A margin-of-the-day online adaptive intensity-modulated radiotherapy strategy for cervical cancer provides superior treatment accuracy compared to clinically recommended margins: A dosimetric evaluation

Figures & data

Figure 1. Schematic representation of the calculation of the DVH parameters during the treatment course. This example illustrates the calculation of bladder V95 for fraction 9 (of 23 fractions) as a weighted sum of the bladder V95 of the pretreatment (V95¹) CT scan and the after 40 Gy CT scan (V95²) that had the nearest bladder volume to the bladder volume measured by US at fraction 9.

Figure 2. a) Distribution of the margin-of-the-day. b) Maximum margin-of-the-day per patient. c) Maximum of the margin-of-the-day for each treatment half.

Figure 3. DVH parameters of the margin-of-the-day strategy and the population-based strategy. a) Percentage of cervix-uterus that received 95% of the prescribed dose b) Absolute volume of small bowel that received 99% of the dose and percentage of c) bladder and d) rectum that received 90% of the dose. The error bar denotes ± 1SD variation around the mean.

Table I. Volume of the PTV using the population-based margin and the frequency-weighted volume of the PTV of the MoD strategy. An * in the last column points out the patients for whom the population-based margin did not provide sufficient coverage of the CTV.

Patient ID	PTV of population margin (ml)	PTV of Margin-of-the-Day (ml)	Difference (%)
1	989	803	−19
2	1320	1127	−15
3	1863	2219	19*
4	1731	1418	−18
5	1593	2452	54*
6	1412	1377	−2
7	1671	2304	38*
8	1659	1375	−17
9	1684	1277	−24
10	1969	2143	9
11	2225	3460	56*
12	1587	1616	2
13	1489	2951	98*
14	1860	2508	35*