HYPO_HSR - Hypofractionation with Tomotherapy: experience...

Info iconThis preview shows pages 1–9. Sign up to view the full content.

View Full Document Right Arrow Icon
Hypofractionation with Hypofractionation with Tomotherapy: experience at HSR Tomotherapy: experience at HSR Radiation Therapy DPT, San Raffaele Hospital, IRCCS Milano, Italy Di Muzio Nadia Napoli 8-9 Giugno 2009
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Summary Summary Classical applied radiobiology Hypofractionated RT: pro’s and con’s Hypofractionated protocols at HSR Lung mets (details) Liver mets (details) Pancreatic carcinoma (details) Pleural Mesothelioma (details) ….. further informations in other course lessons (head- neck, prostate, etc) Conclusions
Background image of page 2
The effect of radiation on cells is described by the Linear-Quadratic (LQ) model – extensively verified provided d > 0.5 Gy and dose-rate not too low Radiobiological basis: from the beginning between - in recovery full ) ( ) ( 2 E e SF and d D d d n E - = + = + = β α where the α and β are coefficients which describe the radiosensitivity of the cells in the normal tissue /tumour
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Using different fractionation regimens the model enables one to convert from one regimen to another, by equating BED Classical applied radiobiology: BED BED= E/ α = D[1+d/( α / β )] Biological Effective Dose Basic assumptions: - Complete repair of sublethal damage between fractions - The effects of proliferation are negligible - Dose distributions are uniform
Background image of page 4
In case of rapid repopulation during treatment: Classical applied radiobiology: BED BED= E/ α = D[1+d/( α / β )]-h(T-T K ) T= Overall treatment time (days) T k =Proliferation starts at T k days (20-30 days) h=0.4-0.8 Gy/day: Rate of loss after T k For tumours with rapid repopulation during treatment the reduction in overall treatment time could increase the local control
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
To convert a total dose D given in fractions of size d into the isoeffective total dose EQD 2 given in 2-Gy fractions β α + + = = 2 D E 2 assuming 2Gy d D Q d ref Classical applied radiobiology: EQD 2 Withers formula (assuming complete repair, negligible repopulation, etc.) d and D are the doses prescribed for the tumour (…nothing about dose distribution and OAR behaviour)
Background image of page 6
Classical applied radiobiology: α and β α / β (Gy): ratio used in the LQ model to quantify the fractionation sensitivity of tissues Normal Tissues: - Low α / β (0.5-6 Gy) late effects, expressed months to years after irradiation - High α / β (7-20Gy) acute effects, expressed within a period of days to weeks after irradiation Tumours: - High α / β (7-20Gy) (few exception in melanomas, sarcomas, prostate (?))
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
But don’t forget the assumptions the absorbed dose of the OAR is the same than the absorbed dose of the tumour: while it’s quite obvious the fact that if we can half the dose to the OAR we could double the dose/fraction without any incremental risk for the OARs • No differences have been considered between serial and parallel organs: while the volume effect could have a great influence in the determination of the toxicity of the treatment in all the parallel OARs
Background image of page 8
Image of page 9
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 05/24/2010 for the course MED 122 taught by Professor Tera during the Winter '08 term at Anadolu University.

Page1 / 70

HYPO_HSR - Hypofractionation with Tomotherapy: experience...

This preview shows document pages 1 - 9. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online