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Radiotherapy Dictionary by , 03 Jul 2016 18:22
29 Dec 2015 14:49
in discussion Radiation Oncology forum / BIOLOGY... » Cell survival curve

Hii..guys I can't understand why low dose region in cell survival curve is lethal and high dose region is reparable and less lethal. In high dose region there is more chances of double strand breaks as compare to low dose region which is usually nonreperable.
Pls guide me.

Cell survival curve by , 29 Dec 2015 14:49

Thank u for providing information. thanks

Re: FRCR oncology by , 30 Jul 2015 04:49

@sunita, FRCR in india is still evolving.
Only FRCR is enough to practice in UK

Re: FRCR oncology by , 17 Jun 2015 13:42

As I said, I did it in a spreadsheet, the details of the required structure is my last post, and the equation for SF [=EXP(D*(-1*((E*F)+(G*(F^2)))))] is also provided. The columns will need a number, but then it should work [e.g., =EXP(D2*(-1*((E2*F2)+(G2*(F2^2)))))],

A

Thank you very much AAM this is what I am trying to understand, how alpha and beta ratio affects the resultant survival.

But I have another question:
What are the advantages of fractionation vs typical dose prescription for two tumours with alpha/beta equal to 10 Gy and 1.7 Gy respectively?
I am trying to understand how the method of therapy can affect the outcome of survival?

Thanks a gain

i m from India..completed my MD radiotherapy….can someone please guide about FRCR exam?? its advantages?? is it possible to practice outside India without clearing PLAB or USMLE??

Re: FRCR oncology by , 21 Feb 2015 15:00

hello . i m from India and have completed MD radiation oncology. can some one please guide about the requirements for giving the FRCR exam….is it necessary to clear PLAB test for it ???

Re: FRCR oncology by , 21 Feb 2015 14:57

I have found the problem!

The solution is very sensitive to the alpha and beta values! If you think that alpha/beta is 3 and use 30 and 10 as the values, the number is too small to register.

Playing with the alpha/beta ratio of 10 for acute reactions (like tumours), 2Gy in 1 Fx should give a SF of 50%, and so the corresponding values are alpha = 0.285, beta = o.0285. So is this what you mean?

 A B C D E F H I Total Dose Total Fractions n alpha fractiondose beta SF note 2 1 1 0.285 2 0.0285 5.05E-001 the 2Gy fraction with SF=1/2 used to calculate alpha & beta values 60 4 4 0.285 15 0.0285 2.72E-019 The 60/4 regime, total SF 15 1 1 0.285 15 0.0285 2.28E-005 the first fraction SF 15 1 1 0.285 15 0.0285 5.21E-010 the second fraction SF 15 1 1 0.285 15 0.0285 1.19E-014 the third fraction SF 15 1 1 0.285 15 0.0285 2.72E-019 the fourth fraction SF 60 30 30 0.285 2 0.0285 3.33E-028 The 60/30 regime for comparison

You can do the same for late values by changing beta to alpha/3 instead of alpha/10.

A

I have tried to do this in a LibreOffice spreadsheet, but I can't get it to work (answers '0' each time).

 A B D E F H Total Dose Total Fractions n alpha fractiondose beta SF =EXP(D*(-1*((E*F)+(G*(F^2))))) 60 4 4 10 15 10 0.00000000000000000000 2 1 1 100 2 10 0.00000000000000000000

I'll try it in Excel, but if I can't get the equation working, I can't help. You should problem solve the equation to see what I have done wrong,

A

what are your alpha and beta values?

A

Hello all,

I am wondering if you could help me with the concept of multi-fraction survival curve.
I want to plot the survival curve as a function of dose for a number of dose fractions.

For example, I have a 60 Gy delivered over 4 fractions. Is it right to use the following equation:
S = e(n*(-alpha * Dose - beta *Dose^2)) .
n is number of fractions and Dose = 60/4= 15 Gy per fraction.
However, this gives me only one point! and I need to plot four different curves at a specific dose fractions (duplicate the shoulder of the curve n times). I tried to post the plot that I want but I am not allowed to do so.

Any help will be appreciated!

Thank you

All preparing 0r planning to undertake FRCR-1 clinical oncology in near future lets share exam material & our preparation. Here its me welcomming u all. Regards

I m from asia , planning to undertake , 1st half 2015 FRCR-1 clinical oncology, anyone else here , preparing must please let me know,,it would be great to share exam material & preparation

FRCR-1 1st Quarter 2015 by , 23 Nov 2014 09:22

Thanks. But how this vanishes whith higher energy photon?
If this is all because of secondary electrons, that shoulhd be more prominant with high energy photons.

Re: RBE of electrons vs photon by , 19 Dec 2013 03:01

The reason why this is true is that orthovoltage produces delta rays when it interacts with the tissue when it deposits dose. In other words, the orthovoltage x-rays create secondary electrons (i.e. delta rays) that have sufficient energy to further ionize atoms and create more dose effect than what was originally intended from the orthovoltage machine. That is why it has a higher RBE than simple electrons as well as photons.

Hope this clarifies the issue.

Re: RBE of electrons vs photon by , 18 Dec 2013 06:15

what were radiation doses in this RCT?

yes you are right. its mean we cannot change the dose on the basis of toxicity either acute or late.how can we decide that we can go beyond 60 Gy?

I have two provocative questions for you:

1. How will you decide to give more than 60Gy? You say "re-evaluate for toxicity esp pulmonary and cardiac", but neither of these will be visible by the end of 60Gy conventional treatment. Only skin toxicity will be evident, and how will that help?
2. How will close follow up make any difference to the outcome? If >60Gy is going to cause long term side effects of radiotherapy, it will do this whether you follow up or not. And there is not really useful treatment to prevent it, is there?
3. Isn't there any evidence to guide you?

The issue of treating LOCALLY ADVANCED BREAST CANCER has been well assessed with randomised trials. They are just old!

Look at a couple of papers which show the pattern well - S+RTh V S+CTh V S+RTh+CTh (Klefstrom), and S+CTh V R+CTh (De Lena). In fact, S+CTh and RTh+CTh give the same outcome, but inferior to all three. There was also a number of reports from Westmead (Boyages) on this issue (which is why it appeared in the exams!). They claimed single institution numbers the equivalent of RTh+CTh (see PMID: 8138439; Ahern, et al).

References
Adjuvant postoperative radiotherapy, chemotherapy, and immunotherapy in stage III breast cancer. II. 5‐year results and influence of levamisole
P. Klefström, P. Gröhn, E. Heinonen, L. Holsti, P. Holsti
Cancer 60(5):936-942,1987

Multi modal treatment for locally advanced breast cancer: Results of chemotherapy-radiotherapy versus chemotherapy-surgery
M. De Lena, M. Varini, R. Zucali, D. Rovini, G. Viganotti, P. Valagussa, U. Veronesi, G. Bonadonna
American Journal of Clinical Oncology 4(3):229-236,1981

Abstract
IN A PROSPECTIVE RANDOMIZED STUDY, the efficacy of two combined modality approaches (chemotherapy plus radiotherapy or chemotherapy plus mastectomy) was tested in a total of 132 women with locally advanced breast cancer. Chemotherapy consisted of Adriamycin plus vincristine (AV) administered for three cycles before either local-regional modality and subsequently for seven additional cycles. Although a higher proportion of women achieved complete remission after mastectomy (100%) compared to women given radiotherapy (60%), the total response rate at the end of combined modality was identical (75%). There was no significant difference between the two treatment groups in terms of patterns of treatment failure, median duration of response, and total survival. Treatment was not influenced by menopausal or estrogen receptor status. Two patients of the surgical group showed Adriamyein-induced cardiomyopathy after cumulative doses less than 500 mg/m2. The results of present study failed to indicate that surgery perse improved the overall results, including local control, over radiotherapy in a combined modality setting. (no PDF available)

Locally advanced breast cancer: defining an optimum treatment regimen.
Ahern V, Barraclough B, Bosch C, Langlands A, Boyages J.
Int J Radiat Oncol Biol Phys. 1994 Mar 1;28(4):867-75.

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