Quality assurance in stereotactic radiosurgery/radiotherapy according to DIN 6875-1.

The new DIN ('Deutsche Industrie-Norm') 6875-1, which is currently being finalised, deals with quality assurance (QA) criteria and tests methods for linear accelerator and Gamma Knife stereotactic radiosurgery/radiotherapy including treatment planning, stereotactic frame and stereotactic imaging and a system test to check the whole chain of uncertainties. Our existing QA program, based on dedicated phantoms and test procedures, has been refined to fulfill the demands of this new DIN. The radiological and mechanical isocentre corresponded within 0.2 mm and the measured 50% isodose lines were in agreement with the calculated ones within less than 0.5 mm. The measured absorbed dose was within 3%. The resultant output factors measured for the 14-, 8- and 4-mm collimator helmet were 0.9870 +/- 0.0086, 0.9578 +/- 0.0057 and 0.8741 +/- 0.0202, respectively. For 170 consecutive tests, the mean geometrical accuracy was 0.48 +/- 0.23 mm. Besides QA phantoms and analysis software developed in-house, the use of commercially available tools facilitated the QA according to the DIN 6875-1 with which our results complied.

[Profile of ambulatory radiosurgery with the gamma knife system. 1: Method and multicenter irradiation concept]. / Profil der ambulanten Radiochirurgie mit dem Gamma-Knife-System. Teil 1: Methode und multizentrisches Bestrahlungskonzept.

Radiosurgery represents a minimally invasive radiologic method for the treatment of intracranial tumours and arteriovenous malformations. In 1994 the radiosurgical device 'Leksell Gamma Knife' (LGK) was installed in a dedicated logistic environment for outpatient treatments. High quality requirements have to be met for radiosurgery. The target point accuracy taking into account the whole system was shown to be reliably below 0.5 mm whereas the spatial therapeutic resolution was 0.035 cm3. Quality parameters of the dose plan were evaluated for the first 500 consecutive treatments. These values and examples of dose plans were used to emphasize the advantages of the treatment principle with multiple isocenters. An analysis of data in the literature revealed that there is no uniform standard of treatment available in radiosurgery. A highly significant correlation between a risk prediction model for the stereotactic linear accelerator on the one hand and a different model for the LGK on the other could be shown. This result could be helpful in order to proceed towards a more uniform treatment standard in radiosurgery and to improve overall treatment results.

[Profile of ambulatory radiosurgery with the gamma knife system. 2: Report of clinical experiences]. / Profil der ambulanten Radiochirurgie mit dem Gamma-Knife-System. Teil 2: Klinischer Erfahrungsbericht.

Gamma Knife radiosurgery (GKRS) was applied in 500 consecutive treatments for 445 patients within 2 years. Indications were arterio-venous malformations (93 patients), schwannomas of cranial nerves (75 patients), meningiomas (79 patients; 73 of the tumors involving the skull base), pituitary adenomas (40 patients), craniopharyngiomas (13 cases), gliomas (13 cases), rare indications (12 cases), and brain metastases (126 patients). In arterio-venous malformations two complications were observed whereas two other patients underwent surgery due to intracranial hemorrhage in the latent period after GKRS. In all cases follow-up with MRI showed evidence of an active obliteration process. Out of 24 patients with a follow-up over 1 year, angiography revealed complete obliteration in 9 patients so far. A partial obliteration was evidenced by MRI in 15 cases. In benign tumors (meningiomas and vestibular schwannomas) tumor control rates of 88% and 89% were achieved, respectively. Treatment related side effects were mild and rare; no facial palsy occured after primary Gamma Knife treatment. GKRS was particularly effective in inoperable skull base meningiomas. Cerebral metastases were controlled in 89.5% by a single Gamma Knife treatment. The mean survival period was 11.8 months. In patients receiving a single Gamma Knife treatment the mean survival time was 9.1 months. For patients undergoing multiple (up to 5) sessions of GKRS (because of new tumors) the mean survival period was 17.2 months. MRI showed evidence of adverse radiation reactions in 10/124 patients (8.1%) which were symptomatic in 3 patients (0.8%). The results obtained in patients with cerebral metastases emphasize that GKRS alone is as effective as the combined treatment of these lesions by surgery and fractionated radiotherapy. Our results demonstrated an attractively high therapeutic gain factor of Gamma Knife treatment in key indications of radiosurgery.

[Approximation errors in the physical planning of radioiodine therapy of the thyroid]. / Näherungsfehler bei der physikalischen Planung der Radiojodtherapie der Schilddrüse.

The approximations in the equations used for the calculation of the radioiodine therapy are reviewed and compared with a reference formula, based on ICRP Publication 30. Applying these equations to two clinical cases, we find pronounced differences compared to the reference method. Investigations of a collective of 314 patients yield in a relatively high fraction delayed maxima in the uptake curves. Simulations prove that serious errors occur when the ascending slope of the uptake curve is neglected. An equation taking care of this effect is presented. Pronounced individual differences are found between uptake curves recorded before and after therapy. The effects on the difference between planned and actually applied dose to the thyroid are shown. The difficulties of the determination of the thyroid mass are discussed and a combined method using scinti- and sonographic data presented.

[Radiotherapy of Hodgkin's disease with extensive mediastinal involvement]. / Strahlentherapie des Morbus Hodgkin bei ausgedehntem Mediastinalbefall.

The radiotherapy of large mediastinal masses in Hodgkin's disease is connected with a high risk of marginal recurrences. Large radiation fields or the irradiation of the whole lung may be followed by pulmonary complications. A low dose irradiation by a large field followed by an early rest for the undisturbed reabsorption of the tumor and a high dose irradiation by a small field in the end is demonstrated as a possible alternative therapy in stage I and II.

[Radiotherapy of prostatic cancer: staging and radiotherapy planning with transrectal ultrasound]. / Strahlentherapie des Prostatakarzinoms: Stadieneinteilung und Bestrahlungsplanung mit dem Transrektalen Ultraschall.

Transrectal ultrasound of the prostate is a cheap and well-reproducible examination for the prostate and seminal vesicles. The local tumor extension of a prostatic carcinoma can be visualized. By documentation of the ultrasound image on a polaroid paper picture, the topometric section of the prostate can be obtained. This picture can be used for dosimetry in individual radiation therapy-planning. Computed tomography is performed for detection of enlarged regional lymph nodes and demonstration of the topographic anatomy of the prostate in the lower pelvis.

[Experimental and mathematical check of the moving-strip irradiation technic]. / Experimentelle und rechnerische Uberprüfung der Moving-strip-Bestrahlungstechnik.

The moving-strip irradiation of the total peritoneal region plays an important role in the adjuvant therapy of the ovarian carcinoma. TLD dosimetric and mathematic investigations of this radiotherapeutic method show that 1. the best dose homogeneity in the longitudinal profile is achieved by 60Co units, if the patients are not too stout, 2. a higher relative depth dose has to be estimated than for an open field of the same total field size, 3. an additional 2,5 cm strip has to be inserted in order to achieve an abrupt drop on the border of the total irradiation field, 4. this method offers a good guarantee against false adjustment, if this is not too grave, 5. the conformity between the dose distribution curves calculated and those measured by TLD is excellent.

[Pre- and postoperative clearance studies in the individual kidneys in juvenile kidney surgery]. / Seitengetrennte Nieren-Clearance im Rahmen prä- und postoperativer Untersuchungen bei Nierenoperationen im Kindesalter.

In 1978 43 patients have been operated in the Department of Pediatric Surgery, Krankenhaus München-Schwabing, because of recurrent urinary-tract infections with ureterovesical reflux or obstructive urinary-tract diseases. In all patients a split whole body clearance-study with a method modified after the method of Mühle with 131J-Hippuran was carried out pre- or postoperatively, respectively. In 78,5% of these cases the clearance-results were corresponding to the results of x-ray examination; 6 of the remaining patients had a worse clearance result and 3 had a better result than the x-ray findings would have suggested.

Effect of phenformin on hepatic balances of gluconeogenic substrates in man.

The effect of a five day pretreatment with phenformin (3 X 50 mg daily) on hepatic metabolism was studied in six healthy volunteers. Arterial and hepatic venous concentrations of substrates and hepatic blood flow were estimated during a basal period and during a low-dose lactate infusion (0,03 mmol . kg-1 . min-1). The results have been compared with those obtained from untreated normal subjects in a previous study (16). During the baseline period arterial concentration of alanine and the hepatic venous concentration ratios of alanine: pyruvate and beta-hydroxybutyrate: acetoacetate were significantly increased with phenformin treatment, while the balances of carbon dioxide and glucose and the fractional extraction of alanine were decreased compared to the values obtained in untreated subjects. During lactate infusion mean arterial lactate concentration was significantly increased and hepatic lactate extraction was decreased compared to untreated persons under the same conditions. In the phenformin-treated group lactate infusion resulted in hepatic output of pyruvate and the hepatic glucose balance remained unchanged compared to baseline. Since the rate of hepatic blood flow was not increased during lactate infusion a significantly smaller glucose output and lactate uptake was obtained with phenformin. These findings support the present view that the hypoglycaemic effect of biguanides is due, at least in part, to inhibition of hepatic gluconeogenesis.

Comparison of different methods of clearance determination.

Clearance determination by compartmental analysis of hippurate renograms was compared in 30 cases to the conventional PAH and to the partly shielded whole body counting technique. Good correlations between compartmental analysis and PAH method (r = 0.96) as well as the whole body technique (r = 0.94) were found. Correlation between PAH and whole body method was not always satisfactory (r = 0.85). In an additional study influence of greater count rates become obvious: correlation coefficients increase from 0.89 (131I-hippurate, n = 97) to 0.95 (123I-hippurate, n = 38). Determination of the divided clearance correlates well (r = 0.95). Using 123I-hippurate all the information available by radioisotopic kidney investigations can be obtained in a one-step procedure.

On gluconeogenesis of human liver. Accelerated hepatic glucose formation induced by increased precursor supply.

In 8 subjects in whom portal vein catheters had been inserted 5-6 days previously during cholecystectomy, arterial and portal concentrations of glucose, lactate, pyruvate, glycerol, alanine, free fatty acids, beta-hydroxybutyrate and acetoacetate revealed no significant differences. This provided the basis for the calculation of hepatic balances from arterio-hepatic venous substrate-differences in 17 healthy volunteers. In eight of them metabolic balances were determined during elevated hepatic lactate supply. Kinetics of the substrates throughout the whole test period in 9 controls showed no gross interference from the catheterization or infusion procedure. The elevated hepatic lactate concentration caused a doubling of hepatic glucose output, which could almost entirely be accounted for by a fivefold increase of hepatic lactate uptake. This acceleration of hepatic gluconeogenesis was accompanied by a significant increment of hepatic free fatty acid uptake, whereas hepatic ketone body production did not change. These data seem to support the view that hepatic energy requirements caused by an accelerated gluconeogenesis might be covered from enhanced free fatty acid oxidation.

[On the analysis of the hepatic-venous 133xenon-clearance after the application of the gas by inhalation]. / Zur analyse der lebervenösen 133Xenon-Clearance nach Zufuhr des Gases durch Inhalation

After the inhalation of 133xenon continuous registrations of portal 133xenon concentrations showed that the monoexponential terminal component of the hepatic-venous 133xenon-clearance might be due to the recirculation of the gas from the gut. Accordingly, in all the cases, with the application of the wellknown "extrapolation and peeling off" of this monoexponential terminal component from this part of the hepatic-venous 133xenon-clearance, not affected any more by arterial recirculation a monoexponential 133xenon-clearance could be separated. The time-constant of the latter was similar to that of the well-knwon specific hepatic 133xenon-clearance after the application of the gas by injection into the portal vein.