Comparative Study of Spinal Cord Toxicity from Dose Per Fraction Delivered to Cervical Spinal Cord in Head-and-neck Cancers by Volumetric-modulated Arc Therapy with Simultaneous Integrated Boost versus Three-dimensional Conformal Radiotherapy in a Mu
Swati Verma, Manoj Kumar Gupta, Shailendra Handu, Shalinee RaoAim:
To assess and compare the radiation-induced effects on the spinal cord of rats following fractionated irradiation with doses of 1.36 Gy and 2.0 Gy per fraction.
Materials and Methods:
The risk of radiation-induced myelopathy and spinal cord tolerance represent the major dose-limiting factors during re-irradiation of head-and-neck cancers since spinal cord is exposed to maximum tolerance dose of 45 Gy in 1.8–2 Gy per fraction during first radiation treatment. However, modern radiotherapy techniques such as Volumetric-modulated Arc Therapy (VMAT) with simultaneous integrated boost (SIB) usually irradiate spinal cord with much less dose per fraction than 2 Gy per fraction of prescription dose. In this experimental study, the cervical spinal cord of male Wistar rats was irradiated to a total biologically effective dose of 120 Gy 2 using different dose-per-fraction, control group was irradiated with 2 Gy per fraction for a total dose of 60 Gy/30F in 6 weeks while experimental group was given 1.36 Gy per fraction for a total dose of 70.72 Gy/52F in 10.5 weeks. The motor function including motor co-ordination and balance, locomotor activity was observed at 1, 3, and 5 months after the completion of radiation and was compared with baseline values.
Results:
Motor co-ordination and balance were preserved until the 3
rd
month in both control and experimental groups, with no significant difference from baseline (0 ± 0). Gradual functional deterioration became evident after 3 months and a significant decline was observed at 5 months in both groups, with a greater reduction in the control group (72 ± 2.4) compared to the experimental group (105 ± 2.8) (
Conclusions:
This study demonstrates that fractionated irradiation of the spinal cord at 1.36 Gy per fraction, as commonly delivered during VMAT SIB, is less damaging in rats compared to the conventional 2 Gy per fraction used in three-dimensional conformal radiotherapy. Motor co-ordination and locomotor activity deterioration were more pronounced in the control group than in the experimental group. These findings suggest that smaller dose-per-fraction schedules may be well within the spinal cord tolerance, thereby potentially enabling safer re-irradiation scenarios.