IEC (International Electronic Commissioning) is the world’s leading organization that prepares and publishes International Standards for all electrical, electronic and related technologies.  Wherever you find electricity and electronics, you find the IEC supporting safety and performance, the environment, electrical energy efficiency and renewable energies.  The IEC also manages conformity assessment systems that certify that equipment, systems or components conform to its International Standards.

Out of the four components (the couch, jaws, collimator and gantry), we cover the couch and the gantry in this post and will discuss the jaws and the collimator in next post.

The answer is 4.5 cm.

The answer is 998.5 cm.

The answer is 8.5 cm.

The answer is 994.5 cm.

The answer is 79 cm.

The answer is 55 cm.

The answer is 25 degrees.

The answer is 105 degrees.

Couch: Vertical Movement
The couch vertical is at 8.5 cm. You need to move the table 4 cm upward toward the ceiling. At what do you set the new vertical position of the table from outside the treatment room: 12.5 cm or 4.5 cm?
Click on this link for the answer. Depending on your screen resolution, you may have to scroll up to see the answer window.
The couch vertical is at 2.5 cm. You need to move the table 4 cm upward toward the ceiling. At what do you set the vertical position of the table from outside the treatment room: 6.5, -1.5 or 998.5 cm?
Click on this link for the answer.
Tip: Table vertical position is at 0 degrees at iso-center. Moving the couch toward the floor down from iso-center, the number increases on this coordinate axes. If you move the couch toward the ceiling up from iso-center, the number decreases from 1000.

Couch: Lateral Movement
The couch lateral position is at 4.5 cm. You need to move the table 4 cm toward the right of the gantry if you face the gantry. What do you set the new lateral position of the table from outside the treatment room: 8.5 cm or -8.5 cm?
Click on this link for the answer.
The couch lateral position is at 2.5 cm. You need to move the table 8 cm toward left of the gantry if you face the gantry. What do you set the new lateral position of the table from outside the treatment room: -5.5 cm or 994.5 cm?
Click on this link for the answer.
Tip: Table lateral position is at 0 degrees at iso-center. When moving the couch toward the right (facing the gantry) from iso-center, the number increases on this coordinate axes. If you move the couch toward left (facing the gantry) from iso-center, the number decreases from 1000.

Couch: Longitudinal Movement
The couch longitudinal is at 55 cm. You need to move the couch 24 cm toward the gantry. What do you set the new longitudinal position of the table from outside the treatment room: 79 cm or 31 cm?
Click on this link for the answer.
The couch longitudinal is at 105 cm. You need to move the couch 50 cm away from the gantry. What do you set the new longitudinal position of the table from outside the treatment room: -55 cm or 55 cm?
Click on this link for the answer.
Tip: Table longitudinal Position increases if the couch moves towards the gantry and decreases if the couch moves away from the gantry.

Gantry
The gantry is at 115 degrees. You need to move gantry 90 CCW. What do you set the position of the gantry from outside the treatment room: -25, 25, 205, or 335 degrees.
Click on this link for the answer.
The gantry is at 15 degrees. You need to move gantry 90 CW. What do you set the position of the gantry from outside the treatment room: -75, 105, or 255 degrees.
Click on this link for the answer.
Tip: The gantry on the Varian IEC 601-2-1 scale is at 0 degrees when the gantry is up at vertical position. The degree increases as gantry rotates CW. It goes to 90 degrees when the gantry is to the right (facing the gantry), to 180 degree when gantry is down at vertical position, to 270 degree when gantry is to the left (facing the gantry) and increases as it rotates CW to 359.9 and then 0 degree up at vertical position. Reversely, the angle decreases as gantry rotates CCW.

References:

Streak artifacts in CT images are generated in conventional CT when implanted objects of high atomic number exist in the patient. The artifact and image degradation associated with the kilovoltage (kV) CT imaging in the presence of high atomic number material greatly hinders the ability to delineate tumors and certain organs, particularly in the treatment planning of a prostate patient with hip prostheses. Such a situation, therefore, precludes precise dose calculation. There are several techniques reported that, if used, can minimize such artifacts, thereby enhancing image visualization for the delineation of tumor and other organs.

1- Charmley et al. (1) suggested that the use of CT-MR image registration to define target volumes in pelvic radiotherapy in the presence of bilateral hip replacements could facilitate target definition of prostate patient with hip replacements. However, a number of factors were found to affect image quality and/or the accuracy of target definition. The standard MR couch, different from a CT or linac treatment couch, might result in different patient positions, and the presence of the metallic implants may create significant distortion.

2- Yazdia M. (2) suggested an adaptive approach to metal artifact reduction in helical computed tomography for radiation therapy planning. At that time, they may require manual image post-processing and most CT scanners available in radiation oncology department are not equipped with these features.

3- The artifact image and degradation associated with the kilovoltage (kV) CT imaging in the presence of high atomic number material is greatly reduced with Megavoltage Cone Beam Computed tomography (MV-CBCT). MV-CBCT has been used in image-guided radiotherapy (IGRT) to correct patient setup immediately before treatment. Hansen et al (3) used this technique to treat paraspinous tumors in the presence of orthopedic hardware. It allows rapid acquisition of 3D images that can be registered with the planning CT with millimeter precision and enhance image visualization by exploiting the predominantly Compton scattering of high-energy photons delivered in the MV-CBCT system. Aubin et al. (4) of the Department of Radiation Oncology at UCSF did a study with the support of Siemens Oncology Care systems on the use of Megavoltage Cone Beam CT to complement CT for target definition in pelvic radiotherapy in the presence of hip replacement. They found the MV-CBCT image could be used to clearly visualize the hip prostheses and provide sufficient soft-tissue contrast to help delineate the prostate, bladder and rectum. The artifacts on the kV CT obscure the border between the prostate and anterior wall of the rectum and the interface between the prostate base and the bladder neck. However, the MV-CBCT images were particularly useful to help delineate these structures as well as the lateral extension of the prostate in the axial plane, the seminal vesicles and the lymph nodes. Also, normal anatomy such as pelvic bones, penile bulb, bladder, femoral heads, rectum and small bowel can be delineated with higher accuracy as well. They evaluate this technique for seven patients. For each patient, the MV-CBCT images were imported into the treatment planning system and registered with the original CT using body anatomy contoured on each image set. The target volumes and organs at risk for prostate treatment were contoured using both the CT and the MV-CBCT for single hip replacement, and using only the MV-CBCT for bi-lateral hip prostheses. For the full article, click on: http://bjr.birjournals.org/cgi/reprint/79/947/918

The following two figures taken from Aubin M. at el (4) show the difference between conventional CT and MV-CBCT images:

1. Chamley N. et al. The use of CT-MR image registration to define target volumes in pelvic radiotherapy in the presence of bilateral hip replacements. BJR 2005; 78:634-636.
2. Yazdia M. et al. An adaptive approach to metal artifact reduction in helical computed tomography for radiation therapy planning: experimental and clinical studies. Int. J. Radiation Oncol Biol Physics 2005; 62(4): 1224-1231.
3. Hansen, E.K. et al. Image guided radiotherapy using Megavoltage Cone-Beam Computer Tomography for treatment of paraspinous tumors in the presence of orthopedic hardware. Int. J. Radiation Oncol Biol Physics 2006; 66(2): 323-326.
4. Aubin M. at el. Use of Megavoltage Cone-Beam CT to complement CT for target definition in pelvic radiotherapy in the presence of hip replacement. Short Communication: British Journal of Radiology 2006.

1- Therapeutic ratio which is defined as Tumor Control/Complication increases by fractionating radiotherapy. Fractionation increases the effectiveness of dose to the tumor and reduces the late effect in normal tissue.

2- There is evidence that dose escalation in prostate radiation therapy improved prostate tumor control. Therefore, these days the prostate is treated with IMRT at a much higher dose than before.

3- In addition to dose escalation, there is evidence that hypofractionation may also increase the therapeutic ratio by increasing better tumor control, as in SBRT using Cyberknife (based on radiobiological outcomes of prostate treatment from HDR and LDR).

4- However, high doses of radiation used either in the case of IMRT or SBRT is limited by the dose to normal tissue and sensitive proximity organs to the prostate (such as bladder and rectum), therefore, the dose delivery should be controlled by IGRT (in case of IMRT) or real-time correction (in case of SBRT).

• In IMRT delivery, the target is localized everyday using either fidutial markers and cone beam CT or trans-abdominal ultrasound imaging.
• In SBRT, however, the system corrects, in real-time, for organ position and targets motion during dose delivery. So, it does control dose to proximity organs and delivers accurate target dose in real time.

5- King at el. examines the rationale and technical feasibility of Cyberknife radiotherapy for localized prostate cancer. Conformal isodose curves and dose volume histograms (DVH) are used to compare with an optimized IMRT plan. They correlated and adjusted the dose in SBRT to compare it with IMRT at 74 Gy. They found:

• Both plans are very conformal, and the 74 Gy isodose provides complete coverage of the target and minimal overlap with the rectum.
• The bladder and rectum DVHs show significantly improved sparing with the Cyberknife as compared to the IMRT plan.
• The GTV coverage is similar for both IMRT and Cyberknife, although one can see that the Cyberknife would deliver a slightly higher mean dose to the prostate.
• Considering the improved normal tissue sparing with the Cyberknife compared with IMRT, the Cyberknife could allow further dose-escalation while keeping normal tissue under current tolerances.

6- Fractioned radiotherapy is based on the shape of the dose-response relationship for early and late-responding tissue and the fact that the α/β ratio for most tumors and normal tissue are quite different (normally 10 Gy for tumors and 3 Gy for late-effects). Therefore, the tumor BED (biological effective dose) is maximized while keeping the late-effects at tolerance doses when smaller dose per fraction is used. If normal tissue late-effects and tumors have the same α/β ratio then this rationale for small fractions disappears.  For further information on BED and fractionation, go to Chapter 13 of “Radiobiologists for Radiologists” by Eric Hall.

7- Cyberknife is more convenient for patients than IMRT since the number of fractions is much lower than IMRT.

8- Cyberknife controls the target motion in real time rather than for each treatment as in IMRT.

9- If an error occurs for a whole fraction, it contributes to a much higher error in Cyberknife than in IMRT, since the fraction size in Cyberknife is much higher than in IMRT.

10- There are already more outcomes and evidence for dose-escalation in IMRT than for hypofractionation in Cyberknife (since SBRT is a relatively new technique compared to IMRT).

11- The cost of SBRT versus IMRT for prostate cancer treatment needs to be evaluated as well.

References that I used in advising my friend in his decision are as follows (I also suggest these references to anyone looking to learn more about IMRT, SBRT and Cyberknife):

IMRT – IGRT – SBRT, John Meyer. “Prostate Cancer Therapy with Stereotactic Body Radiation Therapy,” Todd Pawlicki, Cristian Cotrutz, and Christopher King. Frontiers Of Radiation Therapy and Oncology, Vol 40, pages 395-406.

Christopher R. King, et al. CyberKnife Radiotherapy For Localized Prostate Cancer: Rationale And Technical Feasibility. Technology in Cancer Research and Technology, Volume 2, Number 1, February (2003). Pages 25-29. http://www.tcrt.org/

Radiobiology for the Radiologists, Eric Hall. Chapter 13, pages 211-229.

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