ESTRO 37 Abstract book

S1115

ESTRO 37

EP-2037 First clinical use of a new surface tracking/biofeedback system: DIBH reproducibility and stability E. Steiner 1 , D.D. Campos 2 , P. Keall 1 , K. Makhija 1 , B. Stanley 2 , T. Yamamoto 2 , M. Daly 2 , Y. Rong 2 1 The University of Sydney, Clinical Medical School - Central- ImageX Institute, The University of Sydney, Australia 2 University of California at Davis Comprehensive Cancer Center, Department of Radiation Oncology, Sacramento, USA Purpose or Objective Deep inspiration breath hold (DIBH) halves the cardiac dose for left-sided breast radiotherapy [Nissen2012]. Visual guidance improves the reproducibility and stability of DIBH [Cervino2009]. This work evaluates the reproducibility and stability of DIBH using the novel Breathe Well system for chest tracking and visual breath- hold (BH) guidance compared to the AlignRT (VisionRT, London, UK) surface imaging system for the first patient treated for left-sided breast cancer. Additionally guided vs unguided BHs are compared. Material and Methods The in-house developed Breathe Well system consists of an Intel RealSense sensor (infrared and optical), a screen and a processing unit (Figure 1a). The patient was set up on a breast board with arms placed above her head. A reference DIBH was recorded using Breathe Well during simulation by tracking the skin area around the central chest tattoo of the patient (Figure 1c). For each treatment fraction, the patient was set up following the clinical Align RT workflow. An unguided BH was recorded first with the Breathe Well system. Then the screen was turned on and the patient breathed into the BH tolerance area (reference DIBH±2mm) guided by the Breathe Well software interface, while the AlignRT system monitored the left breast area. The hypotheses were: (1) There is a correlation between the Breathe Well BH measurement and the vertical AlignRT BH measurement. (2) Breathing guidance improves BH reproducibility. Reproducibility was defined as the maximum difference between different DIBH levels [Cervino2009] and stability as the mean value of the single BH standard deviations [Stock2006].

dynamic irradiation techniques in hypo-fractionated lung treatment are discouraged. This work evaluates the dosimetric variations in hypo- fractionated lung irradiations with helical IMRT ( Tomotherapy ), analyzing the influence of the internal tumor volume (ITV) density and the type of target motion (periodic and non-periodic with drift). Material and Methods Longitudinal respiratory movements, both periodic (sinusoidal and cosine to the fourth power, amplitude: 1.5 cm, period: 6 s) and irregular with baseline drift, were simulated using the QUASAR ( Modus ) phantom. A mobile cedar insert containing two 3 cm diameter acrylic semi-spheres was used, thus allowing EBT3 radiochromic films to be inserted in.

Dose distributions were calculated with Tomotherapy planning system to deliver 20 Gy to the whole ITV. The CT imaging studies used correspond to the most representative position of each respiratory pattern (mid or exhale) with the original density of the image acquisition and also forcing the ITV density to that of the sphere. Planning parameters compatible with the technical constraints of the unit (rotation period lower than 60 s) were chosen to allow high dose per fraction: 0.100 pitch, modulation factor lower than 2, and field width of 2.5 cm. For each batch of measurements, a no-motion irradiation with rest phantom was performed to consider for output dose variations. The treatment plans calculated for heterogeneous and homogeneous ITV density were delivered for the respiratory patterns proposed. The films were scanned with an Epson 10000XL and using the green channel to obtain the dose with the ImageJ software. Longitudinal profiles were analyzed. Results The films irradiated on the moving phantom showed the expected penumbra widening, but dose variations at the sphere region were less than 3% for periodic patterns, whereas for the irregular pattern were up to 13%. The dose differences observed between homogeneous and heterogenous ITV density were higher for the irregular pattern (4% vs 3%) with a dose increase for heterogeneous case.

Conclusion For periodic movements, Tomotherapy hypo-fractionated lung treatments do not yield dose perturbations due to the interplay effect. For irregular movements, the dose increases are restricted to the target area. The influence of the ITV density on dose distribution calculation is negligible, although the magnitude of the interplay dose perturbations is reduced by homogenizing the density.