Physics and high-technology advances in radiotherapy: Are they still worth it?

Geometry of volumes in radiotherapy planning. A new method for a quantitative assessment

Aims and background

The purpose of the study was to develop a general method able to quantify the mutual disposition in the 3D space of critical organs with respect to the target when these structures are designed for a radiotherapy treatment plan. To that end, we introduce the “expansion intersection histogram”, a function defined as the intersection between an organ at risk and the target volume, while the target is expanded in 3D.

Methods and study design

A software was developed to calculate the expansion intersection histogram of anatomical structures exported in a DICOM format from a commercial treatment planning system. A virtual phantom with spherical and cylindrical objects arranged in different dispositions in the 3D space was created for testing the software under known conditions.

Results and conclusions

Expansion intersection histogram computation was tested against reference data derived analytically for spherical volumes, with a resulting maximum error of 0.5%. Specific geometric features derived from the expansion intersection histogram, such as the distance between a selected target and each different ideal volume included in the virtual phantom, well matched the corresponding theoretical expected values. The expansion intersection histogram was evaluated also for the anatomical structures of a real patient. Data show this method as a tool to effectively take into account the mutual disposition of each critical organ with respect to the target, summarized in characteristics of distance, shape and orientation. The expansion intersection histogram method integrates and extends other preexisting modalities for evaluating the geometrical relationships among radiotherapy volumes and could be used to improve planning optimization.

A cost-outcome analysis of Image-Guided Patient Repositioning in the radiation treatment of cancer of the prostate

BACKGROUND AND PURPOSE

With Image-Guided Radiation Therapy (IGRT) rapidly gaining acceptance in the clinic it is timely to commence an assessment of its potential outcome benefit versus costs.

MATERIALS AND METHODS

Using Activity-Based Costing we have calculated the incremental cost of adding Image-Guided Patient Repositioning (IGPR), a significant component of IGRT, to both Intensity-Modulated Radiation Therapy (IMRT) and Three-Dimensional Conformal Radiation Therapy (3DCRT) for prostate cancer. The dosimetric outcome benefit resulting from the implementation of IGPR is estimated from a publication describing the improvement in set-up accuracy using each of four correction protocols. In our study outcome is quantified using a metric based on the Equivalent Uniform Dose. Our discussion is limited to image-guided corrective translations of the patient and does not specifically address margin reduction, rotations, organ deformation or major equipment failure modes, all of which are significant additional justifications for implementing an IGRT program.

RESULTS

Image guidance used solely for translational patient repositioning for prostate cancer adds costs with relatively little improvement in dosimetric quality. Full exploitation of the potential of IGRT, particularly through margin reduction, can be expected to result in a reduction in the cost-outcome ratios reported here.

CONCLUSIONS

IMRT benefits more than 3DCRT from IGPR with the Weekly Shrinking Action Level approach yielding the lowest cost-outcome ratio.

Radiotherapy for lung cancer: clinical impact of recent technical advances

Radiation oncology plays an important role in the curative treatment of patients with lung cancer. New technological developments have enabled delivery of higher radiation doses while better sparing surrounding normal tissues, thereby increasing the likelihood of local control without increased toxicity. Multi-modality imaging enables better target definition, improved planning software allows for correct calculation of delivered doses, and tools to verify accurate treatment delivery are now available. A good example of the results of applying these developments is the high local control rates achieved in stage I NSCLC with stereotactic radiotherapy (SRT). These advances are rapidly becoming available outside academic institutions, and pulmonologists, surgeons and medical oncologists need to understand and critically assess the potential impact of such developments in the routine care of their patients. Aspects of cost-effectiveness of technical innovations, as well as the level of evidence required before widespread clinical implementation, will be addressed.