A novel model to correlate hydrogel spacer placement, perirectal space creation, and rectum dosimetry in prostate stereotactic body radiotherapy

Table 4 Coefficient of determination (R²) values from simple linear regression models of rectum maximum 1, 2, and 3 cc point doses (rD_max 1, 2, 3 cc) and rectum volume receiving dose (rV95, 90, 80%) regressed against perirectal distance measurements obtained on CT (A) and hydrogel parameters (B)

		rD_max			rV
		1 cc	2 cc	3 cc	95%	90%	80%
A	Perirectal Distance Measurement
	CTV center	0.44	0.45	0.42	0.6	0.55	0.27
	1 cm inferomedial to CTV center	0.41	0.37	0.31	0.5	0.38	0.15
	2 cm inferomedial to CTV center	0.39	0.35	0.28	0.49	0.33	0.1
B	Hydrogel Parameters
	Hydrogel volume (cc)	0.23	0.22	0.18	0.2	0.14	0.04
	θ	0.36	0.33	0.26	0.43	0.34	0.14
	Normalized θ*gel volume	0.64	0.62	0.55	0.60	0.52	0.25

ISSN: 1748-717X