Clinical evaluation of heart dose changes during proton therapy of esophageal cancer
Richard Canters,
The Netherlands
OC-0102
Abstract
Clinical evaluation of heart dose changes during proton therapy of esophageal cancer
Authors: Richard Canters1, Kim Van der Klugt1, Vicki Taasti1, Jeroen Buijsen1, Fleur Vereijken1, Tina Verstappen1, Karo Limpens1, Sanne Hurkmans1, Maud Van den Bosch1, Femke Visser1, Gloria Vilches-Freixas1, Maaike Berbee1
1Department of Radiation Oncology (MAASTRO), GROW-School for Oncology, Maastricht University Medical Center, Maastricht, The Netherlands
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Purpose or Objective
Following national consensus guidelines, patients with esophageal cancer are treated with proton radiotherapy using a model-based selection approach, based on a significant reduction of the mean heart dose (MHD) associated with improved 2-year survival. In this study, we assessed changes and trends in heart dose during intensity modulated proton therapy (IMPT) for esophageal cancer and the relation to anatomical variations.
Material and Methods
We included 60 esophageal cancer patients, treated at our institute with neo-adjuvant (23x1.8 Gy) (n=54) or definitive (28x1.8 Gy) (n=6) chemo-radiotherapy. Clinical target volume (CTVs) were delineated on all phases of a 4D CT, and combined to an internal target volume (ITV). Treatment plans were robustly optimized with 5mm setup/3% range uncertainty combined with 3mm isotropic margin around the ITV, using 4, 3, or 2 beams IMPT (Figure 1). Each patient received weekly repeat CTs (reCTs) during the course of treatment, on which redelineation and dose recalculation were performed. Dose was summed for the complete course of treatment using deformable registration. To assess the factors influencing MHD changes and heart V40Gy, a multivariate linear regression analysis was performed using all parameters described in Table 1.
Factors in multivariate regression of MHD changes or heart V40Gy
| p-value MHD
| p-value
heart V40Gy
|
Number of beams
| 0.06 | 0.001 |
Weight of oblique beams
| 0.08 | 0.50 |
Change in radiological heart depth in beam direction
| 0.02 | 0.70 |
Shift of the heart center of mass
| 0.43 | 0.52 |
Heart volume change
| <0.001 | 0.44 |
Weight loss
| 0.003 | 0.45 |
ITV volume
| 0.87 | 0.03 |
ITV amplitude
| 0.27 | 0.07 |
ITV amplitude change
| 0.40 | 0.71 |
Diaphragm amplitude
| 0.57 | 0.14 |
Diaphragm amplitude change
| 0.03 | 0.58 |
Diaphragm baseline shift
| 0.008 | 0.37 |
Air volume change
| 0.21 | 0.002 |
Table 1: Multivariate regression analysis factors and results. Bold text indicates significant variables.
Results
A clear trend in an increase in heart dose was observed during treatment course, with linear regression showing an average increase in MHD compared to the planning CT of 0.51 [0.41,0.60] Gy/wk, and an average increase of 0.6 [0.3, 0.9] Gy on summed doses (Figure 2). Significant predictors of MHD changes are radiological depth of the heart in beam direction, heart volume changes, weight loss, diaphragm amplitude changes and baseline shift. Heart V40Gy was significantly predicted by number of beams, air volume changes inside the ITV, and ITV volume (Figure 2).
Conclusion
A clear and clinically significant change in MHD was observed during IMPT treatments of esophagus. Heart position and volume related parameters, as well as weight loss and diaphragm position are factors influencing MHD. Based on this study, we believe that strict adaptation criteria are necessary, including monitoring of MHD, heart position and volume, weight loss, and diaphragm position. Additionally, V40Gy analysis suggests an increase of the number of beams to at least three would be beneficial, as well as strict monitoring criteria for air volume changes inside ITV.