Year-end Sale % OFF 
Abstract
The number of linac monitor units (MU) from intensity modulated sequential tomotherapy (IMST) is substantially larger than the MU delivered in conventional radiation therapy, and the relation between MU and dose is obscure due to complicated variation of the beam intensities. The purpose of this work was to develop a practical method of verifying the MU and dose from IMST so that the MU of each arced beam could be double‐checked for accuracy. MU calculations for 41 arced beams from 14 IMST patients were performed using the variables of vane open fraction time, field size, target depth output factor, TMR, and derived intensity distribution. Discrepancy between planned and checked MU was quantified as 100(MUcal−MUplan)/MUplan percent. All 41 discrepancies were clustered between −5% to +5%, illustrated in a Gaussian‐shaped histogram centered at −1.0±3.5% standard deviation indicating the present MU calculations are in agreement with the planned expectations. To confirm the correctness of the present calculated MUs of the IMST plans, eight of the calculated IMST plans are performed dose verifications using their hybrid plans, which are created by transporting patient's IMST plan beams onto a spherical polystyrene Phantom for dose distribution within the Phantom. The dose was measured with a 0.07 cc ionization chamber inserted in the spherical Phantom during the hybrid plan irradiation. Average discrepancy between planned and measured doses was found to be 0.6±3.4% with single standard deviation uncertainty. The spread of the discrepancies of present calculated MUs relative to their planned ones are attributed to uncertainties of effective field size, effective planned dose corresponding to each arc, and inaccuracy of quantification of scattered dose from adjacent arced beams. Overall, the present calculation of MUs is consistent with what derived from treatment plans. Since the MUs are verified by actual dose measurements, therefore the present MU calculation technique is considered adequate for double‐checking planned IMST MUs.PACS number(s): 87.53.–j, 87.66.–a
Highlights
Intensity modulated sequential tomotherapyIMST, NOMOS Corp., Sewickley, PAis the technique using both field shaping and intensity variation to configure a dose distribution 3D conformal to the target to minimize the dose toxicity to the normal tissues adjacent to the target
To reduce the time required for IMST plan verification, some QA procedure may not have to proceed on every individual patient because of known slowly varying quality condition of the radiotherapy mode without pose any significant risk in a short period of time
In all 41 extrapatient IMST arcs calculations of MUs, we evaluate theDfrom the isodose distribution of the plan on an axial image at the z-coordinate specified by the IMST treatment sheet
Summary
Intensity modulated sequential tomotherapyIMST, NOMOS Corp., Sewickley, PAis the technique using both field shaping and intensity variation to configure a dose distribution 3D conformal to the target to minimize the dose toxicity to the normal tissues adjacent to the target. Tsai et al.,[11] Low et al.,[12] Teh et al.,[13] and Verellen et al.,[14] have performed integrally IMST plan verification, indirectly fulfilling some MUs second check, using a humanoid phantom prior to IMST treatment. This integrated plan verification procedure requires about four hours per patient. To maintain the high vigilant QA, MUs second check, being directly related to dose delivery and varying from patient to patient, is perhaps the non-compromising alternative QA needed
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
