances for causal effects (covariates) were adjusted for by means of the propensity score. Outcome analysis was performed by estimating the linear regression between change in symptom score and propensity score with all data and using this regression line to calculate the change in symptom score which would be expected for each patient. Tumour-associated events (recurrence, metastasis, and death) were evaluated in terms of the number of events observed and time to event. The safety of treatment with OE was analysed in terms of the number and severity of adverse events, their duration, treatment and outcome. RESULTS: For all symptoms except tumour pain, the adjusted mean improvement in symptom scores was larger in the test group than in the control group. The adjusted difference was statistically significant for all symptoms, except tumour pain and infections. The results show that the typical disease- and therapy-associated signs and symptoms in patients on complementary therapy with OE during postoperative treatment were significantly less. For 75% of the test group and 55% of the control group the physician recorded "no signs and symptoms". A clear reduction in the side effects of radiotherapy and chemotherapy was documented in 74% of the test group and 55% of the control group. Analysis of survival, recurrence, and metastasis demonstrated a reduced number of events in the test group. There was evidence of a beneficial influence of OE on time to event, although the median observation time was too short in these breast cancer patients to draw definite conclusions. The safety component was judged in 98% of the test group and 76% of the control group as "very good" or "good". In the total sample of 2,339 patients, the rate of OE-associated adverse reactions was 3.2%. All side effects were mild to moderate gastrointestinal symptoms. CONCLUSION: Complementary treatment of breast cancer patients with OE improves the quality of life by reducing signs and symptoms of the disease and the side effects of adjuvant antineoplastic therapies. This epidemiological retrolective cohort analysis provides evidence that the patients may also gain benefit by a prolongation of the time to event for cancer recurrence, metastasis and survival. OE was generally well tolerated.

Build-up modification of commercial diodes for entrance dose measurements in 'higher energy' photon beams.

BACKGROUND AND PURPOSE: Several commercially available p-type diodes do not provide sufficient build-up for in-vivo dosimetry in 'higher' energy photon beams, and only limited information could be found in the literature describing the correction factor variation and/or the achievable accuracy for in-vivo dosimetry methods in this energy range. The first aim of this study is to assess and analyze the variation of diode correction factors for entrance dose measurements at higher photon energies. In a second step the total build up thickness of the diode has been modified in order to minimize the correction factor variation. MATERIALS AND METHODS: Diode correction factors accounting for non-reference conditions (field size, source surface distance, tray, wedge, and block) are determined in 18-25 MV photon beams provided by different treatment units for Scanditronix p-type diodes recommended for higher energy photon beams: old type and new type EDP-20, and EDP-30 diodes. Hemispherical build-up caps of different materials (copper, iron, lead) are used to increase the total build-up thickness. Perturbation effects with and without additional build-up caps are assessed for the three diode types. RESULTS: For unmodified diodes field size correction factors (C(FS)) vary between 1.7% and 6%, dependent on diode type and treatment unit. For example, for an old type EDP-20 the C(FS) variation at 18 MV is much higher on a GE linac (5%) as compared to the Philips machine (1.7%). Depending on diode type, this variation can be reduced to 1-2% when adding additional build-up. The variation of source to surface distance correction factors is almost independent of build-up thickness. By adding additional build-up the influence of trays and blocks can be almost eliminated. CONCLUSIONS: The correction factor variation of unmodified diodes reflects the variation of the electron contamination with treatment geometry. A total build-up thickness of 30 mm is found to be the 'best compromise' for the three types of diodes investigated when measuring entrance doses in the energy range between 18 and 25 MV.

The effect of carbon fibre inserts on the build-up and attenuation of high energy photon beams.

BACKGROUND AND PURPOSE: The use of new materials in radiotherapy requires an investigation of the effects of these materials on the relevant beam parameters. The high strength and low density of carbon fibre suggest an excellent material for table inserts with minimal attenuation, without changing the skin sparing effect in the build-up zone. MATERIALS AND METHODS: In this paper three different carbon fibre plates and two conventionally table top materials are studied in Co-60, 6 MV and 23 MV photon beams. RESULTS AND CONCLUSIONS: From depth dose measurements it is clear that the dose in the build-up zone is influenced in the qualities of the beams. The mutual differences for the three carbon plates are minimal. For Co-60 the depth of the maximum dose is decreased by carbon from 5 to 2 mm and the surface dose is increased from 18 to 76%. For 6 and 23 MV the surface dose is increased from 21 to 52% and 20 to 32%, respectively, as well as the dose in the build-up region. A transmission of 99% was measured for two carbon plates out of three in Co-60 and for one out of three in 6 MV.

[Investigations on the combined effect of zinc and lead (author's transl)]. / Untersuchungen zur Kombinationswirkung von Zink und Blei

The effect of zinc and the combined effect of zinc and lead on the Ala-D of the erythrocytes were experimentally followed in vivo and vitro. It was demonstrated that the zinc effect on the Ala-D is a function of the zinc-concentrate in blood. It was hence traced that ZnCl2 dosis up to 500 mug/ml blood raises the activity of Ala-D. Higher levels of ZnCl2 on other side leads to supression of the Ala-D activity. The experiments demonstrated further zinc exerts a dosis dependent antagonistic effect on the lead suppression of the Ala-D. Possible explanations of the effect of zinc on the Ala-D, and the antagonistic zinc effect after lead applications are still in discussion.