An integrated treatment delivery system for CSRS and CSRT and clinical applications

A Shiu, B Parker, J-S Ye, J Lii, A Shiu, B Parker, J-S Ye, J Lii

Abstract

An integrated treatment delivery system for conformal stereotactic radiosurgery (CSRS) and radiotherapy (CSRT) has been developed through a collaboration involving Siemens Medical Systems, Inc., Tyco/Radionics, Inc., and The University of Texas M. D. Anderson Cancer Center. The system consists of a 6-MV linear accelerator (LINAC) equipped with a Tyco/Radionics miniature multileaf collimator (mMLC). For the conventional SRS treatment, the circular collimator housing can be attached to the opening window of the mMLC. The treatment delivery system is integrated with a radiotherapy treatment planning system and a record-and-verify system. The purpose of this study is to report the characteristics, performance, benefits, and the clinical applications of this delivery system. The technical specifications of the LINAC and mMLC were tested, and all the specifications were met. The 80% to 20% penumbral width for each mMLC leaf is approximately 3 mm and is nearly independent of the off-axis positions of a leaf. The maximum interleaf leakage is 1.4% (1.1% on average) and the maximum intra-leaf leakage is 1.0% (0.9% on average). The leaf position precision is better than 0.5 mm for all the leaves. The integration of the SRS/SRT treatment planning system, mMLC, and LINAC has been evaluated successfully for transferring the patient treatment data file through radiotherapy treatment planning system to the patient information and treatment record-and-verify server and the mMLC controller. Subsequently, the auto-sequential treatment delivery for SRS, CSRS/CSRT, and the step-and-shoot intensity-modulated radiotherapy has also been tested successfully. The accuracy of dose delivery was evaluated for a 2-cm spherical target in a Radiological Physics Center SRS head phantom with GAFChromic films and TLD. Five non-coplanar arcs, using a 2-cm diameter circular collimator, were used for this simulation treatment. The accuracy to aim the center of the spherical target was within 0.5 mm and the deviation of dose delivery to the isocenter of the target was within 2% of the calculated dose. For the irregularly shaped tumor, a tissue-equivalent head phantom was used to evaluate the accuracy of dose delivery for using either geometric conformal treatment or IMRT. The accuracy of dose delivery to the isocenter was within 2% and 3% of the calculated dose, respectively. From October 26, 1999 to September 30, 2002, we treated over 400 SRS patients and 70 SRT patients. Four representative cases are presented to illustrate the capabilities of this dedicated unit in performing conventional SRS, CSRS, and CSRT. For all the cases, the geometric conformal-plan dose distributions showed a high degree of conformity to the target shape. The degree of conformity can be evaluated using the target-volume-ratio (TVR). Our preferred TVR values for highly conformed dose distributions range from 1.6 to 2.0. The patient setup reproducibility for the Gill-Thomas-Cosman (GTC) noninvasive head frame ranges from 0.5 to 1 mm, and the head and neck noninvasive frame is within 2 mm. The integrated treatment delivery system offers excellent conformation for complicated planning target volumes with the stereotactic setup approach, ensuring that dose delivery can be achieved within the specified accuracy. In addition, the treatment time is comparable with that of single isocenter multiple-arc treatments.

Figures

Figure 1. Illustration of a 2.0 –… — **Figure 1. Illustration of a 2.0–cm×12.6–cm field moved asymmetrically over its full range of travel.**

Figure 2. (Color) The circular collimator is… — **Figure 2. (Color) The circular collimator is attached to the opening window of the mMLC.**

Figure 3. (Color) Display of the entrance… — Figure 3. (Color) Display of the entrance and exit shaped fields. CTV (maroon) and the expansion of the CTV (shaded area: PTV), optic nerve (green) and optic chiasm (yellow‐green), and the expanded areas outside the critical structures.

Figure 4. (Color) The mMLC is a… — **Figure 4. (Color) The mMLC is a part of the PRIMART LINAC.**

Figure 5. The overall system diagram of… — Figure 5. The overall system diagram of the XPlan, mMLC, and PRIMART integration, the mMLC controller identifies the mMLC code and the patient ID from DMIP, which is the Digital Mevatron Interface Protocol using as the setup guidelines for the data to be transferred through serial communication lines. When the mMLC controller has received the mMLC code to set a mMLC field successfully, the mMLC controller sets a value in the block code interface (BCI) box inside the LINAC If the PRIMART control console reads the value and it corresponds to the anticipated value, it allows the treatment to proceed. The BCI box serves as the integration link between the mMLC and the LINAC.

Figure 6. (Color) Comparisons of measured (in… — **Figure 6. (Color) Comparisons of measured (in red) vs calculated axial dose distributions at plane 12 mm superior from isocenter and at isocenter plane from six non‐coplanar conformal fields.**

Figure 7. (Color) Comparisons of measured (in… — **Figure 7. (Color) Comparisons of measured (in red) vs calculated axial dose distributions at plane 12 mm superior from isocenter and at isocenter plane from six non‐coplanar IMRT beams.**

Figure 8. Display of 15 entering shaped… — **Figure 8. Display of 15 entering shaped fields in four couch positions: the target volume, brain stem, eyes, and optic nerves.**

Figure 9. (Color) Display of the 90%… — **Figure 9. (Color) Display of the 90% iso‐surface dose cloud (orange color) conformed to the projected target volume on anterior, left lateral, and vertical views, respectively.**

Figure 10. (Color) The front and back… — **Figure 10. (Color) The front and back view of a customized bite block attached to a GTC frame for a patient is edentulous.**

Figure 11. (Color) Display of isodose distributions… — **Figure 11. (Color) Display of isodose distributions on axial, sagittal, and coronal planes.**

Figure 12. A planning CT/MR fusion axial… — **Figure 12. A planning CT/MR fusion axial image shows the closeness of the lesion to the left optic nerve and the optic chiasm.**

Figure 13. A sample of MR image… — Figure 13. A sample of MR image obtained after 20 out of 35 treatments is fused with the planning CT image. The tumor is seen on the planning CT image, but is almost invisible on the MR image as shown by the red arrow.

Figure 14. (Color) Display of a Tyco/Radionics… — Figure 14. (Color) Display of a Tyco/Radionics noninvasive H&N frame (left) and an H&N localizer box, which is attached to an H&N baseboard (right). This localizer not only provides the spatial coordinates for the target with respect to the frame but also serves to reposition the patient in a specific location for multiple fractionated treatment.

Figure 15. (Color) Display of the integral… — Figure 15. (Color) Display of the integral dose volume histogram and the 39.6 Gy iso‐surface dose (orange), which is highly conformed to the projected target volume on the anterior, lateral, and vertical views, respectively.

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An integrated treatment delivery system for CSRS and CSRT and clinical applications

Abstract

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References

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