ESTRO 2024 - Abstract Book

S1028

Clinical - Gynaecology

ESTRO 2024

Median GTV and median PTV doses were not significantly different between the POP and VMAT plans (Table 1). Maximum point dose and CI were significantly higher in the POP plan compared to the VMAT plan. Reflecting this, doses to rectum, bowel and bladder were significantly higher at all dose levels tested in the POP plans (Figure 1). There was a negative correlation between the PTV volume and the CI in POP plans with a Pearson correlation coefficient of -0.515 (p=0.02). PTV dosimetric parameters were better with VMAT_NTO plans with higher mean PTV V95% and lower mean PTV V105% compared to the VMAT plans. Doses to rectum and bladder were significantly higher at all dose levels tested with VMAT_NTO plans. Median GTV and PTV doses were significantly higher in SBRT-like plan compared to the VMAT plan with maximum point dose reaching 33.2Gy compared to 31.4Gy in VMAT. Doses to rectum, bowel and bladder were significantly higher at all dose levels (apart from V15Gy of rectum).

Conclusion:

There are significant dosimetric benefits with VMAT compared to conventional fields, and although the doses typically used are not high, reduction in any normal tissue toxicity would be beneficial for frail patients. Moving towards the routine use of VMAT in palliative treatments would allow us to deliver higher doses of radiation in this setting whilst minimising toxicity. Dose escalation within the PTV can be achieved by normalising the plans to cover 95% of the PTV with the prescription dose (SBRT-like). VMAT is considered more labour intensive for a radiotherapy department as this requires clinicians to delineate the target volume and OARs. This study supports the use of VMAT_NTO as a good compromise with improved normal tissue sparing and improved CI without a need for OAR contouring. This would facilitate the clinical implementation of routine use of VMAT in practice.

Keywords: palliative radiotherapy, dose escalation, NTO

References:

1. Lewis TS, Kennedy JA, Price GJ, Mee T, Woolf DK, Bayman NA, et al. Palliative Lung Radiotherapy: Higher Dose Leads to Improved Survival? Clin Oncol [Internet]. 2020;32(10):674–84. Available from: https://doi.org/10.1016/j.clon.2020.05.003