Abstract
We aimed to compare prototype treatment plans for a new biology-guided radiotherapy
(BgRT) machine in its intensity-modulated radiation therapy (IMRT) mode with those
using existing IMRT delivery techniques in treatment of nasopharyngeal carcinoma (NPC).
We retrospectively selected ten previous NPC patients treated in 33 fractions according
to the NRG-HN001 treatment protocol. Three treatment plans were generated for each
patient: a helical tomotherapy (HT) plan with a 2.5-cm jaw, a volumetric modulated
arc therapy (VMAT) plan using 2 to 4 6-MV arc fields, and a prototype IMRT plan for
a new BgRT system which uses a 6-MV photon beam on a ring gantry that rotates at 60
rotations per minute with a couch that moves in small incremental steps. Treatment
plans were compared using dosimetric parameters to planning target volumes (PTVs)
and organs at risk (OARs) as specified by the NRG-HN001 protocol. Plans for the three
modalities had comparable dose coverage, mean dose, and dose heterogeneity to the
primary PTV, while the prototype IMRT plans had greater dose heterogeneity to the
non-primary PTVs, with the average homogeneity index ranging from 1.28 to 1.50 in
the prototype plans. Six of all the 7 OAR mean dose parameters were lower with statistical
significance in the prototype plans compared to the HT and VMAT plans with the other
mean dose parameter being comparable, and all the 18 OAR maximum dose parameters were
comparable or lower with statistical significance in the prototype plans. The average
left and right parotid mean doses in the prototype plans were 10.5 Gy and 10.4 Gy
lower than those in the HT plans, respectively, and were 5.1 Gy and 5.2 Gy lower than
those in the VMAT plans, respectively. Compared to that with the HT and VMAT plans,
the treatment time was longer with statistical significance with the prototype IMRT
plans. Based on dosimetric comparison of ten NPC cases, the prototype IMRT plans achieved
comparable or better critical organ sparing compared to the HT and VMAT plans for
definitive NPC radiotherapy. However, there was higher dose heterogeneity to non-primary
targets and longer estimated treatment time with the prototype plans.
Keywords
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Article info
Publication history
Published online: November 30, 2020
Accepted:
November 7,
2020
Received in revised form:
October 8,
2020
Received:
July 7,
2020
Identification
Copyright
© 2020 American Association of Medical Dosimetrists. Published by Elsevier Inc. All rights reserved.
