Robust Intensity Modulated Proton Therapy (IMPT) Increases Estimated Clinical Benefit in Head and Neck Cancer Patients

Abstract

PurposeTo compare the clinical benefit of robust optimized Intensity Modulated Proton Therapy (minimax IMPT) with current photon Intensity Modulated Radiation Therapy (IMRT) and PTV-based IMPT for head and neck cancer (HNC) patients. The clinical benefit is quantified in terms of both Normal Tissue Complication Probability (NTCP) and target coverage in the case of setup and range errors.Methods and MaterialsFor 10 HNC patients, PTV-based IMRT (7 fields), minimax and PTV-based IMPT (2, 3, 4, 5 and 7 fields) plans were tested on robustness. Robust optimized plans differed from PTV-based plans in that they target the CTV and penalize possible error scenarios, instead of using the static isotropic CTV-PTV margin. Perturbed dose distributions of all plans were acquired by simulating in total 8060 setup (±3.5 mm) and range error (±3%) combinations. NTCP models for xerostomia and dysphagia were used to predict the clinical benefit of IMPT versus IMRT.ResultsThe robustness criterion was met in the IMRT and minimax IMPT plans in all error scenarios, but this was only the case in 1 of 40 PTV-based IMPT plans. Seven (out of 10) patients had relatively large NTCP reductions in minimax IMPT plans compared to IMRT. For these patients, xerostomia and dysphagia NTCP values were reduced by 17.0% (95% CI; 13.0–21.1) and 8.1% (95% CI; 4.9–11.2) on average with minimax IMPT. Increasing the number of fields did not contribute to plan robustness, but improved organ sparing.ConclusionsThe estimated clinical benefit in terms of NTCP of robust optimized (minimax) IMPT is greater than that of IMRT and PTV-based IMPT in HNC patients. Furthermore, the target coverage of minimax IMPT plans in the presence of errors was comparable to IMRT plans.

Improve the dosimetric outcome in bilateral head and neck cancer (HNC) treatment using spot-scanning proton arc (SPArc) therapy: a feasibility study

“…Radiation-induced side effects, including xerostomia and dysphagia, have significant impacts on the quality of life of HNC patients [27][28][29]. Dosimetric improvements could potentially improve the treatment outcome by reducing acute and late toxicities.…”

Practical robustness evaluation in radiotherapy – A photon and proton-proof alternative to PTV-based plan evaluation

“…A scenario is commonly called 'error scenario', although in this work terminology 'treatment scenario' is used, see next section. Since becoming available in commercial treatment planning systems, robust optimisation has demonstrated the ability to improve target coverage robustness and/or organ at risk (OAR) sparing compared to PTV-based planning, in both proton [15][16][17][18][19][20][21] and photon therapy [22][23][24][25]. It must be noted however, that robust target coverage is generally one of many variables in the optimisation objective function and therefore is in competition with other objectives, such as OAR dose.…”

Robust beam orientation optimization for intensity‐modulated proton therapy

“…The proton dose uncertainties can lead to severely under-dosed target and over-dosed OARs yet the geometrical margin used in x-ray therapy is ineffective to mitigate the problem. For IMPT, a commonly used method to reduce the effect of uncertainties is worst-case optimization method, [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40] where the estimated worst situations are sparsely sampled in the optimization problem to maintain the dose distribution even with uncertainties above. The plan robustness is better maintained at the cost of substantially increased computational cost.…”