Analysis of treatment parameters for conformal shaped field stereotactic irradiation: comparison with non-coplanar arcs

A dosimetric comparison of linac-based stereotactic fractionated radiotherapy techniques for pituitary adenoma and craniopharyngioma

Aim

To compare the dosimetric outcomes of linear accelerator-based stereotactic radiotherapy (SRT) techniques—static conformal field (SCF), static conformal arc (SCA) and dynamic conformal arc (DCA), for treating pituitary adenoma and craniopharyngioma.

Materials and methods

Computer image sets of 20 patients with pituitary adenoma or craniopharyngioma and treated with post-operative SRT were selected for this study. For each dataset, three SRT plans, with SCF, SCA and DCA techniques were generated using Brain LAB, iPlan RT V.4.5.3, TPS software. The conformity index (CI), homogeneity index (HI), quality of coverage of the target, dose–volume histograms for the target and organs at risk (OARs) and the time taken to deliver treatment was compared across three sets of plan.

Results

There were 12 patients with pituitary adenoma and eight with craniopharyngioma. The CI and HI were comparable across three techniques. The quality of coverage was superior in DCA technique. OARs were better spared in SCF and DCA techniques. Time taken to deliver treatment was least in SCF technique.

Conclusions

The linac-based SRT techniques SCF, SCA and DCA are efficient in delivering highly conformal and homogenous dose to the target in pituitary adenoma and craniopharyngioma. Among these three techniques, SCF and DCA had acceptable quality of coverage. The dose received by OARs was least in the SCF technique.

Does Intensity Modulation Improve Healthy Tissue Sparing in Stereotactic Radiosurgery of Complex Arteriovenous Malformations?

This planning study evaluates the potential of intensity modulated treatment fields and inverse planning techniques in stereotactic radiosurgery to reduce healthy tissue dose. Twenty patients previously treated with stereotactic radiosurgery for arteriovenous malformation (AVM) were replanned with each of 4 techniques: circular non-coplanar arcs, dynamic arcs, static conformal fields, and intensity modulated radiosurgery (IMRS). Patients were selected having a maximum AVM dimension at least 20 mm, or volume greater than 10 cm(3). Target volumes ranged from 2.12 cm(3) to 13.87 cm(3) with a median of 6.03 cm(3). Resulting dose distributions show a statistically significant improvement in target conformality between circular arcs and all other techniques (p </= 0.001), between conformal and both dynamic arcs and IMRS (p </= 0.03) and with no difference between dynamic arcs and IMRS. However, for AVMs of volume greater than 5.5 cm(3), IMRS gives better conformality than dynamic arcs (p = 0.04). IMRS showed consistently lower dose inhomogeneity compared to both dynamic arcs and conformal fields (p < 0.001). At low dose levels, the dynamic arc technique irradiates less healthy tissue than the other techniques (p </= 0.001). Both dynamic arcs and IMRS provide increased ability to conform to the AVM, with IMRS showing greater ability to control dose at the periphery.

Geometric parameter analysis to predetermine optimal radiosurgery technique for the treatment of arteriovenous malformation

PURPOSE

To develop a method of predicting the values of dose distribution parameters of different radiosurgery techniques for treatment of arteriovenous malformation (AVM) based on internal geometric parameters.

METHODS AND MATERIALS

For each of 18 previously treated AVM patients, four treatment plans were created: circular collimator arcs, dynamic conformal arcs, fixed conformal fields, and intensity-modulated radiosurgery. An algorithm was developed to characterize the target and critical structure shape complexity and the position of the critical structures with respect to the target. Multiple regression was employed to establish the correlation between the internal geometric parameters and the dose distribution for different treatment techniques. The results from the model were applied to predict the dosimetric outcomes of different radiosurgery techniques and select the optimal radiosurgery technique for a number of AVM patients.

RESULTS

Several internal geometric parameters showing statistically significant correlation (p < 0.05) with the treatment planning results for each technique were identified. The target volume and the average minimum distance between the target and the critical structures were the most effective predictors for normal tissue dose distribution. The structure overlap volume with the target and the mean distance between the target and the critical structure were the most effective predictors for critical structure dose distribution. The predicted values of dose distribution parameters of different radiosurgery techniques were in close agreement with the original data.

CONCLUSIONS

A statistical model has been described that successfully predicts the values of dose distribution parameters of different radiosurgery techniques and may be used to predetermine the optimal technique on a patient-to-patient basis.