Author: Varsha Jain, Jun Kang, Paul Sulivan, Kate E. Verma, Yevgeniy Vinogradskiy 👨🔬
Affiliation: Thomas Jefferson University 🌍
Purpose:
Patients undergoing treatment for head and neck(H&N) cancers experience significant body contour changes throughout treatment. Body contour changes are due to tumor shrinkage, weight loss, and edema. These changes can impact the dose distribution to critical organs at risk(OARs). This study aims to develop a workflow to evaluate changes in the dose distribution using cone beam CT(CBCT) and establish a framework for when re-CT/re-planning is warranted.
Methods:
Six clinical H&N patients were analyzed using 2 methods to assess dose distribution changes. Method 1 involved 1) importing the CBCT into the planning system and fusing with the planning CT(pCT), 2) copying planning structures(pSt) to the CBCT structure set(cSt), 3) applying a site-specific HU density calibration curve to the CBCT, and 4) re-calculating the dose on the cSt using the same MU as the original plan. Method 2 involved: 1) deforming the body contour from the pSt to CBCT, 2) creating an adjusted structure set(aSt) on pCT, 3) recalculating the plan on aSt with the same MU. For comparison, the original plan was re-calculated on a new CT scan(nCT), which served as the ground truth. The maximum and mean doses were compared among the methods for the Planning Target Volume(PTV).
Results:
Among the six patients, four patients demonstrated tumor shrinkage while two patients developed edema . The average PTVhigh Dmax HN plan on pCT is 108.3%, CBCT is 114.5%, pCT with adjusted Body Contour(aSt) is 111.1%, nCT is 109.2% respectively. The average PTVhigh Dmean HN plan on pCT is 102.5, on CBCT is 103.5%, on pCT with aSt is 101.8%, on nCT is 100.5% respectively.
Conclusion:
Dose parameters calculated on adjusted body contour aSt are more equivalent to the calculations done on nCT compared to those on CBCT. Using aSt on pCT provides a promising way for H&N patient plan evaluation.