Changes in Regional Ventilation During Treatment and Dosimetric Advantages of CT Ventilation Image Guided Radiation Therapy for Locally Advanced Lung Cancer

PURPOSE: Lung functional image guided radiation therapy (RT) that avoids irradiating highly functional regions has potential to reduce pulmonary toxicity following RT. Tumor regression during RT is common, leading to recovery of lung function. We hypothesized that computed tomography (CT) ventilation image-guided treatment planning reduces the functional lung dose compared to standard anatomic image-guided planning in 2 different scenarios with or without plan adaptation. METHODS AND MATERIALS: CT scans were acquired before RT and during RT at 2 time points (16-20 Gy and 30-34 Gy) for 14 patients with locally advanced lung cancer. Ventilation images were calculated by deformable image registration of four-dimensional CT image data sets and image analysis. We created 4 treatment plans at each time point for each patient: functional adapted, anatomic adapted, functional unadapted, and anatomic unadapted plans. Adaptation was performed at 2 time points. Deformable image registration was used for accumulating dose and calculating a composite of dose-weighted ventilation used to quantify the lung accumulated dose-function metrics. The functional plans were compared with the anatomic plans for each scenario separately to investigate the hypothesis at a significance level of 0.05. RESULTS: Tumor volume was significantly reduced by 20% after 16 to 20 Gy (P = .02) and by 32% after 30 to 34 Gy (P < .01) on average. In both scenarios, the lung accumulated dose-function metrics were significantly lower in the functional plans than in the anatomic plans without compromising target volume coverage and adherence to constraints to critical structures. For example, functional planning significantly reduced the functional mean lung dose by 5.0% (P < .01) compared to anatomic planning in the adapted scenario and by 3.6% (P = .03) in the unadapted scenario. CONCLUSIONS: This study demonstrated significant reductions in the accumulated dose to the functional lung with CT ventilation image-guided planning compared to anatomic image-guided planning for patients showing tumor regression and changes in regional ventilation during RT

Application of volumetric modulated arc therapy (VMAT) in a dual-vendor environment

Background and Purpose The purpose of this study was to assess plan quality and treatment time achievable with the new VMAT optimization tool implemented in the treatment planning system Oncentra MasterPlan® as compared to IMRT for Elekta SynergyS® linear accelerators. Materials and methods VMAT was implemented on a SynergyS® linear accelerator (Elekta Ltd., Crawley, UK) with Mosaiq® record and verify system (IMPAC Medical Systems, Sunnyvale, CA) and the treatment planning system Oncentra MasterPlan® (Nucletron BV, Veenendaal, the Netherlands). VMAT planning was conducted for three typical target types of prostate cancer, hypopharynx/larynx cancer and vertebral metastases, and compared to standard IMRT with respect to plan quality, number of monitor units (MU), and treatment time. Results For prostate cancer and vertebral metastases single arc VMAT led to similar plan quality as compared to IMRT. For treatment of the hypopharynx/larynx cancer, a second arc was necessary to achieve sufficient plan quality. Treatment time was reduced in all cases to 35% to 43% as compared to IMRT. Times required for optimization and dose calculation, however, increased by a factor of 5.0 to 6.8. Conclusion Similar or improved plan quality can be achieved with VMAT as compared to IMRT at reduced treatment times but increased calculation times

SU‐GG‐T‐155: Carbon Fiber Couch Effects on Skin Doses for Volumetric Arcs

Purpose: To evaluate carbon fiber couch (CFC) dosimetric effects on delivered skin dose as well as the dose and photon energy interplay for volumetric modulated arc (VMAT) treatments. Method and Materials: A CFC (BrainLab) was incorporated into a commercial TPS (Pinnacle) by auto‐contouring. A retrospective investigation on five lung and five prostate patient plans was performed. Targets and OARs, together with a skin contour of 0.3 cm thickness in contact with the CFC, were delineated in each plan. For each patient two VMAT plans were generated: a single arc with 6MV photons, and two or three arcs with 18MV photons for the posterior arc(s) and 6 MV photons for the anterior arc. Both plans were normalized such that 95% of the PTV was covered by the same dose, escalated to the maximum allowed by the OAR constraints. CFC effects were tallied by the highest dose to 1% of the skin volume. Results: If 18MV rather than 6MV photons are used in the arcs traversing the CFC the skin dose reduction ranges from 12% to more than 80%. In addition, the estimated skin doses range from ∼30% to more then ∼83% of the prescription doses for the mixed energy 6MV/18MV plans, implying even higher fraction of the prescription dose for the 6MV plans. Conclusions: The results indicate that mixed energy VMAT plans would result in a substantial skin sparing of more than ∼80% compared to VMAT plans with only 6MV arc(s). The increase in the treatment time due to the use of additional arcs is insignificant. The high skin doses in some cases (83% of the prescription) suggest that in hypofractionated SRS/SRT the CFC skin effect needs to be considered and promptly evaluated when arc delivery is used. Conflict of Interest: Research sponsored in part by Philips Radiation Oncology Systems

Cross-institutional knowledge-based planning (KBP) implementation and its performance comparison to Auto-Planning Engine (APE)

Item does not contain fulltextBACKGROUND AND PURPOSE: To investigate (1) whether a plan library established at one institution can be applied for another institution's knowledge-based planning (KBP); (2) the performance of cross-institutional KBP compared to Auto-Planning Engine (APE). MATERIAL AND METHODS: Radboud University Medical Center (RUMC) provided 35 oropharyngeal cancer patients (68Gy to PTV68 and 50.3Gy to PTV50.3) with clinically-delivered and comparative APE plans. The Johns Hopkins University (JHU) contributed a three-dose-level plan library consisting of 179 clinically-delivered plans. MedStar Georgetown University Hospital (MGUH) contributed a KBP approach employing overlap-volume histogram (OVH-KBP), where the JHU library was used for guiding RUMC patients' KBP. Since clinical protocols adopted at RUMC and JHU are different and both approaches require protocol-specific planning parameters as initial input, 10 randomly selected patients from RUMC were set aside for deriving them. The finalized parameters were applied to the remaining 25 patients for OVH-KBP and APE plan generation. A Wilcoxon rank-sum test was used for statistical comparison. RESULTS: PTV68 and PTV50.3's V95 in OVH-KBP and APE were similar (p>0.36). Cord's D0.1 cc in OVH-KBP was reduced by 5.1Gy (p=0.0001); doses to other organs were similar (p>0.2). CONCLUSION: APE and OVH-KBP's plan quality is comparable. Institutional-protocol differences can be addressed to allow cross-institutional library sharing

Automated IMRT planning in Pinnacle

Item does not contain fulltex