14. Search for improvement of the therapeutic ratio in radiotherapy for non-small cell lung cancer (NSCLC)

There are several approaches under investigation in view of improvement of the therapeutic ratio of NSCLC radiotherapy in our Department:1/ Dose escalation above 70 Gy using conformal radiotherapy techniques, 2/ accelerated radiotherapy with or without induction chemotherapy addressed to III stage tumours, 3/ conformal postoperative radiotherapy to total minimum dose in PTV of 50 Gy addressed to completely resected III stage tumours.Ad 1/ From XI 1998 to XI 2000 43 patients were included in dose escalation study. Doses from 70 to 74 Gy were delivered. Apart from one toxic death, due to radiation pneumonitis, toxicity was acceptable. Since 1999 for NO patients the study of omission of elective irradiation is conducted. By the time being 10 patients were irradiated with omission of elective fields. There was no relapse in non-treated “elective areas”. The actuarial 1-, 2- and 3-year survival were respectively 84-, 64-, and 42%. There were 14 local relapses in 19 progressions observed in the entire group. In spite of encouraging results a high level of local relapses shows the limits of moderate dose escalation using conformal techniques and conventional fractionation in improvement of local control of NSCLC.Ad 2/ From III 1999 two different accelerated radiation therapy schedules are investigated for III stage tumours. Forty patients were enrolled in the study: 26 were irradiated according to accelerated hyperfractionated radiotherapy (57 Gy in 40 fractions [first week: elective fields −1.2 Gy × 2 per day, 3 remaining weeks 1.8 Gy to elective fields and 1.2 Gy boost to tumour] during 26 days), 14 were irradiated according to accelerated conformal radiotherapy with concurrent boost (56.7 Gy in 21 fractions and 26 days: all treatment was conformally planned and delivered: 1,9 Gy per fraction to the limited elective field and 0.8 Gy as a concurrent boost to the GTV). There was no difference on compliance with treatment plan, toxicity and response rate (80- and 72%) in the both investigated groups.Ad 3/ From I 1999 eleven patients were enrolled in the phase II study of postoperative conformal radiotherapy of the region of the highest probability of microscopic invasion by the disease to the minimum dose of 50 Gy in PTV. The study is conducted in view of the future design of randomised study addressing question of the value of postoperative radiotherapy using modern techniques in management of NSCLC

57. Physical and dosimetric aspects of quality assurance in stereotactic radiotherapy

A quality assurance system in stereotactic radiosurgery and stereotactic fractionated radiotherapy, concerning the physical and dosimetric aspects, may be divided into three elements: (1) the preparation of reliable basic data for the computerized treatment planning system; (2) a control of the accelerator parameters prior to patient treatment; (3) preparation of the optimal treatment plan with the treatment planning system.Due to the small size of the beams formed by circular collimators (7.5–35 mm diameter, BrainLab System) the smallest available detectors should be used for measurements – a diamond diode (0.3 mm thickness) and a 0.015 cm3 ionization chamber (PTW Freiburg) are adequate to measure precisely TMR curves, beam profiles and output factors required for the treatment planning system BrainScan.The full control of accelerator parameters (Clinac 2300 C/D) necessary to safely carry out the treatment requires a comprehensive list of tests (an extended list of weekly checks including Winston-Lutz test). Testing procedure carried out with a set of specialized devices (Med-Tec, Radak, BrainLab) takes about two hours. Proper accelerator check and regulations allow for very precise patient positioning.Treatment planning (with the treatment planning system BrainScan) is based on a series of CT and MR scans with target volume and organs at risk marked on each slice by the radiotherapist. The planner has to select the positions of isocentres (up to 3), collimator diameters, number and range of the arcs. Additional parameters for optimization procedure are the total dose proportions delivered by each arc. The treatment plan evaluation is based on the analysis of DVHs for target volume and also for organs at risk (orbits, optical nerves, brain stem) in order to minimize the dose and volume irradiated. It was accepted that the dose uniformity factor, defined as a ratio Dmin/Dmax within the target volume, should be not less than 0.8, and should approach 0.9 as much as possible.The above-presented system of quality control, specifying tolerance limits of controlled parameters, assures safe and precise dose delivery in stereotactic radiotherapy

Optimization of dose distributions in intraoperative HDR brachytherapy

The authors present their initial experience in physical aspects of treatment planning in HDR intraoperative brachytherapy. The examples are given of implantations in various tumour localizations: head and neck, pancreas, soft tissue sarcomas in the abdomen. The technical and dosimetric problems which may occur in such situations are discussed. The capabilities of dose distribution optimization by the Abacus HDR treatment planning system are presented