A novel external/internal tumor tracking approach to compensate for respiratory motion baseline drifts.

Real-time respiratory tumor tracking as implemented in a robotic treatment unit is based on continuous optical measurement of the position of external markers and a correlation model between them and internal target positions, which are established with X-ray imaging of the tumor, or fiducials placed in or around the tumor. Correlation models are created with fifteen simultaneously measured external/internal marker position pairs divided over the respiratory cycle. Every 45-150 s, the correlation model is updated by replacing the three first acquired data pairs with three new pairs.

Safely achieving single prolonged breath-holds of > 5 minutes for radiotherapy in the prone, front crawl position.

Objective: Breast cancer radiotherapy is increasingly delivered supine with multiple, short breath-holds. There may be heart and lung sparing advantages for locoregional breast cancer of both prone treatment and in a single breath-hold. We test here whether single prolonged breath-holds are possible in the prone, front crawl position.

Small field dosimetry correction factors for circular and MLC shaped fields with the CyberKnife M6 System: evaluation of the PTW 60023 microSilicon detector.

The PTW 60023 microSilicon is a new unshielded diode detector for small-field photon dosimetry. It provides improved water equivalence and a slightly larger sensitive region diameter in comparison to previous diode detectors in this range. In this study we evaluated the correction factors relevant to commissioning a CyberKnife System with this detector by Monte Carlo simulation and verified this data by multi-detector measurement comparison.

The feasibility, safety and optimization of multiple prolonged breath-holds for radiotherapy.

Background & Purpose: Multiple, short breath-holds are now used in single radiotherapy treatment sessions. Here we investigated the feasibility and safety of multiple prolonged breath-holds in a single session. We measured how long is a second breath-hold if we prematurely terminate a single, prolonged breath-hold of >5 min either by using a single breath of oxygen (O), or by reintroducing preoxygenation and hypocapnia.

Benchmarking Monte-Carlo dose calculation for MLC CyberKnife treatments.

Background: Vendor-independent Monte Carlo (MC) dose calculation (IDC) for patient-specific quality assurance of multi-leaf collimator (MLC) based CyberKnife treatments is used to benchmark and validate the commercial MC dose calculation engine for MLC based treatments built into the CyberKnife treatment planning system (Precision MC).

Methods: The benchmark included dose profiles in water in 15 mm depth and depth dose curves of rectangular MLC shaped fields ranging from 7.6 mm × 7.