Emese Fodor

A prospective study of supine versus prone positioning and whole-body thermoplastic mask fixation for craniospinal radiotherapy in adult patients

PURPOSE To evaluate neuroaxis irradiation for adults in the supine position using head body thermoplastic mask fixation, from the aspects of dose distribution, patient comfort and set-up accuracy. METHODS AND MATERIALS Nine of the 12 adult patients were positioned for craniospinal axis irradiation in both prone and supine positions. After mask fixation and planning CTs in both positions, a questionnaire relating to the comfort was completed. The doses to the target and to the organs at risk of the 3D conformal plans in the supine and prone positions were compared. Portal images of all 12 patients irradiated in the supine position were evaluated, the van Herk formulas being used to calculate the systemic and random errors. RESULTS No significant difference was found between the prone and supine positions target coverage, the dose homogeneity and the dose to the organs at risk. The supine position was considered more comfortable by the patients (scores of 2.8 versus 4.29), with a vector random error of 3.27 mm, and a systematic error of 0.32 mm. The largest random set-up error was observed in the lateral direction: 4.83 mm. CONCLUSIONS The more comfortable supine position is recommended for craniospinal irradiation in adult patients. Whole-body thermoplastic mask immobilization provides excellent repositioning accuracy.

The Role of Gafchromic EBT3 Film in the QualityAssurance of Dynamic Irradiation Techniques

Intensitymodulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) techniques that provide improved conformity have become standard treatment options for irradiation of complex target volumes if the goal is to deliver high doses to tumors that are located in the immediate vicinity of sensitive and healthy tissues [1]. Several studies demonstrate that higher survival rates can be achieved by increasing the total dose delivered to the tumor in the case of certain types of neoplasms (e.g., prostate cancer or malignancies in the head and neck region). Treatment of patients with higher total doses requires the use of modern, cuttingedge technologies in order to provide the homogeneous treatment of the tumor in association with a decreased dose burden on healthy tissues. IMRT and VMAT are modern radiotherapy techniques that are capable of meeting the above criteria [2]. Using appropriately chosen radiation directions during the planning of IMRT and VMAT improves the chance for tumor control, increases the dose delivered to the target volume, and reduces the exposure of organs at risk [3]. Compared to the three-dimensional conformal radiation therapy (3DCRT) technique, the use of IMRT or VMAT is associated with decreased toxicity, shortened treatment time, and improved quality of life of the patients [4].

Moving gantry method for electron beam dose profile measurement at extended source-to-surface distances

A novel method has been put forward for very large electron beam profile measurement. With this method, absorbed dose profiles can be measured at any depth in a solid phantom for total skin electron therapy. Electron beam dose profiles were collected with two different methods. Profile measurements were performed at 0.2 and 1.2 cm depths with a parallel plate and a thimble chamber, respectively. 108 cm×108 cm and 45 cm×45 cm projected size electron beams were scanned by vertically moving phantom and detector at 300 cm source‐to‐surface distance with 90° and 270° gantry angles. The profiles collected this way were used as reference. Afterwards, the phantom was fixed on the central axis and the gantry was rotated with certain angular steps. After applying correction for the different source‐to‐detector distances and incidence of angle, the profiles measured in the two different setups were compared. Correction formalism has been developed. The agreement between the cross profiles taken at the depth of maximum dose with the ‘classical’ scanning and with the new moving gantry method was better than 0.5 % in the measuring range from zero to 71.9 cm. Inverse square and attenuation corrections had to be applied. The profiles measured with the parallel plate chamber agree better than 1%, except for the penumbra region, where the maximum difference is 1.5%. With the moving gantry method, very large electron field profiles can be measured at any depth in a solid phantom with high accuracy and reproducibility and with much less time per step. No special instrumentation is needed. The method can be used for commissioning of very large electron beams for computer‐assisted treatment planning, for designing beam modifiers to improve dose uniformity, and for verification of computed dose profiles. PACS numbers: 87.53.Bn, 87.53.Jw, 87.56.jf