An analysis of thoracic and abdominal tumour motion for stereotactic body radiotherapy patients

The objectives of this study were to estimate global uncertainty for patients with thoracic tumors treated in our center using the CyberKnife VSI after placement of fiducial markers and to compare our findings with the standard CTV to PTV margins used to date. Datasets for 16 patients (54 fractions) treated with the CyberKnife and the Synchrony Respiratory Tracking System were analyzed retrospectively based on CT planning, tracking information, and movement data generated and saved in the logs files by the system. For each patient, we analyzed all the main uncertainty sources and assigned a value. We also calculated an expanded global uncertainty to ensure a robust estimation of global uncertainty and to enable us to determine the position of 95% of the CTV points with a 95% confidence level during treatment. Based on our estimation of global uncertainty and compared with our general margin criterion (5 mm in all three directions: superior/inferior [SI], anterior/posterior [AP], and lateral [LAT]), 100% were adequately covered in the LAT direction, as were 94% and 94% in the SI and AP directions. We retrospectively analyzed the main sources of uncertainty in the CyberKnife process patient by patient. This individualized approach enabled us to estimate margins for patients with thoracic tumors treated in our unit and compare the results with our standard 5 mm margin.PACS number: 87.55‐x

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Retrospective evaluation of CTV to PTV margins using CyberKnife in patients with thoracic tumors

Floriano

García²,

Moreno³

et al. 2014

“…One of the main limitations in dose escalation is the additional margin necessary to account for inter‐ and intrafraction setup errors. Respiratory motion of thoracic structures can reach up to 1.5 cm, ( 37 ) and the interfraction setup error using skin marks or bony landmarks can reach up to 1 cm. ( 38 ) This leads to an increase in radiation therapy volume to account for these uncertainties, and limits dose to normal tissues.…”

Section: Technological Advances For Electromagnetic Trackingmentioning

confidence: 99%

Expanding the use of real‐time electromagnetic tracking in radiation oncology

Shah

Kupelian

Willoughby

et al. 2011

In the past 10 years, techniques to improve radiotherapy delivery, such as intensity‐modulated radiation therapy (IMRT), image‐guided radiation therapy (IGRT) for both inter‐ and intrafraction tumor localization, and hypofractionated delivery techniques such as stereotactic body radiation therapy (SBRT), have evolved tremendously. This review article focuses on only one part of that evolution, electromagnetic tracking in radiation therapy. Electromagnetic tracking is still a growing technology in radiation oncology and, as such, the clinical applications are limited, the expense is high, and the reimbursement is insufficient to cover these costs. At the same time, current experience with electromagnetic tracking applied to various clinical tumor sites indicates that the potential benefits of electromagnetic tracking could be significant for patients receiving radiation therapy. Daily use of these tracking systems is minimally invasive and delivers no additional ionizing radiation to the patient, and these systems can provide explicit tumor motion data. Although there are a number of technical and fiscal issues that need to be addressed, electromagnetic tracking systems are expected to play a continued role in improving the precision of radiation delivery.PACS number: 87.63.‐d

“…The AAPM Task Group 765 presented the following summation on review of the literature; “The amount a lung tumor moves during breathing varies widely…There are no general patterns of respiratory behavior that can be assumed for a particular patient prior to observation and treatment”. Many of the reviewed studies6, 7, 8, 9, 10, 11, 12, 13 had focused on quantifying the magnitude of such tumor motion, showing variations as great as 34 mm, 22 mm, and 12 mm in the cranio‐caudal, anterior‐posterior, and lateral directions respectively, in some patients 14. Traditional planning methods provide suitable coverage of mobile Gross Tumour Volumes (GTV) by creation of Internal Target Volumes (ITV) which encompasses the GTV through its respiratory motion.…”

Section: Introductionmentioning

confidence: 99%

Robust optimization of VMAT for lung cancer: Dosimetric implications of motion compensation techniques

Archibald-Heeren

Byrne

et al. 2017

In inverse planning of lung radiotherapy, techniques are required to ensure dose coverage of target disease in the presence of tumor motion as a result of respiration. A range of published techniques for mitigating motion effects were compared for dose stability across 5 breath cycles of ±2 cm. Techniques included planning target volume (PTV) expansions, internal target volumes with (OITV) and without tissue override (ITV), average dataset scans (ADS), and mini‐max robust optimization. Volumetric arc therapy plans were created on a thorax phantom and verified with chamber and film measurements. Dose stability was compared by DVH analysis in calculations across all geometries. The lung override technique resulted in a substantial lack of dose coverage (−10%) to the tumor in the presence of large motion. PTV, ITV and ADS techniques resulted in substantial (up to 25%) maximum dose increases where solid tissue travelled into low density optimized regions. The results highlight the need for care in optimization of highly heterogeneous where density variations may occur with motion. Robust optimization was shown to provide greater stability in both maximum (<3%) and minimum dose variations (<2%) over all other techniques.