[P179] Small field correction factors determination for the IBA razor nano chamber and the IBA razor chamber

Abstract

Finally, manual contours estimated a consistently faster rate of tumour shrinkage (0.018 cm 3 /day) than automatically propagated contours (0.014 cm 3 /day). A linear fit between the manual and propagated gradients per patient found a slope of 0.68 (1 for perfect agreement). Conclusions. The results show that automatic contour propagation performance is acceptable for use in wider research studies. There are differences between the manual and propagated contours, with the clinician estimated a larger rate of tumour shrinkage, which is suggestive of an observer bias. We will now apply this technique to investigate tumour shrinkage and outcome in the CONVERT trial patients. Portugal ⇑ Corresponding author. Purpose. Most of the breast treatments uses a megavoltage photon beams. This kind of energy exhibits a skin-sparing effect that is a concern in some stages of both breast conservative and post-mastectomy irradiation. To overwhelm this effect a bolus material is placed on the skin. However, when using commercial non-customized bolus, small air gaps can occur in certain regions of the treatment area where the bolus cannot establish the perfect match with the irregular skin of the patient, altering locally the expected skin dose. The objective of this study is to verify the improvement in the breast radiotherapy treatment using a customized bolus produced by 3D rapid manufacturing (3D-RM) techniques, and compare it with the commercial ones. Measurement of the surface dose and comparisons with the doses calculated by the Treatment Planning System (TPS) were also performed. Methods. The customized 3D rapid manufactured bolus was prepared for an anthropomorphic female phantom breast area. 3D-CRT treatment plans for right breast were performed on CT scans of the phantom both with the customized and commercial bolus. The skin dose was measured in 5 points on the phantom breast surface using a MOSFET-based system. Results. A better fitting to the surface of the phantom was observed for the customized bolus, reducing the air gaps and improving the daily positioning on the irregular breast surfaces. The average differences between calculated and measured doses in the customized and commercial bolus ranged from 2 to 10%. However , the highest dose difference (approximately 10%) was observed for the commercial bolus. Conclusions. The 3D rapid manufactured bolus can reduce the uncertainty in the daily positioning and help to overcome the dose discrepancy due to unwanted air gaps affecting breast cancer radiation therapy. With the commercial bolus a higher dose difference relatively to TPS was observed. The skin dose increase is observed in the same proportion for both boluses. Purpose. Radiotherapy is an effective treatment method for managing breast cancer, but patients may have cardiac disease as a late radiation effect after completing radiotherapy. The left anterior descending coronary artery (LAD) dose and mean heart dose are playing a major role for cardiac disease. We aimed to compare deep inspiration breath-hold (DIBH) and free breathing (FB) techniques dosimetrically for left breast radiotherapy while using VMAT method. Methods. Sixteen early stage left breast cancer patient's treatment planning were performed using Monaco 5.11 Ò TPS (Elekta AB, Sweden) for DIBH and FB techniques. We used Catalyst Ò (C-RAD AB, Sweden) optical surface guided radiotherapy gating device for DIBH technique. The prescribe dose was 60 Gy to tumor bed and 46 Gy to breast in 28 fractions by simultane integrated boost (SIB). We aimed to achieve a similar dose conformality for PTV (tumor bed) and PTV (whole breast) while optimizing two technique's plan, then we compared mean heart dose, max. heart dose, mean LAD dose, V20 Gy, V10 Gy and V5 Gy doses percentage of lung volume. Results. A statistically significant interaction existed between heart, LAD doses and DIBH technique. We determined an average %20 lower max. heart doses, %32 lower mean heart doses and %27 lower mean LAD doses with DIBH technique, also, an average lung volume were enlarged %66. We didn't determine significant percentage difference for V20 Gy, V10 Gy and V5 Gy doses of lung volume between two techniques. Conclusions. However, we achieved an average 3.7 Gy mean heart doses, 9.2 Gy mean LAD doses and 42.4 Gy max. heart doses with FB technique by using VMAT method, Darby et al. [1] have shown that the relative risk of ishemic heart disease increases with %7.4 per Gy increased mean heart dose. Hence, we even reduced significantly mean heart, max. heart and mean LAD doses with DIBH technique. Therefore, DIBH technique while using VMAT method may reduce cardiac disease possibility for left breast radiotherapy. References 1. Darby SC, Ewertz M, McGale P, et al. Risk of ishemic heart disease in women after rads ßotherapy for breast cancer. N Engl J Med 2013;368:987-98. Purpose. The aim of this study was to measure small beam output factors (OFs) using the IBA Razor Nano Chamber (RNC) and the IBA Razor Chamber (RC) and to determine correction factors for comparison with Gafchromic EBT3 films.