SEGMENT INFORMATION - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 28, 2018	Dec. 29, 2017
Disaggregation of Revenue [Line Items]
Revenues	$ 741.0	$ 678.5
Products transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenues	366.6	338.3
Products and Services transferred over time
Disaggregation of Revenue [Line Items]
Revenues	374.4	340.2
Americas
Disaggregation of Revenue [Line Items]
Revenues	350.4	356.7
EMEA
Disaggregation of Revenue [Line Items]
Revenues	251.0	193.0
APAC
Disaggregation of Revenue [Line Items]
Revenues	139.6	128.8
North America
Disaggregation of Revenue [Line Items]
Revenues	328.7	345.6
International
Disaggregation of Revenue [Line Items]
Revenues	412.3	332.9
Hardware
Disaggregation of Revenue [Line Items]
Revenues	347.2	320.4
Software
Disaggregation of Revenue [Line Items]
Revenues	131.2	115.1
Service
Disaggregation of Revenue [Line Items]
Revenues	262.6	243.0
Oncology Systems
Disaggregation of Revenue [Line Items]
Revenues	702.5	649.4
Oncology Systems | Products transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenues	366.6	338.3
Oncology Systems | Products and Services transferred over time
Disaggregation of Revenue [Line Items]
Revenues	335.9	311.1
Oncology Systems | Americas
Disaggregation of Revenue [Line Items]
Revenues	330.8	337.4
Oncology Systems | EMEA
Disaggregation of Revenue [Line Items]
Revenues	234.5	183.5
Oncology Systems | APAC
Disaggregation of Revenue [Line Items]
Revenues	137.2	128.5
Oncology Systems | North America
Disaggregation of Revenue [Line Items]
Revenues	309.1	326.3
Oncology Systems | International
Disaggregation of Revenue [Line Items]
Revenues	393.4	323.1
Oncology Systems | Hardware
Disaggregation of Revenue [Line Items]
Revenues	313.6	293.1
Oncology Systems | Software
Disaggregation of Revenue [Line Items]
Revenues	131.2	115.1
Oncology Systems | Service
Disaggregation of Revenue [Line Items]
Revenues	257.7	241.2
Proton Solutions
Disaggregation of Revenue [Line Items]
Revenues	38.5	29.1
Proton Solutions | Products transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0
Proton Solutions | Products and Services transferred over time
Disaggregation of Revenue [Line Items]
Revenues	38.5	29.1
Proton Solutions | Americas
Disaggregation of Revenue [Line Items]
Revenues	19.6	19.3
Proton Solutions | EMEA
Disaggregation of Revenue [Line Items]
Revenues	16.5	9.5
Proton Solutions | APAC
Disaggregation of Revenue [Line Items]
Revenues	2.4	0.3
Proton Solutions | North America
Disaggregation of Revenue [Line Items]
Revenues	19.6	19.3
Proton Solutions | International
Disaggregation of Revenue [Line Items]
Revenues	18.9	9.8
Proton Solutions | Hardware
Disaggregation of Revenue [Line Items]
Revenues	33.6	27.3
Proton Solutions | Software
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0
Proton Solutions | Service
Disaggregation of Revenue [Line Items]
Revenues	$ 4.9	$ 1.8