Dosimetric comparison of volumetric modulated arc therapy (VMAT), step and shoot and sliding window IMRT for prostate cancer Introduction: The goal of delivering higher uniform doses to the planning

ID: 17554 Title: Dosimetric comparison of volumetric modulated arc therapy (VMAT), step and shoot and sliding window IMRT for prostate cancer 1 : Baltas D, Kolotas C, Geramani K, et al. A conformal index (COIN) to evaluate implant quality and dose specification in brachytherapy. Int J Radiat Oncol Biol Phys 40, 515-524 (1998). 2 : van’t Riet A, Mak AC, Moerland MA, et al. A conformation number to quantify the degree of conformality in brachytherapy and external beam irradiation: Application to the Prostate. Int J Radiat Oncol Biol Phys 37, 731-736 (1997). 3 : C. L. Tsai, J. K. Wu, H. L. Chao, Y. C. Tsai, and J. C. H. Cheng. Treatment and Dosimetric Advantages Between VMAT, IMRT, and Helical TomoTherapy in Prostate Cancer. Medical Dosimetry 36(3), 264-271 (2011). Dosimetric comparison of volumetric modulated arc therapy (VMAT), step and shoot and sliding window IMRT for prostate cancer Introduction: The goal of delivering higher uniform doses to the planning target volume (PTV), while minimizing dose to critical organs and other healthy tissues, led to the development of the intensity modulated radiation therapy (IMRT). Though there are a variety of techniques for IMRT delivery, the similarities between the dose distributions they produce, as well as the novelty of some of the techniques, mean that there is not yet a definitively superior technique. The development of dynamic multi-leaf collimator (MLC) along with inverse planning software lead to the introduction of static step-and-shoot (SS) and the dynamic sliding window (SW) IMRT techniques, which improved the conformity of dose distributions compared to 3D CRT around the target volumes. Recently, another IMRT delivery technique known as volumetric modulated arc therapy (VMAT) has emerged as well. This study aims to evaluate treatment plans generated by SS, SW and VMAT for prostate cases in order to assess the differences in the dose volume histograms of target and organs at risk (OAR), conformity indices, and plan quality. Conformity Index (COIN): This index proposed by Baltas et al. 1 is a modification of the Conformity Number (CN) published by van’t Riet et al. 2 The CN is the product of a tumor coverage factor and a normal tissue over dosage factor. The COIN takes the CN and goes one step further by including an additional reduction for any critical structures which are covered by the prescription isodose line. For both metrics a value of unity is “perfect” with the target volume and prescription isodose volume coinciding exactly. The conformity is worse with a lower value. van’t Riet et al. Conformation Number (CN) VRI = Volume of the prescription isodose TV = Target Volume TVRI = Target volume covered by the prescription isodose Baltas et al. Conformal Index (COIN) NCO = number of critical structures VCOref = volume of a critical structure covered by the prescription isodose VCO = volume of a critical structure