The volumetric change and dose-response relationship following hypofractionated proton therapy for chordomas

Figures & data

Table I. Patient characteristics.

	64.8 CGE n = 7	69.6 CGE n = 9	74.4 CGE n = 3	79.2 CGE n = 1	Total n = 20
Median age (years) (range)	59 (18–69)	43 (12–61)	62 (51–66)	55	53 (12–69)
Gender
male	4	6	2	1	13
female	3	3	1	0	7
Tumor location
skull base	2	5	1	0	8
cervical spine	2	2	0	0	4
sacrum	3	2	2	1	8
Surgery extent
biopsy	4	5	1	0	10
subtotal resection	3	4	2	1	10
Median EUD/PP ratio for GTV	1.04	1.05	1.05	1.04	1.045
(range)	(1.04–1.07)	(0.97–1.10)	(1.03–1.05)	–	(0.97–1.10)
Median EUD/PP ratio for PTV	1.04	1.05	1.04	1.04	1.04
(range)	(1.04–1.07)	(1.00–1.08)	(1.03–1.05)	–	(1.00–1.08)
Median follow-up (months)	47	44	40	14	43
(range)	(9–53)	(15–48)	(10–41)	–	(9–53)

CGE, cobalt gray equivalent = proton dose in Gy × 1.1; EUD, equivalent uniform dose; PP, prescribed dose; GTV, gross tumor volume; PTV, planning target volume.

Figure 1. Relative volumes measured using follow-up MRI scans with reference to pre-radiotherapy values were plotted on a scattergram and a line of best fit was obtained. Time to a 50% or greater reduction in volume (T₅₀) was 26 months.

Figure 2. Serial sagittal and axial T2-weighted images (short T1 inversion recovery image at 2-year follow-up (FU) sagittal image) of a sacral chordoma in a 62-year-old male. The patient received 74.4 CGE and his tumor shrank gradually. He achieved a near complete response at 3-year FU.

Figure 3. Compilation of 5-year local control rates for the treatment of chordoma achieved in several reports in the literature. a, photon; b, photon + proton; c, carbon; d, proton.