Does TomoDirect 3DCRT represent a suitable option for post-operative whole breast irradiation? A hypothesis-generating pilot study

Radiation Oncology Does TomoDirect 3DCRT represent a suitable option for post-operative whole breast irradiation? A hypothesis-generating pilot study Valeria Casanova Borca 0 1 3 Pierfrancesco Franco 2 Paola Catuzzo 1 3 Fernanda Migliaccio 2 Flora Zenone 1 3 Stefania Aimonetto 1 3 Andrea Peruzzo 1 3 Massimo Pasquino 0 Giuliana Russo 0 Maria Rosa La Porta 2 5 Domenico Cante 5 Piera Sciacero 5 Giuseppe Girelli 5 Umberto Ricardi 4 Santi Tofani 0 1 3 0 Departments of Medical Physics, Azienda Sanitaria ASL TO 4 , Ivrea , Italy 1 Departments of Medical Physics, Ospedale Regionale 'U. Parini', AUSL Valle d'Aosta , Aosta , Italy 2 Department of Radiation Oncology, Ospedale Regionale 'U. Parini', AUSL Valle d'Aosta , Aosta , Italy 3 Departments of Medical Physics, Ospedale Regionale 'U. Parini', AUSL Valle d'Aosta , Aosta , Italy 4 Department of Medical and Surgical Sciences, Radiation Oncology Unit, University of Torino, Ospedale S. Giovanni Battista , Turin , Italy 5 Departments of Radiotherapy, Azienda Sanitaria ASL TO 4 , Ivrea , Italy Background: This study investigates the use of TomoDirectTM 3DCRT for whole breast adjuvant radiotherapy (AWBRT) that represents a very attractive treatment opportunity, mainly for radiotherapy departments without conventional Linacs and only equipped with helical tomotherapy units. Methods: Plans were created for 17 breast cancer patients using TomoDirect in 3DCRT and IMRT modality and field-in-field 3DCRT planning (FIF) and compared in terms of PTV coverage, overdosage, homogeneity, conformality and dose to OARs. The possibility to define patient-class solutions for TD-3DCRT employment was investigated, correlating OARs dose constraints to patient specific anatomic parameters. Results: TD-3DCRT showed PTV coverage and homogeneity significantly higher than TD-IMRT and FIF. PTV conformality was significantly better for FIF, while no differences were found between TD-3DCRT and TD-IMRT. TD-3DCRT showed mean values of the OARs dosimetric endpoints significantly higher than TD-IMRT; with respect to FIF, TD-3DCRT showed values significantly higher for lung V20Gy, mean heart dose and V25Gy, while contralateral lung maximum dose and contralateral breast mean dose resulted significantly lower. The Central Lung Distance (CLD) and the maximal Heart Distance (HD) resulted as useful clinical tools to predict the opportunity to employ TD-3DCRT: positive correlations were found between CLD and both V20Gy and mean lung dose and between HD and both V25Gy and the mean heart dose. TD-3DCRT showed a significantly shorter mean beam-on time than TD-IMRT. Conclusions: The present study showed that TD-3DCRT and TD-IMRT are two feasible and dosimetrically acceptable treatment approach for AWBRT, with an optimal PTV coverage and adequate OARs sparing. Some concerns might be raised in terms of dose to organs at risks if TD-3DCRT is applied to a general population. A correct patients clusterization according to simple quantitative anatomic measures, would help to correctly allocate patients to the appropriate treatment planning strategy in terms of target coverage, but also of normal tissue sparing. - Background Adjuvant whole-breast external beam radiation therapy (AWBRT) is an integral part of the current standard multimodality approach for early stage breast cancer [1]. Intensity modulated radiation therapy (IMRT) has been shown to increase intra-target dose homogeneity and to spare organs at risk [2]. Recent studies on breast irradiation [3] have demonstrated that Helical Tomotherapy (HT) provides superior target dose homogeneity and moderate normal tissue sparing compared to conventional treatments. TomoDirectTM (TD) is a fixed beam treatment mode allowing for planning and delivery at static beams, with the couch moving at a constant rate past a fixed binary multileaf collimator for fluence modulation [4]. A pre-clinical version of the planning system named topotherapy has been investigated in the context of AWBRT, showing adequate target coverage and normal tissue high dose reduction with concomitant PTV inhomogeneous dose in one study [5,6]. In addition to the IMRT mode (TD-IMRT), it is possible to plan TD in a 3D-CRT mode (TD-3DCRT), whereas dose penalties and DVH constraints cannot be specified and a preset optimization algorithm determines fluence maps, resulting in an inherently forward plan still allowing for IMRT. TD-3DCRT might be very attractive, since it provides adequate treatment plans and concomitant significantly lower request in terms of planning, calculation and beam-on time resources than TD-IMRT. Aim of the present study is to investigate TD-3DCRT in the context of AWBRT in terms of dosimetric outcomes of both target and organs at risk and beam-on time and to compare it to TD-IMRT planning and conventional 3DCRT field-in-field technique (FIF). Additionally we defined appropriate patient-class solutions to employ TD-3DCRT in AWBRT, generating the hypotesis that simple anatomic measures could properly drive patient allocation to an appropriate and cost-effective planning modality. Methods Patients selection, CT simulation and target delineation The study population comprised 10 left-sided and 7 right-sided breast cancer patients submitted to conservative surgery and AWBRT. Patients underwent 2.5 mm slice thickness CT acquisition in the supine position on a wing-board with both arms abducted alongside the head. Images were acquired from the lower aspect of the mandible to the base of the lungs, with radiopaque wires marking the clinically detectable breast borders. The whole-breast clinical target volume (CTV) encompassed the palpable residual mammary gland with superior and inferior border delimited within the extent of the radiopaque catheters. The subsequent planning target volume (PTV) was generated by adding a 5 mm margin around the CTV but confined to the interior of the patients outer contours reduced by 5 mm, also excluding heart and lung when needed. Organs at risks (OARs) contoured were both lungs, contralateral breast and heart, outlined up to the level of the pulmonary trunk superiorly, including the pericardium and excluding the major vessels. TD planning TD-IMRT and TD-3DCRT plans were generated with TomoTherapy Hi-Art version 4.0.4 TPS (Accuray Inc., Sunnyvale, CA). For each plan, the treatment field width, pitch (the TD pitch is defined as the distance of couch travel in centimeters per sinogram projection) and modulation factor need to be selected. Then, the dose distribution for each beamlet that passes through the target is calculated by a convolution/superposition algorithm [7]. Once the beamlet calculation step is completed, the optimization process begins and an iterative least-squares minimization method is used to optimize the objective function. During the final dose computation the optimized sinogram is converted to the delivery sinogram, taking into account for leaf fluence output factors and latency data. A fin (...truncated)