Efficacy of IMRT through DMLC and inverse planning:

A preliminary results

James C.Li, Hsiang-Chi Kuo, Chi-Wei Hsu

Department of Radiation Oncology, Chung Shan Medical & Dental College Hospital

Introduction Before the commencement of the intensity modulation radiation treatment (IMRT) technique in our department, We selected some specific disease sites that were deemed good candidate for IMRT treatment with our dynamic multileaf collimator (DMLC) and Helios inverse planning. Our selection criteria are: ) Target with concavity that need IMRT technique to achieve dose conformity, (e.g. prostate cancer, pharyngeal cancer and NPC) and spare critical target that may lie adjacent to it. ) Disease site in thorax or abdomen surrounded by critical tissue or critical organ that need IMRT technique to achieve a tighter margin and lower the integral dose to spare more critical tissue. The implementation of this technique on these sites should also take the respiratory motion into account. ) Multiple lesions that may be difficult to treat with conventional technique without splitting the treatment field and need IMRT technique to localized treatment dose & produce a more conformal dose distribution.

Methods and Materials • From the above criteria we choose NPC, pharyngeal

tumor, prostate, lung, multiple neck node, CNS tumor as a site for the implementation of IMRT technique. The treatments were deliver by a Varian 21EX with 40 pairs DMLC and Helios inverse planning system. Treatment of lung site were couple with respiratory gating technique to compensate for organ motion. The results of IMRT technique for CNS tumors were compared with SRS technique by BrainLab micro mulitleaf collimator (mMLC) SRS system. The results of the other IMRT planning were compared with the more conventional conformal treatment planning.

IMRT technique with DMLC

Intensity ModulatedX-ray image by 40 pairs DMLC

Department of Radiation Oncology, Chung Shan Medical & Dental College Hospital

Leaf sequence calculated by Cadplan LMC

Optimal Fluence generated by inverse planning

Case illustration• Case1: Frontal lobe malignant lymphoma • Case2 : malignant olfactory neuroblastoma• Case3 : Recurrence NPC• Case4 : primary NPC• Case5 : prostate carcinoma• Case6 : hypopharyngeal carcinoma • Case7 : buccal carcinoma with multiple neck nodes• Case8 : endometrial carcinoma • Case9 : Lung cancer

Patient 1: Patient Liu XX, a75 year old female patient diagnosed to have frontal lobe malignant lymphoma post resection and whole brain radiotherapy for dose of 30 Gy/17 fractions, she was setup for a final boost to the local tumor bed region. We did a conventional microMLC planning with eight conformal portals to the isocenter of the tumor, and also simulated with an inversely planned radiation treatment. Comparison of the two plans showed quite similar isodose distribution at the tumor region but an advantage in the lesser normal brain exposed to the prescription dose.

IMRT SRT

SRT, more normal brain accept dose > 90%

IMRT

Patient 2: Patient Chang XX, a 62 years old male patient diagnosed to have a malignant olfactory neuroblastoma of the right orbital region with pressing on the eyeball resulting in proptosis and ptosis. He has surgical extirpation of the main tumor mass and post operative radiation therapy. X-knife multiport conformal radiation planning was done and delivered, but we also simulated with our helios inverse planning system to test the advantage of IMRT to said tumor. Above are comparative images of the resulting IMRT plan and the X-knife multiport conformal therapy, no advantage could be seen in the uniformity of the central tumor dose for the IMRT planning as compare to the X-knife conformal treatment, but a tighter dose distribution in the peripheral region for the X-knife treatment makes it slightly advantageous.

IMRT

SRT spare more left eye and left Len

IMRT for NPC recurrence

Patient 3 Patient Chien XX, 53 years old male patient diagnosed to have NPC two years prior to consultation, with recurrence at the nasopharynx proper. Conventional multiportal conformal radiation therapy was done, with excellent results, but we also simulated with the Helios inverse planning system to determine if a better dose distribution could be achieved. The results shows a better coverage of the tumor site by the IMRT technique. There is better dose uniformity (89%-104%) as compare to the conventional conformal treatment (86%-125%).

Target

TM joint

Brain stemcord

IMRT6 field

Conformal

Patient 4 Patient Chien XX, a 40 years old female patient with primary NPC with no visible neck node metastasis was treated by conventional radiation therapy for dose of 60 Gy with very good tumor response, the primary dose was escalated to a total of 76 Gy, with conventional conformal therapy. We also simulated with Helios inverse planning system to do IMRT treatment. Above is the comparison of the conventionally planned conformal treatment and the IMRT inversely planned treatment. Good tumor homogeneity in the tumor to a level of ±<8% was achieved as compare to the conventional treatment which varied widely in the range of ± > 15%. Aside there was also parotid gland sparing in the IMRT plan with a 30% advantage as compare to the conventional conformal radiation therapy plan.

PTV, IMRT

PTV, 6 field conformal Parotid gland, 6 field conformal

Parotid gland, IMRT

IMRTConformal

Rectum, conformal Bladder, conformal

Rectum, IMRT Bladder, IMRT

Patient 5

Rectum, conformal

Rectum, IMRT

Bladder, conformal

Bladder, IMRT

Patient 6

IMRT6 way conformal

Patient 5 Mr Hsu X, a 73 year old prostate carcinoma patient who has a moderately enlarge prostate gland. Here we shows a conventional conformal treatment given by a 6 fields treatment portal versus an inversely planned IMRT plan using 6 coplanar portals. Results showed the superiority of the latter plan in term of dose uniformity and critical tissues and organs sparring.

Patient 6 Mr Hwang XX, a 75 years old patient diagnosed to have a locally advance prostate carcinoma with a moderately enlarge prostatic gland with slight urinary obstruction. He was treated by conventional 6 field conformal radiation therapy to dose of 60 Gy with a relatively large field, with further reduction of the field and escalation to a total dose of 74 Gy. He responded quite well to the above treatment with good tumor control. We made virtual simulation of this patient plan with the Helios inverse planning system with 6 coplanar IMRT field. The resulting dose distribution and dose histograms were compare. It clearly shows the superiority of the IMRT plan to the conventional conformal plan in term of dose uniformity, and critical organ sparing. This would make us more confident in escalating the local tumor dose to increase TCP, and limiting NTCP, especially to the rectum.

Femur head, conformal

Femur head, IMRT

Patient 7 Mr Tsai XX, a 74 years old male patient diagnosed with hypopharyngeal carcinoma with extension to the adjacent structure leading to obstruction of the upper airway needing tracheostomy, we gave him conventional radiation therapy for dose of 60 Gy/34 fraction and further escalation of local dose to 76 Gy via a 3-field conventional conformal radiation therapy. The patient tumor was totally controlled by the above regimen with minimal fibrosis. We did a comparative study of the conventional conformal therapy and the inversely planned IMRT plan, the dose distribution clearly elucidate the superiority of the IMRT plan vis-à-vis the conventional conformal radiation plan in term of tumor dose homogeneity and critical organ and structure sparring e.g. tongue, mandible and spinal cord.

Primary target

node

tongue

cord

mandible

6 way IMRT

IMRT2 way conventional

Patient 8 A plan for the multiple neck nodes metastasis in a buccal carcinoma patient showed that IMRT plan are superior to the conventionally planned conformal radiotherapy in term of tumor dose uniformity and normal structure or organ sparring e.g. mandible, parotid glands and the adjacent tissues..

Parotid rt., IMRT

Parotid lt., 2 way conventional

Parotid rt., 2 way conventional

Parotid lt., IMRT

Patient 9 Patient Wei XXX, a 72 year old female patient diagnosed to have advance uterine endometrial carcinoma stage IIB with parametrial lymph node metastasis post initial whole pelvis radiation therapy with dose of 50 Gy, with escalation of the dose to the uterus and adjacent parametium via conventional conformal radiation therapy and was compare to a virtual simulated IMRT plan clearly showing greater dose escalation to the uterine cervical region and adjacent parametrium with less critical organ dose ( which include rectum, bladder, small bowl). These clearly shows the advantage of the

IMRT plans.

IMRT4 wayconformal

Patient 10 Mr Tsai XX, a 70 years old male lung cancer patient planned by Helios inversely planning system shows a highly concentrated radiation dose to the tumor region as compared to the normal tissues, with bulk of the lung and the heart spared by the IMRT plan. The conventional conformal treatment plan showed similar dose distribution in the main tumor region, but also delivered a much higher dose to the adjacent normal lung tissue and heart.

IMRT

Lung_left, IMRT

Lung_left, conventional

Conventional

Conformal

IMRT

conclusion• The studies show that only SRS technique is comparable

to or a little better than the IMRT technique. For concave shape tumor like NPC, IMRT was able to spare more cord and parotid gland but still maintains a high uniform dose distribution within the target region. For multiple lesions like neck nodes, IMRT could spare normal tissue e.g. tongue by a factor 0.6 of the prescribe dose.

• Base on these preliminary test, IMRT planned by Helios inverse planning system and delivered by DMLC are shown to be good technique for escalating tumor dose and sparing of normal tissue.