” قالوا سبحانك لا علم لنا إلا ما علمتنا إنك أنت العليم الحكيم“

1. بسم الله الرحمن الرحيم ” قالوا سبحانك لا علم لنا إلا ماعلمتنا إنك أنت العليم الحكيم“

2. Tomotherapy Mostafa EL- Haddad M.B.B.ch., Msc., MD., FRCR.(UK) Lecturer of Oncology Cairo University NEMROCK

3. OUTLINE • Principle of Tomotherapy. • CT scan similarity. • Tomotherapy idea. • Serial and Spiral. • Clinical Application and Overview.

4. Tomotherapy • Tomotherapy is intensity-modulated rotational radiotherapy utilizing a photon fan beam. • Radiation therapy device designed on a CT scanner-based platform. • Tomotherapy means slice therapy coined to describe IMRT using fan beam.

5. Computer TomographyCT

7. Prospective Gating

8. Retrospective Gating

9. Types of CT Scanner

10. Two Flavor

11. Medco, a company formed by neurosurgeon Mark Carol began developing the serial tomotherapy concept. • Their first presentation was in 1992 (Carol et al. 1993) and their first patient was treated with tomotherapy in 1994

12. BasicPrinciple • Rotation therapy is relatively insensitive to the energy of the beam (Johns and Cunningham 1983). • Before megavoltage beams were developed, rotation therapy was used to deliver x-radiation deep within the body. • The lower exit dose of orthovoltage photon beams approximately compensated for the high entrance dose. • of megavoltage beams, rotational delivery fell into disfavor because skin-sparing • could be achieved even for single fields of radiation.

13. IntensityModulation • The linac output can be varied. • The jaw opening can be changed. • The gantry speed can be altered. • The couch speed can be modified. • The leaf states can be changed.

14. TomotherapyInformation • The primary collimator and jaws are fabricated from an alloy containing 95% tungsten. • The thickness of the clamshell is about 22 cm, which reduces the leakage for IMRT with high numbers of monitor units to values typical for conventional delivery with conventional monitor units.

15. At the axis of rotation, the leaf thickness is 0.625 cm and the leaf height is 10 cm of 95% tungsten. The leaves have a tongue-and-groove design that results in an inter- leaf leakage less than 0.5% of its open intensity, which makes it the best-shielded radiotherapy unit used for IMRT.

16. can irradiate up to a 160 cm long field. • The Tomotherapy unit has instead a set of uniform thickness filters before and after the monitor chamber to provide buildup to the monitor chamber, to shield the monitor chamber from the jaws, and to remove extremely low-energy photons.

17. The rate of fall-off at a plane through the machine axis is about 2.5% to 3% per cm so that by the edge of the field (20 cm from the central axis) the output is 40% to 50% of its value at the center of the beam. The intensity variation leaf-to-leaf is about 2%,but this small discretization cannot be discerned dosimetrically.

18. The major advantage of a lack of a field-flattening filter is the beam quality. The thin set of filters produces far less head scatter than a conventional linac equipped with a field-flattening filter.

19. This also improves the imaging characteristics of the beam. The energy spectrum at the center of the field is not significantly harder than the spectrum at the edge of the field. This means that the beam is easier to characterize with model- based dose calculation systems

20. The helical tomotherapy has a conventional xenon ion chamber CT detec- tor system on board the system that acquires a transmission signal from the linac beam. The parameters of the linac radiofrequency system are adjusted for imaging from those for treatment so that the beam has a lower energy (about 3.5 MV),lower pulse repe- tition frequency,and smaller output.

21. Absence Of Metal Artifacts Metal artifacts arise in conventional CT scanners because the attenuation of the metal is non-linear due to the photoelectric effect. In helical CT, the beam is penetrating enough to eliminate metal artifacts arising from hip prostheses and dental filings.

22. This means that a verification CT could be a more reliable CT system for prostate patients with hip replacements and head and neck patients with cancer of the tongue.

23. For a typical 30-fraction treat- ment schedule, daily imaging delivers a total exposure dose to the imaged volume of less than 1 Gy. • For a typical 30-fraction treatment schedule, daily imaging delivers a total exposure dose to the imaged volume of less than 1 Gy.

24. Nonetheless, MV CT images are far superior to planar images (either kV or MV) for the verification of correct patient setup. Moreover, helical MV CT imaging is a slow CT imaging technique that allows for the encoding of target motion in the resulting MV CT data set (see fig. 10 , 11 ), and therefore the pretreatment verification of a motion envelope defined from four-dimensional CT.

26. Tungsten MLC 2cm in width

28. CRANE

31. Rock Mackie with the University of Wisconsin Tomotherapy Research Unit

32. Tomotherapy

35. Hi - ART • H: Highly • I: Integrated • A: Adaptive • R: Radiation • T: Therapy

37. Tomos ’Universal’ Signature

39. Tomotherapy And Adaptive Radiotherapy

40. instead of simply delivering the intended treatment plan, one would take an exit dose measurement during treatment and reconstruct the dose distribution that has been delivered. Using any of a number of metrics, one could then compare this actually delivered dose dis- tribution with the intended one.

41. the pretreatment dose guidance that is currently possible with tomotherapy. The overlaid isodose cloud can be used to visually verify that the intended targets lie within the high-dose region and that organs at risk lie outside the high-dose region.

42. Positioning Verification • However, placing a slippery polyethylene sheet with handholds between the couch top and mattress can easily effect lateral movements. The next generation of couches on helical tomotherapy units has lateral adjustments. Tomotherapy comes equipped with a set of moveable CT-simulator lasers so that the modified position of the patient can be confirmed.

43. The process is not accurate unless a CT of the patient at the time of treatment is used. Dose reconstruc- tion has been tested using the UW tomotherapy benchtop unit but not yet implemented on the UW clinical unit.

44. Deformable Registration And Autocontouring

45. Deformable registration algorithms typically use common features such as contours or points that are identified automatically in both images (Blake and Isard 1998). The intervening space between identifiable features is deformed according to finite element methods using established elastic property parameters (

46. Re-optimization is the modification of subsequent treatment fractions on the basis of the dose reconstruction and deformable registration of the regions of interest and the dose distribution (Wu 2002)

47. While it is not possible to remove the excess dose delivered to a sensitive structure, it may be possible to take this into account in re-optimization so that the dose delivered in the whole course of therapy might be the same or only marginally higher.

48. Re-optimization might also be done if it is decided that the target volume needs to change part way through the course of ther- apy. Re-optimization is a research topic and not yet being tested on the UW clinical unit