Bowel-sparing intensity-modulated radiotherapy (IMRT) for palliation of large-volume pelvic bone metastases: Rationale, technique and clinical implementation

Figures & data

Table I. Treatment characteristics. Treatment plan and delivery characteristics for the first seven patients treated using volumetric modulated arc therapy. For illustrative purposes, data for a treatment plan made with an anterior-posterior/posterior-anterior (APPA) beam arrangement is shown for patient 1.

	1	1 APPA	2	3	4	5	6	7
Re-irradiation?	Yes		No	No	No	No	Yes	No
Target volume	Pelvis, both hips, lumbar (L) vertebrae 4 + 5	Pelvis, both hips, lumbar (L) vertebrae 4 + 5	^2/3 Pelvis, bilateral soft tissue, left hip	Pelvis, right hip, L5	Pelvis, both hips, L4 + 5	½ Pelvis, right hip, L4 + 5	½ Pelvis, left hip	Pelvis, soft tissue right side, both hips, L5
PTV volume (cm^3)	3635	3635	1829	2671	3281	1291	1216	3414
% PTV receiving ≥ 7 Gy 7.6 Gy 8 Gy 9 Gy	100 99 89 13	100 99 81	100 100 96 40	100 99 96 48	98 85 62 2	100 98 71 0	100 97 50 0	100 99 84 0
Mean dose OAR (Gy)	4.3	8.1	3.2	2.5	4.5	3.5	2.7	4.4
% OAR receiving ≥ 4 Gy 8 Gy	46 6	100 75	25 5	17 0	53 2	32 2	21 1	52 7
Number of arcs	3	-	2	4	2	2	2	2
Monitor units	3197	770	2525	5460	2342	1629	2287	3953
Dose rate (MU/min)	600	600	600	600	600	600	600	600
Total treatment time (min:s)^1	18:06	6:41^3	12:23	31:01	19:58	5:48	35:04	19:13
Initial IGRT time (min:s)^2	8:58	4:21^3	7:18	17:59	14:16	2:56	29:59	11:43

¹Defined as time from first IGRT imaging to end of last arc obtained from Offline Review (Varian Medical Systems).

²Defined as time from start of first IGRT imaging to start of first arc, obtained from Offline Review.

³These are average total treatment and initial IGRT times derived from four clinical patients who received conventional radiotherapy.

Figure 1. Conformal, intensity modulated RapidArc (RA) treatment plan (A + B), and conventional anterior-posterior/posterior-anterior (APPA) field arrangement (C + D), demonstrating the dose distribution and the bowel sparing that can be achieved with RA (moving from outside to inside: isodose lines shown for 2, 4, 6 and 7.6 Gy). On the right the dose volume histogram (E) illustrates that in both cases the PTV is covered with at least 7 Gy (RA = squares and APPA = triangles) but the RA plan delivers much less dose to the abdominal contents (light color line, squares) than an APPA field arrangement (light color line, triangles).