Dosimetric effect of body contour changes for prostate and head and neck volumetric modulated arc therapy plans

Abstract

Body contour changes are commonly seen in prostate and head and neck (H&N) patients undergoing volumetric modulated arc therapy (VMAT) treatments, which may cause a discrepancy between the planned dose and the delivered dose. Dosimetrists, radiation oncologists or medical physicists sometimes are required to visually assess the dosimetric impact of body contour changes and make a judgment call on whether further re‐assessment of the plan is needed. However, an intuitive judgment cannot always be made in a timely manner due to the complexity of VMAT plans as well as the complicated forms of body contour changes. This study evaluated the dosimetric effect of body contour changes for prostate and H&N patients to help with clinical decision‐making. By analyzing the one‐dimensional spatial dose profiles from the original body and the body with different body contour deformations, rules of thumb for dose percentage change and isodose line shift due to body contour changes were ascertained. Moreover, based on dose distribution comparison using three‐dimensional gamma analysis, the response of the clinical prostate and H&N VMAT plans to body contour changes was assessed. Within center specific dose deviation tolerances, prostate patients who had less than 2 cm single side body contour change or less than 1 cm uniform body contour change were unlikely to need plan re‐assessment; H&N VMAT plans with less than 1 cm uniform body contour change or less than 1 cm shoulder superior–inferior positional change were also unlikely to trigger further evaluation. Dose percentage change and isodose line shift were considered independently from the problem of volume changes in this study, but clinically, both aspects must be considered.

The application of gradient dose segmented analysis of in‐vivo EPID images for patients undergoing VMAT in a resource‐constrained environment

“…Secondly, it was found that the effective separation change diameter exceeds 1 cm for patients where the GDSA µ exceeds 3%. Sun et al 20 found that uniform body changes less than 1 cm were unlikely to warrant further assessment due to changes in delivered dose. Similarly, Chen et al 21 found that the dose delivered to the PTV significantly increased by 2%-3% for a 2-5 mm change in body contour.…”

“…Secondly, it was found that the effective separation change diameter exceeds 1 cm for patients where the GDSA µ exceeds 3%. Sun et al 20 . found that uniform body changes less than 1 cm were unlikely to warrant further assessment due to changes in delivered dose.…”

Dosimetric comparison of library of plans and online MRI-guided radiotherapy of cervical cancer in the presence of intrafraction anatomical changes

“…This means that for these patients anatomical changes were taken into account to some extent. Sun et al studied the effect of body contour changes on the position of isodose lines for prostate VMAT [27]. They found that the 95% isodose line shifts by less than 1 mm in case of a body contour change of 1 cm in all directions but posterior, which shows that the effect of these kind of anatomical changes is quite small.…”

Novel methodology to quantify dehydration in head and neck cancer radiotherapy using DIXON MRI

“…8 External changes greater than 1 cm can shift the 95% and 93% isodose lines up to 4 mm. 10 This impact on delivered dose can result in unintended overdosage to nearby organs, associated with worsened toxicity, or underdosage to tumour sites, associated with decreased local control. 8 Anatomical changes are observed daily throughout RT via cone-beam computed tomography (CBCT) scans.…”

“…These changes can be due to a combination of weight loss, dehydration, tumour shrinkage, inflammation, muscle atrophy or radiation impacts on normal tissue 8 . External changes greater than 1 cm can shift the 95% and 93% isodose lines up to 4 mm 10 . This impact on delivered dose can result in unintended overdosage to nearby organs, associated with worsened toxicity, or underdosage to tumour sites, associated with decreased local control 8 …”