Telah dilakukan pengukuran Percentage Depth Dose (PDD) pada medium homogen dan nonhomogen dengan menggunakan bilik ionisasi plan paralel Markus. Phantom homogen dibuat dari susunan lapisan akrilik setebal 30 cm, dan phantom nonhomogen dibuat dengan menyisipkan lapisan gabus ekivalen paru-paru setebal 4 cm yang dimasukkan ke dalam susunan akrilik. Penyinaran dilakukan dengan sinar-X 6 MV dan 10 MV yang diproduksi oleh LINAC Varian 2100C. Perbedaan prosentase dosis kedalaman (PDD) pada medium homogen dan nonhomogen rata-rata sebesar 4,3% pada sinar-X 6 MV dan 3,7% pada sinar-X 10 MV. Pemberian gabus pada akrilik mengakibatkan peningkatan dosis sampai 11,7% pada sinar-X 6 MV dan 10,2% pada sinar-X 10 MV. Faktor koreksi yang dihasilkan sebagai akibat adanya material ekivalen paru-paru/gabus mencapai 1,19 pada sinar-X 6 MV dan 1,15 pada sinar-X 10 MV.Kata kunci: Medium tak homogen, Markus chamber, faktor koreksi

Abstract. DSSuperDose v.1.0 is an in-house treatment planning system (TPS) developed by Medical Physics and Biophysics Laboratory (LFMB) Universitas Indonesia as a treatment planning software for Cobalt-60 teletherapy unit. The main objective of this study was the validation of in-house TPS calculation as an essential part in quality assurance (QA) of radiotherapy. Validation of an in-house TPS was performed with two Cobalt-60 teletherapy units by comparison between in-house TPS and ISIS TPS and by measurements of absorbed dose. Mean dose deviations between in-house TPS and measurement were (1.97 ± 2.42)% for open field, (1.32 ± 1.30)% for tray field, and (2.91 ± 2.36)% for wedge field treatments. Inhouse TPS provide optimal planning for open and tray beam conditions with depth fewer than 10 cm (≤ 10 cm) and field sizes up to 20×20 cm 2 , while for wedge beam conditions with field sizes fewer than the physical size of the wedge. Comparison of in-house TPS and ISIS TPS demonstrated a good match of 96%. From the results, it is concluded that DSSuperDose v.1.0 is adequately accurate for treatment planning of radiotherapy.

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Image and treatment quality of radiotherapy are influenced by the position of beam spot, therefore it is important to know the position of the beam spot. Beam spot position measured by the corotational penumbra modulation (CPM) and the image center shift (ICS). The CPM method uses a cylindrical ion chamber that rotate with collimator angle. The position of ion chamber, jaws, central axis are fixed to collimator angle. The signal measured to half blocked field 10x20 cm2 for every 30° collimator angle. The beam spot calculated from signal measurement results. The ICS method uses two radiopaque rings with 8.5 cm diameter. Both of rings are placed at different heights of 64.5 cm and 150 cm SSD. Image acquired by varying both collimator and couch angle for every 30° and the beam spot position calculated by measuring the shift of rings centre. Measurement also performed using ball bearing test. Beam spot shift values from the CAOR using CPM and ICS measurements are closely similar, in the range of 0.05-0.65 mm and 0-0.53 mm respectively. The measurement using CPM and ICS methods can be used for routine quality assurance (QA) to ensure that the beam spot position still in tolerance.

Persahabatan Central Hospital has served radiotherapy treatment for cancer patients using linac, Elekta Precise and XiO treatment planning system (TPS) since May 2017. This study collected 91 breast cancer patients treated from May 2017 until January 2019. Most patients were preceded by surgery either mammae radical mastectomy (MRM) (83.5%) or breast conservative surgery (BCS) (16.5%). Conformal treatment planning generally performed with 2 tangential fields and most included oblique fields for treating axillary lymph nodes. Percentage of patients with clinical tumor volumes >400 cm3 was 29%, in the range of 200-400 cm3 was 36%, and the rest was <200 cm3. The lung volume irradiated with dose ≥20 Gy was used as one of parameters for treatment optimization. The mrm patient number with lung volume irradiated >30% was 9 persons (11.8%), in the range of 20-30% was 65 persons (85.5%), and <20% was 2 persons (2.6%). For the bcs patients, the number followed these criteria with lung volume of 20-30% was 13 persons (86.7%), and <20% was 2 persons (13.3%). Most breast cancer patients treated with radiotherapy were advanced stage preceded by mrm, treatment planning was difficult for achieving lung volume <30% that irradiated with the dose ≥20 Gy.