CONFORMAL RADIATION TREATMENT OF PROSTATE-CANCER USING INVERSELY-PLANNED INTENSITY-MODULATED PHOTON BEAMS PRODUCED WITH DYNAMIC MULTILEAF COLLIMATION

Purpose: To implement radiotherapy with intensity-modulated beams, bas ed on the inverse method of treatment design and using a multileaf col limation system operating in the dynamic mode. Methods and Materials: An algorithm, based on the inverse technique, has been integrated into the radiotherapy treatment-planning computer system in our Center. Th is method of computer-assisted treatment design was used to derive int ensity-modulated beams to optimize the boost portion of the treatment plan for a patient with a Tie cancer of the prostate. A dose of 72 Gy (in 40 fractions) was given with a six-field plan, and an additional 9 Gy (in five fractions) with six intensity-modulated beams. The intens ity-modulated fields were delivered using dynamic multileaf collimatio n(1), that is, individual leaves were in motion during radiation deliv ery, with the treatment machine operating in the clinical mode. Exhaus tive quality assurance measurement and monitoring were carried out to ensure safe and accurate implementation. Results: Dose distribution an d dose-volume histogram of the ''inverse method'' boost plan and of th e composite (72 Gy primary + 9 Gy boost) plan were judged clinically a cceptable. Compared to a manually designed boost plan, the inverse tre atment design gave improved conformality and increased dose homogeneit y in the planning target volume. Film and ion chamber dosimetry, perfo rmed prior to the first treatment, indicated that each of the six inte nsity-modulated fields was accurately produced. Thermoluminescent dosi meter (TLD) measurements performed on the patient confirmed that the i ntended dose was delivered in the treatment. In addition, computer-aid ed treatment-monitoring programs assured that the multileaf collimator (MLC) position file was executed to the specified precision. In terms of the overall radiation treatment process, there will likely be labo r savings in the planning and the treatment phases. Conclusions: We ha ve placed into clinical use an integrated system of conformal radiatio n treatment that incorporated the inverse method of treatment design a nd the use of dynamic multileaf collimation to deliver intensity-modul ated beams. The system can provide better treatment design, which can be implemented reliably and safely. We are hopeful that improved treat ment efficacy will result.