Low Dose Rate Versus High Dose

Rate brachytherapy in Ca.Cervix

DEBATE

Introduction

• Carcinoma cervix is the second most commonly occuring cancer in India.

• Brachytherapy forms the most important part radiation therapy

• Low dose rate Brachytherapy – Gold Standard

• Experience more than a century….

1992 !!

HDR for Ca. Cerix ??

Radiobiological advantages…..

Repair

The lower the dose rate of radiation a cell is exposedto, the greater the likelihood of repair.

Late-reacting normal tissues seem more capable of repair than tumor

The tumor is preferentially killed over normal tissue.

Reoxygenation

• Because of the duration of administration of LDR, acute hypoxia corrects within the tumor during treatment

• Oxygen enhancement ratio is lower for LDR than for HDR.

Reassortment

During the overall treatment time of LDR, tumor cells may pass from the relatively radioresistant phases of late S and early G2 to the more radiosensitive phases of G2 and M

Repopulation

The continuous administration of LDR prevents repopulation during treatment.

Biological equivalent dose

• Calculated from LDR

• a/b ratio…

• Based on formulas !!!!

Toxicity

High dose / Fraction

Increased Late complications

HDR delivery

Total Dose?Dose per fraction?Conversion?Schedule?

NO STANDARD GUIDELINES

Orton et al, Metaanalysis

Optimisation???

URETHRA RECTUM

HDR for all cervix patients??

Small tumor & good vaginal anatomy

Vaginal anatomy – increase in complications

Bulky central disease with high chance of central recurrance

• Severely criticized

• Lacks any description of statistical methods,

• Were not randomized trials

• Many have never been published,

• None were referenced.

• Some of the LDR results used in the comparison are very poor, with complication rates several times higher than those described by Fletcher or Perez

What happens at longer follow up??

DSS

Pelvic recurrance free survival

• Teshima et al ; 1993

• 430 patients reported on 10-year OS

• 44% (114 out of 259) in the HDR arm versus52.6% (90 out of 171) in the LDR arm

Other studies…

Other Factors…

• Patient’s expense…

• Source life…

• Need for intense QA…

• Setup up cost…

Important Msgs…

Radiobiology

Dose, Fraction & Schedule

Long term survival

Optimisation

XXX?

Conclusion

• Carcinoma cervix – Life threatening disease

• For the price of convenience …, survival should never be compromised

• LDR brachytherapy should be the standard of care in carcinoma cervix until long term efficacy of HDR is proven….

Than

k You