Implementation of HybridArc treatment technique in preoperative radiotherapy of rectal cancer: dose patterns in target lesions and organs at risk as compared to helical Tomotherapy and RapidArc

ABSTRACT: Purpose. HybridArc is a novel treatment technique blending aperture-enhanced optimized arcs with discrete IMRT-elements, allowing selection of arcs with a set of static IMRT-beams. This study compared this new technique to helical tomotherapy, and RapidArc, in preoperative radiotherapy of rectal cancer. MATERIAL AND METHODS: Twelve rectal cancer patients treated consecutively with Tomotherapy Hi-Art II system were simulated with HybridArc and RapidArc. Treatment plans were designed to deliver a homogeneous dose of 46.0Gy to mesorectum and draining lymph nodes, with a simultaneous-integrated-boost to the primary tumor up to a total dose of 55.2Gy. Planning objectives were 95% of prescribed dose to 95% of PTVs, while minimizing the volume of small bowel receiving more than 15Gy (V15) and the mean bladder dose. Dose gradient towards simultaneous-integrated-boost (GI), calculated by dividing the volume receiving more then 52.4Gy (95% of PTV55.2Gy) to the volume of PTV55.2Gy, was kept below 1.5. Mean beam-on time and amount of MUs were also analyzed. RESULTS: PTVs were adequately covered by all plans. Significant advantage was found for Tomotherapy in sparing small bowel (V15=112.7cm3 SD73.4cm3) compared to RapidArc (133.4cm3 SD75.3cm3) and HybridArc (143.7cm3 SD74.4cm3) (p<0.01). The mean bladder dose was better with RapidArc (20.6Gy SD2.2Gy) compared to HybridArc (24.2Gy SD4.3Gy) and Tomotherapy (23.0Gy SD4.7Gy) (p<0.01). The mean beam-on time was significantly lower (p<0.01) for HybridArc (2.7min SD0.8) and RapidArc (2.5min SD0.5) compared to Tomotherapy (11.0min SD0.7). The total amount of MUs was significantly (p<0.01) lower for RapidArc (547 SD44) compared to HybridArc (949 SD153). CONCLUSIONS: HybridArc is a feasible solution for preoperative RT with a simultaneous-integrated-boost in rectal cancer patients. It achieved similar PTV coverage with significant lower beam-on time, but less efficient in sparing small bowel and bladder compared to Tomotherapy and RapidArc. The added value of HybridArc is that the treatment modality can be implemented on every LINAC equipped with Dynamic-Conform-Arc and IMRT treatment techniques, while maintaining the same QA-schemes.     

Gating and tracking, 4D in thoracic tumours

The limited ability to control for a tumour's location compromises the accuracy with which radiation can be delivered to tumour-bearing tissue. The resultant requirement for larger treatment volumes to accommodate target uncertainty restricts the radiation dose because more surrounding normal tissue is exposed. With image-guided radiation therapy (IGRT), these volumes can be optimized and tumouricidal doses may be delivered, achieving maximum tumour control with minimal complications. Moreover, with the ability of high precision dose delivery and real-time knowledge of the target volume location, IGRT has initiated the exploration of new indications in radiotherapy such as hypofractionated radiotherapy (or stereotactic body radiotherapy), deliberate inhomogeneous dose distributions coping with tumour heterogeneity (dose painting by numbers and biologically conformal radiation therapy), and adaptive radiotherapy. In short: “individualized radiotherapy”. Tumour motion management, especially for thoracic tumours, is a particular problem in this context both for the delineation of tumours and organs at risk as well as during the actual treatment delivery. The latter will be covered in this paper with some examples based on the experience of the UZ Brussel. With the introduction of the NOVALIS system (BrainLAB, Feldkirchen, Germany) in 2000 and consecutive prototypes of the ExacTrac IGRT system, gradually a hypofractionation treatment protocol was introduced for the treatment of lung tumours and liver metastases evolving from motion-encompassing techniques towards respiratory-gated radiation therapy with audio-visual feedback and most recently dynamic tracking using the VERO system (BrainLAB, Feldkirchen, Germany). This evolution will be used to illustrate the recent developments in this particular field of research.     

A complementary dual-modality verification for tumor tracking on a gimbaled linac system

Background and purpose

For dynamic tracking of moving tumors, robust intra-fraction verification was required, to assure that tumor motion was properly managed during the course of radiotherapy. A dual-modality verification system, consisting of an on-board orthogonal kV and planar MV imaging device, was validated and applied retrospectively to patient data.

Methods and materials

Real-time tumor tracking (RTTT) was managed by applying PAN and TILT angular corrections to the therapeutic beam using a gimbaled linac. In this study, orthogonal X-ray imaging and MV EPID fluoroscopy was acquired simultaneously. The tracking beam position was derived from respectively real-time gimbals log files and the detected field outline on EPID. For both imaging modalities, the moving target was localized by detection of an implanted fiducial. The dual-modality tracking verification was validated against a high-precision optical camera in phantom experiments and applied to clinical tracking data from a liver and two lung cancer patients.

Results

Both verification modalities showed a high accuracy (<0.3 mm) during validation on phantom. Marker detection on EPID was influenced by low image contrast. For the clinical cases, gimbaled tracking showed a 90th percentile error (E90) of 3.45 (liver), 2.44 (lung A) and 3.40 mm (lung B) based on EPID fluoroscopy and good agreement with XR-log file data by an E90 of 3.13, 1.92 and 3.33 mm, respectively, during beam on.

Conclusion

Dual-modality verification was successfully implemented, offering the possibility of detailed reporting on RTTT performance.     

The Potential of Helical Tomotherapy in the Treatment of Head and Neck Cancer

A decade after its first introduction into the clinic, little is known about the clinical impact of helical tomotherapy (HT) on head and neck cancer (HNC) treatment. Therefore, we analyzed the basics of this technique and reviewed the literature regarding HT's potential benefit in HNC. The past two decades have been characterized by a huge technological evolution in photon beam radiotherapy (RT). In HNC, static beam intensity‐modulated radiotherapy (IMRT) has shown superiority over three‐dimensional conformal RT in terms of xerostomia and is considered the standard of care. However, the next‐generation IMRT, the rotational IMRT, has been introduced into the clinic without any evidence of superiority over static beam IMRT other than being substantially faster. Of these rotational techniques, HT is the first system especially developed for IMRT in combination with image‐guided RT. HT is particularly promising for the treatment of HNC because its sharp dose gradients maximally spare the many radiosensitive organs at risk nearby. In addition, HT's integrated computed tomography scan assures a very precise dose administration and allows for some adaptive RT. Because HT is specifically developed for IMRT in combination with (integrated) image‐guidance, it allows for precise dose distribution (“dose painting”), patient setup, and dose delivery. As such, it is an excellent tool for difficult HNC irradiation. The literature on the clinical results of HT in HNC all show excellent short‐term (≤2 years) results with acceptable toxicity profiles. However, properly designed trials are still warranted to further substantiate these results.     

Paramagnetic self‐assembled nanoparticles as supramolecular MRI contrast agents

Nanometer‐sized materials offer a wide range of applications in biomedical technologies, particularly imaging and diagnostics. Current scaffolds in the nanometer range predominantly make use of inorganic particles, organic polymers or natural peptide‐based macromolecules. In contrast we hereby report a supramolecular approach for the preparation of self‐assembled dendritic‐like nanoparticles for applications as MRI contrast agents. This strategy combines the benefits from low molecular weight imaging agents with the ones of high molecular weight. Their in vitro properties are confirmed by in vivo measurements: post injection of well‐defined and meta‐stable nanoparticles allows for high‐resolution blood‐pool imaging, even at very low Gd(III) doses. These dynamic and modular imaging agents are an important addition to the young field of supramolecular medicine using well‐defined nanometer‐sized assemblies. Copyright © 2012 John Wiley & Sons, Ltd.