Online Plan Adaptation in Intensity-Modulated Proton Therapy Based On Planned Versus Cumulative Dose Indices
M Bobic1,2*, K Nesteruk1, H Lee1, A Lalonde1, B Winey1, A Lomax2,3, H Paganetti1, (1) Massachusetts General Hospital and Harvard Medical School, Boston, MA, (2) ETH Zurich, Zurich, CH, (3) Paul Scherrer Institute, Villigen, CH
Presentations
PO-GePV-M-106 (Sunday, 7/10/2022) [Eastern Time (GMT-4)]
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Purpose: To compare online plan adaptation workflows aiming at restoring the nominal planned dose distribution at each fraction versus restoring the cumulative dose distribution based on the progressing treatment for head and neck intensity-modulated proton therapy (IMPT).
Methods: IMPT treatment plans are created for a retrospective cohort of eight representative head and neck cancer patients with daily acquired cone-beam CT (CBCT) images (median=33 per patient). Planning contours are propagated from the CT to each daily CBCT using deformable image registration. The resulting deformation vector fields are used for dose tracking and accumulation to evaluate the treatment. Online adaptation (OA) is performed by adapting the initial plan at each fraction using an in-house developed workflow based on Monte Carlo dose calculations on scatter-corrected CBCTs. Two plan adaptation methods are compared: Online adaptation restoring the nominal planned dose distribution at each fraction (OAn) and online adaptation restoring the cumulative dose distribution based on the progressing treatment (OAc). The former method delivers the best possible dose distribution for each fraction, while the latter uses information from previous fractions to account for delivery errors made thus far. Both approaches are compared with the non-adapted base plan (BP).
Results: Both in terms of target coverage and organ at risk (OAR) sparing, OAn and OAc show remarkably similar results. For the high-risk CTV, the mean D98 was 96.13% and 96.28% for OAn and OAc, respectively. For the low-risk CTV, 95.34% and 95.43% were acquired for the same metrics. Compared to BP, both adaptation methods improved target coverage while reducing the dose to OARs.
Conclusion: Performing daily online plan adaptation to restore the nominally planned dose distribution at each fraction is sufficient for head and neck patients receiving IMPT. Tracking daily cumulative doses did not improve target coverage or OAR sparing over the course of the treatment.
Funding Support, Disclosures, and Conflict of Interest: This work was funded by the National Cancer Institute (NCI), grant number R01 CA229178. One author (KN) is supported by the Swiss National Science Foundation (SNSF), grant number 191125.
Keywords
Protons, Cone-beam CT, Monte Carlo
Taxonomy
TH- External Beam- Particle/high LET therapy: Proton therapy – adaptive therapy
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