title: Variations in clinical estimates of tumor volume regression parameters and time factor during external radiotherapy in cancer cervix: does it mimic the linear-quadratic model of cell survival?
abstract: BACKGROUND
  Tumor regression parameters and time factor during external radiotherapy (EXTRT) are of paramount importance.
  
  
  OBJECTIVE
  To quantify the parameters of tumor regression and time factor during EXTRT in cancer cervix.
  
  
  METHODS
  Patients, treated solely with radiotherapy and enrolled for other prospective studies having weekly tumor regressions recorded were considered.
  
  
  METHODS
  Seventy-seven patients received 50 Gy of EXTRT followed by intracavitary brachytherapy. Loco-regional regressions were assessed clinically and regression fraction (RF) was represented as RF=c + a 1D + a 2 D2 sub - a 3T, with c, D and T as constant, cumulative EXTRT dose and treatment time respectively.
  
  
  METHODS
  Step wise linear regression was performed for RF. Scatter plots were fitted using linear-quadratic fit.
  
  
  RESULTS
  Coefficients of parameters D, D2 sub and T were computed for various dose intervals, namely 0--20 Gy, 0--30 Gy, 0--40 Gy and 0--50 Gy. At 0--20 Gy and 0--30 Gy, only the coefficient of D2 was significant (P 2 sub and T turned significant (P 2 sub and T showed significance, leading to an estimate of 26 Gy for a1/a2 and 0.96 Gy/day for a3/a1.
  
  
  CONCLUSIONS
  As with alpha/beta and gamma/alpha of post-irradiation cell survival curves, a1/a2 and a3/a1 represents the cumulative effect of various radiobiological factors influencing clinical regression of tumor during the course of EXTRT. The dynamic changes in the coefficients of D, D2 sub and T, indicate their relative importance during various phases of EXTRT.
authors.affiliation: Department of Radiotherapy, Sanjay Gandhi Postgraduate Institute of Medical Sciences, Lucknow, India. nrdatta@sgpgi.ac.in
authors.forename: N R
authors.initials: NR
authors.lastname: Datta
authors.forename: A
authors.initials: A
authors.lastname: Rajkumar
authors.forename: R
authors.initials: R
authors.lastname: Basu
mesh_terms: D000230:Adenocarcinoma / Q000401:mortality / Q000473:pathology / Q000532:radiotherapy; D001918:Brachytherapy / Q000379:methods*; D002294:Carcinoma, Squamous Cell / Q000401:mortality / Q000473:pathology / Q000532:radiotherapy; D049109:Cell Proliferation / Q000528:radiation effects; D005260:Female; D006801:Humans; D007194:India / Q000453:epidemiology; D016014:Linear Models; D008499:Medical Records; D008875:Middle Aged; D009367:Neoplasm Staging; D018365:Neoplasm, Residual / Q000473:pathology*; D011379:Prognosis; D011829:Radiation Dosage; D020266:Radiotherapy, Conformal / Q000379:methods*; D015203:Reproducibility of Results; D012189:Retrospective Studies; D013997:Time Factors; D002583:Uterine Cervical Neoplasms / Q000401:mortality / Q000473:pathology / Q000532:radiotherapy*