Dose or ‘LET’ painting – What is optimal in particle therapy of hypoxic tumors?

Figures & data

Figure 1. Oxygen enhancement ratio (OER) as a function of linear energy transfer (LET) and partial pressure of oxygen (pO₂), as appearing using the model parameters in the current work.

Figure 2. (A) Map of the partial pressure of oxygen (pO₂) in a single slice of the tumor prior to the first treatment fraction (upper). Corresponding maps of the optimal dose and LET distribution are also given (middle and lower, respectively). The dose and LET range is indicated by the color bar with a linear and logarithmic scale, respectively. (B) Histograms of the full dose and LET distributions in the tumor in the case of dose- and LET painting, respectively.

Figure 3. Tumor control probability (TCP) as a function of mean tumor dose for the three ions species considered.Four strategies were considered: 1. combined dose and LET painting (DP, LP), 2. dose painting only (DP, no LP), 3. LET painting only (no DP, LP) and 4. conventional radiotherapy (no DP, no LP).

Table I. The therapeutic gain from dose-and/or LET painting, expressed in terms of the dose giving 50% TCP for a conventional treatment relative to the iso-effective dose for painting. In the case of painting, full adaption to day-to-day variations in tumor hypoxia were followed.

Ion species	No painting^a	LET only	Dose only	Dose + LET
Protons	1.00	1.09	1.43	1.45
Lithium ions	1.00	1.24	1.32	1.37
Carbon ions	1.00	1.16	1.23	1.28

^aNo painting corresponds to a conventional treatment with a homogeneous tumor dose, and gives by definition a therapeutic gain of unity.

Table II. The therapeutic gain from replanning of combined dose- and LET painting, expressed in terms of the dose giving 50% cure for a conventional treatment relative to the iso-effective dose for painting.

	Number of planning sessions
Ion species	0^a	1	2	4	16
Protons	1.00	1.24	1.38	1.43	1.45
Lithium ions	1.00	1.26	1.33	1.36	1.37
Carbon ions	1.00	1.20	1.25	1.27	1.28

^aZero sessions corresponds to a conventional treatment, i.e. no painting and homogeneous tumor dose, and gives by definition a therapeutic gain of unity.