Comparison of dosimetric variation between prostate IMRT and VMAT due to patient's weight loss: Patient and phantom study

James C L Chow; Runqing Jiang

doi:10.1016/j.rpor.2013.05.003

Comparison of dosimetric variation between prostate IMRT and VMAT due to patient's weight loss: Patient and phantom study

Rep Pract Oncol Radiother. 2013 Jun 25;18(5):272-8. doi: 10.1016/j.rpor.2013.05.003. eCollection 2013.

Authors

James C L Chow¹, Runqing Jiang²

Affiliations

¹ Radiation Medicine Program, Princess Margaret Cancer Center, University Health Network, Toronto, ON, M5G 2M9, Canada ; Department of Radiation Oncology, University of Toronto, Toronto, ON, M5G 2M9, Canada.
² Medical Physics Department, Grand River Regional Cancer Center, Kitchener, ON, N2G 1G3, Canada ; Department of Physics, University of Waterloo, Waterloo, ON, N2L 3G1, Canada.

Abstract

Aim: This study compared the dosimetric impact between prostate IMRT and VMAT due to patient's weight loss.

Background: Dosimetric variation due to change of patient's body contour is difficult to predict in prostate IMRT and VMAT, since a large number of small and irregular segmental fields is used in the delivery.

Materials and methods: Five patients with prostate volumes ranging from 32.0 to 86.5 cm(3) and a heterogeneous pelvis phantom were used for prostate IMRT and VMAT plans using the same set of dose-volume constraints. Doses in IMRT and VMAT plans were recalculated with the patient's and phantom's body contour reduced by 0.5-2 cm to mimic size reduction. Dose coverage/criteria of the PTV and CTV and critical organs (rectum, bladder and femoral heads) were compared between IMRT and VMAT.

Results: In IMRT plans, increases of the D99% for the PTV and CTV were equal to 4.0 ± 0.1% per cm of reduced depth, which were higher than those in VMAT plans (2.7 ± 0.24% per cm). Moreover, increases of the D30% of the rectum and bladder per reduced depth in IMRT plans (4.0 ± 0.2% per cm and 3.5 ± 0.5% per cm) were higher than those of VMAT (2.2 ± 0.2% per cm and 2.0 ± 0.6% per cm). This was also true for the increase of the D5% for the right femoral head in a patient or phantom with size reduction due to weight loss.

Conclusions: VMAT would be preferred to IMRT in prostate radiotherapy, when a patient has potential to suffer from weight loss during the treatment.

Keywords: Patient's weight loss; Prostate IMRT; Prostate VMAT; Treatment planning evaluation and dose–volume points.