Purpose/Objective: A pseudo-tangential IMRT (PT-IMRT) technique was developed to achieve high uniformity of dose for large left breast (separations >24 cm and volumes > 1200cc) radiation therapy to reduce the early and late skin and subcutaneous reactions. This technique was compared to four other techniques: three dimensional (3D), inverse tangential IMRT (T-IMRT), forward field in field (FIF) and forward electronic compensator (EC). Materials/Methods: CT simulation was performed and the planning target volume (PTV) for left breast (excluding the skin) was drawn along with heart, lungs and right breast volumes in a typical patient with large breasts left breast (PTV=1684 cc). Treatment planning was accomplished using the Helios/Eclipse system. The PT-IMRT technique basically combines two pairs of tangential beams with two additional beams angled less than 10 degrees from each side, set anterior to the tangential plane using 18 MV photons. An additional OAR was drawn around the high dose (>110%) area at the lateral side. The PT-IMRT is an inverse planning approach. After the optimization, 2 cm skin flash was added to each beam. Multiple static segments were used for the IMRT delivery. For comparison purpose, four other plans were also run T-IMRT, 3D, FIF and EC (all use only the tangential 6 and 18 MV photon beams). In-homogeneity correction was included in all plans. The prescribed dose (PD) (50.4 Gy in 28 daily fractions) was to the isocenter placed at the intersection of beams at the center of the PTV.The following parameters were used for evaluation of all the plans: (1) V95 (volume receiving >95% dose) and V90 for PTV; (2)V10Gy, 20Gy, V30Gy and V40Gy for heart; (3)V10Gy,V20Gy,V30Gy and V40Gy for left lung; (4) the maximum dose; (5) the V105% (cc) (volume receiving doses >105% in cc);(6) a reference point dose for the right breast (5 cm to the right and 1 cm deep to the mid-sternum point);(7)V5 (cc) for right breast;(8) Total MUs. Results: The PT-IMRT achieved V95% of 97.8% with V>105% of about 20% and V>110% of 2.4 %. The volumes of heart and left lung for doses less than 30 Gy were 2-3% higher for PT-IMRT. The reference point dose in the right breast was about 3% higher for PT-IMRT and T-IMRT plans compared to the other three plans. The V5% (cc) for right breast PT-IMRT and T-IMRT plans was about 1% compared to the other three techniques where it was 0.6 %. The normal tissue volume for doses ?105% and was significantly reduced with the PT-IMRT, T-IMRT and EC plans compared to the 3D and FIF plans. The required MUs for PT-IMRT were highest followed by EC, T-IMRT, FIF and 3D plans. (See table) Conclusions: The PT-IMRT achieves better PTV coverage and better uniformity of dose distribution among all the five techniques and has the potential to reduce the skin and subcutaneous reactions and improve cosmesis in breast cancer patients with large breasts who opt for breast conservation therapy.
Guan, H,
Comparison of a Pseudo-tangential IMRT Technique to Other Tangential Techniques for Radiation Therapy of Large Left Breast Using Helios/Eclipse System. Radiological Society of North America 2005 Scientific Assembly and Annual Meeting, November 27 - December 2, 2005 ,Chicago IL.
http://archive.rsna.org/2005/4420757.html
