A dosimetric study of half jaw technique applied in the treatment planning for oropharyngeal cancer patients / 中华放射医学与防护杂志

ABSTRACT

Objective To investigate the potential dosimetric advantages of half jaw volumetric modulated arc therapy ( H-VMAT) applied to the Oropharyngeal Cancer, comparing with full jaw VMAT (F-VMAT) and intensity modulated radiotherapy ( IMRT ). Methods Planning CT images of 10 oropharyngeal cancer patients were retrospectively chosen and transferred to Eclipse treatment planning system v. 11. 0 (Varian Medical Systems, Pala Alto, USA), based on which H-VMAT, W-VMAT, and IMRT plans were created. Two full arcs (360°) were adopted for VMAT planning, and the 7 beams were equally distributed for IMRT planning. The optimization constraints remained the same for the three kinds of plans. The dosimetric parameters such as D2 , D98 , D50 , HI, and CI were evaluated for PGTV, PCTV1, PCTV2, PGTVln, and PCTVln. In addition, the maximum dose (Dmax) and D1 cc(minimum dose received by 1cc) of the brainstem and spinal cord were analyzed respectively. The mean dose ( Dmean ) to the parotids, oral cave, larynx, and cervical normal tissues were also reviewed. The monitor units ( MU) for all treatment plans were recorded. Results Comparisons of the three planning techniques showed that H-VAMT improved the HI and CI of the targets (except PCTV2) significantly (HI F =3. 959, 6. 764, 10. 581, 6. 770, 13. 040, P<0. 05;CIF=6. 594, 4. 138, 0. 842, 4. 031, 5. 388, P<0. 05);reduced Dmax(F=4. 509, 20. 331, P<0. 05) and D1 cc for brainstem and spinal cord (F=27. 432, 26. 314, P<0. 05) significantly;reduced Dmean(F=4. 279, 29. 498, 19. 295, P<0. 05) to the normal tissues of the mouth, throat and neck significantly. The V50 of the mouth and throat were slightly lower in IMRT plans (F=8. 140, P<0. 05). IMRT was slightly better than W-VMAT in sparing oral cavity and larynx, but the dose distribution was the worst. The H-VMAT plans showed the best dose distribution in the cervical normal tissues, especially for the lower and posterior parts, where IMRT plans displayed high dose curves. Conclusions H-VMAT is dosimetrically superior than W-VMAT and IMRT for oropharyngeal cancer, which could be considered for clinical applications.