SPATIALLY FRACTIONATED RADIATION THERAPY-SFRT (GRID THERAPY)

SHIJO VARGHESERADIOTHERAPY TECHNOLOGISTACRODr.BALABHAI NANAVATI HOSPITALMUMBAI.

INTRODUCTION

With the advent of megavoltage radiation, the concept of spatially fractionated radiation(SFR) has been abandoned for the last several decades; yet, historically, it has been proven to be safe and effective in delivering large cumulative doses of radiation in the treatment of cancer.SFR has been adapted to megavoltage beams using a specially constructed grid

This treatment modality is used for the palliative treatment of large deeply seated tumors

HISTORICAL BACKGROUND

Kohler (1909)- described radiation through a “perforated screen" creating an effect similar to treatment with multiple small pencil beams.

Liberson (1933)- used this technique for the successful treatment of deep seated cancers.

SPATIALLY FRACTIONATED RADIATION THERAPY(GRID THERAPY)-PRINCIPLE

Delivery of high dose of radiation in clusters of small areas without producing prohibitive normal tissue damage to the skin and subcutaneous tissue.

Small volume of skin could safely tolerate high doses of radiation.

Radio biologically several logs of tumor are likely to be killed thereby allowing for re-oxygenation.

Production of cytokines could lead to Bystander effect.

HIGH DOSE SPATIALY FRACTIONATED (GRID)RADIATION

GRID :50/50(open to closed areas)

Maximum field size :20 x 20 cm Energy : 6- 20 MV SSD :100 cm Dose :12-20 Gy (median 15

Gy) Field placement :single unopposed field Dose prescription :D max in the open area

of the Grid.

SPATIAL FRACTIONATION FOR GRID THERAPY BY MLC

MLC can provide the spatial fractionation for grid therapy.It has many advantages in comparison with cerrobend grid collimators notably the ease of creating a grid of any opening size and pattern by simply programming the leaf positions(limited only by the positional precision of the MLC leaves).

Though the longer delivery time is a disadvantage.

Methods and Materials

Grid is an 8 cm thick lead block containing cylindrical holesThe central axis of each hole was drilled to match the diver-gence of the radiation from its central axis

Holes were arranged in a hexago-nal array. At the isocentre, they pro-jected 1.3 cm diameter Circles separated by 1.8 cm

Targeted and Non-Targeted effects

Targeted Effects

direct indirect

Non Targeted Effects

Bystander EffectsInduced genomic instability

NON-TARGETED EFFECTS

INDUCED GENOMIC INSTABILITY

observed in the progeny of an irradiated cell that may / may not have been subject to energy deposition events.

BYSTANDER EFFECT

Effects observed in cells that were not irradiated but were “bystanders” at the time of irradiation.

Killing or damage of un irradiated cells due to irradiation of adjacent cells.

BYSTANDER EFFECT Bystander effect refers to a theory

that, many of the types of radiation induced damage seen in irradiated cells can also be seen in adjacent non irradiated cells.

Such damages include DNA damage,DNA mutations, chromosomal imbalance and genomic instability,apoptosis,micronuclei formation,oncogenic transformation.

The untargeted cells show responses which are characteristics of irradiated cells.

Manifestation of radiation- induced biological Bystander effect

CYTOKINES

Cytokines are signalling molecules or protein molecules which are secreated by glial cells of nervous system.

A variety of cytokines especially TNF –alpha and TGF –beta are known to be released in response to high dose radiation.

Cytokines can be tumoricidal,tumoristatic or promote neoplastic transformation and growth.

Levels of TNF-alpha and TGF-beta after irradiation

Presence of TNF alpha in serum. Presence of TGF beta in serum.

Survival of patients by TNF-alpha and TNF –beta induction

BEFORE AFTER

Neck nodes from primary squamouscell cancer of oropharynx after 1500 cGy SFR

DRAW BACKS The grid therapy was found to be

advantageous for treating the acutely responding tumors, but not for late responding tumors.

Mobile tumors such as those in the thorax and abdomen respond worse to grid treatments than stationary such as those in head and neck.

Not advicable to treat critical organs such as eye lens, spinal cord etc.

Conclusion

Large and bulky sarcomas have an unfavourable prognosis and are difficult to treat with conventional radiation alone

However with SFR high dose radiation can be used in conjunction with conventional RT to provide rapid relief of pain and other symptoms as well as providing select patients an opportunity for surgical resection of disease.

THANK YOU

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